Galileo Status Report
PUBLIC INFORMATION OFFICE JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
Galileo engineers today continue to prepare the spacecraft for its long-awaited arrival at Jupiter Thursday, when the spacecraft will fly through the harshest environment it will ever encounter.
As planned, selected portions of spacecraft's fault detection and correction software have been reconfigured via radio to ensure that Galileo will respond appropriately to the extreme phenomena it will experience Thursday while flying between Jupiter and its moon Io.
Jupiter's intense radiation and belts of trapped electrons and heavy ions in this area conceivably could disrupt or disable some portion of the spacecraft's electronics. On the inbound leg into the jovian system, Galileo is expected to absorb a radiation dose of 35,000 to 40,000 rads. (One thousand rads will kill a human.) Some of the fault-protection changes sent to the spacecraft today are designed to heighten Galileo's tolerance of disruptions that could occur in this region. "When we were building Galileo, we put in a lot of shielding to offset the expected effects of Jupiter's environment," said Matt Landano, deputy mission director, "but we won't know how well a job we did until we fly through it."
Spacecraft engineers today also prepared Galileo to expect a hiatus in communications from Earth beginning a few days after it arrives at Jupiter due to solar conjunction, when the Sun will be in the path between Earth and Jupiter, disrupting radio contact with the spacecraft. Normally, if Galileo didn't hear from Earth controllers after three days, the spacecraft's computers would automatically switch to a backup receiver. The new instructions provide for the expected disruption in communication during solar conjunction by allowing the spacecraft to wait a full 25 days before switching to a backup receiver.
The Galileo spacecraft continues to operate normally under the control of computer sequences transmitted by the flight team. Galileo is transmitting science and engineering telemetry at 10 bits per second via the stations of NASA's global Deep Space Network.
Galileo is about 3.6 million kilometers (2.2 million miles) from Jupiter. Its velocity relative to the Sun is about 6,500 miles per hour and slowing, while its velocity relative to Jupiter is more than 22,500 miles per hour and increasing. The spacecraft is 932 million kilometers (579 million miles) from Earth, so that its radio signals take almost 52 minutes to reach the Earth.