AMOS Observations of NASA's IMAGE Satellite
Abstract
NASA's Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite stopped transmitting telemetry to ground stations in December 2005, after functioning for more than 5 years on Earth orbit. Before this loss of telemetry, the IMAGE satellite actively maintained a spin-stabilized attitude with spin axis perpendicular to the orbital plane and a nominal rotation rate of about 0.5 rpm. The spinning action served to both stabilize the satellite and keep the 250 m-long radial wire antennas of the satellite's Radio Plasma Imager under tension perpendicular to the satellite spin axis. After loss of telemetry, it was unclear whether the spacecraft remained in this spin-stabilized configuration, or whether it could continue to receive and execute up- linked commands. In late January and early February of 2006 the AMOS 3.6m Advanced Electro Optical System (AEOS) conducted an initial set of observations in an effort to help diagnose the state of the unresponsive spacecraft. The AEOS observations employed the Visible Imager (VisIm) instrument in the photometric I-band as well as the long-wavelength infrared (LWIR) imager. The wide field-of-view VisIm images clearly show the long radial wire antennas glinting in reflected sunlight during each revolution of the spinning spacecraft, creating a photometric signature characterized by large amplitude periodic variations. Analysis of concurrent AEOS LWIR observations indicates radiometric temperatures ranging from 250 to 310 Kelvin, with the higher temperatures occurring when more of the continuously-sunlit portions of the spacecraft were observable from AMOS. A detailed periodic analysis of the VisIm photometric signatures acquired on 2006 day-of-year (DOY) 028, 031 and 034 indicates a spin axis orientation consistent with that reported in the last telemetry down-linked from the satellite approximately seven weeks earlier. However, the periodic variations indicate a satellite spin rate of 0.4741 ° 0.0005 rpm, measurably slower than the last known spin rate from down-linked telemetry. Shortly after these initial AEOS observations were conducted, the NASA IMAGE satellite team up-linked commands to the spacecraft to increase the spin rate up to 0.52 rpm in order to test if the spacecraft could receive and execute such commands. Subsequent AMOS observations conducted 2006 DOY 150, however, did not show evidence of an increased spin rate, but instead indicated a further reduction down to 0.4709 ° 0.0004 rpm. The AEOS observations therefore confirm that the IMAGE spacecraft has lost the ability to receive and/or execute up-linked commands, and indicates that, between 2005-DEC-12 and 2006-MAY-30, the spacecraft's spin axis orientation remained stable to within detection limits but the spin rate declined at a rate of (3.1 ± 0.3) × 10-5 rpm/day, a deceleration most likely caused by magnetically-induced environmental torques.
- Publication:
-
The Advanced Maui Optical and Space Surveillance Technologies Conference
- Pub Date:
- 2006
- Bibcode:
- 2006amos.confE..76H