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arXiv:1001.2657v1 [astro-ph.CO] 15 Jan 2010
Astronomy & Astrophysics
manuscript no. LFI˙Programme˙Paper˙30jun09˙revised˙referee˙editorial c
ESO 2010
January 15, 2010
Planck pre-launch status: the Planck-LFI programme
N. Mandolesi1, M. Bersanelli2, R.C. Butler1, E. Artal7, C. Baccigalupi8,35,6, A. Balbi5, A.J. Banday9,39,
R.B. Barreiro17, M. Bartelmann9, K. Bennett26, P. Bhandari10, A. Bonaldi3, J. Borrill38,49, M. Bremer26, C. Burigana1,
R.C. Bowman10, P. Cabella5,45, C. Cantalupo38, B. Cappellini2, T. Courvoisier11, G. Crone12, F. Cuttaia1, L. Danese8,
O. D’Arcangelo13, R.D. Davies14, R.J. Davis14, L. De Angelis15, G. de Gasperis5, A. De Rosa1, G. De Troia5,
G. de Zotti3, J. Dick8, C. Dickinson14, J. M. Diego17, S. Donzelli22, U. D¨orl9, X. Dupac40, T.A. Enßlin9,
H. K. Eriksen22, M.C. Falvella15, F. Finelli1,34, M. Frailis6, E. Franceschi1, T. Gaier10, S. Galeotta6, F. Gasparo6,
G. Giardino26, F. Gomez18, J. Gonzalez-Nuevo8, K.M. G´orski10,41, A. Gregorio16, A. Gruppuso1, F. Hansen22,
R. Hell9, D. Herranz17, J.M. Herreros18, S. Hildebrandt18, W. Hovest9, R. Hoyland18, K. Huffenberger43, M. Janssen10,
T. Jaffe14, E. Keih¨anen19, R. Keskitalo19,33, T. Kisner38, H. Kurki-Suonio19,33, A. L¨ahteenm¨aki20, C.R. Lawrence10,
S. M. Leach8,35, J. P. Leahy14, R. Leonardi21, S. Levin10, P.B. Lilje22, M. L´opez-Caniego42, S.R. Lowe14, P.M. Lubin21,
D. Maino2, M. Malaspina1, M. Maris6, J. Marti-Canales12, E. Martinez-Gonzalez17, M. Massardi3, S. Matarrese4,
F. Matthai9, P. Meinhold21, A. Melchiorri45, L. Mendes23, A. Mennella2, G. Morgante1, G. Morigi1, N. Morisset11,
A. Moss29, A. Nash10, P. Natoli5,36, R. Nesti24, C. Paine10, B. Partridge25, F. Pasian6, T. Passvogel12, D. Pearson10,
L. P´erez-Cuevas12, F. Perrotta8,6, G. Polenta44,45,46, L.A. Popa27, T. Poutanen33,19,20, G. Prezeau10, M. Prina10,
J.P. Rachen9, R. Rebolo18, M. Reinecke9, S. Ricciardi37,38, T. Riller9, G. Rocha10, N. Roddis14, R. Rohlfs11,
J.A. Rubi˜no-Martin18, E. Salerno47, M. Sandri1, D. Scott29, M. Seiffert10, J. Silk30, A. Simonetto13, G.F. Smoot28,31,
C. Sozzi13, J. Sternberg26, F. Stivoli37,38, L. Stringhetti1, J. Tauber26, L. Terenzi1, M. Tomasi2, J. Tuovinen32,
M. T¨urler11, L. Valenziano1, J. Varis32, P. Vielva17, F. Villa1, N. Vittorio5,36, L. Wade10, M. White48, S. White9,
A. Wilkinson14, A. Zacchei6, A. Zonca2
(Affiliations can be found after the references)
Preprint online version: January 15, 2010
Abstract
This paper provides an overview of the Low Frequency Instrument (LFI) programme within the ESA Planck mission. The LFI instrument has been
developed to produce high precision maps of the microwave sky at frequencies in the range 27–77 GHz, below the peak of the cosmic microwave
background (CMB) radiation spectrum. The scientific goals are described, ranging from fundamental cosmology to Galactic and extragalactic
astrophysics. The instrument design and development are outlined, together with the model philosophy and testing strategy. The instrument is
presented in the context of the Planck mission. The LFI approach to ground and inflight calibration is described. We also describe the LFI ground
segment. We present the results of a number of tests demonstrating the capability of the LFI data processing centre (DPC) to properly reduce
and analyse LFI flight data, from telemetry information to calibrated and cleaned time ordered data, sky maps at each frequency (in temperature
and polarization), component emission maps (CMB and diffuse foregrounds), catalogs for various classes of sources (the Early Release Compact
Source Catalogue and the Final Compact Source Catalogue). The organization of the LFI consortium is briefly presented as well as the role of the
core team in data analysis and scientific exploitation. All tests carried out on the LFI flight model demonstrate the excellent performance of the
instrument and its various subunits. The data analysis pipeline has been tested and its main steps verified. In the first three months after launch, the
commissioning, calibration, performance, and verification phases will be completed, after which Planck will begin its operational life, in which
LFI will have an integral part.
Key words. (Cosmology): cosmic microwave background – Galactic and extragalactic astrophysics – Space vehicles – Calibration – Data analysis
1. Introduction
In 1992, the Cosmic Background Explorer (COBE) team an-
nounced the discovery of intrinsic temperature fluctuations
in the cosmic microwave background radiation (CMB; see
Appendix A for a list of the acronyms appearing in this
paper) on angular scales greater than 7◦and at a level of
a few tens of µK (Smoot et al. 1992). One year later two
The address to which the proofs have to be sent is:
Nazzareno Mandolesi
INAF-IASF Bologna, Via Gobetti 101, I-40129, Bologna, Italy
fax: +39-051-6398681
e-mail: mandolesi@iasfbo.inaf.it
spaceborne CMB experiments were proposed to the European
Space Agency (ESA) in the framework of the Horizon
2000 Scientific Programme: the Cosmic Background Radiation
Anisotropy Satellite (COBRAS; Mandolesi et al. 1994), an ar-
ray of receivers based on High Electron Mobility Transistor
(HEMT) amplifiers; and the SAtellite for Measurement of
Background Anisotropies (SAMBA), an array of detectors based
on bolometers (Tauber et al. 1994). The two proposals were
accepted for an assessment study with the recommendation
to merge. In 1996, ESA selected a combined mission called
COBRAS/SAMBA, subsequently renamed Planck, as the third
Horizon 2000 Medium-Sized Mission. Today Planck forms part
of the “Horizon 2000” ESA Programme.
2 Mandolesi et al.: The Planck-LFI programme
The Planck CMB anisotropy probe1, the first European and
third generation mission after COBE and WMAP (Wilkinson
Microwave Anisotropy Probe), represents the state-of-the-art in
precision cosmology today (Tauber et al. 2009; Bersanelli et al.
2009; Lamarre et al. 2009). The Planck payload (telescope in-
strument and cooling chain) is a single, highly integrated space-
borne CMB experiment. Planck is equipped with a 1.5–m ef-
fective aperture telescope with two actively-cooled instruments
that will scan the sky in nine frequency channels from 30 GHz to
857 GHz: the Low Frequency Instrument (LFI) operating at 20 K
with pseudo-correlation radiometers, and the High Frequency
Instrument (HFI; Lamarre et al. 2009) with bolometers operat-
ing at 100 mK. Each instrument has a specific role in the pro-
gramme. The present paper describes the principal goals of LFI,
its instrument characteristics and programme. The coordinated
use of the two different instrument technologies and analyses
of their output data will allow optimal control and suppression
of systematic effects, including discrimination of astrophysical
sources. All the LFI channels and four of the HFI channels will
be sensitive to the linear polarisation of the CMB. While HFI
is more sensitive and should achieve higher angular resolution,
the combination of the two instruments is required to accurately
subtract Galactic emission, thereby allowing a reconstruction of
the primordial CMB anisotropies to high precision.
LFI (see Bersanelli et al. 2009 for more details) consists of
an array of 11 corrugated horns feeding 22 polarisation-sensitive
(see Leahy et al. 2009 for more details) pseudo-correlation ra-
diometers based on HEMT transistors and MMIC technology,
which are actively cooled to 20 K by a new concept sorption
cooler specifically designed to deliver high efficiency, long du-
ration cooling power (Wade et al. 2000; Bhandari et al. 2004;
Morgante et al. 2009b). A differential scheme for the radiome-
ters is adopted in which the signal from the sky is compared
with a stable reference load at ∼4 K (Valenziano et al. 2009).
The radiometers cover three frequency bands centred on 30 GHz,
44 GHz, and 70 GHz. The design of the radiometers was driven
by the need to minimize the introduction of systematic er-
rors and suppress noise fluctuations generated in the amplifiers.
Originally, LFI was to include seventeen 100 GHz horns with
34 high sensitivity radiometers. This system, which could have
granted redundancy and cross-calibration with HFI as well as a
cross-check of systematics, was not implemented.
The design of the horns is optimized to produce beams of the
highest resolution in the sky and the lowest side lobes. Typical
LFI main beams have full width half maximum (FWHM) resolu-
tions of about 33′, 27′, and 13′, respectively at 30 GHz, 44 GHz,
and 70 GHz,slightly superior to the requirements listed in Table
1 for the cosmologically oriented 70 GHz channel. The beams
are approximately elliptical with and ellipticity ratio (i.e., ma-
jor/minor axis) of ≃1.15–1.40. The beam profiles will be mea-
sured in-flight by observing planets and strong radio sources
(Burigana et al. 2001).
A summary of the LFI performance requirements adopted to
help develop the instrument design is reported in Table 1.
The constraints on the thermal behaviour, required to min-
imize systematic effects, dictated a Planck cryogenic architec-
ture that is one of the most complicated ever conceived for
1Planck (http://www.esa.int/Planck) is a project of the European
Space Agency - ESA - with instruments provided by two scientific
Consortia funded by ESA member states (in particular the lead coun-
tries: France and Italy) with contributions from NASA (USA), and tele-
scope reflectors provided in a collaboration between ESA and a scien-
tific Consortium led and funded by Denmark.
Table 1. LFI performance requirements. The average sensitivity
per 30′pixel or per FWHM2resolution element (δT and δT/T,
respectively) is given in CMB temperature units (i.e. equivalent
thermodynamic temperature) for 14 months of integration. The
white noise (per frequency channel and 1 sec of integration) is
given in antenna temperature units. See Tables 2 and 6 for LFI
measured performance.
Frequency channel 30 GHz 44 GHz 70 GHz
InP detector technology MIC MIC MMIC
Angular resolution [arcmin] 33 24 14
δT per 30′pixel [µK] 8 8 8
δT/T per pixel [µK/K] 2.67 3.67 6.29
Number of radiometers (or feeds) 4 (2) 6 (3) 12 (6)
Effective bandwidth [GHz] 6 8.8 14
System noise temperature [K] 10.7 16.6 29.2
White noise per channel [µK·√s] 116 113 105
Systematic effects [µK] <3<3<3
space. Moreover, the spacecraft has been designed to exploit the
favourable thermal conditions of the L2 orbit. The thermal sys-
tem is a combination of passive and active cooling: passive ra-
diators are used as thermal shields and pre-cooling stages, while
active cryocoolers are used both for instrument cooling and pre-
cooling. The cryochain consists of the following main subsys-
tems (Collaudin & Passvogel 1999):
–pre-cooling from 300 K to about 50 K by means of passive
radiators in three stages (∼150 K, ∼100 K, ∼50 K), which
are called V-Grooves due to their conical shape;
–cooling to 18 K for LFI and pre-cooling the HFI 4 K cooler
by means of a H2Joule-Thomson Cooler with sorption com-
pressors (the Sorption Cooler);
–cooling to 4 K to pre-cool the HFI dilution refrigerator
and the LFI reference loads by means of a helium Joule-
Thomson cooler with mechanical compressors;
–cooling of the HFI to 1.6 K and finally 0.1 K with an open
loop 4He–3He dilution refrigerator.
The LFI front end unit is maintained at its operating tem-
perature by the Planck H2Sorption Cooler Subsystem (SCS),
which is a closed-cycle vibration-free continuous cryocooler de-
signed to provide 1.2 W of cooling power at a temperature of
18 K. Cooling is achieved by hydrogen compression, expansion
through a Joule-Thomson valve and liquid evaporation at the
cold stage. The Planck SCS is the first long-duration system
of its kind to be flown on a space platform. Operations and
performance are described in more detail in Sect. 3.3 and in
Morgante et al. (2009b).
Planck is a spinning satellite. Thus, its receivers will observe
the sky through a sequence of (almost great) circles following a
scanning strategy (SS) aimed at minimizing systematic effects
and achieving all-sky coverage for all receivers. Several parame-
ters are relevant to the SS. The main one is the angle, α, between
the spacecraft spin axis and the telescope optical axis. Given the
extension of the focal plane unit, each beam centre points to its
specific angle, αr. The angle αis set to be 85◦to achieve a nearly
all-sky coverage even in the so-called nominal SS in which the
spacecraft spin axis is kept always exactly along the antisolar di-
rection. This choice avoids the “degenerate” case αr=90◦, char-
acterized by a concentration of the crossings of scan circles only
at the ecliptic poles and the consequent degradation of the qual-
ity of destriping and map-making codes (Burigana et al. 1997;
Maino et al. 1999; Wright et al. 1996; Janssen & Gulkis 1992).
