Peter Waller
Ames Research Center, Mountain View, CA
RELEASE: 95-34
Key operational tests of the atmospheric probe on NASA's Jupiter-bound Galileo spacecraft have been successfully completed, demonstrating that the probe is in good health and ready for the first-ever descent into the atmosphere of an outer planet this December.
The just-completed testing followed NASA's first interrogation of the atmospheric probe in 27 months, and "it went perfectly," said Marcie Smith, Galileo probe project manager at NASA's Ames Research Center, Mountain View, CA. The probe now stands ready to separate from the Galileo orbiter spacecraft in July and then fly the remaining 50 million miles of its flight to Jupiter on a solo trajectory.
"We wanted to be sure the power system was in good shape, and it was," Smith said, "and so were the other probe systems."
"The recent probe tests showed that each of its three lithium battery modules were operating normally," said Charles Sobeck, probe engineering manager. Both accelerometers of the atmosphere structure experiment were normal. The sampling chamber of the Neutral Mass Spectrometer, which will analyze the composition of Jupiter's atmosphere, was pumped out in preparation for descent.
"Engineers also conducted an end-to-end test of the probe data compression system, and it worked very well," Sobeck said. Command systems for the two redundant data systems worked without a flaw, as did the data return link for the primary system.
Further data on the operation of the probe radio receiver aboard the orbiter will be returned and analyzed in coming weeks.
Upon its arrival at Jupiter on December 7, 1995, the probe will make the first entry into the atmosphere of one of the solar system's giant gas planets. This will be the most difficult planetary entry ever attempted, with the probe expected to reach a speed of 106,000 mph before it encounters deceleration forces of up to 350 G's (350 times Earth gravity) through friction with Jupiter's atmosphere.
After entry, the probe will descend about 400 miles into the planet's complex atmosphere, making the first direct measurements of its clouds, lightning, winds and other features.
Jupiter is the largest planet in the solar system, with about 300 times the mass of the Earth. The planet has its own internal heat source, and its spectacular banded appearance and many other active cloud features such as the Great Red Spot make its atmosphere a topic of great scientific interest.
NASA engineers last communicated with the probe in November and December 1992. At that time, it was in "excellent shape," Smith said. While the vacuum of space is considered a safe environment for non-operating spacecraft, "it will be six years after the batteries were built before they get used to power the probe," she explained, "so we wanted to check them one more time before release."
After deploying the probe, the Galileo orbiter will change its course to pass 133,000 miles above Jupiter's clouds, while the probe continues on and descends into the atmosphere. The probe will radio its data to the orbiter, which will store it for later transmission to Earth before beginning two years of orbital-based observations of Jupiter, its moons and its powerful magnetosphere.
"We are delighted that the probe checkout went so well," said Galileo Project Manager William J. O'Neil of NASA's Jet Propulsion Laboratory, Pasadena, CA. The successful probe checkout was the first activity to be carried out under new Galileo flight software that was transmitted to the spacecraft in January and February, indicating that all of the major elements of the mission are ready for the start of its encounter with Jupiter.
The Galileo probe project is managed by NASA Ames. The overall Galileo mission is managed by NASA's Jet Propulsion Laboratory. The probe was built by Hughes Aircraft Co., El Segundo, CA.