Galileo's original two-year mission ended in December 1997, and a two-year extension called the Galileo Europa Mission, ended on January 31, 2000. Galileo engineers are fond of saying that the spacecraft has lived well past its warranty. The spacecraft has already endured nearly three times the radiation it was designed to withstand, but repeated exposure to Jupiter's radiation has taken its toll. Galileo was zapped with particularly high doses of radiation during recent flybys of Io, which lies deep within Jupiter's radiation belts.
"This extended travel ticket enables us to continue studying Jupiter and its fascinating moons," said Jim Erickson, Galileo Project Manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
During this new extension, called the Galileo Millennium Mission, tour planners hope to include three high-priority scientific observations in 2000:
Galileo would team with Cassini for simultaneous observations of the Jupiter system and its magnetic environment from two vantage points. Cassini will visit Jupiter's neighborhood in December 2000. Jupiter's powerful gravity will be used to "slingshot" Cassini toward Saturn.
Galileo will perform two additional flybys of Jupiter's moon Ganymede, the largest moon in the solar system, on May 20 and December 28.
Scientists hope these flybys will tell us more about Ganymede's geologic history, including the highest resolution pictures ever taken of this icy world.
Results will be analyzed from the January 3 flyby of Jupiter's moon Europa and the closest-ever flyby of the volcanic moon Io on February 22.
That encounter, at an altitude of only 200 kilometers (124 miles), may have been the last tour of that unique environment for years to come. The close-up images will add to Galileo's bulging scrapbook, which already contains about 14,000 pictures beamed back to Earth so far.
By April 2001, after the spacecraft transmits to Earth pictures and scientific information stored on its tape recorder during the flybys in 2000, Galileo will have traveled nearly 4- 1/2 billion kilometers (2.8 billion miles).
Here on Earth, that mileage would earn a frequent flyer nearly 85,000 free round-trip tickets to Hawaii, an area with volcanoes remarkably similar to those observed by Galileo on Io.
"For the first time ever, two spacecraft will simultaneously explore an outer planet," Cassini Project Scientist Dr. Dennis Matson said about the planned Jupiter observation by Cassini and Galileo.
"One spacecraft will be inside Jupiter's magnetic envelope, with the other outside where it can observe the powerful solar wind pressing on the envelope. From the two vantage points, we'll watch cause and effect as the wind changes the magnetic properties around Jupiter."
"We have a unique opportunity to study this dynamic system with two highly capable spacecraft at the same time," added Galileo Project Scientist Dr. Torrence Johnson. "It's a real bonus for both missions."
"As Galileo continues operating in Jupiter's harsh radiation environment, it's a challenge for our operations team to keep the spacecraft healthy," Erickson said. "But we like to think of Galileo as the 'little spacecraft that could.'"
Galileo mission planners are currently exploring various options for the mission's eventual conclusion, including possible further encounters with Io and another Jovian moon, Callisto.
Planners are looking into a possible impact with Io or Jupiter for a mission finale, with other options are also being considered.
They are trying to avoid an impact with Europa because recent evidence suggests there may be a liquid ocean beneath its icy crust, raising the possibility that life could exist there.
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