Mars global surveyor: Aerobraking with a broken wing

The Mars Global Surveyor spacecraft was launched successfully on November 7, 1996, on a Delta II 7925. During the initial spacecraft deployment, one of the two solar wings failed to deploy far enough to latch into place. The unlatched configuration was a serious problem because Mars Global Surveyor will use an aerobraking phase much like that used to circularize the orbit of the Magellan spacecraft at Venus. The solar wings supply most of the surface area that provides the drag that will result in a total Delta V of more than 1200 m/s during the four-month aerobraking phase. Aerodynamic moments at the unlatched hinge can be larger than 500 in-lb. Since the 60 in-lb spring force which is holding the unlatched panel in position for the planned aerobraking configuration is clearly not large enough, a new configuration had to be developed for the aerobraking phase. This paper will describe the redesigned aerobraking phase, which will begin on September 17, 1997 3 orbits after a 980 m/s propulsive maneuver captures the MGS spacecraft into a 45 hour, 300 km periapsis altitude orbit around Mars on September 12, 1997 (01:26 UTC).