Citation
Abstract
The Deep Space 1 (DS1) onboard stellar reference unit failed in November 1999, leaving the spacecraft able to achieve only Sun point, with 8.4 GHz (X-band) communications reduced to the low rates supportable via a low-gain antenna. By January 2000, the DS1 project flight team implemented an interim three-axis pointing concept called the "HGA activity" because it made the high-gain antenna (HGA) usable again. The HGA activity involves the telecommunications analyst as an integral part of a closed-loop ground-spacecraft pointing control system. The HGA activity initiates pointing of the high-gain antenna toward the Earth and subsequently maintains pointing for the duration of one or two passes. The concept requires the tracking station to lock its receiver on the X-band carrier and provide carrier signal-to-noise ratio in monitor data in real time. The project telecommunications analyst uses the data to prepare accurate event timing predictions and to assess performance through rapid and precise comparisons of monitor and prediction data. Use of this labor-intensive and real-time process enabled the project to receive high-rate telemetry data from 14 passes through May 2000. Finally, another 14 HGA activities in June 2000 enabled the project to reload several megabytes of flight software at a high rate. The new software brought to an end the routine use of the HGA activity because it operates the science camera to generate star data for onboard pointing control. With full three-axis pointing capability restored for ion-propulsion subsystem thrusting, DS1 has resumed its science mission with a flyby of the comet Borrelly planned for September 2001.
Keywords
Details
- Volume
- 42-144
- Published
- February 15, 2001
- Pages
- 1–23
- File Size
- 3.2 MB