An Optimized Ion Neutral Mass Spectrometer Design for the NASA/ESA
Europa Jupiter System Mission (EJSM), 15-R8201
Principal Investigators
J. Hunter Waite
David T. Young
Timothy Brockwell
Keith Pickens
John Roberts
Greg Miller
Inclusive Dates: 01/01/11 – Current
Background — This project had two primary objectives: 1) determine the science traceability of a mass spectrometer for a mission to the Galilean satellites, and 2) develop a low-resource, mass spectrometer design based on the multi-bounce time-of-flight mass spectrometer that could carry out the proposed science objectives.
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Table E-1. ANGIO Characteristics, Resources and Performance Summary |
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System Characteristics |
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Subsystem |
Type |
Specification |
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GIS - collimator |
Anti-scattering baffle, ST172 coated, single use cover |
FOV: 1π steradian in ram direction |
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GIS - cryotrap |
Cryotrapping/direct inlet, neutral gas |
Sensitivity boost: up to 2,000 counts s-1 per mol cm-3 |
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MS - closed source |
Storage, electron ionization, redundant emitters |
Ambient sensitivity: 0.02 counts s-1 per mol cm-3 |
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MS - ion optics |
Multibounce time-of-flight |
Resolution: 12,300 m/Δm FWHM for HDO |
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MS - detector |
Electron multiplier |
MCP, 3 plate z-stack, 5µm pore |
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Resources - Current Best Estimate (CBE), see §F.1.8 for margin |
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Mass & Volume |
Power (W) |
Average Data Rate |
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7.52 kg, 0.0183 m3 |
38.80 (Peak), 28.80 (Average), 2.00 (Standby), 1.50 (Survival) |
55.12 kbps (peak), 12.33 kbps (average) |
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Performance |
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Measurement |
Requirement |
Capability in 200 km Ganymede Orbit |
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Noble gas abundances wrt H2 (major isotopes) |
Mixing fractions >1 ppm |
Determined in <300 s with cryotrapping (132 hours sampling time) |
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D/H in H2O isotopic ratio |
Ratios >10-6 ±25% |
Determined in <60 s with cryotrapping (132 hours sampling time) |
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Organics, abundance wrt H2 |
Masses to 300 u, >1 ppm |
Determined in 63 min |
Approach — The project was undertaken to place SwRI in a competitive position for the joint NASA/ESA EJSM. However, the scientific focus of the mission changed from Europa to Ganymede in the course of the study, due to the NASA science priorities set by the Planetary Decadal Study and SwRI's proposal, "A Neutral Gas Investigation of Origins (ANGIO)," was submitted to the NASA SALMON PEA K for participation in ESA's JUpiter ICy moons Explorer (JUICE) mission. The science objectives were derived from the Science Requirements document:
- Objective 1 (Origins): Make definitive measurements to constrain the formation conditions of the Galilean satellites: D/H, 18O/16O, 17O/16O, 14N/15N, and noble gases.
- Objective 2 (Habitability): Measure the composition, distribution, and evolution of surface materials from sputtering processes, with emphasis on comparative habitability.
- Objective 3 (Habitability): Investigate geological features that may be linked to ice shell or interior composition.
- Objective 4 (Coupling and Interaction): Determine the spatial structures of the neutral atmospheres and neutral clouds.
These science objectives were addressed with a low-resource multi-bounce time-of-flight mass spectrometer with the characteristics shown in the table below:
Accomplishments — Both primary project goals were met.
