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SPECIAL SECTION: CHANDRAYAAN-1
CURRENT SCIENCE, VOL. 96, NO. 4, 25 FEBRUARY 2009
486
*For correspondence. (e-mail: goswami@prl.res.in)
Chandrayaan-1: India’s first planetary science
mission to the moon
J. N. Goswami1,* and M. Annadurai2
1Physical Research Laboratory, Ahmedabad 380 009, India
2ISRO Satellite Center, Bangalore 560 017, India
Chandrayaan-1, the first Indian planetary exploration
mission, will carry out high resolution remote sensing
studies of the moon to further our understanding
about its origin and evolution. Hyper-spectral imaging
in the UV-VIS-NIR region using three imaging spec-
trometers, along with a low energy X-ray spectrometer
will provide mineralogical and chemical composition
of the lunar surface at high spatial resolution. A terrain
mapping camera will provide high resolution three-
dimensional images of the lunar surface and will be
complemented by a laser ranging instrument that will
provide lunar altimetry. Three payloads – a high energy
X-
γ
ray spectrometer, a sub-keV atom reflecting ana-
lyser, and miniature imaging radar – will be used for
the first time for remote sensing exploration of a
planetary body. They will investigate transport of
volatiles on the lunar surface, presence of localized
lunar mini-magnetosphere and possible presence of
water ice in the permanently shadowed lunar polar
region respectively. A radiation dose monitor will pro-
vide information on energetic particle flux en route to
the moon and in lunar orbit. An impact probe carrying
an imaging system, a radar altimeter and a mass spec-
trometer will be released from the spacecraft to land
at a predestinated lunar site. The design of the one
tonne-class spacecraft is primarily adapted from flight
proven Indian Remote Sensing satellite bus with
several modifications that are specific to the lunar
mission. The spacecraft was launched by using a vari-
ant of the indigenous Polar Satellite Launch Vehicle
(PSLV-XL) and placed in a 100 km circular polar
orbit around the moon with a planned mission life of
two years. An Indian Deep Space Network and an
Indian Space Science Data Center have been esta-
blished as a part of Chandrayaan-1 mission and will
cater to the need of future Indian space science and
planetary missions.
Keywords: Chandrayaan-1, evolution, ISRO, moon,
origin, planetary exploration.
Introduction
THE current decade has seen a revival in the field of
planetary exploration, and in particular in lunar explora-
tion, with several new initiatives by various national
space agencies including the Indian Space Research
Organization (ISRO). Even though the need for further
exploration of the moon has been discussed in the late
nineties, a renewed effort in this direction has formally
begun in 2003 with the Smart-1 mission of ESA that was
followed by the Changé-1 mission of China, the Japanese
mission Kaguya (SELENE), both in late 2007, the Indian
Chandrayaan-1 mission in late 2008 and the US mission
LRO (Lunar Reconnaissance Orbiter) scheduled for
launch in early 2009. The possibility of an Indian mission
to the moon was mooted in the late nineties and was dis-
cussed extensively in different academic forums during
1999 and 2000. On the basis of recommendations from
these forums, ISRO constituted a National Task team to
look into both the technological feasibility and scientific
return from such a mission. The recommendations of the
task team were deliberated at length and ISRO formally
proposed Chandrayaan-1 Mission to the Government of
India in early 2003 and it was approved in November,
2003. The mission is international in character with the
National Aeronautics and Space Administration (NASA),
USA, European Space Agency (ESA) and the Bulgaraian
Academy of Sciences (BAS) providing support for pay-
loads selected for the mission following ISRO’s
announcement of opportunity (AO) to the global scien-
tific community in early 2004. The AO payloads comple-
ment and supplement the Indian payloads and enhanced
the scientific content of the mission. This paper describes
the scientific objectives, the various payloads, mission
details, observational plans and other related aspects of
the Chandrayaan-1 mission. The accompanying papers in
this special section describe in detail the scientific objec-
tives and significant characteristics of each individual
payload.
