ICES-2020-204

Chemical Lidar Science Payload for the Lunar Volatile and Mineralogy Mapping Orbiter

Roman V. Kruzelecky1, Piotr Murzionak2, Ian Sinclair3 MPB Communications Inc., 151 Hymus Blvd., Pointe Claire, Québec, H9R 1E9

Yang Gao4, Chris Bridges5, Andrea Luccafabris6 Surrey Space Centre, University of Surrey, Guildford, UK

Edward Cloutis7 University of Winnipeg, 515 Portage Ave. Winnipeg, Manitoba, R3B 2E9

Amélie St-Amour8 NGC Aerospace Ltd., 995, Boul. Industriel, Sherbrooke, Québec, J1L 2T9 Canada

The spatial distribution and quantity of surficial in-situ lunar resources, such as water ice and ilmenite (FeTiO3), is currently highly uncertain. Moreover, planned lunar orbiter missions are limited to a volatile- mapping resolution of several km in comparison with the typical 500 m traverse range of a rover. VMMO, for Volatile and Mineralogy Mapping Orbiter, is a low-cost 12U Cubesat that comprises the Lunar Volatile and Mineralogy Mapper (LVMM) science payload, a COTS electronics test bed, and the supporting 12U Cubesat platform. VMMO addresses the need to provide mappings of lunar volatiles, such as water ice, at relatively high spatial resolutions by using single-mode fiber-lasers operating simultaneously at 532 nm, 1064 nm and 1560 nm with an instantaneous ground sampling beam diameter under 10 m. This paper discusses the VMMO augmented science configuration and the resultant mission architecture and data products.

Nomenclature AOCS = Attitude and Orbit Control System CDF = Coherent Design facility at the European Space Agency CSA = Canadian Space Agency DFB = Distributed Feedback laser ESA = European Space Agency GSD, iGSD = Ground Sampling Distance, instantaneous Ground Sampling Distance ISRU = In-situ Resource Utilization LCROSS = Lunar CRater Observation and Sensing Satellite LE-LFO = Low-eccentricity Lunar Frozen Orbit LLCD = Lunar Laser Communications Demonstration LRO = Lunar Reconnaissance Orbiter LUCE = Lunar Cubesat Explorer LVMM = Lunar Volatile and Mineralogy Mapper science payload OBC/OBDH = On Board Computer/ On Board Data Handling PSR = Permanently Shadowed Region QE = Quantum Efficiency for converting photons into electrons 1U = 10 cm x 10 cm x 10 cm Cubesat volume unit

1Senior Research Scientist, Space and Photonics, [email protected] 2Mechanical Designer, Space Photonics, [email protected] 3Project Manager, [email protected] 4Professor of Space Autonomous Systems, Head of STAR Lab, Surrey Space Centre, [email protected] 5Lecturer, [email protected] 6Lecturer, [email protected] 7 Professor, Dept. of Geography, [email protected] 8GNC Engineer, [email protected]

1 International Conference on Environmental Systems. SHG = Single Harmonic Generator SM = Single Mode SNR = Signal to Noise Ratio SWIR = Short-wave Infrared UV = Ultraviolet VIS = Visible spectral range VMMO = Volatile and Mineralogy Mapping Orbiter

I. Introduction here are large uncertainties in the volatile content of lunar regolith, especially useful resources such as impact T transferred water/ice that is expected to be sheltered within lunar polar Permanently Shadowed Regions (PSRs). Evidence for this water ice is both direct and indirect, and derives from multiple sources as discussed below. The Lunar Prospector1 has detected elevated concentrations of hydrogen in PSRs, at spatial scales of tens to hundreds of kilometres. It indirectly determines the presence of hydrogen by its effect on epithermal neutrons. Enhanced hydrogen concentrations in the upper ~1 meter of the regolith (the likeliest explanation for variations in epithermal neutrons), particularly in PSRs, are presumed to be due to hydrogen in the form of water ice. Moreover, the Chandrayaan orbiter’s Mini-RF synthetic aperture radar instrument2 has detected areas in lunar PSRs with anomalous reflectance values that are consistent with the presence of surficial (smooth) deposits of water ice. The Lunar Reconnaissance Orbiter’s (LRO) Diviner thermal IR spectrometer3 has detected lunar PSRs with temperatures as low as 20 K (see Figure 1 left), which would enable surficial water ice to persist for billions of years due to the very low resultant sublimation rate (see Figure 1 right).

