Influence of spacecraft outgassing on the exploration of tenuous atmospheres with in situ mass spectrometry

Abstract

[1] In situ mass spectrometry has been a powerful tool in many space missions to investigate atmospheres and exospheres of different bodies in the solar system. Applying new technologies, the mass spectrometers have become increasingly more sensitive. In this study, we show that spacecraft outgassing, which can never be completely prevented, will be the limiting factor in future missions that investigate very tenuous atmospheres and exospheres of moons, asteroids, or comets at large heliocentric distances. The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument on the European Space Agency Rosetta mission has monitored spacecraft outgassing for 6 years during #9the cruise phase with unprecedented instrument sensitivity. It is shown that diffusion of gas from materials and from the spacecraft interior plays an important role in maintaining a relatively permanent thin gas cloud around the spacecraft for many years. The density #9and composition of this gas cloud depends on location on the spacecraft, maneuvers, and payload activity. The main contaminants are water, which is adsorbed on cold surfaces, and organics from the spacecraft structure, electronics, and insulations. Decomposed lubricant material can give a significant contribution to the total background. Fortunately for Rosetta, outgassing of the spacecraft will play a minor role when the comet is close to perihelion; only in the early phase of the mission the outgassing may be larger than the cometary signature.

Composition-dependent outgassing of comet 67P/Churyumov-Gerasimenko from ROSINA/DFMS

“…1) that results from spacecraft outgassing (Schläppi et al 2010). In addition, each of the studied volatile species is clearly resolved by DFMS (e.g., not on the shoulder of another peak; Fig.…”

Time variability and heterogeneity in the coma of 67P/Churyumov-Gerasimenko

“…This mass spectrometer is operated in a variety of modes covering a wide range of masses, but typically measures the major neutral species including H 2 O, CO, and CO 2 . ROSINA detected and characterized a gaseous background due to spacecraft outgassing from the Rosetta spacecraft (15), which is present even after ten years of cruise in space including nearly two years in hibernation. For the following measurements described in this paper, this background was determined from a time period when the spacecraft was far (>800 km) from the comet and subtracted from the total signal.…”

“…The two CO 2 peaks merge, resulting in a shoulder on the main peak and a slight shift of the main CO 2 peak relative to that of H 2 O (~45 min or one measurement point). Statistical uncertainties ( particles) in the signal detected by ROSINA/DFMS are smaller than dots in Figures 1-3 and contributions to the signal due to spacecraft outgassing (15) are subtracted. The diurnal variations at half the rotation rate of the comet that are seen in August are also observed at southern latitudes in the September timeframe (Fig.…”

Cometary Isotopic Measurements

“…2.1.1, Altwegg et al 2014), and further results are expected in summer 2015 when 67P/ChuryumovGerasimentko is at its perihelion. -Some species are already present in the spacecraft background, e.g., CH 4 and HCN (for entire inventory see SchläPpi et al 2010) and have to be accounted for.…”