Interrogating the molecular composition of asteroids from a remote vantage: progress in the laboratory

Mineral deposits on asteroids represent potentially important resources for emerging space exploration. Deep-space missions can contemplate in-situ resource utilization (ISRU), should suitable compounds be present on asteroids in advantageous orbits. Eventual resource exploitation will require characterization of material abundances within candidate asteroids. Remote Laser Evaporative Molecular Absorption (R-LEMA) spectroscopy is a developmental sensor system designed for interrogating asteroid composition from an orbiting spacecraft. A directed energy beam heats the target surface to the point of melting and evaporation. The laser-heated spot serves as a high-temperature blackbody source; ejected molecules create a plume of materials in front of the spot. Molecular composition is investigated by using a spectrometer to view the heated spot through the plume. A laboratory experiment is being conducted to characterize system performance. Target materials are placed in a custom vacuum space equipped with optical ports for laser and spectrometer signal paths. A fiber laser amplifier with focusing optics applies a directed energy beam to the target. The primary sensor is a commercial FTIR spectrometer equipped with external free-space input ports, and an electronic source-intensity feedback correction. A reflective optic setup directs blackbody energy from the heated spot into a spectrometer port. A portion of the incoming beam is also diverted to an infrared photodiode for source-intensity feedback. Spectra of evaporated mineral compounds can be recorded while the laser is activated. Gas-phase spectra of most mineral compounds are not commonly available; transmission spectra of the same mineral specimens are recorded, for comparison between solid and gas phase spectra.