LROC Instrument Requirements
Scott Brylow, Instrument Manager
Malin Space Science Systems
LROC Organizational Chart
09 - 2
LROC Theory of Operation
•
LROC consists of one Wide Angle Camera (WAC) and two Narrow Angle
Cameras (NAC). All camera heads deliver data to the spacecraft through the
Sequence and Compressor System (SCS).
•
The WAC subsystem consists of dual optics (UV and visible), providing multispectral images with 100m/pixel visible resolution and 400m/pixel UV
resolution.
•
Each NAC subsystem consists of a 2.86 ° FOV telescope, co-aligned to
provide a total 5.67° FOV, acquiring high resolution monochrome images
•
The SCS includes electronics for commanding and receiving data from all
cameras, as well as power and data (SpaceWire) interfaces with the
spacecraft.
09 - 3
LROC Solid Model
09 - 4
LROC Heritage
•
WAC heritage –
– Electronics – exact copy of those used on MRO MARCI, other missions
– Optics – same concept, minor changes to FOV, filter bandpasses
– Mechanical – same mounting interface to spacecraft
•
NAC heritage –
– Electronics – copy of those used on MRO CTX, single part substitution for
NAC A/D, system clocked at higher speed.
– Optics – new design, same focal plane mounting interface,
– Mechanical – same concept for spacecraft mounting flexures
•
SCS heritage
– New electrical design, implements MRO-heritage spacecraft interfaces with
WAC, NAC, provides SpaceWire interface to LRO spacecraft.
– New mechanical design, same concept as electronics boxes for NAC, WAC
09 - 5
LROC Instrument
Documents
• LRO Program Requirements Document; ESMD-RLEP0010
– LRO Mission Requirements Document; 431-RQMT-00004
• LRO Technical Resource Allocations; 431-RQMT-000112
• Instrument Payload Assurance Implementation Plan,
• Instrument to Spacecraft Interface Control Documents
– Mechanical 431-ICD-000090, Thermal 431-ICD-000114, Electrical
431-ICD-000099 & Data 431-ICD-000108
– Instrument Requirements Document MSSS-LROC-0100
– MSSS Safety Plan MSSS-SAFE-001, April 2002
– MSSS Quality Plan MSSS-QUAL-001, May 2004
09 - 6
LROC Mission
Level Requirements
ESMD-RLEP-0010
LRO
Req.
Level 1: Requirements
Instr.
RLEP-LROM40
RLEP-LROM80
LROC
LROC
LRO Mission Requirement
Required Data Products
The LRO shall obtain geodetic lunar global
topography (at landing-site relevant scales 30m down-track and 50m cross-track) with
spatial resolution of 50m at the polar regions
(within 5 degrees of the poles), and 1km at
the equator.
For limited areas of high interest (targets),
provide demonstration 2m to 4m scale NAC
photometric stereo Digital Elevation Models
(DEM) for areas 5km x 5km.
The LRO shall assess meter-scale features
of the lunar surface to enable safety analysis
for potential lunar landing sites over targeted
areas of 100km^2 per the LRO Landing Site
Target Specification Document.
Provide up to 50 NAC Mosaics of potential
landing sites with 1 m/pixel resolution.
Acquire 100m/pixel global WAC stereo imaging
(in EDR format, no maps) reducible to 1km/pixel
global topography. Backup for LOLA failure.
Provide crater size density and size distribution
maps of up to TBD potential landing sites.
09 - 7
LROC Mission
Level Requirements
ESMD-RLEP-0010
LRO
Req.
Level 1: Requirements
Instr.
RLEPLRO-M90
LROC
LRO Mission Requirement
The LRO shall characterize the Moon’s polar
region (within 5 degrees of the poles)
illumination environment at relevant temporal
scales (i.e., typically that of hours) to a 100m
spatial resolution and 5 hour average
temporal resolution.
Required Data Products
Provide WAC uncontrolled illumination
movies, 1 each of North and South Lunar
Poles over the course of 1 lunar year at an
average time resolution of 5 hours or
better.
Provide 1 m/pixel resolution NAC summer
(uncontrolled) mosaics of the lunar poles
(+/- 4 degrees). There may be some gores
in the data due to tolerance (20km) of the
nominal 50km orbit altitude.
