Transition Region and Coronal Explorer Mission

The Transition Region and Coronal Explorer (TRACE) mission is the fourth mission in the Small Explorer (SMEX) program series at the National Aeronautics and Space Administration\´s Goddard Space Flight Center. The primary objective of the TRACE mission is to explore the connections between the fine scale magnetic fields in the solar surface and features in the solar photosphere, chromosphere, transition region, and corona. The TRACE spacecraft, including the instrument, weighs 250 kilograms, uses 200 watts of power, and will cost approximately 35 million dollars for the entire mission. It will launch into a Sun-synchronous Low Earth Orbit (LEO) in September 1997 and collect movie-like images of the Sun with one are second spatial and 1 second temporal resolution; these images will be made available on the Internet daily. This paper shows NASA\´s approach to small spacecraft development It discusses some trades in the design of each subsystem to accommodate instrument and spacecraft heritage as well as new mission requirements. Topics include: a solid state Command and Data Handling (C&DH) system, solid state memory using 20 Megabyte modules approximately 1"×1"×0.2" each; a fully digital Attitude Control System (ACS); a guide telescope fine error sensor for spacecraft attitude and control as well as image motion compensation to better than are second levels. Adaptations in ground systems and operations are also included as well as the systems engineering approach