•A:This path gives us nearly all science originally planned. We expect that we may pay a performance penalty of only 20% or so in termsof sensitivity, but most of our sensitivity limits are driven by background count rates, so we may not pay much of a price at all.
•B:This path gives us full capability for soil and ice analyses, but it precludes us from analyzing the atmosphere with maximum sensitivity (which requires using the atmosphere inlet to the EGA). We can still measure Arabundances and CO2 abundances and isotopic ratios in the atmosphere by using the much less sensitive TA sample inlet. Later in the mission, perhaps after all eight ovens have been used, we can use the atmosphere inlet to get maximum sensitivity for other noble gases (Ne, Kr, and Xe) by using the gas enrichment cell, which only connects via the atmosphere inlet valve. Although we could use the much more sensitive atmosphere inlet at the end of the mission, we could not measureD/H ratio because we expect the background water signal would be too high by this point. We could consider accepting the risk of another actuationof the atmosphere valve and make one or two measurements of D/H ratio early in the mission.
TEGA Characterization Activity Status
•Can do with EGA in current state
–Cover Retract (without Ion Pump)
–Door Open
–Sample Acquire (receipt)
•Can NOT do with EGA in current state
–Atmosphere Run
–Sample Process surface sample
–Low, Mid or High Temp Ramps
Fault propagation from filament drive to control electronics
•Because of the high voltages present in the EGA, great care was taken in
the design, both electronically and mechanically, to prevent a fault in the
EGA high voltage sections from propagating into the control electronics.
The high voltage sections in the EGA are potted and encased in their own
Faraday shields, and isolated from the low voltage sections by high voltage
opto-isolators and transformers with grounded shields between the primary
and secondary windings. Zap traps are used on all ground connections to
block the high frequency pulses resulting from any electric discharges.
Because of the nature of the emission control circuit (the wholecircuit floats
at the 300 -2000V sweep potential), an additional layer of transformer
isolation exists between the filament, ionization, and J-plate supplies and
the low voltage section.
Finally, the interface between the EGA low voltage section and the main
control electronics is also very robust. It consists of a current limiting FET
switch followed by two stages of both common-mode and single ended
filtering for the +28V, opto-isolated control and status lines, and a
bidirectional RS-422 link based on Intersil26C31/32 drivers and receivers.
