Navigation for MUSES-A (HITEN) aerobraking in the earth's atmosphere. Preliminary report

On 19 March 1991, the MUSES-A (HITEN) spacecraft, launched by the Japanese Institute of Space and Astronautical Science (ISAS), successfully completed the first aerobraking technology demonstration for an object in cis-lunar orbit. A second demonstration was performed on 30 March 1991. Perigee altitudes during the two passes were 125 km and 120 km respectively. Spacecraft orbit velocity at closest approach was 11.0 km/sec, within 0.1 km/sec of escape velocity. Analysis at ISAS indicated a 5 km perigee altitude error might result in fatal spacecraft damage. This led to a requirement for perigee altitude prediction better than 1 km in time to assess the need for possible final trim maneuvers. Covariance analysis performed at JPL indicated an ability to support final trim maneuver design with perigee altitude predictions better than 200 meters through use of radio metric tracking data generated by the worldwide NASA/JPL Deep Space Network (DSN). Final targeting maneuvers were executed near apogee prior to each aerobrake pass. In both cases, subsequent orbit determination indicated that no final trim maneuver was required. Preliminary post flight perigee reconstructions indicate the achieved minimum altitude on each pass was within 50 meters of the predicted value. This paper presents the JPL aerobraking phase covariance study results and preliminary joint JPL/ISAS orbit determination results. Possible explanations for the differences in the JPL and ISAS perigee altitude results are discussed.