Galileo Probe Mass Spectrometer

The Atmospheric Experiments Laboratory developed the mass spectrometer on the Galileo Probe. Shortly before arrival at Jupiter, the Probe separated from the Galileo Orbiter, entered the upper atmosphere, and then descended on a parachute into the deep Jovian atmosphere. The Galileo Probe Mass Spectrometer (GPMS) was one of six instruments on the Probe and was the primary Probe instrument to measure chemical and isotopic composition of the atmosphere of Jupiter. Data transmission from the descending Probe lasted 58 minutes, during which time the ambient gas pressure increased from 0.4 to 23 times the sea level surface pressure of the atmosphere of Earth.

The GPMS was highly integrated quadrupole mass spectrometer and electronics package designed to be lightweight and compact. The instrument weight was 13.2 kg. (29.1 lb.) and average power consumption was 22 watts. An intricate system of microvalves, gas plumbing, sample enrichment cells, and chemical getter pumps were utilized to obtain a series of chemical composition measurements throughout the descent sequence. The instrument housing, made of titanium, was sealed with just over one atmosphere of nitrogen inside, in order to protect the sensor and electronics from the wide variations of pressure and temperature during the descent. The housing was designed to survive to an external pressure of approximately 22 times earth sea level pressure (i.e., 330 pounds per square inch), at which time it was expected to implode.                                                                                                                                                                                         

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