M3 Instrument Design and Expected Performance Robert O. Green 12 May 2005

M3 Science Measurement Requirements Spectral Range: 400 to 3000 nm at 10 nm sampling –Spectral signatures of interest High spectral and spatial uniformity –Enables scientific imaging spectroscopy High Precision (Signal-to-noise ratio) –Low concentration components, low illumination areas of the Moon Spatial swath 40 km with sampling ~70m –Global coverage from planned orbit and data downlink limits Excellent calibration (spectral, radiometric, spatial) –Enables scientific imaging spectroscopy High Instrument and Team heritage –Low risk and science success

M3 Instrument Approach A simple, high uniformity and high throughput “Zakos” Offner imaging spectrometer design JPL convex three zone blazed e-beam lithographic grating 640 by 480 element substrate removed HgCdTe detector array and 6604A readout (sensitive from 400 to 3000 nm) K508 Ricor cryocooler with backup (Clementine, CRISM, etc.) Deployable calibration panel for solar view radiometric calibration

20 mm 25 degree FOV unobscured F/3.5 TMA Telescope JPL e-beam curved grating Slit OS Filter MCT Detector 400 to 3000 nm Single spherical mirror M 3 Optical Configuration 1) Telescope mirrors aligned to machine tolerance w/ shims 2) Spectrometer components held to machine tolerance w/ shims plus fine rotation only on grating and detector.

24 degree FOV unobscured F/3.5 TMA Telescope Slit JPL e-beam curved grating 640 cross-track MCT Detector 400 to 3000 nm Single spherical mirror OS Filter M 3 Optical Configuration 1) Telescope mirrors aligned to machine tolerance w/ shims 2) Spectrometer components held to machine tolerance w/ shims plus fine rotation only on grating and detector.

The M3 “Zakos” Design Provides a Uniform Imaging Spectrometer Depiction -Grids are the detectors -Spots are the IFOV centers -Colors are the wavelengths Spectral Cross-Track <5% Spectral-IFOV-Shift <5% The keys to M3 are: - Design - Manufacture - Alignment - Stability Wavelength Cross Track Sample

Pushbroom Imaging Spectrometer are Not Inherently Uniform Example: Cross-Track Spectral Non-Uniformity Failure by Frown Failure by Twist Depiction -Grids are the detectors -Spots are the IFOV centers -Colors are the wavelengths Hyperion 40% non-uniform Wavelength Cross Track Sample

Pushbroom Imaging Spectrometer are Not Inherently Uniform Example: Spectral-IFOV-Shift Wavelength Failure by Spectral-IFOV-shift Spectral-IFOV-Shift creates spectra where different wavelengths arrive from different locations on the ground. Example 80% SIS Depiction Below -Grids are the detectors -Spots are the IFOV centers -Colors are the wavelengths

The M3 “Zakos” Design Provides a Uniform Imaging Spectrometer M3 is designed with: Spectral Cross-Track <5% Spectral-IFOV-Shift <5% Wavelength Cross Track Sample

M3 Instrument Selected Component Heritage

M3 JPL Three Zone Convex e-Beam Grating The ability to control the area and blaze of multiple zones allows optimization of throughput and signal-to-noise ratio. These gratings also have very low scattered light.

M3 Technology Readiness JPL Detector Focal Plane and Drive Electronics* RSC 6604A - Dimension 640 by Detector pitch 27 microns - Full well ~650,000 e- JPL 6604A Drive electronics Test 6604A Image *These are currently not flight qualified, but exist and function

Example JPL Offner Spectrometer Assembly SWIR Detector Array Grating location Entrance Slit Spectrometer Mirror 1 and 2

M3 Instrument Characteristics Diagram

M3 Instrument Measurement Characteristics

M3 Instrument Characteristics Spectral Range: 400 to 3000 nm Sampling: 10 nm across spectral range Response: <=1.2 of sampling FWHM Accuracy: Calibrated to 5% of sampling Precision: Stable within 1% of sampling Note: There are three filter zone boundaries where performance will be degraded. (~750, 1400, 2500 nm)

