LOS ANGELES -- NASA's Galileo spacecraft was set to make its last flyby of one of Jupiter's moons early today, marking the likely end of the science-gathering part of its 13-year mission.
Galileo was on course to fly within 99 miles of Amalthea, a brilliant red, egg-shaped moon, at 12:19 a.m. Engineers estimated Galileo would streak past 168-mile-wide Amalthea at 41,160 mph.
About an hour later, the spacecraft was to make its closest approach to Jupiter during the 34 orbits it has made of the giant planet since 1995. It was to pass within 44,500 miles of the tops of the brilliant clouds that shroud the planet.
Intense radiation from Jupiter's environment was likely to cause glitches aboard the aging Galileo during the flyby, blasting the craft with several hundred times the amount that would be lethal to humans.
Flight controllers at NASA's Jet Propulsion Laboratory do not expect to learn how well Galileo fared until later today, said Eilene Theilig, Galileo project manager at JPL.
During the flyby, Galileo's instruments were to measure Amalthea's gravitational tug, allowing scientists to calculate the moon's mass and density and provide important clues about its composition.
"We know what Amalthea looks like, but we don't know what it's made of," said Galileo project scientist Torrence Johnson.
Galileo also was to measure the radiation surrounding Jupiter and use detectors to examine the size and movement of dust particles in the planet's gossamer ring. No picture-taking was planned.
The measurements will likely be the last Galileo makes before it slams into Jupiter in September 2003, at the conclusion of its 35th and last orbit of the planet.
"We know it's our final shot and it's nice to be able to do new and unique science on this final passage through the Jupiter system," Theilig said.
Galileo has made more than 30 flybys of other Jovian moons, including Europa and Io, but never Amalthea. Galileo was launched in 1989 and arrived at Jupiter in December 1995.