Mandolesi et al.: The Planck-LFI programme 3
Since the Planck mission is designed to minimize straylight con-
tamination from the Sun, Earth, and Moon (Burigana et al. 2001;
Sandri et al. 2009), it is possible to introduce modulations of the
spin axis from the ecliptic plane to maximize the sky coverage,
keeping the solar aspect angle of the spacecraft constant for ther-
mal stability. This drives us towards the adopted baseline SS 2
(Maris et al. 2006a). Thus, the baseline SS adopts a cycloidal
modulation of the spin axis, i.e. a precession around a nominal
antisolar direction with a semiamplitude cone of 7.5◦. In this
way, all Planck receivers will cover the whole sky. A cycloidal
modulation with a 6-month period satisfies the mission opera-
tional constraints, while avoiding sharp gradients in the pixel
hit count (Dupac & Tauber 2005). Furthermore, this solution al-
lows one to spread the crossings of scan circles across a wide
region that is beneficial to map-making, particularly for polari-
sation (Ashdown et al. 2007). The last three SS parameters are:
the sense of precession (clockwise or anticlockwise); the initial
spin axis phase along the precession cone; and, finally, the spac-
ing between two consecutive spin axis repointings, chosen to be
2′to achieve four all-sky surveys with the available guaranteed
number of spin axis manoeuvres.
Fifteen months of integration have been guaranteed since the
approval of the mission. This will allow us to complete at least
two all-sky surveys using all the receivers. The mission lifetime
is going to be formally approved for an extension of 12 months,
which will allow us to perform more than 4 complete sky sur-
veys.
LFI is the result of an active collaboration between about a
hundred universities and research centres, in Europe, Canada,
and USA, organized by the LFI consortium (supported by more
than 300 scientists) funded by national research and space
agencies. The principal investigator leads a team of 26 co-
Investigators responsible for the development of the instrument
hardware and software. The hardware was developed under the
supervision of an instrument team. The data analysis and its sci-
entific exploitation are mostly carried out by a core team, work-
ing in close connection with the Data Processing Centre (DPC).
The LFI core team is a diverse group of relevant scientists (cur-
rently ∼140) with the required expertise in instrument, data
analysis, and theory to deliver to the wider Planck community
the main mission data products. The core cosmology programme
of Planck will be performed by the LFI and HFI core teams. The
core team is closely linked to the wider Planck scientific com-
munity, consisting, besides the LFI consortium, of the HFI and
Telescope consortia, which are organized into various working
groups. Planck is managed by the ESA Planck science team.
The paper is organized as follows. In Sect. 2, we describe the
LFI cosmological and astrophysical objectives and LFI’s role in
the overall mission. We compare the LFI and WMAP sensitivi-
ties with the CMB angular power spectrum in similar frequency
bands, and discuss the cosmological improvement from WMAP
represented by LFI alone and in combination with HFI. Section 3
describes the LFI optics, radiometers, and sorption cooler set-up
and performance. The LFI programme is set forth in Sect. 4. The
LFI Data Processing Centre organisation is presented in Sect. 6,
following a report on the LFI tests and verifications in Sect. 5.
Our conclusions are presented in Sect. 7.
2The above nominal SS is kept as a backup solution in case of a
possible verification in-flight of unexpected problems with the Planck
optics.
2. Cosmology and astrophysics with LFI and Planck
Planck is the third generation space mission for CMB
anisotropies that will open a new era in our understanding of the
Universe (The Planck Collaboration 2006). It will measure cos-
mological parameters with a much greater level of accuracy and
precision than all previous efforts. Furthermore, Planck’s high
resolution all-sky survey, the first ever over this frequency range,
will provide a legacy to the astrophysical community for years
to come.
2.1. Cosmology
The LFI instrument will play a crucial role for cosmology. Its
LFI 70 GHz channel is in a frequency window remarkably clear
from foreground emission, making it particularly advantageous
for observing both CMB temperature and polarisation. The two
lower frequency channels at 30 GHz and 44 GHz will accurately
monitor Galactic and extra-Galactic foreground emissions (see
Sect. 2.2), whose removal (see Sect. 2.3) is critical for a suc-
cessful mission. This aspect is of key importance for CMB po-
larisation measurements since Galactic emission dominates the
polarised sky.
The full exploitation of the cosmological information con-
tained in the CMB maps will be largely based on the joint analy-
sis of LFI and HFI data. While a complete discussion of this as-
pect is beyond the scope of this paper, in the next few subsections
we discuss some topics of particular relevance to LFI or a com-
bined analysis of LFI and HFI data. In Sect. 2.1.1, we review the
LFI sensitivity to the angular power spectrum on the basis of the
realistic LFI sensitivity (see Table 6) and resolution (see Table
2) derived from extensive tests. This instrument description is
adopted in Sect. 2.1.2 to estimate the LFI accuracy of the extrac-
tion of a representative set of cosmological parameters, alone
and in combination with HFI. Section 2.1.3 addresses the prob-
lem of the detection of primordial non-Gaussianity, a topic of
particular interest to the LFI consortium, which will require the
combination of LFI and HFI, because of the necessity to clean
the foreground. On large signal angular scales, WMAP exhibits
a minimum in the foreground in the V band (61GHz, frequency
range 53–69 GHz), thus we expect that the LFI 70 GHz channel
will be particularly helpful for investigating the CMB pattern on
large scales, a topic discussed in Sect. 2.1.4.
It is important to realise that these are just a few examples
of what Planck is capable of. The increased sensitivity, fidelity
and frequency range of the maps, plus the dramatic improvement
in polarisation capability will allow a wide discovery space. As
well as measuring parameters, there will be tests of inflationary
models, consistency tests for dark energy models, and significant
new secondary science probes from correlations with other data-
sets.
2.1.1. Sensitivity to CMB angular power spectra
The statistical information encoded in CMB anisotropies, in both
temperature and polarisation, can be analyzed in terms of a
“compressed” estimator, the angular power spectrum, Cℓ(see
e.g., Scott & Smoot 2008). Provided that the CMB anisotropies
obey Gaussian statistics, as predicted in a wide class of mod-
els, the set of Cℓs contains most of the relevant statistical infor-
mation. The quality of the recovered power spectrum is a good
predictor of the efficiency of extracting cosmological parameters
4 Mandolesi et al.: The Planck-LFI programme
Figure1. CMB temperature anisotropy power spectrum (black
solid line) compatible with WMAP data is compared to WMAP
(Ka band) and LFI (30 GHz) sensitivity, assuming subtraction
of the noise expectation, for different integration times as re-
ported in the figure. Two Planck surveys correspond to about
one year of observations. The plot shows separately the cos-
mic variance (black three dot-dashes) and the instrumental noise
(red and green lines for WMAP and LFI, respectively) assuming
a multipole binning of 5%. This binning allows us to improve
the sensitivity of the power spectrum estimation. For example,
around ℓ=1000 (100) this implies averaging the angular power
spectrum over 50 (5) multipoles. Regarding sampling variance,
an all-sky survey is assumed here for simplicity. The use of the
camb code is acknowledged (see footnote 3).
Figure2. As in Fig. 1 but for the sensitivity of WMAP in V band
and LFI at 70 GHz.
by comparing the theoretical predictions of Boltzmann codes3.
Strictly speaking, this task must be carried out using likelihood
analyses (see Sect. 2.3). Neglecting systematic effects (and cor-
related noise), the sensitivity of a CMB anisotropy experiment
to Cℓ, at each multipole ℓ, is summarized by the equation (Knox
1995)
δCℓ
Cℓ≃s2
fsky(2ℓ+1) "1+Aσ2
NCℓWℓ#,(1)
3http://camb.info/
where Ais the size of the surveyed area, fsky =A/4π,σis the
rms noise per pixel, Nis the total number of observed pixels,
and Wℓis the beam window function. For a symmetric Gaussian
beam, Wℓ=exp(−ℓ(ℓ+1)σ2
B), where σB=FWHM/√8ln2
defines the beam resolution.
Even in the limit of an experiment of infinite sensitivity
(σ=0), the accuracy in the power spectrum is limited by so-
called cosmic and sampling variance, reducing to pure cosmic
variance in the case of all-sky coverage. This dominates at low
ℓbecause of the relatively small number of available modes m
per multipole in the spherical harmonic expansion of a sky map.
The multifrequency maps that will be obtained with Planck will
allow one to improve the foreground subtraction and maximize
the effective sky area used in the analysis, thus improving our
understanding of the CMB power spectrum obtained from pre-
vious experiments. However, the main benefits of the improved
foreground subtraction will be in terms of polarisation and non-
Gaussianity tests.
Figures 1 and 2 compare WMAP4and LFI 5sensitivity to the
CMB temperature Cℓat two similar frequency bands, displaying
separately the uncertainty originating in cosmic variance and in-
strumental performance and considering different project life-
times. For ease of comparison, we consider the same multipole
binning (in both cosmic variance and instrumental sensitivity).
The figures show how the multipole region, where cosmic vari-
ance dominates over instrumental sensitivity, moves to higher
multipoles in the case of LFI and that the LFI 70GHz chan-
nel allows us to extract information about an additional acoustic
peak and two additional throats with respect to those achievable
with the corresponding WMAP V band.
As well as the temperature angular power spectrum, LFI can
measure polarisation anisotropies (Leahy et al. 2009). A some-
what similar comparison is shown in Figs. 3 and 4 but for the
‘E’ and ‘B’ polarisation modes, considering in this case only
the longest mission lifetimes (9 yrs for WMAP, 4 surveys for
Planck) reported in previous figures and a larger multipole bin-
ning; we note the increase in the signal-to-noise ratio compared
to previous figures. Clearly, foreground is more important for
measurements of polarisation than for measurements of temper-
ature. In the WMAP V band and the LFI 70 GHz channels, the
polarised foreground is minimal (at least considering a very large
fraction of the sky and for the range of multipoles already ex-
plored by WMAP). Thus, we consider these optimal frequencies
to represent the potential uncertainty expected from polarised
foregrounds. The Galactic foreground dominates over the CMB
B mode and also the CMB E mode by up to multipoles of several
tens. However, foreground subtraction at an accuracy of 5−10%
of the map level is enough to reduce residual Galactic contam-
ination to well below both the CMB E mode and the CMB B
mode for a wide range of multipoles for r=T/S≃0.3 (here
ris defined in Fourier space). If we are able to model Galactic
polarised foregrounds with an accuracy at the several percent
level, then, for the LFI 70 GHz channel the main limitation will
come from instrumental noise. This will prevent an accurate E
mode evaluation at ℓ∼7–20, or a B mode detection for r<
∼0.3.
Clearly, a more accurate recovery of the polarisation modes will
be possible from the exploitation of the Planck data at all fre-
quencies. In this context, LFI data will be crucial to model more
accurately the polarised synchrotron emission, which needs to
4http://lambda.gsfc.nasa.gov/
5In this comparison, we exploit realistic LFI optical and instrumen-
tal performance as described in the following sections.
Mandolesi et al.: The Planck-LFI programme 5
Figure3. CMB E polarisation modes (black long dashes) com-
patible with WMAP data and CMB B polarisation modes (black
solid lines) for different tensor-to-scalar ratios of primordial per-
turbations (r≡T/S=1,0.3,0.1, at increasing thickness) are
compared to WMAP (Ka band, 9 years of observations) and LFI
(30 GHz, 4 surveys) sensitivity to the power spectrum, assum-
ing the noise expectation has been subtracted. The plots include
cosmic and sampling variance plus instrumental noise (green
dots for B modes, green long dashes for E modes, labeled with
cv+sv+n; black thick dots, noise only) assuming a multipole bin-
ning of 30% (see caption of Fig. 1 for the meaning of binning and
of the number of sky surveys). Note that the cosmic and sam-
pling (74% sky coverage; as in WMAP polarization analysis, we
exclude the sky regions mostly affected by Galactic emission)
variance implies a dependence of the overall sensitivity at low
multipoles on r(again the green lines refer to r=1,0.3,0.1,
from top to bottom), which is relevant to the parameter estima-
tion; instrumental noise only determines the capability of detect-
ing the B mode. The B mode induced by lensing (blue dots) is
also shown for comparison.
be removed to greater than the few percent level to detect pri-
mordial B modes for r<
∼0.1 (Efstathiou & Gratton 2009).
2.1.2. Cosmological parameters
Given the improvement relative to WMAP Cℓachievable with the
higher sensitivity and resolution of Planck (as discussed in the
previous section for LFI), correspondingly superior determina-
tion of cosmological parameters is expected. Of course, the bet-
ter sensitivity and angular resolution of HFI channels compared
to WMAP and LFI ones will highly contribute to the improve-
ment in cosmological parameters measured using Planck.
We present here the comparison between determinations of a
suitable set of cosmological parameters using data from WMAP,
Planck, and Planck LFI alone.
