PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
Contact: Franklin O'Donnell
FOR IMMEDIATE RELEASE October 20, 1995
GALILEO SPACECRAFT TAPE RECORDER TO BE TESTED
Engineers will transmit a series of commands to NASA's Jupiter-bound Galileo spacecraft today in an effort to assess the state of its balky onboard tape recorder.
The flight team, meanwhile, was buoyed by a preliminary assessment from Galileo's science team reporting that at least half the mission's original scientific objectives could be obtained in the event the tape recorder is found to be unusable.
The tape recorder, which is mainly used for onboard storage of imaging and spectral data from Galileo's instruments, apparently malfunctioned October 11. The problem was detected shortly after Galileo, due to reach Jupiter on December 7, took three consecutive images through different filters to produce a color image of Jupiter and its major moons. The tape recorder failed to stop rewinding as expected after recording the imaging data. Commands were sent to halt the tape recorder, which has since remained in a standby mode.
"For the past week, we've looked in detail both at data from the spacecraft and from an identical tape recorder in the testbed laboratory here," said Galileo Project Manager William J. O'Neil at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA. "We've identified a number of both mechanical and electrical failures in the tape recorder system that could explain this problem. Our efforts today and in coming days will help us determine whether the tape recorder can be restored to operation."
Commands will be radioed to the spacecraft this afternoon to play back a small sample of data stored on the tape recorder. The tape-recorded data, along with engineering data reporting on the recorder's performance, first will be stored in memory located in Galileo's central data subsystem, then transmitted to the receiving stations of NASA's Deep Space Network this evening.
"By early next week, we will be in a position to report the results of our efforts to operate the tape recorder," said O'Neil. "Successful commanding of the device would still mean additional assessment and troubleshooting." Work concurrently continues on a backup plan to preserve the return of imaging and spectral data in the event the tape recorder cannot be used, he added.
Galileo's tape recorder and the spacecraft's guidance control computer were called into service as data compression and storage links in a sophisticated alternative method devised to maximize data return from Jupiter after Galileo's main high-gain antenna failed to open properly. Loss of the high-gain antenna meant that all spacecraft communications must be conducted at much lower data rates through a low-gain antenna.
New techniques have been developed to edit, compress and encode Galileo's data, including images, in the spacecraft's computers, then store that data for playback to Earth. Additionally, new hardware and software changes at ground receiving stations have been installed to further increase the amount of data transmitted from Galileo's low-gain antenna.
Project Scientist Dr. Torrence Johnson of JPL reported that at least 50 percent of the mission's original science objectives could still be achieved if the tape recorder is found not to be working.
"The impact of a possible loss of the tape recorder is not as bad as people assumed when we first heard about the problem," said Johnson. "Even without the tape recorder, we have an exciting mission that allows us to address all our primary objectives. Although the total number of pictures and spectra we receive would be lower than with a tape recorder, we would still have enough to do the job."
According to Johnson, among the mission's three major areas of science investigations, it is the data return from remote sensing instruments such as cameras and spectrometers that would be impacted most by loss of the tape recorder. Data from these instruments can be saved by re-routing them directly to memory areas in the flight computer.
"The mission will still study all aspects of the Jovian system -- Jupiter's atmosphere, its moons and its magnetic environment -- and we plan to make a majority of the scientific measurements that had already been planned," said Johnson.
One hundred percent of the atmospheric probe's science objectives can be achieved without the tape recorder, in addition to all of the Galileo orbiter's survey of the Jovian magnetic and charged-particle environment, Johnson said.
"The principal loss of data, if the tape recorder is not usable, would be the number of images and other high-rate spectral data that could be returned by the spacecraft," said Johnson. Galileo spacecraft and software engineers, however, are devising new backup methods to store imaging and spectral data in available memory areas within the spacecraft's central data processor.
Preliminary assessments indicate that at least 150 to 300 high-resolution images of the Galilean moons of Jupiter and additional hundreds of Jupiter and Io volcanoes-monitoring images could be returned over the course of Galileo's two-year orbital tour.
The Galileo mission consists of an orbiter spacecraft and an atmospheric probe, which was released from the orbiter in July. The probe will parachute into and directly sample Jupiter's atmosphere on December 7. Its data will be radioed to the Galileo orbiter overhead. Also on December 7, shortly after the completion of the probe's mission, the Galileo orbiter's rocket engine will fire to brake the spacecraft into orbit around Jupiter, beginning a two-year detailed study of the Jovian system.