Figure 1. (left) LRO Diviner radiometer temperature estimations3 of the lunar south-pole regions showing areas with temperatures below 100 K and (right) estimates of the water ice sublimation rate on the Moon4.

Figure 2. Data from the LCROSS lunar impact experiment into Cabaeus crater (Oct. 9th, 2009) as measured by the LRO spectrometer. (Credit: NASA, 2009).5 2 International Conference on Environmental Systems

The LCROSS lunar impactor experiment5 found concentrations of water ice in ejecta from the south polar region Cabeus crater at the few percent level based on infrared spectral measuresments (see Figure 2) of light reflected from the ejecta as it was illuminated by incident solar radiation. The red curve shows how the spectra would look with water vapour and ice added in appropriate amounts to match the dips in the observations. The yellow areas indicate the water absorption bands. However, the water ice vertical distribution and lateral extent remains unknown. While the evidence for lunar water ice in PSRs is compelling, as discussed above, major uncertainties exist in terms of its: • lateral extent and vertical distribution in the regolith, • presence in significant surficial concentrations, • associated lunar diurnal water cycle. Planned lunar missions such as the Lunar Flashlight6, LunaH-Map7 and Lunar IceCube8 Cubesats will improve our understanding of the spatial distribution of water ice in PSRs. Lunar Flashlight will conduct active illumination of PSRs to try and directly detect water ice in them. However, its spatial resolution is on the order of 1-2 km. Thus, smaller concentrations of surficial water ice may be missed if they are present in dry regolith (i.e. their signal would be diluted in a single pixel). LunaH-Map will map the polar concentrations of near-surface (down to ~1 m) hydrogen, at higher spatial resolution than Lunar Prospector (but still at a few km resolution). Lunar IceCube will look at sun-lit regions for evidence of water and water-ice related absorption bands at ~10 km resolution. The spatial resolution of the observations of the prior and planned relevant lunar missions is on the order of one to many kilometers. Given that future lunar landers or rovers destined for PSRs will likely have limited mobility, there is a need to improve the spatial accuracy of maps of water ice in the lunar PSRs. The Volatile and Mineralogy Mapping Orbiter9 (VMMO) , is a low-cost 20 kg 12U Cubesat that comprises • the Lunar Volatile and Mineralogy Mapper (LVMM) multi-wavelength chemical lidar science payload; • the supporting 12U Cubesat bus with propulsion, direct to Earth S-band and 1560 nm optical communications, on board data processing and a suite of altitude and pointing sensors for semiautonomous vision-assisted navigation from lunar orbit. The compact LVMM payload is a multi-wavelength Chemical Lidar (<6.1 kg) which will use high-power, single-mode (SM) fiber lasers emitting simultaneously at 532 nm, 1064 nm and 1560 nm. This will permit stand-off mapping of the lunar water ice distribution using active laser illumination, with a focus on selected permanently- shadowed craters in the lunar south pole; Shackleton, Faustini and Cabeus. Based on prior laboratory predevelopment9, this combination of selected laser spectral channels can provide very sensitive discrimination of water/ice in various types of Mare and Highland regolith to about 0.5% mass fraction, based on breadboard validation. The use of the SM fiber lasers enables a small laser beam divergence to provide high spatial resolution in the 10 m range at the lunar surface. There is some relevant flight heritage as part of the Fiber Sensor Demonstrator (FSD)10 payload on ESA’s Proba-2 spacecraft that is still operational after more than 10 years in low earth orbit. LVMM can also be used in a passive multispectral mode at 300 nm, 532 nm, 1064 nm and 1560 nm to map the lunar ilmenite in-situ resource distribution during the lunar day using the characteristic surface-reflected solar illumination. By combining the passive lunar day measurements with the active lunar night measurements, some new insights into the lunar diurnal water cycle should be possible. The VMMO science maturity is relatively well-developed. Over 50 years of active lunar exploration activities have provided a mature and comprehensive understanding of the Moon. However, critical gaps exist in this knowledge, and these gaps are well understood. VMMO is designed to address some of these knowledge gaps: 1) Is/are water ice/volatiles present in lunar permanently shadowed regions (PSRs)? 2) Can we map variations in surface ilmenite abundance using optical remote sensing? 3) How does space weathering affect lunar surface optical properties, and can we separate these effects from compositional variations? 4) How does the lunar surface frosting vary diurnally (for insight into the lunar water ice cycle)?