In Fig. 5 we compare the forecasts for 1σand 2σcontours
for 4 cosmological parameters of the WMAP5 best-fit ΛCDM
cosmological model: the baryon density; the cold dark matter
(CDM) density; reionization, parametrized by the Thomson op-
tical depth τ; and the slope of the initial power spectrum. These
results show the expectation for the Planck LFI 70 GHz chan-
nel alone after 14 months of observations (red lines), the Planck
combined 70 GHz, 100 GHz, and 143 GHz channels for the same
integration time (blue lines), and the WMAP five year observa-
Figure4. As in Fig. 3 but for the sensitivity of WMAP in V
band and LFI at 70 GHz, and including also the comparison with
Galactic and extragalactic polarised foregrounds. Galactic syn-
chrotron (purple dashes) and dust (purple dot-dashes) polarised
emissions produce the overall Galactic foreground (purple three
dot-dashes). WMAP 3-yr power-law fits for uncorrelated dust
and synchrotron have been used. For comparison, WMAP 3-
yr results derived directly from the foreground maps using the
HEALPix package (G´orski et al. 2005) are shown over a suitable
multipole range: power-law fits provide (generous) upper lim-
its to the power at low multipoles. Residual contamination lev-
els by Galactic foregrounds (purple three dot-dashes) are shown
for 10%, 5%, and 3% of the map level, at increasing thickness.
The residual contribution of unsubtracted extragalactic sources,
Cres,PS
ℓand the corresponding uncertainty, δCres,PS
ℓare also plot-
ted as thick and thin green dashes. These are computed assuming
a relative uncertainty δΠ/Π = δSlim/Slim =10% in the knowl-
edge of their degree of polarisation and the determination of the
source detection threshold. We assumed the same sky coverage
as in Fig. 3. Clearly, foreground contamination is lower at 70
GHz than at 30 GHz, but, since CMB maps will be produced
from a component separation layer (see Sects. 2.3 and 6.3) we
considered the same sky region.
tions (black lines). We assumed that the 70 GHz channels and
the 100 GHz and 143 GHz are the representative channels for
LFI and HFI (we note that for HFI we have used angular reso-
lution and sensitivities as given in Table 1.3 of the Planck scien-
tific programme prepared by The Planck Collaboration (2006),)
for cosmological purposes, respectively,and we assumed a cov-
erage of ∼70% of the sky. Figure 5 shows that HFI 100 GHz
and 143 GHz channels are crucial for obtaining the most accu-
rate cosmological parameter determination.
While we have not explicitly considered the other chan-
nels of LFI (30 GHz and 44 GHz) and HFI (at frequencies ≥
217 GHz) we note that they are essential for achieving the accu-
rate separation of the CMB from astrophysical emissions, par-
ticularly for polarisation.
The improvement in cosmological parameter precision for
LFI (2 surveys) compared to WMAP5 (Dunkley et al. 2009;
Komatsu et al. 2009) is clear from Fig. 5. This is maximized for
the dark matter abundance Ωcbecause of the performance of the
LFI 70 GHz channel with respect to WMAP5. From Fig. 5 it is
clear that the expected improvement for Planck in cosmological
6 Mandolesi et al.: The Planck-LFI programme
0.022 0.024
0.1 0.12
0.05 0.1 0.15
0.92 0.96 1
ns
Ωc h2
0.022 0.024
0.09
0.1
0.11
0.12
0.13
τ
0.022 0.024
0.05
0.1
0.15
Ωb h2
ns
0.022 0.024
0.92
0.94
0.96
0.98
1
0.1 0.12
0.05
0.1
0.15
Ωc h2
0.1 0.12
0.92
0.94
0.96
0.98
1
τ
0.05 0.1 0.15
0.92
0.94
0.96
0.98
1
Figure5. Forecasts of 1σand 2σcontours for the cosmological
parameters of the WMAP5 best-fit ΛCDM cosmological model
with reionization, as expected from Planck (blue lines) and from
LFI alone (red lines) after 14 months of observations. The black
contours are those obtained from WMAP five year observations.
See the text for more details.
parameter determination compared to that of WMAP5 can open
a new phase in our understanding of cosmology.
2.1.3. Primordial non-Gaussianity
Simple cosmological models assume Gaussian statistics for the
anisotropies. However, important information may come from
mild deviations from Gaussianity (see e.g., Bartolo et al. 2004
for a review). Planck total intensity and polarisation data will ei-
ther provide the first true measurement of non-Gaussianity (NG)
in the primordial curvature perturbations, or tighten the existing
constraints (based on WMAP data, see footnote 3) by almost an
order of magnitude.
Probing primordial NG is another activity that requires fore-
ground cleaned maps. Hence, the full frequency maps of both
instruments must be used for this purpose.
It is very important that the primordial NG is model depen-
dent. As a consequence of the assumed flatness of the inflaton
potential, any intrinsic NG generated during standard single-
field slow-roll inflation is generally small, hence adiabatic per-
turbations originated by quantum fluctuations of the inflaton
field during standard inflation are nearly Gaussian distributed.
Despite the simplicity of the inflationary paradigm, however, the
mechanism by which perturbations are generated has not yet
been fully established and various alternatives to the standard
scenario have been considered. Non-standard scenarios for the
generation of primordial perturbations in single-field or multi-
field inflation indeed permit higher NG levels. Alternative sce-
narios for the generation of the cosmological perturbations, such
as the so-called curvaton, the inhomogeneous reheating, and
DBI scenarios (Alishahiha et al. 2004), are characterized by a
typically high NG level. For this reason, detecting or even just
constraining primordial NG signals in the CMB is one of the
most promising ways to shed light on the physics of the early
Universe.
The standard way to parameterize primordial non-
Gaussianity involves the parameter fNL, which is typically
small. A positive detection of fNL ∼10 would imply that all
standard single-field slow-roll models of inflation are ruled out.
In contrast, an improvement to the limits on the amplitude of
fNL will allow one to strongly reduce the class of non-standard
inflationary models allowed by the data, thus providing unique
insight into the fluctuation generation mechanism. At the same
time, Planck temperature and polarisation data will allow
different predictions of the shape of non-Gaussianities to be
tested beyond the simple fNL parameterization. For simple,
quadratic non-Gaussianity of constant fNL, the angular bis-
pectrum is dominated by “squeezed” triangle configurations
with ℓ1≪ℓ2, ℓ3. This “local” NG is typical of models that
produce the perturbations immediately after inflation (such as
for the curvaton or the inhomogeneous reheating scenarios).
So-called DBI inflation models, based on non-canonical kinetic
terms for the inflaton lead to non-local forms of NG, which are
dominated by equilateral triangle configurations. It has been
pointed out (Holman & Tolley 2008) that excited initial states of
the inflaton may lead to a third shape, called “flattened” triangle
configuration.
The strongest available CMB limits on fNL for local NG
comes from WMAP5. In particular, Smith et al. (2009) obtained
−4<fNL <80 at 95% confidence level (C.L.) using the op-
timal estimator of local NG. Planck total intensity and polar-
isation data will allow the window on |fNL|to be reduced be-
low ∼10. Babich & Zaldarriaga (2004) and Yadav et al. (2007)
demonstrated that a sensitivity to local non-Gaussianity ∆fNL ≈
4 (at 1σ) is achievable with Planck. We note that accurate
measurement of E-type polarisation will play a significant role
in this constraint. Note also that the limits that Planck can
achieve in this case are very close to those of an “ideal” ex-
periment. Equilateral-shape NG is less strongly constrained at
present, with −125 <fNL <435 at 95% C.L. (Senatore et al.
2009). In this case, Planck will also have a strong impact
on this constraint. Various authors (Smith & Zaldarriaga 2006;
Bartolo & Riotto 2009) have estimated that Planck data will al-
low us to reduce the bound on |fNL|to around 70.
Measuring the primordial non-Gaussianity in CMB data to
these levels of precision requires accurate handling of possible
contaminants, such as those introduced by instrumental noise
and systematics, by the use of masks and imperfect foreground
and point source removal.
2.1.4. Large-scale anomalies
Observations of CMB anisotropies contributed significantly to
the development of the standard cosmological model, also
known as the ΛCDM concordance model. This involves a set of
basic quantities for which CMB observations and other cosmo-
logical and astrophysical data-sets agree: spatial curvature close
to zero; ≃70% of the cosmic density in the form of dark energy;
≃20% in CDM; 4−5% in baryonic matter; and a nearly scale-
invariant adiabatic, Gaussian primordial perturbations. Although
the CMB anisotropy pattern obtained by WMAP is largely con-
sistent with the concordance ΛCDM model, there are some inter-
esting and curious deviations from it, in particular on the largest
angular scales. Probing these deviations has required careful
analysis procedures and so far are at only modest levels of sig-
nificance. The anomalies can be listed as follows:
Mandolesi et al.: The Planck-LFI programme 7
–lack of power on large scales. The angular correlation func-
tion is found to be uncorrelated (i.e., consistent with zero)
for angles larger than 60◦. In Copi et al. (2007, 2008), it
was shown that this event happens in only 0.03% of real-
izations of the concordance model. This is related to the sur-
prisingly low amplitude of the quadrupole term of the an-
gular power spectrum already found by COBE (Smoot et al.
1992; Hinshaw et al. 1996), and now confirmed by WMAP
(Dunkley et al. 2009; Komatsu et al. 2009).
–Hemispherical asymmetries. It is found that the power com-
ing separately from the two hemispheres (defined by the
ecliptic plane) is quite asymmetric, especially at low ℓ
(Eriksen et al. 2004a,b; Hansen et al. 2004).
–Unlikely alignments of low multipoles. An unlikely
(for a statistically isotropic random field) alignment
of the quadrupole and the octupole (Tegmark et al.
2003; Copi et al. 2004; Schwarz et al. 2004; Weeks 2004;
Land & Magueijo 2005). Both quadrupole and octupole
align with the CMB dipole (Copi et al. 2007). Other un-
likely alignments are described in Abramo et al. (2006),
Wiaux et al. (2006) and Vielva et al. (2007).
–Cold Spot. Vielva et al. (2004) detected a localized non-
Gaussian behaviour in the southern hemisphere using a
wavelet analysis technique (see also Cruz et al. 2005).
It is still unknown whether these anomalies are indicative of
new (and fundamental) physics beyond the concordance model
or whether they are simply the residuals of imperfectly removed
astrophysical foreground or systematic effects. Planck data will
provide a valuable contribution, not only in refining the cosmo-
logical parameters of the standard cosmological model but also
in solving the aforementioned puzzles, because of the superior
foreground removal and control of systematic effects, as well as
Planck’s different scan strategy and wider frequency range com-
pared with WMAP. In particular, the LFI 70 GHz channel will
be crucial, since, as shown by WMAP, the foreground on large
angular scales reaches a minimum in the V band.
2.2. Astrophysics
The accuracy of the extraction of the CMB anisotropy pat-
tern from Planck maps largely relies, particularly for polarisa-
tion, on the quality of the separation of the background sig-
nal of cosmological origin from the various foreground sources
of astrophysical origin that are superimposed on the maps (see
also Sect. 2.3). The scientific case for Planck was presented by
The Planck Collaboration (2006) and foresees the full exploita-
tion of the multifrequency data. This is aimed not only at the ex-
traction of the CMB, but also at the separation and study of each
astrophysical component, using Planck data alone or in combi-
nation with other data-sets. This section provides an update of
the scientific case, with particular emphasis on the contribution
of the LFI to the science goals.
2.2.1. Galactic astrophysics
Planck will carry out an all-sky survey of the fluctuations in
Galactic emission at its nine frequency bands. The HFI chan-
nels at ν≥100 GHz will provide the main improvement with
respect to COBE characterizing the large-scale Galactic dust
emission6, which is still poorly known, particularly in polari-
6At far-IR frequencies significantly higher than those cov-
ered by Planck, much information comes from IRAS (see e.g.,
Miville-Deschˆenes & Lagache 2005 for a recent version of the maps).
sation. However, since Galactic dust emission still dominates
over free-free and synchrotron at 70 GHz (see e.g. (Gold et al.
2009) and references therein), LFI will provide crucial informa-
tion about the low frequency tail of this component. The LFI
frequency channels, in particular those at 30 GHz and 44 GHz,
will be relevant to the study of the diffuse, significantly polarised
synchrotron emission and the almost unpolarised free-free emis-
sion.
Results from WMAP’s lowest frequency channels inferred
an additional contribution, probably correlated with dust (see
Dobler et al. 2008 and references therein). While a model
with complex synchrotron emission pattern and spectral in-
dex cannot be excluded, several interpretations of microwave
(see e.g. Hildebrandt et al. 2007; Bonaldi et al. 2007) and radio
(La Porta et al. 2008) data, and in particular the ARCADE 2 re-
sults (Kogut et al. 2009), seem to support the identification of
this anomalous component as spinning dust (Draine & Lazarian
1998; Lazarian & Finkbeiner 2003). LFI data, at 30 GHz in par-
ticular, will shed new light on this intriguing question.
Another interesting component that will be studied by
Planck data is the so-called “haze” emission in the inner
Galactic region, possibly generated by synchrotron emission
from relativistic electrons and positrons produced in the anni-
hilations of dark matter particles (see e.g., Hooper et al. 2007;
Cumberbatch et al. 2009; Hooper et al. 2008 and references
therein).
Furthermore, the full interpretation of the Galactic dif-
fuse emissions in Planck maps will benefit from a joint
analysis with both radio and far-IR data. For instance,
PILOT (Bernard et al. 2007) will improve on Archeops results
(Ponthieu et al. 2005), measuring polarised dust emission at fre-
quencies higher than 353 GHz, and BLAST-Pol (Marsden et al.
