TRMM ON-ORBIT PERFORMANCE REASSESSED AFTER CONTROL CHANGE

摘要

The Tropical Rainfall Measuring Mission (TRMM) spacecraft, a joint mission between the United States and Japan, was launched from the Tanegashima Space Center, Japan on November 28, 1997, and transitioned in August, 2001, from an operating altitude of 350 kilometers to 402.5 kilometers. Due to problems using the Earth sensor at the higher altitude, TRMM switched to a backup attitude control mode. Initially TRMM controlled pitch and roll to the local vertical using Earth horizon measurements while using yaw gyro data to propagate yaw between updates using Sun sensors. After the orbit boost, a 6-state Kalman filter used 3-axis gyro data with Sun sensor and magnetometer data to estimate onboard attitude and gyro rate biases. To better evaluate the onboard pointing performance, roll attitude errors were independently estimated using science instrument radar data, providing a novel insight into various correlations and patterns in the attitude errors. Originally the backup Kalman filter control mode was intended to meet a degraded attitude accuracy of 0.7 degrees; however after improving the onboard ephemeris accuracy and adjusting an onboard magnetometer calibration, it proved possible to meet the original 0.2 degree accuracy requirement.