SPACE.com -- NASA Spacecraft Expected to Fall to Earth This Week

Entire celestial sky, as it appears in the extreme ultraviolet and created by combining multiple EUVE scans. Click to enlarge.

Scientists Fail to Save Ultraviolet Explorer Spacecraft

NASA to Pull Plug On Astronomy Satellite


	NASA Spacecraft Expected to Fall to Earth This Week *By SPACE.com* Staff** posted: 03:00 pm ET 29 January 2002

CAPE CANAVERAL, Fla. -- Heads up, another orbiting satellite is about to fall from the sky.

This time it's NASA's Extreme Ultraviolet Explorer (EUVE) spacecraft that prompted the space agency Tuesday to issue a "Chicken Little" alert as the 7,000-pound (3,175-kilogram) telescope is expected to re-enter Earth's atmosphere between 10 p.m. EST Wednesday and 7 a.m. EST Thursday (0300 and 1200 GMT Thursday).

Launched atop a Boeing Delta 2 rocket from Cape Canaveral in 1992, the satellite's orbit on Tuesday was said to be 124 miles (200 kilometers) high and decaying about 15.5 miles (25 kilometers) each day. By Thursday night it is expected to be broken up into small pieces and likely laying at the bottom of an ocean.

"The probability of the few EUVE surviving pieces falling into a populated area and hurting someone is very small. It is more likely that the small pieces will fall into the ocean or fall harmlessly to the ground," said Ronald Mahmot, a NASA project manager Goddard Space Flight Center in Greenbelt, Md.

Engineers predict that whatever does survive the fiery plunge through the atmosphere will be scattered along a debris field that is between 500 to 625 miles (800 to 1,000 kilometers) long. Estimates show that up to nine objects made of titanium and stainless steel -- ranging in weight from about four to 100 pounds (1.8 to 45 kilograms) -- may survive re-entry.

Satellite re-entries are fairly common and despite the "sky is falling" reaction such events trigger in some people, the fact is that no human has ever been harmed by space debris, but part of the U.S. space station Skylab reportedly killed a cow in Australia when it fell to Earth in 1979.

Massive spacecraft such as the Mir space station and the Compton Gamma Ray Observatory have been steered during their final orbits to help avoid striking civilization, but the much smaller EUVE does not have an on-board propulsion system to allow engineers to control its re-entry.

According to a NASA statement, EUVE will start to break up when it falls to within 50 miles (80 kilometers) of Earth. At this point, EUVE will have only four or five 90-minute orbits left before re-entering the Earth's atmosphere. Engineers will not know the re-entry point until approximately 12 hours prior to impact.

EUVE is in an orbit that could re-enter over any location between 28.5 degrees north latitude and 28.5 degrees south latitude. This ranges includes areas as far north as Orlando, Fla., and as far south as Brisbane, Australia.

Designed to last about three years, the spacecraft remained operational for eight years, prompting NASA to twice extend EUVE's scientific mission, which was to observe nearby sources of extreme ultraviolet radation.

Rather than seeing about 24 nearby objects as many scientists predicted, EUVE observed more than 1,000 nearby sources, including more than three dozen objects outside the Milky Way galaxy.