RLEPLRO-M100
LROC
The LRO shall obtain high spatial resolution
global resources assessment including
elemental composition, mineralogy, and
regolith characteristics to a 20% accuracy
and a 5km resolution.
Global WAC imaging 400m/pixel in the
ultraviolet (UV) bands and 100m/pixel in
the visible bands, ten uncontrolled
demonstration multi-spectral mosaics for
high priority targets.
09 - 8
LROC Instrument System
Level Requirements
Level 1
Req.
Instrument Level 2: Requirements MSSSLROC-IRD
Requirement
Location
Concept/Realizability/Comment
LROC Instrument Measurement Requirement
M40LROC
IRD3.1.1
2m scale digital elevation models (DEM) require
that NAC images be taken at varying sun
angles/azimuths (at least 4 per site)
Ensure repeated high-resolution images of
same ground spot are acquired with NAC.
M40LROC
IRD3.1.2
100m/pixel global stereo imaging requires WAC
images taken on consecutive orbits to provide
overlap with similar lighting geometries
WAC 90 degree FOV provides sufficient
overlap to compile stereo data set, even at
equator.
M80LROC
IRD3.2.1
Acquire NAC image pairs of potential landing
sites with ability to identify meter-scale hazards
with areal coverage of 100km^2
2 NAC imagers aligned side-by-side provide
5km crosstrack, while buffer size allows
25km downtrack for 125km^2 areal
coverage
M90LROC
IRD3.3.1
Acquire WAC images of lunar illumination which
fully overlap at latitudes > 88 degrees and repeat
frequently at latitudes > 85 degrees so that per
orbit acquisitions can be combined into a hightemporal-frequency (1 frame every 5 hours on
average) movie.
The WAC monochrome mode offers 90deg
FOV for full overlap poleward of 88 degrees
and sufficient repeat frequency poleward of
85 degrees to create movie data products
M90LROC
IRD3.3.2
Acquire NAC images for the lunar surface
poleward of 86 degrees latitude during respective
summers
Full coverage at NAC 1 m/pixel resolution
requires summing to allow downtrack of
>100 km per buffer
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LROC Instrument System
Level Requirements
Level 1
Req.
Instrument Level 2: Requirements MSSS-LROCIRD
Requirement
Location
Concept/Realizability/Comment
LROC Instrument Measurement Requirement
M100LROC
3.4.1
Complete global WAC maps of all visible (100m
resolution) and UV (400m resolution) bands
Framelet repeat rate <0.54sec for
WAC to prevent downtrack gores in
the global maps. Use all filter band
framelets.
M80LROC
3.5.1
Meter-scale images of landing sites with sufficient
S/N ratio so that image quality supports analysis of
crater counts and sizes
50cm resolution with S/N ratio >40:1 at
70deg solar incidence and albedo
=0.12, 2x summing at poles to
maintain adequate SNR
09 - 10
LROC Instrument Subsystem
Level Requirements - I
Level 2 Req.
Level 3: Requirements
IRD
Paragraph
Concept/Realizability/ Comment
LROC Design Requirements
IRD3.1.1
4.1.1
Each NAC shall be able to acquire images at a resolution of up to
0.5 m per pixel at the nadir in the nominal LRO orbit (50 km
altitude.)
Requires 10 microradian
IFOV and adequate
spacecraft pointing accuracy
IRD3.1.1
4.3.1
The NAC images shall have a SNR of at least 40:1 when imaging a
surface on the Moon with an albedo of 0.12 at a solar incidence
angle of 70° (solar elevation angle of 20°) at 50 km altitude.
Large aperture (8”) to get
photons for high SNR
IRD3.1.1
4.4.1
Each NAC shall acquire images over a swath width of 2.5 km (5 km
total for both NACs) in the cross-track direction from 50 km altitude.
2.86 degree FOV for swath
width requirement
IRD3.1.2
4.1.2,
4.1.3
The WAC shall acquire images in the visible spectrum with a
resolution of 100 m/ pixel (visible) and 400 m/pixel (UV) at nadir in
nominal LRO orbit (50 km).
Required for polar temporal
illumination characterization
and global morphology/color
mapping
IRD3.1.2
4.4.2
From an altitude of 50 km, WAC shall have the capability to acquire
contiguous images from pole to pole in each orbit. From the
nominal orbit and an altitude of 50 km, WAC full-width images shall
have 50% overlap with previous and subsequent orbits.