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VMMO has successfully completed the SysNova mission concept study with the European Space Agency (ESA) and the follow-on ESA Coherent Design Facility (CDF) mission concept review, as well as an Augmented Science Study with the Canadian Space Agency (CSA). VMMO is currently in the Phase A mission study with the European Space Agency. This paper discusses the VMMO science requirements, the supporting 12U Cubesat platform and the LVMM multiwavelength chemical lidar payload and some of the associated design trade-offs.

II. VMMO Team The VMMO Science is led by Prof. Edward Cloutis from the University of Winnipeg on the lunar mineralogy and in-situ resources and by Prof. Yang Gao from the University of Surrey on the lunar volatiles and icy regolith. Prof. Mike Daly from York University is a co-I on the LVMM multi-wavelength chemical lidar requirements. The following table summarizes the current extended VMMO technical team. Table 1. Summary of the VMMO Extended Team.

Company/Organization Country Key Personnel Mission Role

Canada Dr. R. V. Kruzelecky Mission Prime Dr, Ian Sinclair LVMM Science Payload and Test Scripts Piotr Murzionak 1560 nm Optical Data Link

Dr. Qi-Yang Peng LVMM Operations Paul Burbulea

United Prof. Yang Gao Lunar icy regolith science, data calibration Kingdom Dr. Chris Bridges 12U Cubesat Bus AIT, CLAIRE Radiation Dr. Andreas Luccafabris Sensor, Power and Propulsion Subsystems

Dr. Nicola Baresi On Board Computer (LEON 3)

Canada Prof. Edward Cloutis Lunar volatiles, mineralogy and in-situ Alexis Parkinson, resources, LVMM data analysis Brynn Dagdick

Canada Amélie St-Amour Cubesat Fine Pointing Knowledge Estimation Dr. Jean de Lafontaine LVMM Data Lunar Geo-location

Portugal Nuno Silva GNC with vision-based lunar navigation using Paulo Rosa the LVMM imagers Failure Detection, Isolation and Resolution

Assist with Ground Network

Portugal Mauro Gameiro System Software Integration and Testing Assist Surrey with the Platform Software

Canada Doug Sinclair, Reaction Wheels

Cordell Grant Star Tracker

Netherlands Johan Leijtens Sun Sensors

Canada Prof.Mike Daly LVMM Chemical lidar co_I Prof. Jinjun Shan LVMM laser pan/tilt micro-mirror PID control

Xiphos Technologies Canada Francesco Ricci Q8 microcontroller

Netherlands Anna Kalabina 12U Cubesat Deployment Mechanism

DHV Technology Spain VincenteDiaz Deployable triple-junction Solar pcell arrays CanadenSys Canada Dr. Nadeem Ghafoor Miniature wide field-of-vew imager