2008) at even higher frequencies. All-sky surveys at 1.4 GHz
(see e.g., Burigana et al. 2006 and references therein) and in
the range of a few GHz to 15 GHz will complement the
low frequency side (see e.g., PGMS, Haverkorn et al. 2007;
C-BASS, Pearson & C-BASS collaboration 2007; QUIJOTE,
Rubino-Martin et al. 2008; and GEM, Barbosa et al. 2006) al-
lowing an accurate multifrequency analysis of the depolarisation
phenomena at low and intermediate Galactic latitudes. Detailed
knowledge of the underlying noise properties in Planck maps
will allow one to measure the correlation characteristics of the
diffuse component, greatly improving physical models of the in-
terstellar medium (ISM). The ultimate goal of these studies is the
development of a consistent Galactic 3D model, which includes
the various components of the ISM, and large and small scale
magnetic fields (see e.g., Waelkens et al. 2009), and turbulence
phenomena (Cho & Lazarian 2003).
While having moderate resolution and being limited in flux
to a few hundred mJy, Planck will also provide multifrequency,
all-sky information about discrete Galactic sources. This will in-
clude objects from the early stages of massive stars to the late
stages of stellar evolution (Umana et al. 2006), from HII regions
to dust clouds (Pelkonen et al. 2007). Models for both the en-
richment of the ISM and the interplay between stellar formation
and ambient physical properties will be also tested.
Planck will also have a chance to observe some Galactic
micro-blazars (such as e.g., Cygnus X-3) in a flare phase and per-
form multifrequency monitoring of these events on timescales
from hours to weeks. A quick detection software (QDS) system
was developed by a Finnish group in collaboration with LFI DPC
(Aatrokoski et al. 2009). This will be used to identify of source
flux variation, in Planck time ordered data.
8 Mandolesi et al.: The Planck-LFI programme
Figure6. Integral counts of different radio source populations
at 70 GHz, predicted by the de Zotti et al. (2005) model: flat-
spectrum radio quasars; BL Lac objects; and steep-spectrum
sources. The vertical dotted lines show the estimated complete-
ness limits for Planck and WMAP (61 GHz) surveys.
Finally, Planck will provide unique information for mod-
elling the emission from moving objects and diffuse interplan-
etary dust in the Solar System. The mm and sub-mm emis-
sion from planets and up to 100 asteroids will also be studied
(Cremonese et al. 2002; Maris & Burigana 2009). The zodiacal
light emission will also be measured to great accuracy, free from
residual Galactic contamination (Maris et al. 2006b).
2.2.2. Extragalactic astrophysics
The higher sensitivity and angular resolution of LFI compared
to WMAP will allow us to obtain substantially richer samples of
extragalactic sources at mm wavelengths. Applying a new multi-
frequency linear filtering technique to realistic LFI simulations
of the sky, Herranz et al. (2009) detected 1600, 1550, and 1000
sources with 95% reliability at 30, 44, and 70 GHz, respectively,
over about 85% of the sky. The 95% completeness fluxes are
540, 340, and 270 mJy at 30, 44, and 70 GHz, respectively. For
comparison, the total number of |b|>5◦sources detected by
Massardi et al. (2009) at ≥5σin WMAP5 maps at 33, 41, and
61 GHz (including several possibly spurious objects), are 307,
301, and 161, respectively; the corresponding detection limits
increase from ≃1 Jy at 23 GHz, to ≃2 Jy at 61 GHz. The number
of detections reported by Wright et al. (2009) is lower by about
20%.
As illustrated in Fig. 6, the far larger source sample expected
from Planck will allow us to obtain good statistics for differ-
ent subpopulations of sources, some of which are not (or only
poorly) represented in the WMAP sample. The dominant radio
population at LFI frequencies consists of flat-spectrum radio
quasars, for which LFI will provide a bright sample of ≥1000
objects, well suited to cover the parameter space of current phys-
ical models. Interestingly, the expected numbers of blazars and
BL Lac objects detectable by LFI are similar to those expected
from the Fermi Gamma-ray Space Telescope (formerly GLAST;
Abdo 2009; Fermi/LAT Collaboration: W.B. Atwood 2009). It
is likely that the LFI and the Fermi blazar samples will have
a substantial overlap, making it possible to more carefully de-
fine the relationships between radio and gamma-ray properties of
these sources than has been possible so far. The analysis of spec-
tral properties of the ATCA 20 GHz bright sample indicates that
quite a few high-frequency selected sources have peaked spec-
tra; most of them are likely to be relatively old, beamed objects
(blazars), whose radio emission is dominated by a single knot in
the jet caught in a flaring phase. The Planck sample will allow
us to obtain key information about the incidence and timescales
of these flaring episodes, the distribution of their peak frequen-
cies, and therefore the propagation of the flare along the jet. A
small fraction of sources exhibiting high frequency peaks may be
extreme high frequency peakers (Dallacasa et al. 2000), under-
stood to be newly born radio sources (ages as low as thousand
years). Obviously, the discovery of just a few of these sources
would be extremely important for sheding light on the poorly
understood mechanisms that trigger the radio activity of Galactic
cores.
WMAP has detected polarised fluxes at ≥4σin two or more
bands for only five extragalactic sources (Wright et al. 2009).
LFI will substantially improve on this, providing polarisation
measurements for tens of sources, thus allowing us to obtain
the first statistically meaningful unbiased sample for polarisation
studies at mm wavelengths. It should be noted that Planck po-
larisation measurements will not be confusion-limited, as in the
case of total flux, but noise-limited. Thus the detection limit for
polarised flux in Planck-LFI channels will be ≃200–300 mJy,
i.e., lower than for the total flux.
As mentioned above, the astrophysics programme of Planck
is much wider than that achievable with LFI alone, both be-
cause the specific role of HFI and, in particular, the great sci-
entific synergy between the two instruments. One noteworthy
example is the Planck contribution to the astrophysics of clus-
ters. Planck will detect ≈103galaxy clusters out to redshifts
of order unity by means of their thermal Sunyaev-Zel’dovich
effect (Leach et al. 2008; Bartlett et al. 2008). This sample will
be extremely important for understanding both the formation of
large-scale structure and the physics of the intracluster medium.
To perform these measurements, a broad spectral coverage, i.e.,
the combination of data from both Planck instruments (LFI and
HFI), is a key asset. This combination, supplemented by ground-
based, follow-up observations planned by the Planck team, will
allow, in particular, accurate correction for the contamination by
radio sources (mostly due to the high quality of the LFI chan-
nels) and dusty galaxies (HFI channels), either associated with
the clusters or in their foreground/background (Lin et al. 2009).
2.3. Scientific data analysis
The data analysis process for a high precision experiment such as
LFI must be capable of reducing the data volume by several or-
ders of magnitude with minimal loss of information. The sheer-
ing size of the data set, the high sensitivity required to achieve
the science goals, and the significance of the statistical and sys-
tematic sources of error all conspire to make data analysis a far
from trivial task.
The map-making layer provides a lossless compression by
several orders of magnitude, projecting the data set from the time
domain to the discretized celestial sphere (Janssen & Gulkis
1992; Lineweaver et al. 1994; Wright et al. 1996; Tegmark
1997). Furthermore, timeline-specific instrumental effects that
are not scan-synchronous are reduced in magnitude when pro-
jected from time to pixel space (see e.g., Mennella et al. 2002)
and, in general, the analysis of maps provides a more convenient
means of assessing the level of systematics compared to timeline
analysis.
Mandolesi et al.: The Planck-LFI programme 9
Several map-making algorithms have been proposed to pro-
duce sky maps in total intensity (Stokes I) and linear polarisation
(Stokes Qand U) from the LFI timelines. So-called “destriping”
algorithms have historically first been applied. These take ad-
vantage of the details of the Planck scanning strategy to suppress
correlated noise (Maino et al. 1999). Although computationally
efficient, these methods do not, in general, yield a minimum vari-
ance map. To overcome this problem, minimum-variance map-
making algorithms have been devised and implemented specif-
ically for LFI (Natoli et al. 2001; de Gasperis et al. 2005). The
latter are also known as generalized least squares (GLS) meth-
ods and are accurate and flexible. Their drawback is that, at the
size of the Planck data set, they require a significant amount
of massively powered computational resources (Poutanen et al.
2006; Ashdown et al. 2007, 2009) and are thus infeasible to use
within a Monte Carlo context. To overcome the limitations of
GLS algorithms, the LFI community has developed so-called
“hybrid” algorithms (Keih¨anen et al. 2005; Kurki-Suonio et al.
2009; Keih¨anen et al. 2009). These algorithms rely on a tunable
parameter connected to the 1/fknee frequency,a measure of the
amount of low frequency correlated noise in the time-ordered
data: the higher the knee frequency, the shorter the “baseline”
length needed to be chosen to properly suppress the 1/fcontri-
bution. From this point of view, the GLS solution can be thought
of as the limiting case when the baseline length approaches the
sampling interval. Provided that the knee frequency is not too
high, hybrid algorithms can achieve GLS accuracy at a fraction
of the computational demand. Furthermore, they can be tuned to
the desired precision when speed is an issue (e.g., for timeline-
to-map Monte Carlo production). The baseline map-making al-
gorithms for LFI is a hybrid code dubbed madam.
Map-making algorithms can, in general, compute the corre-
lation (inverse covariance) matrix of the map estimate that they
produce (Keskitalo et al. 2009). At high resolution this compu-
tation, though feasible, is impractical, because the size of the
matrix makes its handling and inversion prohibitively difficult.
At low resolution, the covariance matrix will be produced in-
stead: this is of extreme importance for the accurate characteri-
zation of the low multipoles of the CMB (Keskitalo et al. 2009;
Gruppuso et al. 2009).
A key tier of Planck data analysis is the separation of as-
trophysical from cosmological components. A variety of meth-
ods have been developed to this end (e.g., Leach et al. 2008).
Point source extraction is achieved by exploiting non-Planck cat-
alogues, as well as filtering Planck maps with optimal functions
(wavelets) capable of recognizing beam-like patterns. In addition
to linearly combining the maps or fitting for known templates,
diffuse emissions are separated by using the statistical distribu-
tions of the different components, assuming independence be-
tween them, or by means of a suitable parametrization and fit-
ting of foreground unknowns on the basis of spatial correlations
in the data or, in alternative, multi-frequency single resolution
elements only.
The extraction of statistical information from the CMB usu-
ally proceeds by means of correlation functions. Since the CMB
field is Gaussian to a large extent (e.g. Smith et al. 2009), most
of the information is encoded in the two-point function or equiv-
alently in its reciprocal representation in spherical harmonics
space. Assuming rotational invariance, the latter quantity is well
described by the set of Cℓ(see e.g., Gorski 1994). For an ideal
experiment, the estimated power spectrum could be directly
compared to a Boltzmann code prediction to constrain the cos-
mological parameters. However, in the case of incomplete sky
coverage (which induces couplings among multipoles) and the
presence of noise (which, in general, is not rotationally invari-
ant because of the coupling between correlated noise and scan-
ning strategy), a more thorough analysis is necessary. The likeli-
hood function for a Gaussian CMB sky can be easily written and
provides a sound mechanism for constraining models and data.
The direct evaluation of this function, however, poses intractable
computational issues. Fortunately, only the lowest multipoles re-
quire exact treatment. This can be achieved either by direct eval-
uation in the pixel domain or sampling the posterior distribu-
tion of the CMB using sampling methods such as the Gibbs ap-
proach (Jewell et al. 2004; Wandelt et al. 2004). At high multi-
poles, where the likelihood function cannot be evaluated exactly,
a wide range of effective, computationally affordable approxima-
tions exist (see e.g., Hamimeche & Lewis 2008 and Rocha et al.
2009 and references therein). The low and high ℓapproaches to
power spectrum estimation will be joined into a hybrid proce-
dure, pioneered by Efstathiou (2004).
The data analysis of LFI will require daunting computational
resources. In view of the size and complexity of its data set, ac-
curate characterization of the scientific results and error propaga-
tion will be achieved by means of a massive use of Monte Carlo
simulations. A number of worldwide distributed supercomputer
centres will support the DPC in this activity. A partial list in-
cludes NERSC-LBNL in the USA, CINECA in Italy, CSC in
Finland, and MARE NOSTRUM in Spain. The European cen-
tres will benefit from the Distributed European Infrastructure for
Supercomputer Application 7.
3. Instrument
3.1. Optics
During the design phase of LFI, great effort was dedicated to
the optical design of the Focal Plane Unit (FPU). As already
mentioned in the introduction, the actual design of the Planck
telescope is derived from COBRAS and specially has been
tuned by subsequent studies of the LFI team (Villa et al. 1998)
and Thales-Alenia Space. These studies demonstrated the im-
portance of increasing the telescope diameter (Mandolesi et al.
2000), optimizing the optical design, and also showed how com-
plex it would be to match the real focal surface to the horn
phase centres (Valenziano et al. 1998). The optical design of LFI
is the result of a long iteration process in which the optimiza-
tion of the position and orientation of each feed horn involves a
trade-offbetween angular resolution and sidelobe rejection lev-
els (Sandri et al. 2004; Burigana et al. 2004; Sandri et al. 2009).
Tight limits were also imposed by means of mechanical con-
straints. The 70 GHz system has been improved in terms of the
single horn design and its relative location in the focal surface.
As a result, the angular resolution has been maximized.