90 degree FOV provides
overlap required to provide
stereo data. Limited data
processing planned.
IRD3.2.1
4.4.1
Down-track length of NAC images shall be limited only by the
volume of the NAC-internal 256 MB buffer.
Full buffer image size is 5km
x 25km (no summing)
09 - 11
LROC Instrument Subsystem
Level Requirements - II
Level 2
Req.
Level 3: Requirements
IRD
Paragraph
Concept/Realizability/ Comment
LROC Design Requirements
IRD3.3.1
4.4.2
From the nominal orbit and an altitude of 50 km, WAC full-width
images shall have full overlap with previous and subsequent orbits
poleward of 88 degrees latitude.
The WAC monochrome
mode provides full overlap
IRD3.3.2
4.3.1
NAC images shall have a signal to noise ratio of at least 30:1 when
imaging a surface on the moon with an albedo of 0.12 at a solar
incidence angle of 85° at 50 km altitude (with 2x summing)
8” aperture ensures enough
incident energy to meet SNR
IRD3.3.2
4.4.1
Down-track length of NAC images shall be limited only by the
volume of the NAC-internal 256 MB buffer.
Summing to 1m/pixel allows
for 100 km downtrack
IRD3.4.1
4.4.2
From the nominal orbit and an altitude of 50 km, WAC visible shall
have the capability to acquire contiguous images from pole to pole in
each orbit
<0.54 sec framelet timing to
prevent downtrack gores
IRD3.5.1
4.1.1
The system modulation transfer function (MTF) shall be greater than
0.2 at the maximum sampling (Nyquist) frequency of the detector.
Diffraction limited optics,
known MTF of detector,
minimal scattered light
IRD3.5.1
4.3.1
The NAC images shall have a signal to noise ratio of at least 40:1
when imaging a surface on the Moon with an albedo of 0.12 at a
solar incidence angle of 70° (solar elevation angle of 20°) at 50 km
altitude.
8” aperture ensures enough
incident energy to meet SNR
09 - 12
LROC Data Product
Traceability
Data
Description
Required Inputs
Level 0
Raw unprocessed NAC and WAC Image files (EDR) from the
spacecraft.
Instrument data
Level 1
Calibrated Data Records (CDR) including background
removal, flat fielding, absolute calibration.
Calibration data, instrument and spacecraft
thermal data
Level 2
Reduced Data Records (RDR) such as NAC landing site
mosaics, uncontrolled best effort NAC polar summer mosaics,
and WAC best effort demonstration products (small regional
mosaics).
Spacecraft OD and pointing data
Level 3
Temporal movies, monochrome global morphological maps
and multi-spectral images created from WAC data,
Photometric and radiometric adjustments performed, DEM,
photogrammetric stereo analysis complete
Level 1 products
09 - 13
LROC Constraints on LRO
Title
Requirement
Rationale
Traceability
Sun
Avoidance
No continuous sun pointing within 30
degrees of the NACs and a minimum
slew rate of 1.0 deg/sec in the
instrument bore-sight.
Need to keep focal plane temp below survival limits during sunviewing.
Derived by analysis
SpaceWire
S/C shall be able to drain the NAC
buffer in less than 160 seconds.
S/C shall accept WAC packets every
0.54s.
LROC NAC buffer to SCS design takes 160 seconds, S/C must keep
up to prevent loss of data (no flow control in SCS implementation).
LROC WAC images acquired every 0.54s with no storage
mechanism except for 2 image-sized buffers in the SCS. Failure to
accept WAC packets on that schedule will lead to irrevocable loss of
science data.
Targeting flexibility for
NAC images – no NAC
images can be acquired
while draining NAC
buffer (RLEP-LROM40, M80)
SpaceWire
Flow
Control
LROC shall write 8 bit data to the
Transmit FIFO at a clock rate for the
SpaceWire STROBE signal of 40MHz
without invocation of Transmit FIFO
flow control.
