Open! Open! Open! Galileo High Gain Antenna anomaly workarounds

This paper discusses the Galileo (GLL) High Gain Antenna (HGA) anomaly that occurred in the operations phase of the mission in April 1991. The spacecraft was scheduled to deploy its 4.8-meter-diameter (16-foot) high-gain antenna as Galileo moved away from the Sun and the risk of overheating ended. The antenna, however, failed to fully deploy. A special team performed extensive tests and determined that a few (probably three) of the antenna's 18 ribs were in the closed position. Despite exhaustive efforts to free the ribs, the antenna would not fully deploy. From 1993 to 1996, extensive new flight and ground software was developed, and ground stations of NASA's Deep Space Network were enhanced in order to perform the mission using the spacecraft's low-gain antennas [19]. This paper serves as a systems engineering case study that provides highlights of the GLL mission, overviews of the hardware, software, and aspects of the systems engineering and operations approaches. It then describes the approach to develop several workarounds to accomplish the GLL mission objectives despite the HGA anomaly.