Ground Systems and Flight Operations of the THEMIS Constellation Mission

THEMIS, a five-spacecraft constellation mission to study magnetospheric phenomena leading to auroral outbursts was launched on February 17, 2007 on a single Delta II rocket into a 31.4-hour, low-inclination insertion orbit. After an initial on-orbit check-out and science instrument commissioning period, the five spacecraft called probes were maintained in temporary coast phase orbits to control orbital dispersions. Beginning in early September 2007, four of the five probes were maneuvered into their highly elliptical, synchronized mission orbits with 1, 2 and 4-day periods in preparation for the primary winter observing season. The fifth probe, acting as an on-orbit spare, was maneuvered into its 4/5-day period orbit, once the four primary probes were completely deployed. This paper describes the concept of constellation operations including a description of the flight and ground systems, as well as mission, science and flight dynamics operations, and discusses challenges encountered and lessons learned during the first year of on-orbit operations.