INSTRUMENT_HOST_DESC |
Instrument Host Overview
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The LCROSS (Lunar CRater Observation and Sensing Satellite)
mission was conceived as a low-cost means of determining the
nature of hydrogen detected at the polar regions of the moon.
LCROSS was selected as the Lunar Reconnaissance Orbiter (LRO)
secondary payload on April 10th, 2006 and launched with LRO on
June 18th, 2009. To meet the requirements of a secondary
payload, the LCROSS Shepherding Spacecraft (SSC) was built
around an EELV Secondary Payload Adapter (ESPA) ring, originally
designed as a mating interface for up to six small spacecraft or
experiments as secondary payloads on Delta IV and Atlas V
launches. Developed by Northrop Grumman, the SSC featured five
equipment panels and a solar array mounted radially at the ESPA
mate ports. A single monopropellant tank was mounted within the
ESPA ring. For launch, the nearly 900 kg (wet mass) LCROSS
SSC was mated between the Centaur upper stage and LRO.
The SSC utilized copies of several LRO avionics units, including
its RAD750-based single-board computer, power and thruster
control electronics, S-band communications electronics, and
SpaceWire bus electronics. LCROSS flight software derived
heavily from software on previous programs, including EO-1 and
WMAP. LCROSS communicated in S-band via two omnidirectional
antennas and two medium-gain antennas. Transponder electronics
enabled downlink at data rates up to 1 Mbps and uplink at 16
kbps. Following launch and LRO separation, attitude control was
passed from the Centaur to the SSC. The attitude control system
(ACS) provided three-axis control using an inertial reference
unit (IRU; no accelerometers), a star tracker, coarse sun
sensors for emergency automated sun-relative attitude capture
and tracking, and a set of eight monopropellant 5 N thrusters.
Two additional 22 N thrusters provided orbit maneuvering
capability. The ACS featured twelve control mode/submode
combinations, six tailored for specific operations while
attached to the Centaur, and a second set for use after Centaur
separation. The LCROSS propellant tank contained just over 305
kg of hydrazine for both attitude control and orbit maneuvering.
The LCROSS power system featured a 368 W solar array and four 20
A-h batteries. LCROSS performed thermal control using a
combination of resistive heaters, passive radiators, and
multi-layer insulation.
The LCROSS Payload
The LCROSS Payload consists of nine science instruments, their
supporting electrical, mechanical and optical harnesses, a
central data handling unit (DHU) assembly, and thermal hardware
(heaters, thermistors, and thermostats), all assembled onto the
LCROSS spacecraft R6 Radiator Panel. Eight of the nine science
instruments are configured with their apertures in the +X
direction (spacecraft body frame/SBF) and are accommodated in
the Payload Observation Deck (POD). The ninth instrument, near
infrared spectrometer #2 (NSP2), has its entrance optical
element orientated in the -Z direction (spacecraft body
frame/SBF). The Payload is located on the inboard side of the
LCROSS spacecraft R6 Panel.
Visible Camera
The LCROSS visible camera (VIS) is a ruggedized analog video
camera from the RocketCamTM camera family developed by Ecliptic
Enterprises, Inc. The unit consists of a camera module and a
lens. The camera's focal plane CCD sensor is 752 [H] x 582 [V]
pixel format, operating at 30 Hz (60 fields/sec). The flight
unit's lens is a 12 mm (focal length), f/1.2 lens providing a
30.1 degree [H] x 22.8 degree [V] (37.8 degree [Diagonal]) field-of-view.
Interlaced NTSC fields are sampled by the Data Handling Unit
(DHU) at 720 x 243 resolution resulting in a final image
resolution of 720 x 486 pixels. Each pixel is 24-bit RGB with 8
bits per color channel. These images are compressed using a
lossy compression algorithm performed by the Analog Devices 611
Video Codec set on 80% quality and decompressed on the ground.
The LCROSS visible camera contains no cryogenic liquids or
moving parts. The visible camera's peak power during operation
is 2.9 W. The visible camera has been fixed to an
auto-gain/white balance setting.
Near-Infrared Cameras
The LCROSS payload contains two near infrared (IR) (0.9-1.7 um)
cameras (NIR1/NIR2). Each camera consists of a Goodrich Sensors
Unlimited model SU320-KTX and a CCTV lens. Each camera's focal
plane InGaAs sensor has a 320 [H] x 240 [V] pixel format. The
25 mm, f/1.4 C-mount glass lens provides a 28.7 degree [H] x 21.7
degree [V] (36.0 degree [Diagonal]) field-of-view. Although the
camera's native format provides 320 [H] x 240 [V] 12-bit images,
the images are converted within the camera to an analog NTSC
signal before transfer to the DHU where they are captured at 720
[H] x 486 [V]. Due to similar processing within the DHU as
needed for the VIS images, the two NIR camera images are
captured as 24-bit per pixel RGB. Because the NIR cameras
provide grayscale images, the three RGB channels are identical
except for noise introduced in the conversion to and from
NTSC. These images are compressed in the DHU using a lossy
compression algorithm performed by the Analog Devices 611 Video
Codec set on 80% quality and decompressed on the ground. In
addition to a camera body and a lens, near infrared camera #1
(NIR1) also contains a long-pass filter (wavelength > 1.4 um).
