NASAs Compton Gamma-Ray Observatory did just that on June 4, when the biggest spacecraft to fall from orbit since Skylab broke up over the South Pacific.

The fall from grace, orchestrated by nervous NASA officials, ended the spacecrafts nine-year mission to study everything from quasars to gamma-ray bursts. A last-ditch effort to save Compton came to naught.

NASA opted to yank Compton from orbit after one of its three onboard gyroscopes failed. Were a second, much less a third, gyroscope to have failed, NASA feared it could lose control of the 17-ton (15,422-kilogram) Compton.

That raised the specter of a repeat of Skylab, which made an uncontrolled fall to Earth in July 1979, raining down on Australia bits of wreckage that are still being sold as souvenirs to this day.

Rather than leave things to chance this time around, NASA brought down Compton in a series of four burns designed to lower it from its orbital roost roughly 315 miles (500 kilometers) above the Earth.

An estimated 6 tons (5,400 kilograms) of the spacecraft eventually hit the Earth, splashing harmlessly into the South Pacific well southeast of Hawaii. NASA had pegged the probability of any portion of the satellite striking and killing someone at one in 29 million. Russias Mir space station will enter a watery grave in the same region come February.

Compton was one of NASAs four Great Observatories and the second of the group to be launched, after the Hubble Space Telescope in 1990. In 1999, the Chandra X-ray Observatory joined the two.

In 2002, NASA hopes to launch the fourth satellite of the series, the Space Infrared Telescope Facility, or SIRTF. Together, the four cover a wide swath of the electromagnetic spectrum.

During its time in space, the $670-million Compton named for Nobel Prize-winning physicist Arthur Holly Compton orbited the Earth nearly 52,000 times. It was deployed in orbit by the shuttle Atlantis in April 1991.

-- Andrew Bridges, Pasadena Bureau Chief