Spaceflight Now: Breaking News

Galileo completes successful encounter with Europa
Galileo Millennium Mission considered
Posted: Jan. 4, 2000

A file photo of Europa captured from Galileo. Photo: NASA
NASA's Galileo spacecraft has kicked off the new year with a successful flyby of Jupiter's icy moon Europa on its 27th orbit around the gas giant since arrival in December 1995. The spacecraft swooped past Europa at an altitude of 351 kilometers (218 miles), about the same altitude the space shuttle orbits Earth, on Monday at 10:38 a.m. Pacific Standard Time.

The spacecraft is operating normally, and it appears that its instruments have completed their observations of the magnetic fields and charged particles around Europa. These observations were designed to detect any magnetic disturbances that may occur because of electrical currents set up in an ocean that may lie beneath Europa's icy crust. The prospect of a liquid ocean on Europa is intriguing, since water is one of the ingredients essential for life.

Because Galileo passed behind Europa during the flyby, its radio signal to Earth was blocked for a while. Scientists took advantage of this situation by studying the way the radio signal changed as the spacecraft entered this "silent zone." These radio science experiments teach us more about Europa's ionosphere -- the region of charged particles surrounding the moon -- and any possible atmosphere.

The flyby occurred approximately 697 million kilometers (433 million miles) from Earth, taking radio signals just under 39 minutes to travel between the spacecraft and Earth.

Observations of three of Jupiter's small natural satellites -- Amalthea, Thebe, and Metis - were planned for Galileo Monday evening, with observations of Jupiter's volcanic moon Io on the spacecraft's agenda for early Tuesday morning. Galileo will pass at an altitude of 214,000 kilometers (133,000 miles) above Io's surface.

All data gathered during this flyby are being stored on Galileo's onboard tape recorder. They will be transmitted to Earth during the coming weeks.

Galileo has been orbiting Jupiter and its moons since December 1995, beaming to Earth unprecedented images and other information. JPL, a division of the California Institute of Technology, Pasadena, CA, manages the Galileo mission for NASA's Office of Space Science, Washington, DC.

NASA Headquarters has agreed in principle to extend the Galileo mission past its planned January 31 finale. Details of funding and itinerary for the new extended mission, to be called the Galileo Millennium Mission, must still be resolved. A Europa encounter took place January 3, 2000, and is technically still part of the current, extended Galileo Europa Mission. Another Io flyby is planned for February 22, with flybys of Ganymede on May 30 and December 28, and joint observations of Jupiter with the Cassini spacecraft in December 2000.

The Galileo Europa Mission, a two-year extension of Galileo's primary mission, began in December 1997 and was comprised of eight flybys of Europa, four flybys of Callisto and two flybys of Io. The last flyby of Io occurred on November 25, 1999. Galileo's time at Jupiter has provided a wealth of science information about Jupiter and its many moons.

Galileo engineers like to say that the spacecraft has already lived "well past its warranty", surviving radiation exposure more than twice the level it was designed to withstand. Although the radiation has created some problems with spacecraft instruments, Galileo is still functioning well. There's no way to predict how long the spacecraft will remain healthy, but as long as it does, it provides valuable opportunities for exploration. In addition, it will serve as a flying testbed of how electronic parts really survive through high radiation exposure over long periods.

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