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III. VMMO Mission Overview

Figure 3. Preliminary schematic of the VMMO mission. The VMMO mission system, as summarized in Figure 3, is based on the science requirements and the 12U Cubesat mission constraints. The LVMM payload is configured for the required Active water ice and Passive in-situ resource monitoring. The 12U Cubesat platform needs to accommodate the VMMO science payload and the supporting AOCS, OBC, propulsion, power and communications subsystems. This, in turn, needs to be accommodated within a suitable deployer such as the ISIS Quadpack-XL The integrated deployer/Cubesat/payload then needs to be accommodated on the available transport vehicle, such as a NASA CLPS lunar lander or Artemis 2. The preliminary VMMO mission development has assumed Earth to lunar injection orbit transportation on a commercial Peregrine lander from Astrobotics in the 2023 timeframe. The VMMO mission schedule needs to be compliant with the schedule and review requirements of the selected NASA CLPS or Artemis 2 missions. The baseline mission communications are based on S-band due to the wide availability of relevant ground stations. The nominal communications is based on the SSTL Pathfinder Communications orbiter as a relay to the Goonhilly ground station. Approximately 120 minutes of data link time per mission earth day is available for the data downlinks and the command uplinks at a rate of 1 Mbps for the data downlinks to Pathfinder. A direct-to-Earth communications capability, at a reduced rate of about 9.6 kbps, is also being incorporated. The selected potential VMMO operational lunar frozen orbit, about 40 km perilune by about 200 km at apogee elliptical, will be achieved from the available lunar injection orbit using the VMMO “on board’ propulsion. This is still at a trade-off stage between the use of chemical or ion propulsion. The ion propulsion option would require about 90 mission earth days for the orbit transition but provides a much larger Δv~700 m/s. VMMO will perform nadir-pointing scientific measurements (semi-autonomously based on a script) in both the Active and Passive LVMM modes, focusing on the lunar South Pole region. The spacecraft nadir pointing will be provided using a configuration of four reaction wheels, with one redundant. A Surrey cold-gas thruster will be used to periodically de-spin the reaction wheels. Pointing and rotation information will be provided using a suite of miniaturized sensors that includes two Star Trackers, Sun sensors, 3-axis accelerometers and a Miniature Electro- Mechanical System (MEMS) based gyroscope. The baseline mission duration is 12 months. The two key targets for the Active measurements (see Figure 4) are 2-D regions centered about Shackleton Crater (89.54°S, 0.0°E) with 21 km diameter, as considered for a future potential manned lunar base, and Faustini Crater(87.2°S, 75.8°E) with 39 km diameter, as an example of a younger crater. The Faustini PSR regions exhibit

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enhanced Lyman-ɑ albedo indicative of the presence of excess H based on the LRO Lyman Alpha Mapping Project (LAMP). The VMMO 2-D water-ice mapping will require the relevant cross-track mappings to be accumulated and compiled over multiple lunar orbits. Based on the estimated VMMO position knowledge, the mappings can be provided on a 200 m cross-track grid. (b) (c) (a)

Figure 4. (a) Shackleton crater (ESA), (b) Faustini crater (NASA LRO) and (c) Cabeus crater (NASA LRO).

The LVMM Active measurements (see Figure 5) will employ the 532 nm, 1064 nm and 1560 nm fiber-laser controlled illumination to probe water/ice in and near lunar south-pole PSRs below 80°S, focusing on the Shackleton and Faustini craters(see Figure 4). The diffusely reflected laser illumination from the lunar surface will be detected using the LVMM receiver with a 7.8 cm diameter primary optical collector. The measurements will be largely conducted during the lunar night to minimize the background solar radiation signal and associated shot noise. The spectral signal distribution will employ passive dichroic optics to direct the reflected 532 nm signal to a back- illuminated CMOS UV/Vis camera and the corresponding reflected 1064 nm and 1560 nm signals to miniature InGaAs cameras. Summary of the VMMO Active Mode operations: . nadir spacecraft pointing; . LVMM 4W 532 nm and 4W 1560 nm fiber lasers powered on with 3 minute warm-up, providing about 4­m spot radius on the lunar surface at 26­km perilune; . LVMM UV/Vis and SWIR imagers powered on using 12×12 pixel window mode; . miniature piezo-driven pan/tilt fine-pointing mirror for the laser illumination; . pushbroom geo-colocated line scans with typical 4 m × 44 m GSD per measurement point for altitudes below 100 km or Point and Track measurements of targets at higher altitudes for an Figure 5. Artist’s rendition of VMMO measurements increased integration time; in the LVMM Active mode using 4W 532 nm and . data acquisition on the dark lunar surface from the 1560 nm fiber-laser active illumination of the lunar 80°S latitude to the lunar South Pole. surface.

