Zonal wind calculations from Mars Global Surveyor accelerometer and rate data

The Mars Global Surveyor spacecraft was initially placed into a high-eccentricity, nearly polar orbit about Mars with a 45-h period. To accomplish the science objectives of the mission, a 2-h circular orbit was required. Using a method known as aerobraking, numerous passes through the upper atmosphere slowed the spacecraft, thereby reducing the orbital period and eccentricity. To successfully perform aerobraking, the spacecraft was designed to be longitudinally, aerodynamically stable in pitch and yaw. Because the orbit was nearly polar, the yaw orientation of the spacecraft was sensitive to disturbances caused by the zonal components of wind (east to west or west to east) acting on the spacecraft at aerobraking altitudes. Zonal wind velocities were computed by equating the aerodynamic and inertia-related torques acting on the spacecraft. Comparisons of calculated zonal winds with those computed from the Mars thermospheric general-circulation model are discussed.