The Timed Spacecraft: A Thermal Design Perspective 1999-01-2133

The Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) spacecraft will be placed in a 625 km, 74.1 degree inclination low earth orbit, with four scientific instruments on board. The TIMED spacecraft will be launched from Vandenberg Air Force Base in May 2000 on a Delta II rocket. The TIMED spacecraft is a co-manifested launch with the JASON spacecraft (TOPEX follow-on). The TIMED spacecraft is encapsulated in a Dual Payload Attach Fitting (DPAF), with the JASON spacecraft mounting to the top of the DPAF. The TIMED instruments are designed to characterize the Earth’s upper atmosphere using visible, UV and IR sensors. Due to the stringent thermal requirements for the instruments, the spacecraft must maintain a Nadir pointing side, as well as, a sun keep out zone on the backside of the spacecraft. These basic requirements, along with instrument field of view requirements have resulted in a very interesting spacecraft design.

The TIMED spacecraft has the subsystems on board necessary to provide the instruments with the power, attitude control and thermal stability they require. The spacecraft sports an optical bench containing four single axis gimbaled telescopes, two star trackers and two GPS antennas. The spacecraft has a 50 Amp-Hour, 22 cell Nickel-Hydrogen battery split into two halves placed on opposites of the spacecraft. The Ni-H battery is just one component on the TIMED spacecraft which requires careful thermal control. The TIMED spacecraft is implementing an Integrated Electronics Module (IEM) that contains several different spacecraft subsystems, like C&DH, S-band receiver and transmitter, solid-state recorder and more. The combination of all these subsystems into one box, normally packaged in separate card cages, has resulted in some challenging thermal design problems. This paper will discuss the thermal control approach, the thermal testing conducted to date and thermal testing to be completed for the TIMED spacecraft.