Table 2 summarizes the estimated Signal-to-Noise Ratio (SNR) versus altitude for the nadir-pointing push- broom and the Step_and_Track Active measurement modes. A minimum SNR of about 30 is needed for a water ice detectivity of about 2% by mass fraction in the near-surface regolith. For altitudes of 100 km and higher, the Step and Track observation methodology in the LVMM Active Mode can provide adequate SNR for altitudes to over 200 km. The trade-off is a larger along-track grid size due to the Cubesat along-track motion over the selected integration time, as shown in column 4 of Table 2. In the LVMM Active Mode, the total laser illumination power available at the lunar surface is fixed and finite. The available signal at the LVMM receiver decreases as the square of the spacecraft altitude due to the reduced 6 International Conference on Environmental Systems

collection solid angle for the diffusely reflected laser signal.The nominal nadir pointing measurement mode can provide useful SNR (SNR > 20) to above 100 km altitude. Table 2. SNR variation with Altitude and the Active measurement mode using 7.8 cm primary aperture receiver with 4 W laser illumination at 532 nm and 1560 nm, respectively, and a lunar surface albedo of 0.12. Altitude Measurement Integration SWIR along- SNR Mode Pointing Time track GSD km s m 532 nm 1560 nm 26 Nadir 0.024 44 208 341 50 Nadir 0.024 46 108 165 75 Nadir 0.024 49 72 100 100 Nadir 0.024 52.5 53 67 100 Step and Track 0.2 52 155 219 150 Step and Track 0.2 78 103 125 200 Step and Tack 0.2 104 77 80 For a given altitude, the Active Mode SNR can be improved by trading off the measurement spatial resolution for a longer signal integration time. Moreover, the LVMM laser fine-pointing mirror could be used to track a target over an extended integration time to allow high SNR with relatively good spatial resolution. This is given by the SNR for the Step and Track measurement mode in Table 2. By using the different software-selectable measurement methodologies, the LVMM measurements can be relatively robust to uncertainties in the achievable Cubesat orbit. During the lunar day, at altitudes below 500 km, the LVMM will be used in the Passive Mode with the lasers powered off to provide multispectral measurements of the lunar near-surface mineralogy and ilmenite in-situ resources based on their unique spectral characteristics. This will make use of diffusely reflected solar illumination of the lunar surface, observed using selected spectral windows near 300 nm, 532 nm, 1064 nm and 1560 nm. The UV/Vis and SWIR imagers will be used with pixel binning to provide a cross-track multi-spectral line scan in 87 binned pixels with a 24-m × 24­m ground sampling distance (GSD) (see Figure 6). Summary of the VMMO Passive Mode operations: . nadir pointing mode; . data acquisition on sunlit lunar surface; . LVMM 532nm and 1560 nm fiber lasers off; . LVMM UV/Vis and SWIR imagers powered on; . pixel binning for 87 effective cross-track pixels . 24m x 24m GSD/binned pixel; . 300 nm, 532 nm, 1064 nm, and 1560 nm multi- spectral water-ice, mineralogy and ilmenite mapping; . data calibration using measurements over former

