In the end, the Galileo spacecraft will get a taste of
Jupiter before taking a final plunge into the planet’s
crushing atmosphere, ending the mission on Sunday, Sept. 21.
The team expects the spacecraft to transmit a few hours of
science data in real time leading up to impact.
The spacecraft has been purposely put on a collision course
with Jupiter to eliminate any chance of an unwanted impact
between the spacecraft and Jupiter’s moon Europa, which
Galileo discovered is likely to have a subsurface ocean. The
long-planned impact is necessary now that the onboard
propellant is nearly depleted.
Without propellant, the spacecraft would not be able to point
its antenna toward Earth or adjust its trajectory, so
controlling the spacecraft would no longer be possible.
“It has been a fabulous mission for planetary science, and it
is hard to see it come to an end,” said Dr. Claudia
Alexander, Galileo project manager at NASA’s Jet Propulsion
Laboratory, Pasadena, Calif. “After traversing almost 3
billion miles and being our watchful eyes and ears around
Jupiter, we’re keeping our fingers crossed that, even in its
final hour, Galileo will still give us new information about
Jupiter’s environment.”
Although scientists are hopeful to get every bit of data back
for analysis, the likelihood of getting anything is unknown
because the spacecraft has already endured more than four
times the cumulative dose of harmful jovian radiation it was
designed to withstand. The spacecraft will enter an
especially high-radiation region again as it approaches
Jupiter.
Launched in the cargo bay of Space Shuttle Atlantis in 1989,
the mission has produced a string of discoveries while
circling the solar system’s largest planet, Jupiter, 34
times. Galileo was the first mission to measure Jupiter’s
atmosphere directly with a descent probe and the first to
conduct long-term observations of the jovian system from
orbit.
It found evidence of subsurface liquid layers of salt water
on Europa, Ganymede and Callisto and it examined a diversity
of volcanic activity on Io. Galileo is the first spacecraft
to fly by an asteroid and the first to discover a moon of an
asteroid.
The prime mission ended six years ago, after two years of
orbiting Jupiter. NASA extended the mission three times to
continue taking advantage of Galileo’s unique capabilities
for accomplishing valuable science. The mission was possible
because it drew its power from two long-lasting radioisotope
thermoelectric generators provided by the Department of
Energy.
From launch to impact, the spacecraft has traveled
4,631,778,000 kilometers (about 2.8 billion miles).
Its entry point into the giant planet’s atmosphere is about
1/4 degree south of Jupiter’s equator. If there were
observers floating along at the cloud tops, they would see
Galileo streaming in from a point about 22 degrees above the
local horizon. Streaming in could also be described as
screaming in, as the speed of the craft relative to those
observers would be 48.2 kilometers per second (nearly 108,000
miles per hour). That is the equivalent of traveling from Los
Angeles to New York City in 82 seconds. In comparison, the
Galileo atmospheric probe, aerodynamically designed to slow
down when entering, and parachute gently through the clouds,
first reached the atmosphere at a slightly more modest 47.6
kilometers per second (106,500 miles per hour).
“This is a very exciting time for us as we draw to a close on
this historic mission and look back at its science
discoveries. Galileo taught us so much about Jupiter but
there is still much to be learned, and for that we look with
promise to future missions,” said Dr. Charles Elachi,
director of JPL.
JPL, a division of the California Institute of Technology in
Pasadena, manages the Galileo mission for NASA’s Office of
Space Science, Washington.
Additional information about the Galileo mission and its
discoveries is available online at:
http://galileo.jpl.nasa.gov
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