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