Apollo 16 or 17 landing sites; Figure 6. Artist's sketch of the LVMM passive mode . data "on board" real time processing. measurements. The Passive Mode will be used to map any surface frost during the lunar day as well as lunar in-situ resources such as ilmenite using solar illumination diffusely reflected by the lunar surface. The focus is on lunar regions that may be considered for future manned bases, such as Marius Hills, with the uncovered lava tube entrance as a potential habitat and radiation shelter, and the South Aitkin Basin and rim of the Shackleton crater. Table 3. SNR variation with Altitude in the Passive Mode for a lunar surface albedo of 0.12. Altitude Integration IGSD SNR Time km s m 300 nm 532 nm 1064 nm 1560 nm 26 0.002 4 209 527 444 350 50 0.002 7.7 209 527 444 350 75 0.002 11.5 209 527 444 350 100 0.002 15.4 209 527 444 350 200 0.002 23 209 527 444 350 7 International Conference on Environmental Systems

Table 3 provides the estimated SNR for the LVMM Passive Mode versus altitude. In the LVMM Passive Mode, the increase in the ground pixel size compensates for the decrease in the solid collection angle with the spacecraft altitude. As a result, the SNR is largely independent of the spacecraft altitude.

IV. VMMO Science

A. Lunar Water Ice Mapping It is theorized that significant amounts of ice may have migrated to and are being sheltered within permanently shadowed polar lunar regions. The water ice mapping will be performed using geocolocated Active LVMM measurements at 532 nm, 1064 nm, and 1560 nm. The along-track mappings will be compiled over multiple orbits on a 200 km cross-track grid near the selected primary targets. Figure 7 (left) shows the spectral-reflectance curves of bare glacier ice, coarse-grained snow, and fine-grained snow. The vertical lines at 532 nm, 1064 nm and 1560 nm represent the selected emission wavelengths for the fiber lasers. The diffuse optical reflectance with snow and/or ice surface coverage decreases at longer wavelengths and also exhibits pronounced optical absorption bands associated with H2O and OH molecular vibrational modes. The spectral reflectance of the various lunar-relevant minerals typically shows relatively strong or increasing optical reflectance with the optical wavelength. The addition of ice causes distinct systematic spectral reflectance changes with a characteristic higher VIS/NIR reflectance ratio, as shown in Figure 7 (right). This can be used to discriminate the ice and the various minerals based on a suitable selection of the fiber-laser lidar emission wavelengths.

Figure 7. Diffuse spectral reflectance of (left) snow and ice10 with superimposed laser lines at 532 nm, 1064 nm and 1560 nm and (right) lunar Highland simulant spectra with different water ice mixtures by mass. As summarized in Figure 8, using the relative reflectance ratio R(1560 nm)/R(532 nm), as opposed to R(1560 nm)/R(1064 nm), provides a steeper slope corresponding to a higher measurement sensitivity for small fractions of ice in the regolith. The estimated detection limit is better than 0.5% ice fraction for a SNR of about 100.

Figure 8. Relative measured reflectance ratio versus the water ice fraction by mass in lunar regolith. 8 International Conference on Environmental Systems

B. Lunar Night-time Frosting and the Diurnal Water Cycle It is postulated that lunar near-surface volatiles outside the PSRs are largely vaporized during the lunar day, leaving the surface very dry. The vapors then condense on the lunar surface during the relatively cold lunar night. This can lead to a set of ballistic steps that results in the transport of some fraction of the lunar near-surface volatiles to the PSRs where their sublimation rate would be very low due to the low temperatures within the PSRs.3,4, 11 Active diffuse reflectance measurements using the LVMM laser illumination at 532nm, 1064 nm and 1560 nm will be performed at latitudes below 80°S during the lunar night to observe the night-time frosting. Corresponding Passive measurements at 300 nm, 532 nm, 1064 nm and 1560 nm will be performed during the lunar day using the reflected solar illumination to observe the potential changes of the lunar non-PSR near-surface volatiles. This study of the lunar diurnal water cycle requires observing the same region on the lunar surface during the lunar night and then again during a subsequent lunar day to provide a comparison of the water/ice diurnal content.