Science objectives
Astronomical observations of the moon to understand the
brightness variation over its surface led to identification
of distinctly different regions of the moon. However,
relating these differences to different types of lunar mate-
rial became possible only through laboratory studies of
reflection properties of various minerals and analysis of
lunar samples returned by Apollo and Luna missions dur-
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CURRENT SCIENCE, VOL. 96, NO. 4, 25 FEBRUARY 2009 487
ing the late sixties and early seventies. These studies led
to a broad understanding of the evolution of the moon
and led to the suggestion that an impact of a mars-sized
object on the early earth resulted in the formation of the
moon. The concept of a magma ocean resulting from a
global scale melting of the moon, soon after its forma-
tion, was also proposed. A calendar of events for the first
one and half billion years of lunar evolution was drawn
up based on the nature, chemical composition and ages of
the returned lunar samples. However, both the remote
sensing and surface exploration of the moon by the
Apollo and Luna missions were restricted to the equato-
rial region of the moon. The next major advance came
with the launch of the Clementine and Prospector remote
sensing missions to the moon in 1994 and 1998 respec-
tively, which provided the first set of data on lunar min-
eralogy and chemistry at a global scale. While these data
provided new insight on lunar evolution, they also raised
many new questions. Further, the mineralogical and
chemical mappings of the lunar surface were done with
either low spectral resolution (mineralogy) or with low
spatial resolution (chemical composition). The need for
studies with high spectral and spatial resolutions was
obvious for furthering our understanding of the origin and
evolution of the moon. The Chandrayaan-1 mission aimed
to achieve this goal by carrying out remote sensing ob-
servations over a wide range of the electromagnetic spec-
trum for simultaneous mineralogical, chemical and photo-
geological mapping of the lunar surface at resolutions
better than previous and contemporary lunar missions.
Global interest in long duration mission to the moon
and the possibility of using moon as a base for further
exploration of the solar system also brought into focus
the possible indigenous lunar resources that may be uti-
lized during such missions. Expected excess of volatiles,
including water ice, mixed with the near surface material
in permanently shadowed lunar polar region, is a prime
candidate in this regard. The Chandrayaan-1 mission will
explore the nature of volatile transport on the moon using
radioactive radon and its decay products as tracers, and
also probe permanently shadowed base of deep craters in
the lunar polar region using radio waves to look for possi-
ble presence of water ice in such areas. Devoid of an
atmosphere and global magnetic field, the moon also
provides free access to energetic particles of both solar
and galactic in origin. The Chandrayaan-1 mission will
conduct studies of interactions of low energy solar wind
ions with the lunar surface to identify lunar mini-
magnetospheres created by localized magnetic field. These
studies are based on novel approaches that will be adopted
for planetary exploration for the first time.
The payloads
A suite of baseline payloads, identified initially to meet
the scientific objectives, include a Terrain Mapping Cam-
era (TMC), a Hyper-Spectral Imager (HySI), a Low
energy x-ray spectrometer, a High Energy X-
γ
ray Spec-
trometer (HEX) and a Lunar Laser Ranging Instrument
(LLRI). These payloads will provide simultaneous min-
eralogical, chemical and photo-geological data that will
allow (i) three-dimensional mapping of the lunar surface
and lunar altimetry at 5 m resolution, (ii) mineralogical
mapping of the lunar surface at a resolution of ~100 m,
(iii) direct estimation of lunar surface concentration of
the elements Mg, Al, Si, Ca, Ti and Fe with spatial reso-
lution of ~25 km, and (iv) probing the nature of volatile
transport on the moon, particularly to the colder lunar po-
lar region. An impact probe carrying a mass spectrome-
ter, an imaging system and a radar altimeter will
complement these baseline payloads and will be a techno-
logical forerunner for future proposed lunar landing mis-
sions.