Latency nearly zero – when a packet is delivered to the SBC, we will
expect a command telling us the SBC is ready for more. We can
and do wait for that signal, but failure to present us with an empty
buffer means we’ll leave science data on the floor as we are
acquiring as much as our downlink budget will allow. Timing
diagram in Data ICD will show latency in normal use case
(RLEP-LRO-M40, M80)
Pointing
Accuracy
+/- 2.5 milli-radian
0.14°, approximately 5% of a NAC FOV. Acquisition of contiguous
cross-track imaging to build up areal coverage of each landing site
with no gores requires pointing control to be equal to or better than
planned sequence overlap to insure mosaic integrity.
(RLEP-LRO-M40, M80)
Pointing
Knowledge
+/- 0.75 milli-radian
Reconstruct geometry of WAC observations to within 1 pixel. As
pointing knowledge degrades geometric integrity of uncontrolled
mosaics increases. Real time support of future surface operations
will demand highest possible cartographic accuracy for both LROC
and LOLA.
(RLEP-LRO-M90,
M100)
09 - 14
LROC Constraints on LRO
Title
Rationale
Traceability
NAC1 +1.42° cross-track from Nadir.
NAC2 -1.42° cross-track from Nadir.
Required crosstrack coverage means relative NAC alignment
must be accurate to 50 NAC pixels. S/C will verify orientation of
alignment cube(s).
(RLEP-LRO-M40,
M90)
Jitter
(blur)
Less than 5 micro-radian total (peak-to-peak)
jitter in 0.3 milliseconds
To meet resolution requirements camera/spacecraft jitter must
not blur IFOV >0.5 pixel.
(RLEP-LRO-M40,
M80)
Stability
(geometric)
Less than 10 micro-radian total (peak to peak)
stability in 30 milliseconds
Geometric reconstruction for landing site maps, polar maps, and
stereo analysis (remove long wavelength cross-track wobble).
(RLEP-LRO-M40,
M80)
Timing
Time of rising edge of Spacewire tickout signal
to be accurately reported by corresponding time
message to +/- 100 milliseconds of UTC.
Required to minimize overall orbital knowledge errors, which
affects ability to successfully target NAC at sites of interest.
Derived
Dark Signal
Check
Require occasional (TBD) noon-midnight
nighttime images on farside for dark signal
check once a month. Data can be collected in
less than one minute, but all camera electronics
must be at typical operating temperatures camera remains on throughout orbit.
Calibrate WAC multispectral observations to allow quantitative
mineralogic interpretation for resource assessment
Calibrate NAC monochrome observations to allow quantitative
reflectance measurements (photometric stereo, albedo)
10% absolute, 5%
relative
photometric
accuracy (RLEPLRO-M40, M80,
M100)
Calibration
Require WAC absolute calibration with (UV and
Visible) star observation for absolute
calibrations. Possibly tie into same star
calibration sequences for LAMP on a monthly
basis. Calibration star catalog for LROC needs
to be derived.
Calibrate WAC multispectral observations to allow quantitative
mineralogic interpretation for resource assessment
10% absolute, 5%
relative
photometric
accuracy (RLEPLRO-M100)
Mount
Alignment
Requirement
09 - 15
LROC Constraints on LRO
Title
Requirement
Rationale
Traceability
Require 15° to 20° off-point down-track or crosstrack for stereo imaging three times a day.
Stereo image of same ground spot under similar
lighting conditions. Issue with LOLA’s coverage
spec regarding time off-nadir (less than 3% of total
time). Working issue. Thermally OK for 20° offpoint for 20 minutes total.
Stereogrammetric and
photometric stereo data set
generation (RLEP-LROM40)
Mosaicking
Off-nadir pointing to get contiguous coverage over
wider ground swath three times a day. Off-pointing
requests would range from 2° to 20°.
Allow acquisition of contiguous NAC swaths to cover
entire landing site error ellipses and region of
surface operations.
Landing Site safety (RLEPLRO-M80)
Data Link
LROC shall receive all commanding and distribute
all telemetry over the SpaceWire high speed bus.
Simplify spacecraft to instrument interface at GSFC
request
Science requirements for
high resolution, high
temporal resolution, etc.
data require high bandwidth
download (RLEP-LROM40, M80, M90, M100)
Data Rate
LROC shall write 8 bit data to the Transmit FIFO at
a clock rate for the SpaceWire STROBE signal of
40MHz without invocation of Transmit FIFO flow
control.
