Bill Elliott, mechanical engineer, shows how a part on the electrostatic analyzer (ESA) moves. This part is responsible for opening a metal “door” that covers the ESA aperture. This “door” is closed to protect the detector as the satellite is shot into space on a rocket. It is then opened to allow charged particles to enter through the ESA aperture. The ESA is the scientific instrument that measures the number of particles coming from a particular direction in a particular area that are going a particular speed.