NIR2, in comparison, is filter-less.
Lenses for both cameras were provided by UkaOptics
(http://www.ukaoptics.com/ #2514M) as part of the standard
Goodrich package. These lenses are not optimized for the IR.
The IR throughput of the lenses has not been documented, but is
expected to be ~40%. The near-infrared cameras contain no
cryogenic liquids or moving parts. There is an internal
thermo-electric cooler that actively cools the InGaAs sensor.
The manufacturer default settings for this cooler are used.
Each camera's peak power during operation is 1.6 W. Both gain
and exposure times are configurable by commands sent to the
camera.
Mid-Infrared Cameras
The LCROSS payload contains two mid-infrared (MIR) (6.0-13.5 um)
cameras (MIR1/MIR2). Mid-infrared camera #1 (MIR1) is a
ruggedized vanadium oxide (VOx) microbolometer MIRIC TB2-30,
from Thermoteknix Ltd. Mid-infrared camera #2 (MIR2) is model
ThermoVision Micron from Flir Systems/Indigo Operations. Each
camera's uncooled microbolometer focal plane sensor has a 164
[H] x 128 [V] pixel format and is digitized at 14-bit
resolution. Each camera has a 30 mm, f/1.6 lens providing a
15.0 degree [H] x 11.0 degree [V] (18.6 degree [Diagonal]) field-of-view.
MIR1 also contains a 6-10 Om bandpass filter. MIR2 is
filter-less. MIR1 is backfilled with dry Argon gas to prevent
degradation due to humidity for terrestrial applications and
does not contain any component volatile in vacuum. Internal to
both MIR modules is an instrumented-motorized shutter to provide
a reference for temperature measurements. Each camera's peak
power during operation is 1.3 W. A camera gain, which
determines the sensitivity to temperature scenes (high gain: -20
degC < T < +150 degC, low gain: +150 degC < T < +500 degC), is
configurable with a command sent to the camera.
Total Luminance Photometer
The Total Luminance Photometer (TLP) provides visible light
(400-1000 nm) intensity data at a 1000 Hz sampling rate. The
TLP instrument consists of two elements: (1) the Sensor
Electronics Module (SEM), which contains the optics and sensor
assembly and signal filtering, and (2) the Digital Electronics
Module (DEM), which converts the analog sensor signal to a
digital output, as well as higher order functionality. The DEM
is a commercial package that was modified for LCROSS. This
instrument is designed and manufactured by NASA Ames Research
Center. The optics in the SEM delivers an unobstructed ~10
degree diameter field-of-view. The TLP's sensor element is an
uncooled Advanced Photonix, Inc. (API) avalanche photo diode
(APD) packaged in a dryair sensor container that can operate in
a vacuum. The TLP SEM is connected by an electrical harness to
the TLP DEM. The SEM and DEM are located within the Payload
Observation Deck (POD) and on the R6 Panel, respectively. The
DEM is interfaced with the DHU (also on the R6 Panel) via a
second cable, from which it is controlled. The SEM and DEM's
peak power during operation are 2.5 W and 12.0 W, respectively.
Visible Spectrometer
The LCROSS visible spectrometer (VSP) is a modified-commercial
model from Ocean Optics Ltd., with its core operation based on
their COTS QE65000 model. It has been adapted for space use and
is of similar design to a recently delivered spectrometer to Los
Alamos for a Mars Science Laboratory (MSL) payload for launch in
2011. The VSP spectrometer design consists of an FC optical
fiber input (0.11 NA) feeding a 25 micron x 1 mm entrance slit,
where light is diffracted by a 1-inch f/4 optical cross
Czerny-Turner spectrometer (grating 600 lines/mm, blazed at 350
nm) with an oversized camera mirror. The ~263-650 nm spectrum
from the slit is imaged onto a 1044 x 64 pixel Hamamatsu CCD
detector. The data is co-added within the spectrometer,
delivering a 16- bit, 1 x 1044 pixel spectra to the DHU
electronics for packaging. The first 1024 pixels contain
spectral data. The remaining 20 pixels contain provide
temporally coincident but off-slit dark reference pixels. The
VSP resolving power is R~300, 500, and 850 at 300, 400 and 600
nm, respectively. The VSP contains no moving parts. The CCD
detector is cooled by an internal Thermoelectric Cooler (TEC),
whose set point is programmable. The VSP power is 4.8 W (TEC
off), and can reach 11.8 W (at TEC setting -10 degC at operating
temperature +19-20 degC). Integration time (between 8 ms and 65.5
s) is configurable. Additionally, the VSP supports two
operation modes - single and bracket spectra. The former is a
single spectra acquisition of the appropriate requested
integration time. The latter is a three-spectra acquisition
defined by a base integration time and a multiplier that is
divided or multiplied by the base integration time to yield a
shorter or longer exposure time, respectively. The VSP is fed
by a 75 cm length 600-micron core-diameter UV/Vis glass fiber
attached to a fore-optics unit in the POD. This fore-optics
unit (see below) is a fixed two-mirror and one lens system
designed to provide a one degree diameter field-of-view.