The feed horn development programme started in the
early stages of the mission with prototype demonstra-
tors (Bersanelli et al. 1998), followed by the elegant bread
board (Villa et al. 2002) and finally by the qualification
(D’Arcangelo et al. 2005) and flight models (Villa et al. 2009).
The horn design has a corrugated shape with a dual profile
(Gentili et al. 2000). This choice was justified by the complexity
of the optical interfaces (coupling with the telescope and focal
plane horn accommodation) and the need to respect the inter-
faces with HFI.
Each of the corrugated horns feeds an orthomode transducer
(OMT) that splits the incoming signal into two orthogonal po-
7http://www.deisa.eu
10 Mandolesi et al.: The Planck-LFI programme
larised components (D’Arcangelo et al. 2009a). The polarisa-
tion capabilities of the LFI are guaranteed by the use of OMTs
placed immediately after the corrugated horns. While the incom-
ing polarisation state is preserved inside the horn, the OMT di-
vides it into two linear orthogonal polarisations, allowing LFI
to measure the linear polarisation component of the incoming
sky signal. The typical value of OMT cross-polarisation is about
−30dB, setting the spurious polarisation of the LFI optical inter-
faces at a level of 0.001.
Table 2 shows the overall LFI optical characteristics ex-
pected in-flight (Tauber et al. 2009). The edge taper (ET) values,
quoted in Table 2, refer to the horn taper; they are reference val-
ues assumed during the design phase and do not correspond to
the true edge taper on the mirrors (see Sandri et al. 2009 for de-
tails). The reported angular resolution is the average full width
half maximum (FWHM) of all the channels at the same fre-
quency. The cross-polar discrimination (XPD) is the ratio of the
antenna solid angle of the cross-polar pattern to the antenna solid
angle of the co-polar pattern, both calculated within the solid an-
gle of the −3 dB contour. The main- and sub-reflector spillovers
represent the fraction of power that reach the horns without be-
ing intercepted by the main- and sub-reflectors, respectively.
Table 2. LFI optical performance. All the values are averaged
over all channels at the same frequency. ET is the horn edge
taper measured at 22◦from the horn axis; FWHM is the angular
resolution in arcmin; eis the ellipticity; XPD is the cross-polar
discrimination in dB; Ssp is the Sub-reflector spillover (%); Msp
is the Main-reflector spillover (%). See text for details.
ET FWHM eXPD Ssp Msp
70 17 dB at 22◦13.03 1.22 −34.73 0.17 0.65
44 30 dB at 22◦26.81 1.26 −30.54 0.074 0.18
30 30 dB at 22◦33.34 1.38 −32.37 0.24 0.59
3.2. Radiometers
LFI is designed to cover the low frequency portion of the
wide-band Planck all-sky survey. A detailed description of the
design and implementation of the LFI instrument is given in
Bersanelli et al. (2009) and references therein, while the results
of the on-ground calibration and test campaign are presented
in Mennella et al. (2009) and Villa et al. (2009b). The LFI is
an array of cryogenically cooled radiometers designed to ob-
serve in three frequency bands centered on 30 GHz, 44 GHz, and
70 GHz with high sensitivity and practically no systematic error.
All channels are sensitive to the I,Q, and UStokes parameters,
thus providing information about both temperature and polari-
sation anisotropies. The heart of the LFI instrument is a com-
pact, 22-channel multifrequency array of differential receivers
with cryogenic low-noise amplifiers based on indium phosphide
(InP) high-electron-mobility transistors (HEMTs). To minimise
the power dissipation in the focal plane unit, which is cooled to
20 K, the radiometers are divided into two subassemblies (the
front-end module, FEM, and the back-end module, BEM) con-
nected by a set of composite waveguides, as shown in Fig. 7.
Miniaturized, low-loss passive components are implemented in
the front end for optimal performance and compatibility with the
stringent thermo-mechanical requirements of the interface with
the HFI.
Figure7. The LFI radiometer array assembly, with details of
the front-end and back-end units. The front-end radiometers
are based on wide-band low-noise amplifiers, fed by corrugated
feedhorns which collect the radiation from the telescope. A set
of composite waveguides transport the amplified signals from
the front-end unit (at 20 K) to the back-end unit (at 300 K). The
waveguides are designed to meet simultaneously radiometric,
thermal, and mechanical requirements, and are thermally linked
to the three V-Groove thermal shields of the Planck payload
module. The back-end unit, located on top of the Planck ser-
vice module, contains additional amplification as well as the de-
tectors, and is interfaced to the data acquisition electronics. The
HFI is inserted into and attached to the frame of the LFI focal-
plane unit.
The radiometer was designed to suppress 1/f-type noise in-
duced by gain and noise temperature fluctuations in the ampli-
fiers, which would otherwise be unacceptably high for a simple,
total-power system. A differential pseudo-correlation scheme is
adopted, in which signals from the sky and from a black-body
reference load are combined by a hybrid coupler, amplified by
two independent amplifier chains, and separated by a second hy-
brid (Fig. 8). The sky and the reference load power can then
be measured and their difference calculated. Since the refer-
ence signal has been affected by the same gain variations in
the two amplifier chains as the sky signal, the sky power can
be recovered to high precision. Insensitivity to fluctuations in
the back-end amplifiers and detectors is realized by switching
phase shifters at 8 kHz synchronously in each amplifier chain.
The rejection of 1/fnoise as well as immunity to other sys-
tematic effects is optimised if the two input signals are nearly
equal. For this reason, the reference loads are cooled to 4 K
(Valenziano et al. 2009) by mounting them on the 4 K structure
of the HFI. In addition, the effect of the residual offset (<1 K
in nominal conditions) is reduced by introducing a gain mod-
ulation factor in the onboard processing to balance the output
signal. As shown in Fig. 8, the differencing receiver greatly im-
proves the stability of the measured signal (see also Fig. 8 in
Bersanelli et al. 2009).
The LFI amplifiers at 30 GHz and 44 GHz use discrete InP
HEMTs incorporated into a microwave integrated circuit (MIC).
At these frequencies, the parasitics and uncertainties introduced
by the bond wires in a MIC amplifier are controllable and
Mandolesi et al.: The Planck-LFI programme 11
Figure8. Schematic of the LFI front-end radiometer. The front-
end unit is located at the focus of the Planck telescope, and com-
prises: dual-profiled corrugated feed horns; low-loss (0.2 dB),
wideband (>20%) orthomode transducers; and radiometer
front-end modules with hybrids, cryogenic low noise amplifiers,
and phase switches. For details see Bersanelli et al. (2009).
the additional tuning flexibility facilitates optimization for low
noise. At 70 GHz, there are twelve detector chains. Amplifiers at
these frequencies use monolithic microwave integrated circuits
(MMICs), which incorporate all circuit elements and the HEMT
transistors on a single InP chip. At these frequencies, MMIC
technology provides not only significantly superior performance
to MIC technology, but also allows faster assembly and smaller
sample-to-sample variance. Given the large number of ampli-
fiers required at 70 GHz, MMIC technology can rightfully be
regarded as an important development for the LFI.
Fourty-four waveguides connect the LFI front-end unit,
cooled to 20 K by a hydrogen sorption cooler, to the back-end
unit (BEU), which is mounted on the top panel of the Planck ser-
vice module (SVM) and maintained at a temperature of 300 K.
The BEU comprises the eleven BEMs and the data acquisition
electronics (DAE) unit, which provides adjustable bias to the
amplifiers and phase switches as well as scientific signal con-
ditioning. In the back-end modules, the RF signals are ampli-
fied further in the two legs of the radiometers by room tem-
perature amplifiers. The signals are then filtered and detected
by square-law detector diodes. A DC amplifier then boosts the
signal output, which is connected to the data acquisition elec-
tronics. After onboard processing, provided by the radiometer
box electronics assembly (REBA), the compressed signals are
down-linked to the ground station together with housekeeping
data. The sky and reference load DC signals are transmitted
to the ground as two separated streams of data to ensure opti-
mal calculation of the gain modulation factor for minimal 1/f
noise and systematic effects. The complexity of the LFI sys-
tem called for a highly modular plan of testing and integration.
Performance verification was first carried out at the single unit-
level, followed by campaigns at sub-assembly and instrument
level, then completed with full functional tests after integration
into the Planck satellite. Scientific calibration has been carried
out in two main campaigns, first on the individual radiometer
chain assemblies (RCAs), i.e., the units comprising a feed horn
and the two pseudo-correlation radiometers connected to each
arm of the orthomode transducer (see Fig. 8), and then at in-
strument level. For the RCA campaign, we used sky loads and
reference loads cooled close 4 K which allowed us to perform
an accurate verification of the instrument performance in near-
flight conditions. Instrument level tests were carried out with
loads at 20 K, which allowed us to verify the radiometer per-
formance in the integrated configuration. Testing at the RCA
and instrument level, both for the qualification model (QM) and
the flight model (FM), were carried out at Thales Alenia Space,
Vimodrone (Milano, Italy). Finally, system-level tests of the LFI
Figure9. Top panel: picture of the LFI focal plane showing
the feed-horns and main frame. The central portion of the main
frame is designed to provide the interface to the HFI front-end
unit, where the reference loads for the LFI radiometers are lo-
cated and cooled to 4K. Bottom panel: A back-view of the LFI
integrated on the Planck satellite. Visible are the upper sections
of the waveguides interfacing the front-end unit, as well as the
mechanical support structure.
integrated with HFI in the Planck satellite were carried out at
Centre Spatial de Liege (CSL) in the summer of 2008.
3.3. Sorption Cooler
The sorption cooler subsystem (SCS) is the first active element
of the Planck cryochain. Its purpose is to cool the LFI radiome-
ters to their operational temperature of around 20 K, while pro-
viding a pre-cooling stage for the HFI cooling system, a 4.5 K
mechanical Joule-Thomson cooler and a Benoit-style open-cycle
dilution refrigerator. Two identical sorption coolers have been
fabricated and assembled by the Jet Propulsion Laboratory (JPL)
under contract to NASA. JPL has been a pioneer in the devel-
12 Mandolesi et al.: The Planck-LFI programme
opment and application of these cryo-coolers for space and the
two Planck units are the first continuous closed-cycle hydrogen
sorption coolers to be used for a space mission (Morgante et al.
2009b).
Sorption refrigerators are attractive systems for cooling in-
struments, detectors, and telescopes when a vibration-free sys-
tem is required. Since pressurization and evacuation is accom-
plished by simply heating and cooling the sorbent elements se-
quentially, with no moving parts, they tend to be very robust and
generate essentially no vibrations on the spacecraft. This pro-
vides excellent reliability and a long life. By cooling using Joule-
Thomson (J-T) expansion through orifices, the cold end can also
be located remotely (thermally and spatially) from the warm end.
This allows excellent flexibility in integrating the cooler with the
cold payload and the warm spacecraft.
3.3.1. Specifications
The main requirements of the Planck SCS are summarized be-
low:
–Provision of about 1 W total heat lift at instrument interfaces
using a ≤60 K pre-cooling temperature at the coldest V-
groove radiator on the Planck spacecraft;
–Maintain the following instrument interface temperatures:
LFI at ≤22.5 K [80% of total heat lift],
HFI at ≤19.02 K [20% of total heat lift];
–Temperature stability (over one full cooler cycle ≈6000 s):
≤450 mK, peak-to-peak at HFI interface,
≤100 mK, peak-to-peak at LFI interface;
–Input power consumption ≤470 W (at end of life, excluding
electronics);
–Operational lifetime ≥2 years (including testing).
3.3.2. Operations
The SCS consists of a thermo-mechanical unit (TMU, see
Fig. 10) and electronics to operate the system. Cooling is pro-
duced by J-T expansion with hydrogen as the working fluid. The
key element of the 20 K sorption cooler is the compressor, an
absorption machine that pumps hydrogen gas by thermally cy-
cling six compressor elements (sorbent beds). The principle of
operation of the sorption compressor is based on the properties
of a unique sorption material (a La, Ni, and Sn alloy), which can
absorb a large amount of hydrogen at relatively low pressure,
and desorb it to produce high-pressure gas when heated within
a limited volume. Electrical resistances heat the sorbent, while
cooling is achieved by thermally connecting, by means of gas-
gap thermal switches, the compressor element to a warm radiator
at 270 K on the satellite SVM. Each sorbent bed is connected to
both the high-pressure and low-pressure sides of the plumbing
system by check valves, which allow gas flow in a single direc-
tion only. To dampen oscillations on the high-pressure side of
the compressor, a high-pressure stabilization tank (HPST) sys-
tem is utilized. On the low-pressure side, a low-pressure storage
bed (LPSB) filled with hydride, primarily operates as a storage
bed for a large fraction of the H2inventory required to oper-
ate the cooler during flight and ground testing while minimiz-
ing the pressure in the non-operational cooler during launch and
transportation. The compressor assembly mounts directly onto
the warm radiator (WR) on the spacecraft. Since each sorbent
bed is taken through four steps (heat up, desorption, cool-down,
absorption) in a cycle, it will intake low-pressure hydrogen and
output high-pressure hydrogen on an intermittent basis. To pro-
duce a continuous stream of liquid refrigerant, the sorption beds
phases are staggered so that at any given time, one is desorbing
while the others are heating up, cooling down, or re-absorbing
low-pressure gas.
Figure10. SCS thermo-mechanical unit. See Appendix A for
acronyms.
