LOS ANGELES -- The Galileo spacecraft, which on Thursday began its final fly-by past one of Jupiter's four major moons, was unable to collect data after mistakenly shutting down on-board computers, U.S. space scientists said.

Eileen Theilig, project manager at NASA's jet propulsion laboratory in Pasadena said Galileo, which has been orbiting Jupiter since 1995, had placed itself into "standby mode" while approaching the giant gas planet's volcano-studded moon Io.

Theilig is quoted by Reuters as saying Galileo's flight team was sending commands to the 6,000-pound (2,223 kg) spacecraft in hopes that it would switch the computers back on in time for the rest of the Io fly-by.

"We're not totally surprised because Galileo has already outlived expectations and we knew that it might encounter additional difficulties from the high-radiation environment on this fly-by," she said.

"Galileo has already lasted more than four years past its original mission and has survived three-and-a-half times the radiation it was designed to withstand so it's not unexpected that this fly-by would be interrupted by a problem," she said.

Galileo, which was launched in October of 1989 from the Kennedy Space Center in Florida, was making its sixth and final pass of Io before scientists crash it into Jupiter to end the craft's mission.

The spacecraft was expected to fly just 62 miles (100 km) above the surface of Io, giving scientists a last look at the Jovian moon's volatile surface, before it exhausts its supply of propellant.

Scientists will then send Galileo plunging into the heart of Jupiter, where it will be crushed in a planned death by the planet's enormous atmospheric pressure.

Galileo's mission will end with the death plunge to avoid the slim chance that the craft could go out of control and crash into the Moon Europa, which it has found to contain a deep ocean of melted seawater under a frozen surface.

Scientists, who are eager to explore Europa for possible signs of past or present life, want to keep the moon pristine.

Scientists say Io, the innermost of Jupiter's four large moons, is the most volcanically active world in our solar system, thanks to heat from Jupiter's gravitational pull.