Engineers are studying data returned by NASA's Spitzer Space Telescope, to determine what caused the observatory to enter safe mode on Friday, Aug. 18 at 2:52 p.m. Pacific time. After an unexpected reboot of Spitzer's main onboard computer, the spacecraft autonomously followed pre-programmed procedures, switched to the backup electronics system, and entered safe mode. The engineering and science teams have so far found no hardware or software problem to explain the unplanned reboot. In response to the safe mode entry, the Spitzer team has carefully maneuvered the spacecraft, which is in an Earth-trailing orbit around the sun, to point its high-gain antenna toward Earth. This change in attitude enables engineers to receive critical engineering data as quickly as possible. The project's engineers are carefully analyzing the data, trying to determine the next course of action to bring the spacecraft back to nominal operations.