The compressed refrigerant then travels in the Piping and
Cold-End Assembly (PACE, see Fig. 10), through a series of
heat exchangers linked to three V-Grooveradiators on the space-
craft that provide passive cooling to approximately 50 K. Once
pre-cooled to the required range of temperatures, the gas is ex-
panded through the J-T valve. Upon expansion, hydrogen forms
liquid droplets whose evaporation provides the cooling power.
The liquid/vapour mixture then sequentially flows through the
two Liquid Vapour Heat eXchangers (LVHXs) inside the cold
end. LVHX1 and 2 are thermally and mechanically linked to the
corresponding instrument (HFI and LFI) interface. The LFI is
coupled to LVHX2 through an intermediate thermal stage, the
temperature stabilization assembly (TSA). A feedback control
loop (PID type), operated by the cooler electronics, is able to
control the TSA peak-to-peak fluctuations down to the required
level (≤100mK). Heat from the instruments evaporates liquid
hydrogen and the low pressure gaseous hydrogen is circulated
back to the cold sorbent beds for compression.
3.3.3. Performance
The two flight sorption cooler units were delivered to ESA in
2005. Prior to delivery, in early 2004, both flight models under-
Mandolesi et al.: The Planck-LFI programme 13
SCS Unit Warm Rad. 3 rdVGroove Cold-End T(K) Heat Lift Input Power Cycle Time
T(K) T(K) HFI I/F LFI I/F (mW) (V) (s)
270.5 45 17.2 18.7 a,b1100 297 940
Redundant 277 60 18.0 20.1 a,b1100 460 492
282.6 60 18.4 19.9 a,b1050 388 667
Nominal 270 47 17.1 18.7 a1125 304 940
273 48 17.5 18.7 aN/Ac470 525
aMeasured at temperature stabilization assembly (TSA) stage
bIn SCS-redundant test campaign TSA stage active control was not enabled
cNot measured
Table 3. SCS flight units performance summary.
went subsystem-level thermal-vacuum test campaigns at JPL. In
spring 2006 and summer 2008, respectively, SCS redundant and
nominal units were tested in cryogenic conditions on the space-
craft FM at the CSL facilities. The results of these two major test
campaigns are summarized in Table 3 and reported in full detail
in Morgante et al. (2009b).
4. LFI Programme
The model philosophy adopted for LFI and the SCS was cho-
sen to meet the requirements of the ESA Planck system which
assumed from the beginning that there would be three develop-
ment models of the satellite:
–The Planck avionics model (AVM) in which the system bus
was shared with the Herschel satellite, and allowed basic
electrical interface testing of all units and communications
protocol and software interface verification.
–The Planck qualification model (QM), which was limited to
the Planck Payload Module (PPLM) containing QMs of LFI,
HFI, and the Planck telescope and structure that would al-
low a qualification vibration test campaign to be performed
at payload level, as well as alignment checks, and would,
in particular, allow a cryogenic qualification test campaign
to be performed on all the advanced instrumentation of the
payload that had to fully perform in cryogenic conditions.
–The Planck protoflight model (PFM) which contained all the
flight model (FM) hardware and software that would un-
dergo the PFM environmental test campaign, culminating
in extended thermal and cryogenic functional performance
tests.
4.1. Model philosophy
In correspondence with the system model philosophy, it was de-
cided by the Planck consortium to follow a conservative incre-
mental approach involving prototype demonstrators.
4.1.1. Prototype demonstrators (PDs)
The scope of the PDs was to validate the LFI radiometer design
concept giving early results on intrinsic noise, particularly 1/f
noise properties, and characterise systematic effects in a prelim-
inary fashion to provide requirement inputs to the remainder of
the instrument design and at satellite level. The PDs also have the
advantage of being able to test and gain experience with very low
noise HEMT amplifiers, hybrid couplers, and phase switches.
The PD development started early in the programme during the
ESA development pre-phase B activity and ran in parallel with
the successive instrument development phase of elegant bread-
boarding.
4.1.2. Elegant breadboarding (EBB)
The purpose of the LFI EBBs was to demonstrate the maturity
of the full radiometer design across the whole frequency range
of LFI prior to initiating qualification model construction. Thus,
full comparison radiometers (two channels covering a single
polarisation direction) were constructed, centred on 100 GHz,
70 GHz, and 30 GHz, extending from the expected design of the
corrugated feed-horns at their entrance to their output stages at
their back-end. These were put through functional and perfor-
mance tests with their front-end sections operating at 20 K as
expected in-flight. It was towards the end of this development
that the financial difficulties that terminated the LFI 100 GHz
channel development hit the programme.
4.1.3. The qualification model (QM)
The development of the LFI QM commenced in parallel with
the EBB activities. From the very beginning, it was decided that
only a limited number of radiometer chain assemblies (RCA),
each containing four radiometers (and thus fully covering two
orthogonal polarisation directions) at each frequency should be
included and that the remaining instrumentation would be repre-
sented by thermal mechanical dummies. Thus, the LFI QM con-
tained 2 RCA at 70 GHz and one each at 44 GHz and 30 GHz.
The active components of the data acquisition electronics (DAE)
were thus dimensioned accordingly. The radiometer electronics
box assembly (REBA) QM supplied was a full unit. All units and
assemblies went through approved unit level qualification level
testing prior to integration as the LFI QM in the facilities of the
instrument prime contractor Thales Alenia Space Milano.
The financial difficulties also disrupted the QM development
and led to the use by ESA of a thermal-mechanical representa-
tive dummy of LFI in the system level satellite QM test cam-
paign because of the ensuing delay in the availability of the LFI
QM. The LFI QM was however fundamental to the development
of LFI as it enabled the LFI consortium to perform representa-
tive cryo-testing of a reduced model of the instrument and thus
confirm the design of the LFI flight model.
4.1.4. The flight model (FM)
The LFI FM contained flight standard units and assemblies that
went through flight unit acceptance level tests prior to integra-
tion in to the LFI FM. In addition, prior to mounting in the LFI
FM, each RCA went through a separate cryogenic test campaign
14 Mandolesi et al.: The Planck-LFI programme
after assembly to allow preliminary tuning and confirm the over-
all functional performance of each radiometer. At the LFI FM
test level the instrument went through an extended cryogenic test
campaign that included further tuning and instrument calibration
that could not be performed when mounted in the final configu-
ration on the satellite because of schedule and cost constraints.
At the time of delivery of the LFI FM to ESA for integration on
the satellite, the only significant verification test that remained
to be done was the vibration testing of the fully assembled ra-
diometer array assembly (RAA). This could not be performed
in a meaningful way at instrument level because of the problem
of simulating the coupled vibration input through the DAE and
the LFI FPU mounting to the RAA (and in particular into the
waveguides). Its verification was completed successfully during
the satellite PFM vibration test campaign.
4.1.5. The avionics model (AVM)
The LFI AVM was composed of the DAE QM, and its secondary
power supply box removed from the RAA of the LFI QM, an
AVM model of the REBA and the QM instrument harness. No
radiometers were present in the LFI AVM, and their active in-
puts on the DAE were terminated with resistors. The LFI AVM
was used successfully by ESA in the Planck System AVM test
campaigns to fulfill its scope outlined above.
4.2. The sorption cooler subsystem (SCS) model philosophy
The SCS model development was designed to produce two cool-
ers: a nominal cooler and a redundant cooler. The early part of
the model philosophy adopted was similar to that of LFI, em-
ploying prototype development and the testing of key compo-
nents, such as single compressor beds, prior to the building of an
EBB containing a complete complement of components such as
in a cooler intended to fly. This EBB cooler was submitted to an
intensive functional and performance test campaign. The sorp-
tion cooler electronics (SCE) meanwhile started development
with an EBB and was followed by a QM and then FM1/FM2
build.
The TMUs of both the nominal and redundant sorption cool-
ers went through protoflight unit testing prior to assembly with
their respective PACE for thermal/cryogenic testing before de-
livery. To conclude the qualification of the PACE, a spare unit
participated in the PPLM QM system level vibration and cryo-
genic test campaign.
An important constraint in the ground operation of the sorp-
tion coolers is that they could not be fully operated with their
compressor beds far from a horizontal position. This was to
avoid permanent non-homogeneity in the distribution of the hy-
drides in the compressor beds and the ensuing loss in efficiency.
In the fully integrated configuration of the satellite (the PFM
thermal and cryogenic test campaign) for test chamber configu-
ration, schedule and cost reasons would allow only one cooler
to be in a fully operable orientation. Thus, the first cooler to be
supplied, which was designated the redundant cooler (FM1), was
mounted with the PPLM QM and put through a cryogenic test
campaign (termed PFM1) with similar characteristics to those
of the final thermal balance and cryogenic tests of the fully in-
tegrated satellite. The FM1 was then later integrated into the
satellite where only short, fully powered, health checking was
performed. The second cooler was designated as the nominal
cooler (FM2) and participated fully in the final cryo-testing of
the satellite. For both coolers, final verification (TMU assem-
bled with PACE) was achieved during the Planck system-level
vibration-test campaign and subsequent tests.
The AVM of the SCS was supplied using the QM of the SCE
and a simulator of the TMU to simulate the power load of a real
cooler.
4.3. System level integration and test
The Planck satellite and its instruments, were integrated at the
Thales Alenia Space facilities at Cannes in France. The SCS
nominal and redundant coolers were integrated onto the Planck
satellite before LFI and HFI.
Prior to integration on the satellite, the HFI FPU was in-
tegrated into the FPU of LFI. This involved mounting the LFI
4 K loads onto HFI before starting the main integration process,
which was a very delicate operation considering that when per-
formed the closest approach of LFI and HFI would be of the
order of 2 mm. It should be remembered that LFI and HFI had
not “met” during the Planck QM activity and so this integration
was performed for the first time during the Planck PFM cam-
paign. The integration process had undergone much study and
required special rotatable ground support equipment (GSE) for
the LFI RAA, and a special suspension and balancing system to
allow HFI to be lifted and lowered into LFI at the correct orien-
tation along guide rails from above. Fortunately the integration
was completed successfully.
Subsequently, the combined LFI RAA and HFI FPU were in-
tegrated onto the satellite, supported by the LFI GSE, which was
eventually removed during integration to the telescope. The pro-
cess of electrical integration and checkout was then completed
for LFI, the SCS and HFI, and the proto-flight model test cam-
paign commenced.
For LFI, this test campaign proceeded with ambient func-
tional checkout followed by detailed tests (as a complete subsys-
tem prior to participation with the SCS and HFI in the sequence
of alignment), electromagnetic compatibility (EMC), sine and
random acoustic vibration tests, and the sequence of system level
verification tests with the Mission Operations Control Centre
(MOC, at ESOC, Darmstadt) and LFI DPC. During all of these
tests, at key points, both the nominal and redundant SCS were
put through ambient temperature health checks to verify basic
functionality.
The environmental test campaign culminated with the ther-
mal balance and cryogenic tests carried out at the Focal 5 facility
of the Centre Spatial de Liege, Belgium. The test was designed to
follow very closely the expected cool-down scenario after launch
through to normal mission operations, and it was during these
tests that the two instruments and the sorption cooler directly
demonstrated together not only their combined capabilities but
also successfully met their operational margins.
5. LFI test and verification
The LFI had been tested and calibrated before launch at various
levels of integration, from the single components up to instru-
ment and satellite levels; this approach, which is summarised
schematically in Fig. 11, provided inherent redundancy and op-
timal instrument knowledge.
Passive components, i.e., feed-horns, OMTs, and waveg-
uides, were tested at room conditions at the Plasma Physics
Institute of the National Research Council (IFP-CNR) using a
Vector Network Analyser. A summary of the measured per-
formance parameters is provided in Table 4; measurements
Mandolesi et al.: The Planck-LFI programme 15
and results are discussed in detail in Villa et al. (2009a) and
D’Arcangelo et al. (2009a,b).
Table 4. Measured performance parameters of the LFI passive
components.
Feed Horns Return Loss 1, Cross-polar (±45◦) and Co-polar
patterns (E, H and ±45◦planes) in amplitude
and phase, Edge taper at 22◦
OMTs Insertion Loss, Return Loss, Cross-polarisation,
Isolation
Waveguides Insertion Loss, Return Loss, Isolation
1Return loss and patterns (E,H for all frequencies, also ±45◦and cross-
polar for the 70 GHz system) have been measured for the assembly Feed
Horn +OMT as well.
In addition, radiometric performance was measured several
times during the LFI development on individual subunits (e.g.,
amplifiers, phase switches, detector diodes) on integrated front-
end and back-end modules (Davis et al. 2009; Artal et al. 2009;
Varis et al. 2009) and on the complete radiometric assemblies,
both as independent RCAs (Villa et al. 2009b) and in RAA, the
final integrated instrument configuration (Mennella et al. 2009).
In Table 5 (taken from Mennella et al. 2009), we list the main
LFI radiometric performance parameters and the integration lev-
els at which they have been measured. After the flight instru-
ment test campaign, the LFI was cryogenically tested again after
integration on the satellite with the HFI, while the final char-
acterisation will be performed in-flight before starting nominal
operations.
Table 5. Main calibration parameters and where they have been
/will be measured. The following abbreviations have been used:
SAT =Satellite; FLI =In-flight; FE =Front-end; BE =Back-
end; LNA =Low Noise Amplifier; PS =Phase Switch; Radiom
=Radiometric; and Susc =Susceptibility.