C. Ilmenite in-situ Resource Mapping The University of Winnipeg has studied the spectral characteristics of suites of basalt + ilmenite, one of which is shown below in Figure 9. These mineral mixtures are being used to assess the wavelength coverage and spectral resolution necessary to permit detection of ilmenite and constraints to be placed on ilmenite abundances.

Figure 9. Reflectance spectra of intimate mixtures of <45 μm powdered samples of basalt + ilmenite. The extensive study of the spectroscopic properties of lunar minerals showed that ilmenite is spectrally distinct from other lunar minerals, provided that both ultraviolet and visible wavelengths are used for such determinations. Ilmenite exhibits a characteristic blue slope in its spectral reflectance relative to the other relevant lunar minerals, as shown in Figure 9, with an enhanced reflectance in the UV.

V. LVMM Science Payload The compact LVMM is a multi-wavelength Chemical Lidar employing fiber lasers emitting at 532 nm, 1064 nm and 1560 nm for stand-off mapping of the lunar water ice distribution using active laser illumination. A diagram of the LVMM system with the preliminary 3-D packaging is shown in Figure 10. The net mass with 15% margin is about 6.1kg. The LVMM optical system includes: • 4W 532-nm/8-10 W 1064-nm fiber laser, • 4 W 1560­nm fiber laser, • laser beam expander/combiner with dichroic beam combiner and fine pan/tilt mirror, • 7.8 cm OD broad-band imaging optical multispectral photoreceiver with about ± 1.4° Field of View (FOV). Single-mode fiber laser sources operating at 532/1064 nm and 1560 nm with about 4 W output optical power each at 532 nm and 1560 nm are used for the active illumination of the lunar surface. A passive dichroic filter is used to combine the two laser beams. A miniature PI piezo-actuated pan/tilt mirror will be used to provide fine pointing of the combined laser beam within an angular range of about ±1°. The associated fiber-laser technology has about 10 years of flight heritage as part of the MPBC Fiber Sensor Demonstrator flying on ESA's Proba-2 spacecraft. 9 International Conference on Environmental Systems

Figure 10. Preliminary 3-D Model of the LVMM multiwavelength chemical lidar Lunar Volatile and Mineralogy Mapper payload. Figure 11 shows a schematic of the preliminary design of the 1560 nm fiber laser. This is based on a 1560 nm stabilized distributed-feedback (DFB) laser seed. The DFB laser seed is then optically amplified to the desired 4 W optical output. The 1560 nm fiber laser uses two 11 W diode pumps for redundancy. The pumps can either be at 980 nm for the highest overall power efficiency or at 940 nm for better thermal stability. A single pump is typically sufficient for a 4 W optical output at 1560 nm. A 99:1 fiber optic signal splitter is used to sample the output beam to monitor the output optical power. Current breadboards at MPBC operate to over 10 W optical power near 1560 nm.

Figure 11. Preliminary design of the 1560 nm fiber laser with either 980 nm or 940 nm pumps. Figure 12 shows the preliminary design of the 532 nm/1064 nm fiber laser. This employs two flight-grade pumps at 915 nm, each providing up to 25 W of optical output pump power. One of the pumps is redundant. FBG gratings written in the active Yt-doped optical fiber are used to define the 1064 nm fiber laser cavity. The selected Single Harmonic Generator (SHG) crystal for the 1064 nm to 532 nm signal conversion is rated to over 40 W.

Figure 12: Preliminary design of the 532 nm/1064 nm fiber laser (two 915 nm diode pumps, one active, one redundant). 10 International Conference on Environmental Systems

Figure 13 shows the preliminary inner details of the LVMM imaging photoreceiver. The input includes a short baffle with inner ribs to reduce stray light scattering. The baseline is a 7.8 cm OD primary optical signal collector. The overall structure is based on a MPBC flight-proven optical train. A UV/Vis/SWIR optical filter dichroic is used to reflect the optical signal below 900 nm onto the UV/Vis CMOS imager and transmit the optical signal above 950 nm to the InGaAs imagers.