Near-Infrared Spectrometers
The LCROSS payload contains two near-infrared spectrometers
(NSP1/NSP2), located on the R6 Panel. Their electronics units
are identical, but they have different fore-optics designs.
Near infrared spectrometer #1, NSP1, also known as the nadir
NSP, is located inside the POD and its aperture is positioned in
the +X direction (spacecraft body frame/SBF). Near infrared
spectrometer #2, NSP2, also known as the solar-viewer or
occultation NSP, has its wide-field aperture centered along the
-Z direction (spacecraft body frame/SBF). Both spectrometers
provide 1.20-2.45 um spectral coverage and nominal resolution
0.035 um/pixel, yielding resolving powers R ~ 37-65 (NSP1) and R
~ 36-77 (NSP2). Both spectrometers are manufactured by
Polychromix, a company whose primary spectrometer line is
designed for material analysis and chemical sensing. The
spectrometers are designed to take a single SMA NA=0.22 fiber as
input instead of a slit, whose diameter defines the instrument
resolution. Since each spectrometer contains a single
TEC-cooled InGaAs sensor element, a 1D-spectrum is created using
an innovative electronically-tunable MEMS device that spatially
masks the dispersed spectrum within the instrument. This series
of masks undergoes a digital transform on the ground to recreate
the spectral information. The spectrometer contains no moving
parts (excluding the MEMS chip) and the peak power for each NSP
is 2.5 W. NSP1 and NSP2 are each fed by a single 600-micron
core-diameter low-OH glass fiber of length 75 cm and 1.45 m,
respectively, attached to a fore-optic. The NSP1 fore-optics
unit (see below) is located within the POD and is a fixed
two-mirror and one lens system designed to provide 1 degree
diameter field-of-view. The NSP2 fore-optic (see below) is a
diffuser providing ~130 degree fieldof- view, and is located external
to the POD housing. Both spectrometers have three modes, Impact
Flash (IF), Hadamard Spectrum (HS) and Diagnostic Mode (DM),
which are configurable by sending a command to the units.
Fore-Optics and Fibers
The LCROSS payload contains two fore-optic units and three
fibers. The three single-core fibers connect the electrical
units of the three LCROSS spectrometers to their respective
fore-optics (i.e., light-gathering optics). All fibers are
manufactured by Fiberguide Industries. The two fore-optics, a
dual-scope fore-optic feeding the NSP1 and VSP spectrometers and
a diffuser fore-optic feeding the NSP2 spectrometer, have been
designed specifically for the LCROSS mission by Aurora
Technologies. The dualscope fore-optic provides 1 degree
diameter field-of-view (per scope) and a separation between the
two scopes of < 0.1 degrees. The diffuser fore-optic provides
an unattenuated ~130 degree field-of-view. The fibers were chosen to
optimize for the band-pass and be compatible with the throughput
and entrance optic requirements by the spectrometers. For the
VSP, the fiber is a 75 cm SuperguideG UV/VIS Spectral Range with
NA=0.12+/-0.02. For the NSPs, the fibers are AnhydroguideG Low
OH fibers with NA=0.22+/-0.02, with lengths 75 cm and 145 cm for
NSP1 and NSP2, respectively. All three fibers have 600 Om
core-diameters and are encased in a 1/8 inch (ID) stainless
steel monocoil for ruggedization.
Data Handling Unit
The LCROSS Data Handling Unit (DHU) is a ruggedized video camera
controller and data handling system based on the ruggedized
Digital Video Systems (DVS) developed by Ecliptic Enterprises,
Inc. It captures and transmits compressed digital spectrometer,
video and photometric data telemetry (in CCSDS format) from all
nine instruments from the LCROSS science payload. The DHU is a
single conduction-cooled chassis designed to operate as
independently as possible from its host vehicle. In the
limiting case, DHU operation is completely self-contained except
for activation/deactivation commands that originate from the
ground. The DHU can store up to 10 slots of Non- Volatile
Memory (NVM), which can be used for sequencing power and
operational commands to the science instruments. The DHU
contains no moving parts, operates from the 32 V power supply by
the spacecraft power bus, and its peak power during operation is
13.5 W. The DHU also provides the time-stamping function of all
the science instruments and itself and provides error logs for
when science data frames are dropped or corrupted due to
bandwidth or performance issues.
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