Category Parameters RCA RAA SAT FLI
Tuning FE LNAs Y Y Y Y
FE PS Y Y Y Y
BE offset and
gain Y Y Y Y
Quantisation /
compression N Y Y Y
Radiom. Photometric
calibration Y Y Y Y
Linearity Y Y Y Y
Isolation Y Y Y Y
In-band re-
sponse Y N N N
Noise White noise Y Y Y Y
Knee freq. Y Y Y Y
1/fslope Y Y Y Y
Susc. FE temperature
fluctuations Y Y Y Y
BE temperature
fluctuations Y Y N N
FE bias fluctua-
tions Y Y N N
The RCA and RAA test campaigns have been important
to characterizing the instrument functionality and behaviour,
and measuring its expected performance in flight conditions.
In particular, 30 GHz and 44 GHz RCAs were integrated and
tested in Italy, at the Thales Alenia Space (TAS-I) laboratories
in Milan, while the 70 GHz RCA test campaign was carried
out in Finland at the Yilinen-Elektrobit laboratories (Villa et al.
2009b). After this testing phase, the 11 RCAs were collected
and integrated with the flight electronics in the LFI main frame
at the TAS-I labs, where the instrument final test and calibra-
tion has taken place (Mennella et al. 2009). Custom-designed
cryofacilities (Terenzi et al. 2009b; Morgante et al. 2009a) and
high-performance black-body input loads (Terenzi et al. 2009a;
Cuttaia et al. 2009) were developed to test the LFI in the most
flight-representative environmental conditions.
A particular point must be made about the front-end bias tun-
ing, which is a key step in determining the instrument scientific
performance. Tight mass and power constraints called for a sim-
ple design of the DAE box so that power bias lines were divided
into five common-grounded power groups with no bias voltage
readouts. Only the total drain current flowing through the front-
end amplifiers is measured and is available to the housekeeping
telemetry.
This design has important implications for front-end bias
tuning, which depends critically on the satellite electrical and
thermal configuration. Therefore, this step was repeated at all in-
tegration stages and will also be repeated during ground satellite
tests and in-flight before the start of nominal operations. Details
about the bias tuning performed on front-end modules and on the
individual integrated RCAs can be found in Davis et al. (2009),
Varis et al. (2009), and Villa et al. (2009b).
Parameters measured on the integrated instrument were
found to be essentially in line with measurements performed on
individual receivers; in particular, the LFI shows excellent 1/f
stability and rejection of instrumental systematic effects. On the
other hand, the very ambitious sensitivity goals have not been
fully met and the white noise sensitivity (see Table 6) is ∼30%
higher than requirements. Nevertheless, the measured perfor-
mance makes LFI the most sensitive instrument of its kind, a
factor of 2 to 3 superior to WMAP8at the same frequencies.
Table 6. Calibrated white noise from ground-test results extrap-
olated to the CMB input signal level. Two different methods are
used to provide a reliable range of values (see Mennella et al.
2009 for further details). The final verification of sensitivity will
be derived in-flight during the commissioning performance ver-
ification (CPV) phase.
Frequency channel 30 GHz 44 GHz 70 GHz
White noise per νchannel 141–154 152–160 130–146
[µK·√s]
6. LFI Data Processing Centre (DPC)
To take maximum advantage of the capabilities of the Planck
mission and achieve its very ambitious scientific objectives,
proper data reduction and scientific analysis procedures were de-
fined, designed, and implemented very carefully. The data pro-
cessing was optimized so as to extract the maximum amount of
8Calculated on the final resolution element per unit integration
time.
16 Mandolesi et al.: The Planck-LFI programme
useful scientific information from the data set and deliver the
calibrated data to the broad scientific community within a rather
short period of time. As demonstrated by many previous space
missions using state-of-the-art technologies, optimal scientific
exploitation is obtained by combining the robust, well-defined
architecture of a data pipeline and its associated tools with the
high scientific creativity essential when facing unpredictable fea-
tures of the real data. Although many steps required for the trans-
formation of data were defined during the development of the
pipeline, since most of the foreseeable ones have been imple-
mented and tested during simulations, some of them will remain
unknown until flight data are obtained.
Planck is a PI mission, and its scientific achievements
will depend critically on the performance of the two instru-
ments, LFI and HFI, on the cooling chain, and on the tele-
scope. The data processing will be performed by two Data
Processing Centres (DPCs, Pasian et al. 2000; Pasian & Gispert
2000; Pasian & Sygnet 2002). However, despite the existence of
two separate distributed DPCs, the success of the mission relies
heavily on the combination of the measurements from both in-
struments.
The development of the LFI DPC software has been per-
formed in a collaborative way across a consortium spread over
20 institutes in a dozen countries. Individual scientists belong-
ing to the software prototyping team have developed prototype
codes, which have then been delivered to the LFI DPC integra-
tion team. The latter is responsible for integrating, optimizing,
and testing the code, and has produced the pipeline software to
be used during operations. This development takes advantage of
tools defined within the Planck IDIS (integrated data and infor-
mation system) collaboration.
A software policy has defined, to allow the DPC perform the
best most superior algorithms within its pipeline, while fostering
collaboration inside the LFI consortium and across Planck, and
preserving at the same time the intellectual property of the code
authors on the processing algorithms devised.
The Planck DPCs are responsible for the delivery and archiv-
ing of the following scientific data products, which are the deliv-
erables of the Planck mission:
–Calibrated time series data, for each receiver, after removal
of systematic features and attitude reconstruction.
–Photometrically and astrometrically calibrated maps of the
sky in each of the observed bands.
–Sky maps of the main astrophysical components.
–Catalogues of sources detected in the sky maps of the main
astrophysical components.
–CMB power spectrum coefficients and an associated likeli-
hood code.
Additional products, necessary for the total understanding of
the instrument, are being negotiated for inclusion in the Planck
Legacy Archive(PLA). The products foreseen to be added to the
formally defined products mentioned above are:
–Data sets defining the estimated characteristics of each de-
tector and the telescope (e.g. detectivity, emissivity, time re-
sponse, main beam and side lobes, etc.).
–“Internal” data (e.g. calibration data-sets, data at intermedi-
ate level of processing).
–Ground calibration and assembly integration and verification
(AIV) databases produced during the instrument develop-
ment; and by gathering all information, data, and documents
relative to the overall payload and all systems and subsys-
tems. Most of this information is crucial for processing flight
data and updating the knowledge and performance of the in-
strument.
The LFI DPC processing can be logically divided into three lev-
els:
–Level 1: includes monitoring of instrument health and be-
haviour and the definition of corrective actions in the case of
unsatisfactory function, and the generation of time ordered
information (TOI, a set of ordered information on either a
temporal or scan-phase basis), as well as data display, check-
ing, and analysis tools.
–Level 2: TOIs produced at Level 1 will be cleaned by re-
moving noise and many other types of systematic effects on
the basis of calibration information. The final product of the
Level 2 includes “frequency maps”.
–Level 3: “Component maps” will be generated by this level
through a decomposition of individual “frequency maps” and
by also using products from the other instrument and, possi-
bly, ancillary data.
One additional level (“Level S”) is also implemented to develop
the most sophisticated simulations based on true instrument pa-
rameters extracted during the ground test campaigns.
In the following sections, we describe the DPC Levels and
the software infrastructure, and we finally report briefly on the
tests that were applied to ensure that all pipelines are ready for
the launch.
6.1. DPC Level 1
Level 1 takes input from the MOC’s data distribution system
(DDS), decompresses the raw data, and outputs time ordered in-
formation for Level 2. Level 1 does not include scientific pro-
cessing of the data; actions are performed automatically by using
pre-defined input data and information from the technical teams.
The inputs to Level 1 are telemetry (TM) and auxiliary data as
they are released by the MOC. Level 1 uses TM data to perform
a routine analysis (RTA – real time assessment) of the spacecraft
and instrument status, in addition to what is performed at the
MOC, with the aim of monitoring the overall health of the pay-
load and detecting possible anomalies. A quick-look data anal-
ysis (TQL – Telemetry Quick Look) of the science TM is also
done, to monitor the operation of the observation plan and verify
the performance of the instrument. This processing is meant to
lead to the full mission raw-data stream in a form suitable for
subsequent data processing by the DPC.
Level 1 also deals with all activities related to the production
of reports. This task includes the results of telemetry analysis,
but also the results of technical processing carried out on TOI
to understand the current and foreseen behaviour of the instru-
ment. This second item includes specific analysis of instrument
performance (LIFE – LFI Integrated perFormance Evaluator),
and more general checking of time series (TSA – Time Series
Analysis) for trend analysis purposes and comparison with the
TOI from the other instrument. The additional tasks of Level 1
relate to its role as an instrument control and DPC interface with
the MOC. In particular, the following actions are performed:
–Preparation of telecommanding procedures aimed at modi-
fying the instrument setup.
–Preparation of Mission Information dataBases (MIBs).
–Communicate to the MOC “longer-term” inputs derived
from feedback from DPC processing.
–Calibration of REBA parameters to fit long-term trends in
the instrument setup.
Mandolesi et al.: The Planck-LFI programme 17
Figure12. Level 1 structure.
In Level 1, all actions are planned to be performed on a
“day-to-day” basis during operation. In Fig. 12, the structure of
Level 1 and required timings are shown. For more details, we
refer to Zacchei et al. (2009).
6.2. DPC Level 2
At this level, data processing steps requiring detailed instrument
knowledge (data reduction proper) will be performed. The raw
time series from Level 1 will also be used to reconstruct a num-
ber of calibrated scans for each detector, as well as instrumental
performance and properties, and maps of the sky for each chan-
nel. This processing is iterative, since simultaneous evaluation
of quite a number of parameters should be made before the as-
trophysical signal can be isolated and averaged over all detectors
in each frequency channel. Continuous exchange of information
between the two DPCs will be necessary at Level 2 to identify
any suspect or unidentified behaviour or any results from the de-
tectors.
The first task that the Level 2 performs is the creation of
differenced data. Level 1 stores data from both Sky and Load.
These two have to be properly combined to produce differenced
data, therefore reducing the impact of 1/fnoise achieved by
computing the so-called gain modulation factor R, which is de-
rived by taking the ratio of the mean signals from both Sky and
Load.
After differenced data are produced, the next step is the pho-
tometric calibration that transforms the digital units into physical
units. This operation is quite complex: different methods are im-
plemented in the Level 2 pipeline that use the CMB dipole as
an absolute calibrator allowing for the conversion into physical
units.
Another major task is beam reconstruction, which is imple-
mented using information from planet crossings. An algorithm
was developed that performs a bi-variate approximation of the
main beam section of the antenna pattern and reconstructs the
position of the horn in the focal plane and its orientation with
respect to a reference axis.
The step following the production of calibrated timelines
is the creation of calibrated frequency maps. To achieve this,
pointing information will be encoded into time-ordered pixels
i.e, pixel numbers in the given pixelisation scheme (HEALPix)
by identifying a given pointing direction that is ordered in time.
To produce temperature maps, it is necessary to reconstruct the
beam pattern along the two polarisation directions for the main,
intermediate, and far parts of the beam pattern. This will allow
the combination of the two orthogonal components into a sin-
gle temperature timeline. On this temperature timeline, a map-
making algorithm will be applied to produce a map from each
receiver.
The instrument model allows one to check and control sys-
tematic effects and the quality of the removal performed by
map-making and calibration of the receiver map. Receiver maps
cleaned of systematic effects at different levels of accuracy
will be stored into a calibrated map archive. The production of
frequency-calibrated maps will be performed by processing to-
gether all receivers from a given frequency channel in a single
map-making run. In Figs. 13 and 14, we report the steps per-
formed by Level 2, together with the associated times foreseen.
6.3. DPC Level 3
The goal of the DPC Level 3 is to estimate and characterise
maps all the different astrophysical and cosmological sources of
emission (“components”) present at Planck wavelengths. Using
the CMB component obtained after point-source extraction and
cleaning from diffuse, Galactic emission, the angular power
spectrum of the CMB is estimated for temperature, polarisation,
and cross temperature/polarisation modes.
The extraction of the signal from Galactic point-like objects,
and other galaxies and clusters is achieved as a first step, ei-
ther using pre-existing catalogues based on non-Planck data, or
filtering the multi-frequency maps with optimal filters to detect
and identify beam-like objects (see Herranz et al. 2009 and ref-
erences therein).
The algorithms dedicated to the separation of diffuse emis-
sion fall into four main categories, depending on the criteria
exploited to achieve separation, and making use of the wide
frequency coverage of Planck (see Leach et al. 2008 and refer-
ences therein). Internal linear combination and template fitting
achieves linear mixing and combination of the multi-frequency
data with other data sets, optimized for CMB or foreground re-
covery. The independent component analysis works in the sta-
tistical domain, without using foreground modelling or spatial
correlations in the data, but assuming instead statistical inde-
pendence between the components that are to be recovered. The
correlated component analysis, on the other hand, makes use of
a parametrization of foreground unknowns, and uses spatial cor-
relations to achieve separation. Finally, parametric methods con-
sist of modelling foreground and CMB components by treating
each resolution element independently, achieving fitting of the
unknowns and separation by means of a maximum likelihood
analysis. The LFI DPC Level 3 includes algorithms that belong
to each of the four categories outlined above. The complemen-
tarity of different methods for different purposes, as well as the
cross-check on common products, are required to achieve reli-
able and complete scientific products.