Required to deliver NAC data from SCS to use up
downlink allocation, maximize science return, avoid
data loss (heritage design does not use flow
control).
See Data ICD
(RLEP-LRO-M40, M80,
M90, M100)
Mass
Allocation
16.5 kg with margin
Includes 20% contingency over CBE.
Based on proposal
estimates
NAC: 2.86° per NAC, total 5.7° crosstrack. WAC:
90° crosstrack.
Required for swath width
(RLEP-LRO-M40, M80,
M90, M100)
Stereo
Imaging
Science
FOV
09 - 16
LROC Block Diagram
Narrow-Angle
Camera 1
(NAC1)
Wide-Angle
Camera 2
(WAC)
Narrow-Angle
Camera 2
(NAC2)
LVDS sync-serial
Sequencing and
Compression
RS-422 System (SCS)
SpaceWire
(to S/C
C&DH)
LVDS sync-serial
09 - 17
LROC NAC
Development Flow
NAC Optics
NAC Structure
NAC Sunshade
NAC Adapter
Plate
Integrate
Integrate
Integrate
NAC Electronics
NAC Ancillary
Hardware
(heater, blanket,
cabling, etc.)
Integrate
Completed NAC
Instrument
Integrate
NAC Electronics
Housing
09 - 18
LROC WAC
Development Flow
WAC Optics
WAC Optical
Housing
WAC Baffle
WAC Ancillary
Hardware
(heater, cabling,
etc.)
Integrate
Integrate
Integrate
WAC Electronics
Completed WAC
Instrument
Integrate
WAC Electronics
Housing
09 - 19
LROC NAC Validation
• Component / Subassembly Validation
• Focal Length
• Transmission
• Bandpass filter: transmission as a function of wavelength
• Subsystem Validation
• Focus and MTF • Geometric - collimator w/pinhole and bar target sources, instrument on rotation stage
• Radiometric - imaging a reflectance screen illuminated by a NIST traceable calibrated lamp with
known geometry. Also provides flat field and system noise performance
• Stray Light - imaging reflectance screen with fixed illumination, instrument on rotation stage
• Orbiter Validation
• NAC-NAC alignment – locating the NAC FOV’s accurately with respect to each other.
• Recording and Reporting
• Data archived locally on completion of each test
• Data used to create instrument calibration report for science team and LRO mission
09 - 20
LROC WAC Validation
• Component / Subassembly Validation
• Geometric Distortion
• Filter Bandpass
• Subsystem Validation
• Focus and MTF – FPA mounted to electronics, system MTF measured and maximized.
• Radiometric and Spectral - imaging a reflectance screen illuminated by a NIST traceable calibrated
lamp with known geometry. Also provides flat field and system noise performance.
• Stray Light - imaging reflectance screen with fixed illumination, instrument on rotation stage
• Geometric – Vis: grid target of known geometry imaged. UV: point source imaged on rotation stage
• Environment testing as required by the GEVS (number?)
• Recording and Reporting
• Data archived locally on completion of each test
• Data used to create instrument calibration report for science team and LRO mission
09 - 21
LROC Current Status
• Trade Studies Completed:
– NAC optics aperture, bandpass, sunshade,
– WAC filter bandpass, lens design, FOV vs. groundtrack
– Pallet vs. Spacecraft Mount
• Ongoing trade studies
– None
• Analysis currently being performed:
–
–
–
–
FEM
Thermal
MTF
CTE
• Current Hardware Status:
– NAC breadboard complete
– WAC breadboard complete
– SCS breadboard complete
09 - 22
LROC Schedule
09 - 23
LROC Summary
• We understand the data products that must be produced
• We have rigorously constructed traceability from the data products
back to a set of design requirements for the instrument.
• We understand the spacecraft environment and have been assured
by the spacecraft that all of our driving requirements have been
agreed to and will be met by the spacecraft and placed in the MRD.
• We have a complete plan for product assurance
• We have a complete plan for verification and validation of the
instrument performance requirements
• A breadboard exists for each individual subsystem (NAC, WAC, SCS)
• High-heritage pieces of the design (NAC and WAC electronics) have
flight hardware available
• All spacecraft interfaces low-risk, with the data ICD already signed off.
09 - 24