ISRO also offered possibility for the international sci-
entific community to participate in the Chandrayaan-1
mission through an AO in early 2004. The response was
overwhelming and several payloads that complement and
supplement the basic objectives of the Chandrayaan-1
mission have been selected based on peer reviews. These
are: a miniature imaging radar instrument (Mini-SAR) to
explore the polar regions of the moon to look for possible
presence of water ice, two infrared spectrometers (SIR-2
and Moon Mineralogy Mapper: MMM) for extending the
wavelength coverage beyond that of the HySI, a
low-energy X-ray Spectrometer (C1XS) for high resolu-
tion chemical mapping, a Sub-keV Atom Reflecting Ana-
lyser (SARA) for studying solar wind–lunar surface
interactions and lunar surface magnetic anomalies and a
RAdiation DOse Monitor (RADOM) for monitoring
energetic particle flux en route to the moon and in the
lunar environment. Three of the payloads, SIR-2, C1XS
and SARA, developed at the Max-Planck Institute, Lin-
dau, Germany, Rutherford Appleton Laboratory, UK, and
Swedish Institute of Space Physics respectively were
provided by the ESA. NASA provided Mini-SAR, deve-
loped by Applied Physics Laboratory at John Hopkins
University and NAWC, and the Moon Mineralogy Map-
per, developed by Brown University and the Jet Propul-
sion Laboratory. RADOM was provided by the Bulgarian
Academy of Sciences. Two of the AO payloads, C1XS
and SARA, have Indian collaborations and realized with
significant technical and scientific contributions from the
ISRO Satellite Center, Bangalore, and the Vikram Sarab-
hai Space Center (VSSC), Thiruvananthapuram respec-
tively. A schematic of the Chandrayaan-1 spacecraft with
the location of the ten payloads and the Moon Impact
Probe is shown in Figure 1. In the following, the basic
characteristics of the payloads are described; more exten-
sive description of each payload is presented in the
accompanying papers in this special section. The
Chandrayaan-1 spacecraft integrated with all the flight
payloads prior to various pre-flight tests is shown in Fig-
ure 2.
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CURRENT SCIENCE, VOL. 96, NO. 4, 25 FEBRUARY 2009
488
Figure 1. A schematic depiction of the Chandrayaan-1 spacecraft.
The eleven payloads on board are also marked. The blue panel is the
canted solar array.
Figure 2. The Chandrayaan-1 spacecraft.
HySI, SIR-2, MMM
Three payloads [Hyper-Spectral Imager (HySI), Near
Infrared Spectrometer (SIR-2) and Moon Mineralogy
Mapper (MMM)], will study solar reflected energy from
the lunar surface covering the wavelength range of 0.4 to
3 micron and will provide high resolution mineralogical
map of the entire lunar surface. HySI operates in the
400–950 nm range employing a wedge filter and will
have spectral resolution of ~15 nm and a spatial (pixel)
resolution of 80 m. SIR-2, a compact, monolithic grating
near infrared point spectrometer covers the wavelength
region 0.9–2.4 micron with a spectral resolution of 6 nm
and spatial (pixel) resolution of ~80 m. MMM is a high
throughput push broom imaging spectrometer operating
in 0.7–3.0 micron range with high spatial (70 m per pixel)
and spectral (10 nm) resolution. Intracalibration of the
three instruments will be carried out in the overlap wave-
length region from 700 to 950 nm. The flight models of
these three payloads and the other eight payloads are
shown in Figure 3.
C1XS
The Chandrayaan-1 X-ray Spectrometer (C1XS; Figure
3) is a collimated low energy (1–10 keV) X-ray spectro-
meter that employs a swept-charge X-ray detector (SCD)
and has a field of view of ~25 km. It will detect fluores-
cence X-rays, characteristic of elements (magnesium to
iron) on the lunar surface, produced by incident X-rays
from the Sun during solar flares and allow direct deter-
mination of lunar surface abundances of the elements,
Mg, Al and Si and also of Ca, Ti and Fe during major
solar flares. An X-ray solar monitor (XSM) will provide
data on the incident solar X-ray flux necessary for esti-
mation of the elemental abundances.
HEX
The High-Energy X-
γ
ray Spectrometer (HEX; Figure 3)
will use solid-state pixilated cadmium–zinc–telluride
(CZT) arrays for detecting energetic photons in the energy
range 30–270 keV from the lunar surface. An anti-coinci-
dence system consisting of CsI(Tl) scintillator coupled
with two PMTs is positioned below the CZT detector arrays
to minimize the background events. A stainless steel col-
limator is mounted above the CZT arrays to limit the
FOV to a 33 km × 33 km area on the lunar surface from
the 100 km orbit of Chandrayaan-1. HEX is primarily
intended for the study of volatile transport on Moon using
the 46.5 keV
γ
ray line from 210Pb (a decay product of
volatile 222Rn) as tracer. HEX will make the first attempt
to detect low energy (<300 keV)
γ
rays from a planetary
surface.
