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Science Goals and First Light Analysis from the Miniature X-ray Solar Spectrometer (MinXSS) CubeSat

Authors:

Abstract

The Miniature X-ray Solar Spectrometer (MinXSS) is a 3U CubeSat with deployment from the ISS planned in Q2 2016. Its goal is to measure the solar soft X-ray (SXR) spectral irradiance, an observational signature of hot plasma in the solar corona. Over the last few decades, there have been very few spectrally resolved observations from ~0.2 to ~4 keV (~0.3-6 nm). This range is sensitive to high-temperature plasma and contains many spectral lines (e.g., Mg, Si, Fe, S, Ar), the abundances of which probe plasma transport and provide valuable constraints on plasma heating mechanisms during both flares and quiescence. This solar SXR emission is primarily absorbed in the E-region of Earth's ionosphere, and the subsequently driven dynamical processes are still poorly understood, in large part because the energy distribution of the incident SXRs is not yet well characterized. MinXSS flies a miniature commercial off-the-shelf soft X-ray (SXR) spectrometer, the Amptek X123-SDD. The silicon drift detector has 0.5 mm fully depleted thickness and a 25 mm^2 physical area, with a ~16 micron Be entrance window; with on-board thermoelectric cooling and pulse pile-up rejection, it is sensitive to solar SXRs from ~0.5 to 30 keV with ~0.15 keV FWHM resolution. MinXSS also includes a broadband SXR photometer, providing an integrated intensity over a similar energy range for comparison, cross-calibration, and additional data, especially useful during more intense flares at the upper end of the X123 dynamic range. We present the MinXSS science goals for studying hot plasma in the solar corona, including impulsive flare heating and quiescent coronal heating, and the impact of the resultant SXR emission on Earth's ionosphere, thermosphere, and mesosphere. We present analysis of MinXSS first light results (depending on deployment date from the ISS), as well as modeling and predictions of future observations over the MinXSS 6-12 month mission lifetime.
Science Goals and First Light Analysis from the
Miniature X-ray Solar Spectrometer (MinXSS) CubeSat
Amir Caspi1, Thomas N. Woods2, Harry Warren3, Phillip C. Chamberlin4, Andrew Jones2,
James Mason2, James McTiernan5, Christopher Moore2, Scott Palo6, Stanley Solomon7
1Southwest Research Institute, Boulder; 2Laboratory for Atmospheric and Space Physics, Univ. of CO, Boulder;
3Naval Research Laboratory; 4NASA Goddard Space Flight Center; 5Space Sciences Laboratory, Univ. of CA, Berkeley;
6Dept. of Aerospace Engineering Sciences, Univ. of CO, Boulder; 7NCAR High Altitude Observatory
P3.06
Temperature change
with height
D
Ionosphere
E F
Flare
Quiescent
Original image courtesy NOAA
OVERVIEW: The MinXSS CubeSat, Flight Model (FM) #1, deployed
from the ISS on 16 May 2016 and is currently being commissioned. We
review the MinXSS science objectives, data pipeline, current status,
and expected future results.
Yohkoh HXT (4 ch)
Example
Flare
Example
Quiescent
Soft X-ray emission is an observational signature of hot plasma in the solar corona,
from ares, active regions, and the quiet Sun. [Left] Over the last few decades, there
have been very few spectrally resolved observations from ~0.2 to ~4 keV (~0.3–6 nm).
[Right] This range is sensitive to high-temperature plasma and contains many spectral
lines (e.g., Mg, Si, Fe, S, Ar), the abundances of which probe plasma transport and pro-
vide valuable constraints on plasma heating mechanisms during both ares and qui-
escence. MinXSS lls a signicant portion of this observational gap.
Solar soft X-ray emission is absorbed in Earth’s ionosphere D- and E-regions. These en-
ergetic photons ionize primarily N2, O2, and O, and the resultant photoelectrons can
produce secondary ionizations; this can cause high-frequency radio blackouts, and
changes the Hall and Pedersen conductivities that contribute to magnetospheric-ion-
ospheric coupling. [Left, Center] Higher photon energies (shorter wavelengths), e.g.,
from ares, penetrate more deeply and deposit energy at preferentially lower alti-
tudes. The cross-sections for the above processes change by an order of magnitude in
the crucial ~0.25–1.25 keV (~1–5 nm) range, and therefore the ionization cascade and
the resulting dynamics induced in the ionosphere depend critically on the spectral
shape of the soft X-ray emission.
[Right] A quantitative example highlighting the sensitivity of the E-region response to
the spectral distribution: the quiescent (active region) and are spectra are scaled to
the same 0–7 nm integrated energy. The altitude of mean energy deposition varies by
