Jan. 25, 2000
Status 25 January 2000 Because Terra is normally not in continuous contact with the TDRSS geostationary communications satellites, the spacecraft carries a solid-state recorder (SSR), which is a large memory buffer that records data for later playback. Late last night, an unexpected "hang-up" of the SSR occurred during playback of some engineering telemetry. This event rendered all subsequent recording of science data inoperable, and also put at risk the ability to play back engineering data acquired while out of contact with TDRSS. Consequently, instrument activation plans have been suspended until normal SSR capability is restored. The MISR flight software load has been postponed until Friday, January 28 at the earliest. There is encouraging news regarding the orbit ascent maneuvers. Spacecraft engineers have concluded that the thruster hardware and the controller that detects and recovers from an anomaly during a burn are working properly. They believe that the problem on January 11 occurred because the controller which orchestrates the ascent maneuvers was designed and validated using a simulator that contained errors in the thruster performance model. In light of these conclusions, a scenario involving many small burns to achieve orbit is being developed. The new plan has a goal of starting the burns on January 31, contingent upon successful completion of additional thruster checkout tests. Further schedule details are expected to be released tomorrow. The cooling system for the ASTER thermal-infrared (TIR) instrument has improved its performance, and it now appears to be sufficiently stable to enable turn-on of the TIR once instrument activation activities re-commence. Additional engineering evaluations will be performed before the system is declared operational. MODIS has transitioned to science mode, though its Earth-view door remains closed so it is acquiring "dark" data. MODIS uses individual detectors whose view of the Earth are swept from side-to-side using a scan mirror, which was successfully activated yesterday. This method contrasts with MISR, which uses linear arrays of detectors to cover the width of its swath; however, MODIS can observe a much broader swath than we do. In both instruments, two-dimensional images are generated as a result of the motion of the spacecraft along its orbit. MISR's "push-broom" type of operation is similar to how a flatbed scanner or a fax machine works. In a flatbed scanner like one you can attach to your computer, the photo you are scanning is kept stationary and the line of detectors is moved, whereas in a fax machine the paper moves while the detectors are stationary. MISR's push-broom operation is therefore most analogous to the flatbed scanner. Because of the additional side-to-side sweeping used in MODIS, it is called a "whisk-broom" scanner. Many people, including our operations staff, were not able to get to work at the EOS Operations Center today due to the blizzard on the East coast, and Goddard Space Flight Center was officially closed. Fortunately, the system to monitor MISR's telemetry at JPL became operational a few days ago, so we also have the capability to observe the instrument's performance from Pasadena. MISR continues to do well. You can see earlier status reports by checking the "News" link of the MISR web site at
http://www-misr.jpl.nasa.gov.
David Diner