A document highlights a means to complement remote spectroscopy while also providing in situ surface samples without a landed system. Historically, most compositional analysis of small body surfaces has been done remotely by analyzing reflection or nuclear spectra. However, neither provides direct measurement that can unambiguously constrain the global surface composition and most importantly, the nature of trace composition and second-phase impurities.
Recently, missions such as Deep Space 1 and Dawn have utilized electric propulsion (EP) accelerated, high-energy collimated beam of Xe+ ions to propel deep space missions to their target bodies. The energies of the Xe+ are sufficient to cause sputtering interactions, which eject material from the top microns of a targeted surface. Using a mass spectrometer, the sputtered material can be determined. The sputtering properties of EP exhaust can be used to determine detailed surface composition of atmosphereless bodies by electric propulsion induced secondary mass spectroscopy (EPI-SMS).
EPI-SMS operation has three high-level requirements: EP system, mass spectrometer, and altitude of about 10 km. Approximately 1 keV Xe+ has been studied and proven to generate high sputtering yields in metallic substrates. Using these yields, first-order calculations predict that EPI-SMS will yield high signal-to-noise at altitudes greater than 10 km with both electrostatic and Hall thrusters.
This work was done by Rashied Amini of Caltech and Geoffrey Landis of Glenn Research Center for NASA’s Jet Propulsion Laboratory. NPO-47798
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Electric Propulsion Induced Secondary Mass Spectroscopy
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Overview
The document discusses Electric Propulsion Induced Secondary Mass Spectroscopy (EPI-SMS), a novel technique developed to analyze the surface composition of small celestial bodies from orbit without the need for landing. This method leverages electric propulsion (EP) systems, which utilize accelerated xenon ions (Xe⁺) to generate in-situ surface samples through sputtering. The technique is particularly advantageous for missions targeting atmosphere-less bodies, where traditional methods of surface analysis, such as remote spectroscopy, may not provide definitive results.
EPI-SMS operates by directing a high-energy beam of Xe⁺ ions at the surface of a target body. Upon impact, these ions sputter material from the surface, which can include minerals, ices, and salts. The ejected particles are then analyzed using an open-source mass spectrometer onboard the spacecraft. This process allows for detailed characterization of surface composition, identification of second-phase impurities, and isotopic ratio determination, addressing various scientific goals, including astrobiology and the study of regolith weathering.
The document highlights the historical context of surface analysis, noting that previous methods often relied on remote sensing techniques that lacked the precision needed to unambiguously determine surface composition. EPI-SMS presents a lower-risk and cost-effective alternative to traditional landers and sample return missions, which can be complex and expensive. By enabling surface analysis from orbit, EPI-SMS complements existing remote spectroscopy techniques and enhances our understanding of small body surfaces.
The document also outlines the operational requirements for EPI-SMS, emphasizing the need for an electric propulsion system and a compatible mass spectrometer. It suggests that this technology is feasible for future NASA missions, particularly within the Discovery or New Frontiers programs, where budget constraints and risk management are critical considerations.
In summary, EPI-SMS represents a significant advancement in planetary science, providing a reliable method for in-situ surface analysis of small bodies in space. By utilizing electric propulsion technology, this technique opens new avenues for exploration and understanding of the composition and history of celestial objects, ultimately contributing to our knowledge of the solar system.
