The mass spectrometer takes the atmospheric gas in through the leaks into a vacuum, which is an airtight chamber. Creating a vacuum is easier said than done. If the GCMS were on earth, scientists could simply run a vacuum pump and wouldn’t have to worry about the size, weight, and power—they would have continual access to as much power as they needed. In space, however,the pumps must run off of a battery. To overcome this difficulty, this instrument uses 2 different types of pumps:
These are chemical pumps. They use chemical reactions to remove gases from the vacuum chamber. These pumps run continuously throughout the voyage.
These pumps are used to ionize the gas coming in. The ion is then accelerated through an electric field so it gets physically buried into the walls of the vacuum chamber. These pumps are turned on at specified times during the mission, and, just like the getter pumps, their primary purpose is to get rid of any unwanted chemicals in the vacuum chamber.