A plasma instrument (called PIMS) sensor assembly is loaded into a thermal vacuum (TVAC) chamber in the Space Simulation Laboratory (SSL) at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland. The chamber is able to simulate the very cold temperatures the instrument will experience in deep space en route to Jupiter’s moon Europa. This test, called a thermal balance test by engineers developing the instrument, involved cooling parts of the instrument to −100°C and monitoring its performance. Chad Cook (left) and Erik Hohlfeld.