Figure 13. Preliminary inner details of the LVMM imaging receiver. The UV/Vis optical imaging will be provided using a 2400×2400 pixel Prime BSI Exporess UV/VIS imager from Teledyne/Photometrics12 with an integral 300 nm/532 nm two-band filter mosaic. This provides a low read-out noise (typically under 2e rms), high detection QE (peak QE of about 94% near 532 nm) and low dark signal. The imager will be based on a custom OEM package with TEC temperature stabilization. A second dichroic will be used to separate the 1064 nm and 1560 nm optical signals. The SWIR imaging will be provided using two miniature OEM-version 640×512 pixel InGaAs imagers from Collins Aerospace13 with integral 1064 nm and 1560 nm band-pass filters.

VI. VMMO 12U Cubesat LVMM • 4 W 532nm, 8 W 1064 nm, 4 W 1560 nm in Active Mode • 300 nm, 532 nm, 1064 nm and 1560 nm multispectral imaging in Passive Mode

Structures • 12 U Cubesat form factor (23 x 24 x 36 cm³) , < 24 kg wet mass • ISIS 12U Quadpack–XL Dispenser

Propulsion • 2x IFM Nano Thrusters (0.35 mN at 35 W each), 0.5 kg of propellant

C&DH • Radiation Tolerant LEON 3 system: Xilinx XCKU060

Power • 2x rotatable Solar arrays, each with 3 panels • 2x GOMSpace batteries (2x2600mah) • GOMSpace P60 EPS controller

Comms • Dual S-band transceivers with omnidirectional antennas

ADCS • 4x Reaction Wheels (RW0-03, Sinclair Interplanetary): • 8x RCS butane thrusters • ST-16RT2 star tracker(s) • 3 sun sensors, MEMS IMU

Figure 14. Updated VMMO 12U Cubesat Overview for the Ion Propulsion Option. 11 International Conference on Environmental Systems

Figure 14 provides a preliminary 3-D mechanical layout of VMMO for the ion and/or chemical propulsion options. The table on the left provides a summary of the corresponding VMMO key subsystems. The total wet mass of the 12U Cubesat in the selected configuration is expected to be less than 23 kg with 15% margin based on relevant breadboards and designs. The preliminary 3-D modelling indicates that it is feasible to accommodate all of the selected components within the 12U platform for either the Ion Propulsion or the Chemical Propulsion Options.

VII. Conclusions The baseline proposed VMMO mappings of water ice within the lunar PSR regions will focus on relevant south- polar craters, including Shackleton, Faustini and Cabeus, where there is some indication of the presence of permanently-shadowed regions and excess hydrogen or water-ice based on prior lunar missions such as LRO and LCROSS. The LVMM relevant multispectral data will be accumulated on a nominal 200 m cross-track grid and 50 m along-track grid over several orbits. The cross-track geolocation grid spacing is limited by the estimated attainable VMMO Cubesat orbit absolute position knowledge for the data co-registration as accumulated on different orbits. Information about the diurnal Lunar water cycle will be inferred by combining geo-colocated LVMM Active (lunar night-time) and LVMM Passive (lunar day-time) diffuse spectral reflectance data for the lunar south pole region below 80oS. The ilmenite in-situ resource mappings will be based on the characteristic blue-shifted UV-enhanced reflectance of ilmenite relative to other lunar minerals. The level 0 data set would consist of diffuse spectral reflectance data at 300 nm, 532nm, 1064 nm and 1560 nm, as accumulated over multiple orbits during the lunar day-time.

Acknowledgments

The authors would like to acknowledge the European Space Agency (ESA) for enabling the initial mission concept study through the ESA LUCE Cubesat SysNova Challenge program, the ESA CDF Study and the Canadian Space Agency (CSA) for the follow-on VMMO Augmented Mission Concept LVMM science study. Special thanks to Dr. Roger Walker and Johan Vennekens at ESA, and James Doherty, Dr. Timothy Haltigin, Dr. Vicky Hipkin and Dr. Alex Koujelev at CSA.

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