Image: International Space Station
Backdropped by rugged Earth terrain, the International Space Station is featured in this image photographed by an STS-130 crew member on space shuttle Endeavour after the station and shuttle began their post-undocking relative separation.
updated 9/25/2011 1:55:22 PM ET 2011-09-25T17:55:22

If a dead bus-size satellite's crash-landing can cause such a stir, global panic may well ensue when it's time for the enormous International Space Station to come down to Earth.

But that panic would be misplaced, NASA officials say. Though the orbiting lab is far larger than the space agency's defunct Upper Atmosphere Research Satellite (UARS), which made an uncontrolled re-entry through Earth's atmosphere late Friday night, the station's eventual demise will pose little threat to folks on Earth.

That's because — unlike UARS — the huge structure will be deorbited in a controlled way, with its debris shower aimed into a stretch of empty ocean. [ Complete coverage of NASA's falling satellite ]

"We've done a lot of studies," said Kirk Shireman, deputy manager of NASA's space station program. "We have found an orbit and a change in velocity that we believe is achievable, and it creates a debris footprint that’s all in water in an unpopulated area."

Guiding the station down
UARS had a mass of approximately 6.5 tons. NASA officials estimate that about 1,170 pounds of that bulk survived re-entry and smashed into Earth's surface. [ Video: Amateur Photographs Doomed, Tumbling Satellite ]

Judging by its size, the International Space Station would seem to pose a much bigger threat to folks on the ground than the UARS satellite did. The $100 billion orbiting lab is as big as a football field and tips the scales at 431 tons, so its re-entry debris shower should dwarf that of UARS.

NASA and its international partners plan to operate the space station through at least 2020, and perhaps until 2028 or so. But when the orbiting lab's time is up, managers won't just let it drift toward an uncontrolled re-entry. Rather, they'll guide the complex to a fiery death over large stretches of trackless ocean, so that any surviving pieces will not conk anybody on the head.

Image: NASA map of satellite's path
DoDʼs Joint Space Operations Center at Vandenberg AFB has assessed that NASAʼs Upper Atmosphere Research Satellite reentered the atmosphere sometime between 0323 and 0509 GMT on Sept. 24. During this period the satellite passed over Canada, the African continent, and the Pacific, Atlantic and Indian Oceans. The mid-point of that groundtrack and a possible reentry location is 31 N latitude and 219 E longitude (green circle marker on the map).

"We've been working on plans and update the plans periodically," Shireman told "We don’t want to ever be in a position where we couldn’t safely deorbit the station. It's been a part of the program from the very beginning."

The plan to deorbit the space station
Bringing the space station down is a long and involved process that will begin in earnest about one year from its planned re-entry, NASA officials have said. Around this time, managers will let the station's orbit start decaying from its normal 240-mile altitude.

They'll also dock one or more unmanned spacecraft to the station then, to get ready for future deorbit burns. The station is so massive that it'll need some help to make these maneuvers.

Officials aren't sure yet which vehicle(s) will be called into service, Shireman said. It might be a cargo craft, such as a modified Russian Progress spaceship or a European Automated Transfer Vehicle (ATV). NASA's Orion Multi-Purpose Crew Vehicle (MPCV), which is still in development, might also do the trick.

Before the station circles too low, its crew will be evacuated. When the space station gets down to about 115 miles above the Earth, engineers will perform a series of deorbit burns with the docked vehicle(s) to take it even lower, Shireman explained.

One final burn will send the gigantic structure tumbling toward Earth's atmosphere, hopefully over a wide-open stretch of ocean. [ 6 Biggest Spacecraft to Fall Uncontrolled From Space ]

"There's a nice long track from the South Pacific up off the West Coast of the United States, almost 6,000 kilometers of water," Shireman said.

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Learning from Mir and other experiments
The Russian space station Mir was deorbited purposefully back in 2001; operators ditched the 135-ton station into the South Pacific.

NASA officials watched Mir's managed re-entry carefully and learned from it, Shireman said.

NASA has also closely examined how spacecraft break up in Earth's atmosphere. For example, two robotic space station resupply craft — one European ATV and one Japanese H-2 Transfer Vehicle (HTV) — were loaded up with instruments, then studied as they made their fiery descents through the atmosphere and disintegrated.

"All those things will help us better pinpoint how [the space station] will break up and, consequently, where the debris will fall," Shireman said.

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So hopefully none of that debris will endanger anyone when the massive complex falls to Earth in 2020 or beyond. But if you happen to be on a well-placed boat in the vast Pacific when the station does come down, be sure to look up, as the descending outpost could put on quite a show for interested skywatchers.

"It would be amazing if they saw it," Shireman said. But, he added, "it would be just blind luck, because we can't predict where it's going to be and exactly when." Senior Writer Clara Moskowitz contributed to this story. You can follow senior writer Mike Wall on Twitter:@michaeldwall. Follow for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.

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Video: Coast clear from flying space ‘junk’

  1. Closed captioning of: Coast clear from flying space ‘junk’

    >>> after days of hysteria we can all rest a bit easier. a decommissioned six-ton nasa satellite plunged back to earth today. it didn't land on anyone's house or head for that matter. here's nbc's lee cowem.

    >> reporter: to climate scientists, the upper atmosphere research satellite was a hero.

    >> it was really a star of the earth observation program.

    >> reporter: but last night, after orbiting the earth nearly 80,000 times, somewhere over the remote north pacific , nasa's work horse became space junk .

    >> it's the size of a school bus , i think it was?

    >> there it is.

    >> reporter: that orange and white dot captured over san diego was all that most people saw of that school bus . a rather unflatering end for such a faithful servant. in fact, there is a lot of space debris that breaks up and falls to earth. on average there's about a piece every single day. thing it, it's got to be either very, very big or very precise to get any notoriety.

    >> sky lab fell to earth today. as far as we know, no one was hit by any of the pieces.

    >> reporter: when sky lab ended up littering an australian sheep ranch in 1979 , it was the end of what had to come a big joke john belushi style.

    >> here's john with a part of new york here. he's not worried about sky lab . no.

    >> reporter: it's not that space junk doesn't hit people. it happened to this woman while out for a walk in oklahoma back in 1977 .

    >> my first instinct was that it was something from a shooting star , which meant that maybe it might be radioactive or something, you know?

    >> reporter: but she's the only person to have that. even when a 20-pound smoldering hunk of sputnik landed in the middle of a street in wisconsin in 1962 , not a soul was harmed. so maybe chicken little was right when he warned the sky is falling. it is, we just rarely notice. lee cowan, nbc news,


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