TMC, LLRI
The Terrain Mapping Camera (TMC; Figure 3) in the
500–850 nm band hosts three linear array detectors for
nadir, fore and aft viewing and will have a swath of
20 km. TMC will provide 3D images of the lunar surface
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CURRENT SCIENCE, VOL. 96, NO. 4, 25 FEBRUARY 2009 489
Figure 3. Flight model of the eleven payloads on board Chandrayaan-1. Four of the Indian payloads (TMC, HySI, HEX and LLRI) are displayed
on the top panel; the middle panel displays the Moon Impact Probe and two of the instruments on it along with two AO payloads (C1XS and SARA
from ESA) that have significant Indian collaborations. The four payloads shown in the lower panel are AO payloads provided by NASA (Mini-
SAR, MMM), ESA (SIR-2) and BSA (RADOM).
with a ground resolution of 5 m with base to height ratio
of one that will be used to generate topographic map of
the Moon. The Lunar Laser Ranging Instrument (LLRI)
employs an Nd–Yag laser with energy 10 mJ and has a
20 cm optics receiver. It will be operating at 10 Hz (5 ns
pulse) and will provide a height resolution better than
5 m. Data from LLRI will provide accurate lunar alti-
metry with focus on the polar region, and the data will be
used to generate a quantitative lunar gravity model.
Mini-SAR
The multi-function Mini-SAR (Figure 3), consisting of
synthetic aperture radar, altimeter, scatterometer and
radiometer, will be operating at 2.5 GHz. This instrument
will probe the permanently shadowed areas near lunar
poles to look for signature of water ice mixed within the
top meter of the lunar surface material. Mini-SAR will
transmit Right Circular Polarization (RCP) and receive
both Left Circular Polarization (LCP) and RCP, and uti-
lizes a unique hybrid polarization architecture, which
allows determination of the Stokes parameters of the
reflected signal to infer possible presence of water ice.
The SAR system has a pixel resolution of 150 m and
8 km swath. This will be the first systematic approach to
look for water ice in the lunar polar region.
SARA
The SARA payload (Figure 3) consists of two packages,
the Chandrayaan-1 Low Energy Neutral Atom (CENA),
and the Solar Wind Monitor (SWIM). CENA detects
solar wind sputtered low energy (10 eV–2 keV) neutral
atoms from the lunar surface and can broadly resolve H,
O, Na–Mg, K–Ca groups and Fe atoms, and represents
first such study in planetary context. SWIM is an ion
mass analyser for determining energy and mass of the
incident solar wind ions. SARA will study the solar
wind–planetary surface interaction via measurements of
the sputtered atoms and neutralized back-scattered solar
wind hydrogen. SARA will image the lunar surface mag-
netic anomalies and also provide elemental surface com-
position including that of permanently shadowed areas.
RADOM
The miniature (98 g 100 mW) Radiation Dose Monitor
(RADOM; Figure 3) uses a single 0.3 mm thick small
area (2 cm2) silicon detector and measure the deposited
energy from primary and secondary particles of solar and
galactic in origin using a 256 channel pulse analyser.
The deposited energy spectrum can then be converted to
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490
deposited dose and flux of charged particles incident on
the silicon detector.
MIP
The Moon Impact Probe (MIP; Figure 3) will be released
at the beginning of the mission, after the spacecraft reach
the designated 100 km lunar polar orbit. Its planned path
will fly over the Malapert Mountain and the impact point
will be close to the lunar South Pole. MIP will carry a
moon imaging system for surface photography along its
path in addition to a radar altimeter and an extremely sen-
sitive mass spectrometer to detect possible presence of
trace gases in the lunar exosphere.
The Spacecraft
The Chandrayaan-1 spacecraft design is adapted from
flight proven Indian Remote Sensing (IRS) Satellite bus.
Apart from the solar array, TTC and data transmission,
that are specific to the lunar mission, other aspects of sys-
tem design have flight heritage. Some changes specific to
the mission such as extending the thrust cylinder and hav-
ing an upper payload deck to accommodate MIP and
other payloads have been implemented. Chandrayaan-1
will have a canted solar array since the orbit around the
moon is inertially fixed, resulting in large variation in
solar incidence angle. A gimbaled high gain antenna sys-
tem will be employed for downloading the payload data
to the Indian Deep Space Network (IDSN) established
near Bangalore. The spacecraft is cuboid in shape of
approximately 1.5 m side (Figures 1 and 2), with a liftoff
mass of ~1300 kg with the bus elements accounting for
~400 kg, payload ~90 kg and propellant ~800 kg; the
mass after reaching lunar orbit will be ~600 kg. It is a
three-axis stabilized spacecraft generating about 750 W
of peak power using the solar array and will be supported
by a Li–ion battery for eclipse operations. The spacecraft
adopted bipropellant system to carry it from the elliptical
transfer orbits through lunar transfer orbit and finally in
the designated 100 km lunar polar orbit, and for orbit and
attitude maintenance in lunar orbit. The TTC communica-
tion would be in the S-band. The scientific payload data
will be stored in two solid state recorders (SSR#1 & #2)
and subsequently played back and down-linked in X-band
through 20 MHz bandwidth by a steerable antenna point-
ing at IDSN.
