Спутник USA-205 (STSS-ATR), запущен 5 мая 2009

Two very important factors affecting the MSX thermal design are its orbit and attitude. The lifetime and performance requirements of the primary instrument necessitate strict control of direct sunlight on the spacecraft. MSX is to operate in a high-altitude, circular, polar orbit with a precession rate of less than 0.04° per day. Over the 5-year mission goal, the Sun line/orbit plane angle will increase from 45° through 120°; significantly,that angle is never less than about 45°. This orbit allows the spacecraft to fly in a roughly Earth-oriented attitude while keeping direct sunlight out of the instrument apertures. Controlling the spacecraft’s attitude relative to the Sun is one requirement that shapes the whole mission.The MSX spacecraft and its coordinate axes are shown in Fig. 2. The x axis is parallel to the line of sight of the instruments. The z axes form a line parallel to the drive axes for the solar array. The y axis completesa right-handed coordinate system. In this system, the spacecraft flies with the 2x axis pointed to Earth and the 1x axis pointed to space.Preferably, both from a thermal and power stand-point, the Sun will remain in the xy plane, constrained between ±90° from the 2y axis. This orientation allows the solar panels to develop full power and provides a stable, cold environment for the SPIRIT III cryostat