~5 km, roughly a scale height. MinXSS will provide accurate soft X-ray spectral
measurements to better understand the solar-driven ionospheric dynamics.
CubeSat
MinXSS
Level 0A
“raw” telemetry
Level 0B
receive-sorted packets
Level 0C
time-sorted packets
Level 0D
time-sorted science packets
SolarSoft
& SunPy
Level 1
spectral irradiance
Level 2
spectral irradiance (corrected)
Level 3
spectral irradiance (daily avg.)
LISIRD
Level denitions:
0A – raw telemetry, binary
0B – decoded packets, sorted by time
received on the ground (.sav)
0C – unique packets, sorted by time
generated onboard (.sav)
0D – science packets (native time bins)
w/ ancillary data interpolated to
observation time (.sav, .ts)
1 – spectral irradiance (native time and
energy bins) from 0D, corrected
for instrument response, 1 AU,
pointing, etc. (.sav, .ts)
2 – spectral irradiance from L1 (native
time and energy bins) corrected
for long-term degradation
3 – spectral irradiance from L2 (native
energy bins), daily average
FIRST LIGHT: The X123 was enabled on 27 May 2016; rst light
was downlinked on 30 May 2016, a total of 190 seconds of observa-
tions. A preliminary examination shows that the averaged spectrum is
roughly consistent with prior results from X123 observations on the
SDO/EVE sounding rocket ights in 2012/2013 (Caspi et al. 2015).
CURRENT STATUS: MinXSS was successfully deployed from the ISS
on 16 May 2016 at 12:05:26 UT. Solar panels and the UHF antenna de-
ployed autonomously, and MinXSS is currently being commissioned
during multiple daily contacts with the CU/LASP ground station.All subsys-
tems appear healthy and are operating nominally. Subsystem parameters
are being adjusted to optimize performance on-orbit.
MinXSS’s routinely-observed soft X-ray spectra will be openly released to
the solar physics community and can be used to, e.g., calculate dierential
emission measures (temperature distributions) of the hot solar plasma, to
better understand plasma heating in solar ares and the quiescent corona.
Joint observations with, e.g., RHESSI, Hinode/XRT, and SDO/AIA will be
made. Calibrated irradiance products will also be released to the geophys-
ics community to be used as input to atmospheric modeling, to improve
understanding of solar X-ray forcing of ionospheric dynamics.
EXPECTED FUTURE RESULTS:
Uncalibrated
The ~10x lower count rate is due
to overactive onboard pileup re-
jection due to RF noise on the fast
counter; the spike <0.5 keV is
thermal noise on the slow chan-
nel. We are adjusting the X123
and radio parameters during
commissioning to optimize de-
tector performance for nominal
science mode.
Flare
Quiescent
Amptek X123 silicon drift detector
soft X-ray spectrometer
Blue Canyon Technologies XACT
attitude determination & control
The primary MinXSS science instrument is the Amptek X123-SDD, a silicon drift detec-
tor operating in photon-counting mode. An integrated thermoelectric cooler reduces
thermal noise and enables the best-yet spectral resolution for wide-band, spectral-
ly-resolved solar soft X-ray observations. Parallel fast and slow shaper-amplier chan-
nels provide on-board pulse pileup rejection for accurate spectroscopy up to
~10K-20K counts/s, and counting capability up to ~100K cts/s. Photons are automati-
cally binned into spectra with 1024 bins (~0.03 keV/channel), with 10-sec cadence.
Because of the copious solar soft X-ray ux, MinXSS uses an aperture of ~170 µm.
OBSERVING PARAMETERS:
Mission length is limited by the orbital lifetime
at 400 km initial altitude. MinXSS observes the
entire Sun at all times in science mode. Ca-
dence is congurable by uplink command; all
mission data is stored on-board for later
downlink. Duty cycle is limited by eclipses and
the passages through the South Atlantic
Anomaly (data is contaminated).
SCIENCE-ENABLING TECHNOLOGIES:
MinXSS DATA PIPELINE:
Size
Window
Energy
Range
Resolution
5 x 5.6 mm2
16 µm Be
0.5–30 keV
0.15 keV FWHM
MinXSS science is enabled by 3-axis high-precision
pointing from the Blue Canyon Technologies XACT.
With an integrated star tracker, reaction wheels,
torque rods, magnetometer, and IMU, the XACT pro-
vides ~10–20 arcsec (1 sigma) pointing knowledge
and control for precise solar pointing.
Quiescent
Flare
6.0 6.5 7.0 7.5 8.0
Log T (K)
1
10
100
1000
DEM (1040 cm−3 K−1)
Recovered DEM
Binning
Cadence
Duty
Cycle
Downlink
Latency
1024 channels
(~0.03 keV/bin)
FOV ~ ±5°
Mission
Lifetime 6–12 months
~10 sec
~50%
(eclipse/SAA)
~days
FILLING A SOFT X-RAY OBSERVATIONAL GAP:
THE INFLUENCE OF SOLAR X-RAYS ON EARTH:
ITM Community
(ionospheric modeling)
DEMS (solar physics)
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