Lunar observation plans
The varying solar illumination of the lunar surface dic-
tates the operation of the imaging instruments (TMC,
HySI, MMM, SIR-2) to within ±60° latitude during two
prime imaging seasons, each of 60 days, in a given year.
During intervening non-prime imaging seasons, 60° to
90° of North/South polar region will be covered to com-
plete the coverage of the entire moon during the two-year
mission. Mini-SAR polar imaging is planned during non-
imaging seasons. Data from the imaging instruments and
the mini-SAR will be stored in SSR#1 for subsequent
transmission to ground. RADOM, LLRI, SARA and the
two X-ray payloads will be kept ‘ON’ continuously and a
second SSR (#2) will record data from these instruments.
Two ground terminals (18 m and 32 m antenna), esta-
blished at the IDSN provide communication link for the
Chandrayaan-1 mission. The 18 m terminal was tested
during SMART-1 EOL mission and other ongoing plane-
tary missions and the newly built indigenous 32 m
antenna (Figure 4) has undergone extensive tests and will
support not only the Chandrayaan-1 mission but also pro-
posed future Indian planetary missions to other inner
solar system objects. The raw data along with auxiliary
data will be stored at the newly commissioned Indian
Space Science Data Centre (ISSDC), also set up at the
ISDN site, for processing and archiving. It will be the
focal point for Chandrayaan-1 science team. ISSDC will
house and archive data from all future Indian space sci-
ence missions.
Mission sequence
The Chandrayaan-1 spacecraft was launched on 22 Octo-
ber 2008 using a variant of the flight proven indigenous
Polar Satellite Launch Vehicle (PSLV-XL) and injected
into a 255 km × 22,860 km orbit. After separation from
the launcher, the solar panel was deployed and the space-
craft raised to moon rendezvous orbit by five consecutive
in-plane perigee manoeuvres to achieve the required
386,000 km apogee that placed it in a lunar transfer
Figure 4. The 32 m Indian Deep Space Network antenna with the
Moon in the background.
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Figure 5. A schematic view (not to scale) of the Chandrayaan-1 mis-
sion profile. The spacecraft placed in the initial orbit (IO) by PSLV-XL
was followed by five consecutive in-plane perigee manoeuvres in earth
bound orbits (EBO) to place it in the lunar transfer trajectory (LTT).
The next major manoeuvre, lunar orbit insertion, led to lunar capture in
an elliptical initial lunar orbit (ILO). Four further orbit manoeuvres in
lunar space placed the spacecraft in the operational lunar orbit (OLO)
around the pole at 100 km altitude.
trajectory. The major manoeuvre, lunar orbit insertion
leading to lunar capture, was executed to place the space-
craft in an elliptical (500 km × 7500 km) polar orbit. After
checks of various spacecraft sub-systems, three further
orbit manoeuvres were conducted to place the spacecraft
at the designated 100 km circular polar orbit. The mission
profile and the various orbit manoeuvres are schemati-
cally shown in Figure 5.
Commissioning of the payloads
The RADOM was switched on soon after launch of the
Chandrayaan-1 to monitor the energetic particle fluence
during the multiple passages of the spacecraft through the
earth’s radiation belts. The TMC was commissioned
while the spacecraft was in earth bound orbit for tests and
capture images of the Earth and the Moon. The MIP was
released once the spacecraft was placed in its designated
lunar polar orbit. All the other instruments are sequen-
tially commissioned within a couple of weeks following
MIP release.
Project management
Chandrayaan-1 is carrying eleven scientific instruments
from an equal number of institutions. Accommodation of
these instruments and meeting their stringent technical
requirements in a small satellite bus was a challenging
task. The difficulty and complexity of the task was fur-
ther accentuated by the varying approaches in the design
and development of the instruments at various Indian and
foreign laboratories. Nevertheless, Chandrayaan-1 pro-
vided ISRO with a unique opportunity to demonstrate
true international cooperation in the field of planetary
exploration in general, and of lunar exploration, in parti-
cular.
