Abstract
Lunar Flashlight (LF) is an innovative National Aeronautics and Space Administration (NASA) CubeSat mission that is dedicated to quantifying and mapping the water ice that is harbored in the permanently shadowed craters of the lunar South Pole. The primary goal is to understand the lunar resource potential for future human exploration of the Moon. To this end, the LF spacecraft will carry an active multi-band reflectometer, based on an optical receiver aligned with four high-power diode lasers emitting in the 1 to 2-μm shortwave infrared band, to measure the reflectance of the lunar surface from orbit near water ice absorption peaks. We present the detailed optical, mechanical, and thermal design of the receiver, which is required to fabricate this instrument within very demanding CubeSat resource allocations. The receiver has been optimized for solar stray light rejection from outside its field of view, and utilizes a 70 × 70-mm, aluminum, off-axis paraboloidal mirror with a focal length of 70 mm, which collects the reflected light from the Moon surface onto a single-pixel InGaAs detector with a 2-mm diameter, hence providing a 20-mrad field of view. The characterization of the flight receiver is also presented, and the results are in agreement with the expected performance obtained from simulations. Planned to be launched by NASA on the first Space Launch System (SLS) test flight, this highly mass-constrained and volume-constrained instrument payload will demonstrate several firsts, including being one of the first instruments onboard a CubeSat performing science measurements beyond low Earth orbit, and the first planetary mission to use multi-band active reflectometry from orbit.
Highlights
For almost a century, predictions have been made for the existence of frosted lunar volatiles in the Permanently Shadowed Regions (PSRs) of the lunar South Pole [1,2]
The National Aeronautics and Space Administration (NASA) has defined Strategic Knowledge Gaps (SKGs), among which are mapping and quantifying lunar volatiles associated with these PSRs, with the goal to use these frosted volatiles, water ice, as a resource for future human exploration of the Moon [6]
Δz )LDPλdθx dθz where Rλ is the responsivity of the detector at λ, Pλ is the emitted optical power by the laser at λ that depends on the temperature Tlaser of the laser and the pump current Ilaser, αλ is the regolith normal reflectance at zero-phase angle at λ for a given water ice content W, Γ is the receiver aperture area, δx and δz are the misalignment angles between the lasers and the receiver, PSTλ(θx,θz) is the receiver point source transmittance function at λ, LDPλ(θx,θz) is the laser divergence profile normalized by the integrated radiance over θx and θz for the laser emitting at λ, and A is the altitude of the spacecraft above the lunar surface
Summary
Predictions have been made for the existence of frosted lunar volatiles in the Permanently Shadowed Regions (PSRs) of the lunar South Pole [1,2]. The National Aeronautics and Space Administration (NASA) has defined Strategic Knowledge Gaps (SKGs), among which are mapping and quantifying lunar volatiles associated with these PSRs, with the goal to use these frosted volatiles, water ice, as a resource for future human exploration of the Moon [6] These data will help to improve our planetary science knowledge regarding the delivery and retention of water and other volatiles in the inner solar system. Li et al have shown definitive evidence for surface-exposed water ice in the lunar polar regions by using scattered sunlight in the PSRs to measure NIR reflectance spectra [27] These detections demonstrate the presence of water frost in quantities that are sufficient to produce detectable absorption features in the same spectral region probed by Lunar Flashlight (LF). After a brief description of the CubeSat and the mission in the two sections, this paper focuses on the receiver’s optical, mechanical, and thermal design, as well as on its characterization
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