M3 Instrument Characteristics Radiometric Range: 0 to twice equatorial reference radiance Sampling: 14 bits measured, 12 reported Response: Linear to 99.5% (after calibration) Stability: 5% between calibrator views Accuracy: 10% absolute radiometric calibration Precision: SNR > 400 equatorial reference, > 100 polar reference

M3 Proposal Benchmark Reflectance

M3 Proposal Instrument SNR Problem: high signal at 1500 nm drives detector read rate to at least 4 reads per ground sample. This drives power, data handling, mass and risk saturation.

M3 Current Instrument SNR Solution: Adjust the efficiency spectrum of the grating. This is possible with JPL ebeam lithographic grating technology. Less risk of saturation and better SNR margin at 3000 nm.

M3 Instrument Characteristics Spatial Range: 40 km swath (24 degree field-of-view) Sampling: 70 meters average cross and along track (600 cross-track samples) Response: FWHM of <1.2 of sampling Accuracy: 0.1of IFOV

M3 Instrument Characteristics Spatial Surface Projected slit images has degrees of curve over FOV Will be calibrated and included in georectification Less than distortions imposed by topography Less than distortions from framing camera approach Basically, this degree of freedom is used to help gain the spectral cross-track and spectra-IFOV-Shift uniformity

M3 Instrument Characteristics Uniformity Spectral-Uniformity: < 10% variation of spectral position and FWHM across the field of view Spectral-IFOV-Shift: < 10% IFOVs variation over the spectral range Vignetting: Radiometric response within 10% across the field-of-view Wavelength Cross Track Sample

Calibration Panel Normal +Y (Velocity) +Z (Anti Sun) +X (Moon Nadir) Sun Vector (At Calibration) Calibration S/C REFERENCE FRAME

M3 Data Modes and Limitations Global Mode –Lossless compression sufficient to map the lunar globe in one optical imaging period within data rate constraints –Nominally 2 by 2 spatial and 3 spectral averaging –335 Orbits Target Mode (three optical imaging periods) –Full spectral and spatial resolution –Nominally 600 by 600 scene –As many scenes as permitted within available data rate –~3800 per optical imaging period The available data rate may be less than assumed in the proposal A NASA Deep Space Network option is being explored. DSN would help greatly.

M3 Additional Characteristics Baseline dark signal data will be acquired from the un-illuminated portion of the moon on each imaging orbit. Cross-track elements 1-10 and are masked and used to monitor dark signal levels during the imaging orbit. Cross-track elements and are not illuminated by the spectrometer slit and are used to monitor scattered light.

M3 Instrument Science Commands These are the envisioned basic instrument commands for science data measurement. –Global Mode Maybe upload averaging table –Target mode –Start collect –Stop collect –Deploy calibration panel –Retract calibration panel –Integrations per ground sample (1,2 or possibly 3) There will be many other derived commands to allow the instrument to function

The team, approach and capability to achieve these M3 Science Measurement Requirements is in Place Spectral Range: 400 to 3000 nm at 10 nm sampling –Spectral signatures of interest High spectral and spatial uniformity –Enables scientific imaging spectroscopy High Precision (Signal-to-noise ratio) –Low concentration components, low illumination areas of the Moon Spatial swath 40 km with sampling ~70m –Global coverage from planned orbit and data downlink limits Excellent calibration (spectral, radiometric, spatial) –Enables scientific imaging spectroscopy High Instrument and Team heritage –Low risk and science success

25 degree FOV unobscured F/3.5 TMA Telescope Slit JPL e-beam curved grating 640 cross-track MCT Detector 400 to 3000 nm Single spherical mirror OS Filter M 3 Optical Configuration 1) Telescope mirrors aligned to machine tolerance w/ shims 2) Spectrometer components held to machine tolerance w/ shims plus fine rotation only on grating and detector.