The TIMED Spacecraft Mission Orbital Performance Fifteen Years in LEO

The Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) spacecraft is a NASAspacecraft designed, built and operated by The Johns Hopkins University Applied Physics Laboratory. The spacecraft was launched on December 7, 2001 for a two-yearmission. The TIMED instruments continue to provide global coverage of the Mesosphere and Lower Thermosphere Ionosphere(MLTI)region of the atmosphere (60 km to 180 km). The TIMED mission has observedthe effects of the sun on the MLTI region over a full solar cycle. TIMED has exceeded allscientific programgoals for the mission. TIMED is a low earth orbiting spacecraft with an altitude of 625 km and an inclination of 74.1\textdegree. The requirements imposed by the instruments; fields of view, pointing accuracy, jitter requirements, andanti-sun pointing of one spacecraft side;along with the sun angle variationsduring the year imposesspecial demands on the power system design. The power subsystem chosen for TIMED is an unregulated peak power tracking system with a single 50 AHr 22-cell individual pressure vessel NiH2 battery. The two driven solar array wings are populated with 140-micron single junction GaAs/Ge cells.The power system has been performing as designed with expecteddegradations tothe solar array and battery over the last fifteen years in low earth orbit.