Quadrupole Ion Trap Mass Spectrometer for Ice Giant Atmospheres Exploration

• Published in: Space science reviews 2021-02, Vol.217 (1), Article 13
• Main Authors: Simcic, J., Nikolić, D., Belousov, A., Atkinson, D., Lee, C., Madzunkov, S., Almodiel, D.
• Format: Article
• Language: English
• Subjects: Abundance; Aerospace Technology and Astronautics; Astrophysics and Astroparticles; Atmosphere; Atmospheric entry; Atmospheric pressure; Atomic properties; Comets; Composition; Descent; Exploration; Gas flow; Gases; Helium; Ice; Ice giant planets; In Situ Exploration of the Ice Giants: Science and Technology; Ions; Jupiter; Jupiter probes; Laboratories; Lander vehicles; Mars missions; Mars probes; Mass flow; Mass spectra; Mass spectrometers; Mass spectrometry; Moon; Nitrogen isotopes; Physics; Physics and Astronomy; Planetology; Quadrupoles; Rare gases; Solar system; Space Exploration and Astronautics; Space missions; Space Sciences (including Extraterrestrial Physics; Spectrometers; Titan; Tropopause; Venus atmosphere; Venus probes
• ISSN: 0038-6308; 1572-9672
• DOI: 10.1007/s11214-020-00785-5

To date, a variety of different types of mass spectrometers have been utilized on missions to study the composition of atmospheres of solar system bodies, including Venus, Mars, Jupiter, Titan, the moon, and several comets. With the increasing interest in future small probe missions, mass spectrometers need to become even more versatile, lightweight, compact, and sensitive. For in situ exploration of ice giant atmospheres, the highest priority composition measurements are helium and the other noble gases, noble gas isotopes, including 3 He/ 4 He, and other key isotopes like D/H. Other important but lower priority composition measurements include abundances of volatiles C, N, S, and P; isotopes 13 C/ 12 C, 15 N/ 14 N, 18 O/ 17 O/ 16 O; and disequilibrium species PH 3 , CO, AsH 3 , GeH 4 , and SiH 4 . Required measurement accuracies are largely defined by the accuracies achieved by the Galileo (Jupiter) probe Neutral Mass Spectrometer and Helium Abundance Detectors, and current measurement accuracies of solar abundances. An inherent challenge of planetary entry probe mass spectrometers is the introduction of material to be sampled (gas, solid, or liquid) into the instrument interior, which operates at a vacuum level. Atmospheric entry probe mass spectrometers typically require a specially designed sample inlet system, which ideally provides highly choked, nearly constant mass-flow intake over a large range of ambient pressures. An ice giant descent probe would have to operate for 1-2 hours over a range of atmospheric pressures, possibly covering 2 or more orders of magnitude, from the tropopause near 100 mbar to at least 10 bars, in an atmospheric layer of depth beneath the tropopause of about 120 km at Neptune and about 150 km at Uranus. The Jet Propulsion Laboratory’s Quadrupole Ion Trap Mass Spectrometer (QITMS) is being developed to achieve all of these requirements. A compact, wireless instrument with a mass of only 7.5 kg, and a volume of 7 liters (7U), the JPL QITMS is currently the smallest flight mass spectrometer available for possible use on planetary descent probes as well as small bodies, including comet landers and surface sample return missions. The QITMS is capable of making measurements of all required constituents in the mass range of 1–600 atomic mass units (u) at a typical speed of 50 mass spectra per second, with a sensitivity of up to 10 13  counts/mbar/sec and mass resolution of m / Δ m = 18000 at m/q = 40. (Throughout this paper we us