As for power spectrum estimation, two independent
and complementary approaches have been implemented (see
Gruppuso et al. 2009, and references therein): a Monte-Carlo
method suitable for high multipoles (based on the master ap-
proach, but including cross-power spectra from independent re-
ceivers); and a maximum likelihood method for low multipoles.
A combination of the two methods will be used to produce the
final estimation of the angular power spectrum from LFI data,
before its combination with HFI data. In Fig. 15, we report
18 Mandolesi et al.: The Planck-LFI programme
the steps performed in the Level 3 pipeline with the associated
timescales foreseen.
The inputs to the Level 3 pipeline are the three calibrated
frequency maps from LFI together with the six calibrated HFI
frequency maps that should be exchanged on a monthly basis.
The Level 3 pipeline has links with most of the stages of the
Level 1 and Level 2 pipelines, and therefore the most complete
and detailed knowledge of the instrumental behaviour is impor-
tant for achieving its goals. Systematic effects appearing in the
time-ordered data, beam shapes, band width, source catalogues,
noise distribution, and statistics are examples of important in-
puts to the Level 3 processing. Level 3 will produce source cat-
alogues, component maps, and CMB power spectra that will be
delivered to the Planck Legacy Archive (PLA), together with
other information and data needed for the public release of the
Planck products.
6.4. DPC Level S
It was widely agreed within both consortia that a software sys-
tem capable of simulating the instrument footprint, starting from
a predefined sky, was indispensable for the full period of the
Planck mission. Based on that idea, an additional processing
level, Level S, was developed and upgraded whenever the knowl-
edge of the instrument improved (Reinecke et al. 2006). Level
S now incorporates all the instrument characteristics as they
were understood during the ground test campaign. Simulated
data were used to evaluate the performance of data-analysis al-
gorithms and software against the scientific requirements of the
mission and to demonstrate the capability of the DPCs to work
using blind simulations that contain unknown parameter values
to be recovered by the data processing pipeline.
6.5. DPC software infrastructure
During the entire Planck project, it has been (and will con-
tinue to be) necessary to deal with aspects related to informa-
tion management, which pertain to a variety of activities con-
cerning the whole project, ranging from instrument informa-
tion (e.g., technical characteristics, reports, configuration con-
trol documents, drawings, public communications) to software
development/control (including the tracking of each bit pro-
duced by each pipeline). For this purpose, an Integrated Data and
Information System (IDIS) was developed. IDIS (Bennett et al.
2000) is a collection of software infrastructure for supporting the
Planck Data Processing Centres in their management of large
quantities of software, data, and ancillary information. The in-
frastructure is relevant to the development, operational, and post-
operational phases of the mission.
The full IDIS can be broken down into five major compo-
nents:
–Document management system (DMS), to store and share
documents.
–Data management component (DMC), allowing the inges-
tion, efficient management, and extraction of the data (or
subsets thereof) produced by Planck activities.
–Software component (SWC), allowing the system to admin-
ister, document, handle, and keep under configuration con-
trol the software developed within the Planck project.
–Process Coordinator (ProC), allowing the creation and run-
ning of processing pipelines inside a predefined and well
controlled environment.
–Federation layer (FL), which allows controlled access to the
previous objects and acts as a glue between them.
The use of the DMS has allowed the entire consortia to in-
gest and store hundreds of documents and benefit from an ef-
ficient way of retrieving them. The DMC is an API (applica-
tion programming interface) for data input/output, connected
to a database (either relational or object-oriented) and aimed
at the archiving and retrieval of data and the relevant meta-
information; it also features a user GUI. The ProC is a controlled
environment in which software modules can be added to cre-
ate an entirely functional pipeline. It stores all the information
related to versioning of the modules used, data, and temporary
data created within the database while using the DMC API. In
Fig. 16, an example of the LFI pipeline is shown. Finally, the
FL is an API that, using a remote LDAP database, assigns the
appropriate permission to the users for data access, software ac-
cess, and pipeline run privileges.
6.6. DPC test performed
Each pipeline and sub-pipeline (Level 1, Level 2, and Level 3)
has undergone different kinds of tests. We report here only the
official tests conducted with ESA, without referring to the inter-
nal tests that were dedicated to DPC subsystems. Level 1 was the
most heavily tested, as this pipeline is considered launch-critical.
As a first step, it was necessary to validate the output with respect
to the input; to do that, we ingested inside the instrument a well
known signal as described in Frailis et al. (2009) with the pur-
pose of verifying whether the processing inside Level 1 was cor-
rect. This also had the benefit of providing an independent test of
important functionalities for the REBA software responsible for
the onboard preprocessing of scientific data. Afterwards, more
complete tests, including all interfaces with other elements of
the ground segment, were performed. Those tests simulate one
week of nominal operations (SOVT1 – system operation valida-
tion test; Keck 2008) and, during the SOVT2, one week of the
commissioning performance verification (CPV) phase. During
these tests, it was demonstrated that the LFI Level 1 is able to
deal with the telemetry as it would be acquired during opera-
tions.
Tests performed on Level 2 and Level 3 were more science-
oriented to demonstrate the scientific adequacy of the LFI DPC
pipeline, i.e., its ability to produce scientific results commensu-
rate with the objectives of the Planck mission. These tests were
based on blind simulations of growing complexity. The Phase
1 test data, produced with Level S, featured some simplifying
approximations:
–the sky model was based on the “concordance model” CMB
(no non-Gaussianity);
–the dipole did not include modulations due to the Lissajous
orbit around L2;
–Galactic emission was obtained assuming non-spatially
varying spectral index;
–the detector model was “ideal” and did not vary with time;
–the scanning strategy was “ideal” (i.e., no gaps in the data).
The results of this test were in line with the objectives of the
mission (see Perrotta & Maino 2007)).
The Phase 2 tests are still ongoing. They take into account
more realistic simulations with all the known systematics and
known problems (e.g., gaps) in the data.
Mandolesi et al.: The Planck-LFI programme 19
7. Pre-launch status
We have provided an overview of the Low Frequency Instrument
(LFI) programme and of its organization within the ESA Planck
mission. After a brief description of the Planck main properties
and observational strategy, the main scientific goals have been
presented, ranging from fundamental cosmology to Galactic and
extragalactic astrophysics by focusing on those more relevant
to LFI. The LFI design and development have been outlined,
together with the model philosophy and testing strategy. The
LFI approach to on-ground and in-flight calibration and the LFI
ground segment have been described. We have reported on the
data analysis pipeline that has been successfully tested.
Ground testing shows that the LFI operates as anticipated.
The observational program will begin after the Planck/Herschel
launch on May 14th, 2009.
A challenging commissioning and final calibration phase
will prepare the LFI for nominal operations that will start about
90 days after launch. After ∼20 days, the instrument will be
switched on and its functionality will be tested in parallel with
the cooling of the 20 K stage. Then the cooling period of the HFI
focal plane to 4 K will be used by the LFI to tune voltage biases
of the front end amplifiers, phase switches, and REBA parame-
ters, which will set the final scientific performance of the instru-
ment. Final tunings and calibration will be performed in parallel
with HFI activities for about 25 days until the last in-flight cali-
bration phase, the so-called “first light survey”. This will involve
14 days of data acquisition in nominal mode that will benchmark
the whole system, from satellite and instruments to data trans-
mission, ground segment, and data processing levels.
The first light survey will produce the very first Planck maps.
This will not be designed for scientific exploitation but will
rather serve as a final test of the instrumental and data process-
ing capabilities of the mission. After this, the Planck scientific
operations will begin.
Note that at the time of publishing this article, Planck was
launched successfully with Herschel on May 14th, 2009, and it
is in the process of completing its first full sky survey as foreseen.
8. Acknowledgements
Planck is a project of the European Space Agency with instru-
ments funded by ESA member states, and with special contribu-
tions from Denmark and NASA (USA). The Planck-LFI project
is developed by an International Consortium led by Italy and in-
volving Canada, Finland, Germany, Norway,Spain, Switzerland,
UK and USA. The Italian contribution to Planck is supported by
the Agenzia Spaziale Italiana (ASI) and INAF. We also wish to
thank the many people of the Herschel/Planck Project and RSSD
of ESA, ASI, THALES Alenia Space Industries and the LFI
Consortium that have contributed to the realization of LFI. We
are grateful to our HFI colleagues for such a fruitful collabora-
tion during so many years of common work. The German partic-
ipation at the Max-Planck-Institut f¨ur Astrophysik is funded by
the Bundesministerium f¨ur Wirtschaft und Technologie through
the Raumfahrt-Agentur of the Deutsches Zentrum f¨ur Luft-
und Raumfahrt (DLR) [FKZ: 50 OP 0901] and by the Max-
Planck-Gesellschaft (MPG). The Finnish contribution is sup-
ported by the Finnish Funding Agency for Technology and
Innovation (Tekes) and the Academy of Finland. The Spanish
participation is funded by Ministerio de Ciencia e Innovacion
through the project ESP2004-07067-C03 and AYA2007-68058-
C03. The UK contribution is supported by the Science and
Technology Facilities Council (STFC). C. Baccigalupi and
F. Perrotta acknowledge partial support of the NASA LTSA
Grant NNG04CG90G. We acknowledge the use of the BCX
cluster at CINECA under the agreement INAF/CINECA. We
acknowledge the use of the Legacy Archive for Microwave
Background Data Analysis (LAMBDA). Support for LAMBDA
is provided by the NASA Office of Space Science. We acknowl-
edge use of the HEALPix (G´orski et al. 2005) software and anal-
ysis package for deriving some of the results in this paper.
Appendix A: List of Acronyms
AIV =Assembly Integration and Verification
API =Application Programming Interface
APS =Angular Power Spectrum
ASI =Agenzia Spaziale Italiana (Italian Space Agency)
ATCA =Australian Telescope Compact Array
AVM =AVionics Model
BEM =Back-End Module
BEU =Back-End Unit
CDM =Cold Dark Matter
COBE =COsmic Background Explorer
COBRAS =COsmic Background Radiation Anisotropy
Satellite
CMB =Cosmic Microwave Background
CPV =Commissioning Performance Verification
CSL =Centre Spatial de Liege
DAE =Data Acquisition Electronics
DBI =Dirac-Born-Infeld (inflation)
DC =Direct Current
DDS =Data Distribution System
DMC =Data Management Component
DMS =Document Management System
DPC =Data Processing Centre
EBB =Elegant BreadBoarding
EMC =ElectroMagnetic Compatibility
ESA =European Space Agency
ESOC =European Space Operations Centre
ET =Edge Taper
FEM =Front-End Module
FL =Federation Layer
FM =Flight Model
FPU =Focal Plane Unit
FWHM =Full Width Half Maximum
GLAST =Gamma-ray Large Area Space Telescope
GLS =Generalized Least Squares
GSE =Ground Support Equipment
GUI =Graphical User Interface
HEALPix =Hierarchical Equal Area isoLatitude Pixelization
HEMT =High Electron Mobility Transistor
HFI =High Frequency Instrument
HPST =High-Pressure Stabilization Tank
IDIS =Integrated Data and Information System
IR =Infra Red
ISM =Inter-Stellar Medium
JPL =Jet Propulsion Laboratory
JT =Joule-Thomson
LDAP =Lightweight Directory Access Protocol
LFI =Low Frequency Instrument
LIFE =LFI Integrated perFormance Evaluator
LNA =Low Noise Amplifier
LPSB =Low-Pressure Storage Bed
LVHX =Liquid Vapour Heat eXchange
MIB =Mission Information Base
20 Mandolesi et al.: The Planck-LFI programme
MIC =Microwave Integrated Circuit
MMIC =Monolithic Microwave Integrated Circuit
MOC =Mission Operation Centre
NASA =National Aeronautics and Space Administration (USA)
NG =Non Gaussianity
OMT =Orthomode Transducer
PACE =Piping and Cold-End Assembly
PD =Prototype Demonstrator
PFM =Planck ProtoFlight Model
PI =Principal Investigator
PID =Proportional Integral Derivative
PLA =Planck Legacy Archive
PPLM =Planck PayLoad Module
ProC =Process Coordinator
PS =Phase Switch
QM =Qualification Model
RAA =Radiometer Array Assembly
RCA =Radiometer Chain Assembly
REBA =Radiometer Electronics Box Assembly
RF =Radio Frequency
RTA =Real Time Assessment
SAMBA =SAtellite for Measurement of Background
Anisotropies
SCE =Sorption Cooler Electronics
SCS =Sorption Cooler Subsystem
SOVT =System Operation Validation Test
SS =Scanning Strategy
SVM =SerVice Module
SWC =SoftWare Component
TM =TeleMetry
TMU =Thermo-Mechanical Unit
TOI =Time Order Information
TQL =Telemetry Quick Look
TSA =Temperature Stabilization Assembly; Time Series
Analysis
WMAP =Wilkinson Microwave Anisotropy Probe
WR =Warm Radiator
XPD =Cross-Polar Discrimination
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Mandolesi et al.: The Planck-LFI programme 23
Figure11. Schematic of the various calibration steps in the LFI development.
Figure13. Level 2 calibration pipeline.
24 Mandolesi et al.: The Planck-LFI programme
Figure14. Level 2 Map-making pipeline.
Mandolesi et al.: The Planck-LFI programme 25
Figure15. Level 3 pipeline structure.
Figure16. IDIS ProC pipeline editor.
