HOLMS, Heterodyne OH Lunar Miniaturized Spectrometer

There are many indications in recent lunar studies that water ice and other volatiles are present near the lunar poles. Temperatures of the lunar cold traps are low enough to prevent substantial sublimation losses over billion-year time scales. Understanding the source and the processes that affect the delivery of lunar volatiles is key to understanding the formation of the moon, and early volatiles in the inner solar system. It also has a great importance for lunar mining and possibly utilizing volatiles in future missions. Lunar remote sensing by orbital spacecraft, and the Lunar Crater Observation and Sensing Spacecraft (LCROSS) impact experiment provided compelling evidence for the existence of cold-trapped volatiles, but their abundance, composition, and distribution remain uncertain. This is, in part, because the most commonly used technique for remote sensing spectroscopic measurements is grating spectrometers. These instruments are broadband, but they have small fields of view (FOV) and relatively low throughput and have to be paired with large aperture telescopes for high spectral resolving power (R) applications. Here, we demonstrate a lunar volatile remote sensing technology, by employing a Spatial Heterodyne Spectrometer (SHS) in an orbiter around Earth. SHS is a relatively novel candidate for high throughput spectroscopy in compact, low-mass, a low-power architecture using no or small aperture (D<10cm) telescope for UV to IR wavelengths. SHS provides integrated spectra at high R (R>50,000), over a wide FOV (FOV 40 arcmin) in compact designs in which it offers the ability to search for OH volatiles at 308nm. SHS can be implemented on ISS or a dedicated SmallSat that can sit at a GEO altitude and stare at lunar exosphere for the long duration of time that cannot be done from the ground or on big missions. SHS measurements will improve constraints on lunar volatile composition and could help identify possible origins, including comet and asteroid impacts, solar wind ion implantation, and outgassing of primordial volatiles from the lunar interior.