From: Jet Propulsion Laboratory
Posted: Friday, January 18, 2002
NASA's Galileo spacecraft resumed gathering scientific information at about 4:00 today Universal Time (8:00 p.m. Jan. 17 Pacific Time) after commands radioed from Earth took the Jupiter orbiter out of the passive standby mode it entered on Thursday.
Galileo passed within about 102 kilometers (63 miles) of Jupiter's moon Io on Thursday. Planned observations for the remainder of the spacecraft's current swing near Jupiter include a series of images of the planet's atmosphere, a farewell color study of its icy moon Europa and navigational imaging of the small moon Amalthea.
Galileo hit its target point for the Io flyby so accurately that a scheduled post-encounter firing of thrusters to fine-tune the trajectory was cancelled as unnecessary, said Dr. Eilene Theilig, Galileo project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The close flyby was calculated to use Io's gravity to put Galileo on course for its next encounters. Galileo will pass near Amalthea in November 2002 and plunge to its demise in Jupiter's crushing atmosphere in September 2003.
"As expected, visiting Io has proved to be a challenging and risky endeavor," Theilig said. "It's disappointing not to get the observations of Io that were planned for this encounter, but I am very proud of the flight team that has kept Galileo functioning in orbit more than three times longer than originally planned and revived it once more yesterday."
Galileo detected a computer reset and placed itself in a standby or "safe" mode Thursday at 13:41 Universal Time (5:41 PacificTime), about half an hour before its closest approach to Io. The reset was apparently caused by exposure to the intense radiation environment at Io's distance from Jupiter. Since the spacecraft began orbiting Jupiter in 1995, it has endured a cumulative radiation exposure about three-and-a-half times what it was originally designed to withstand.
NASA has repeatedly extended Galileo's original two-year mission in orbit. The spacecraft is now nearly out of the hydrazine propellant needed to keep its antenna pointed toward Earth. Knowing they would eventually lose contact and control of the spacecraft, the Galileo team chose the planned impact with Jupiter to ensure there was no chance the spacecraft might hit Europa. One of Galileo's important discoveries has been the likelihood of a melted saltwater ocean under Europa's icy crust, making that moon of great interest for future study of the possibility of extraterrestrial life.
Additional information about the Galileo mission is available at http://galileo.jpl.nasa.gov .
Galileo was launched from the Space Shuttle Atlantis on Oct. 18, 1989. After a long journey to Jupiter, Galileo began orbiting the huge planet on Dec. 7, 1995, and successfully completed its two-year primary mission in 1997. That has been followed by three mission extensions. JPL, a division of the California Institute of Technology in Pasadena, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C.
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