North America Safe From NASA's Doomed 6.5-Ton Satellite

A dead NASA satellite will plummet to Earth will on Friday (Sept. 23), and while the U.S. space agency doesn't know exactly where pieces of the massive spacecraft will hit, one thing is certain: North America is in the clear.

NASA's Upper Atmosphere Research Satellite, or UARS, is set to make an uncontrolled re-entry into Earth's atmosphere on Friday. However, it is still too early to tell exactly where the 6.5-ton spacecraft will fall. Scientists will likely have a much better idea of where the debris will land about two hours before the impact, NASA officials said.

But, NASA was able to rule out North America as being in the potential debris drop zone. 

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"Re-entry is expected sometime during the afternoon of Sept. 23, Eastern Daylight Time," agency officials said in a statement. "The satellite will not be passing over North America during that time period. It is still too early to predict the time and location of re-entry with any more certainty, but predictions will become more refined in the next 24 to 48 hours."

In the meantime, NASA and the U.S. Air Force will be closely monitoring the satellite and its decaying orbit.

"With re-entry we're always interested in day-by-day and hour-by-hour details," Mark Matney, a scientist with NASA's Orbital Debris Program Office, told SPACE.com. "It's very difficult to predict how it's going to happen. With our models, we try to figure out what parts of the spacecraft — what materials — will interact with the atmosphere in terms of temperature and melting, and determine which of those will survive. But it's a very dynamic environment, the force is very intense." [Photos of NASA's Huge Falling Satellite UARS]

 

Wide range of possibilities

Current predictions of the potential impact zone cover a giant swath of the planet — anywhere between the latitudes of northern Canada and southern South America. Scientists will be able to refine these projections as the spacecraft makes its fiery journey through the atmosphere.

"It's partly a matter of not knowing enough," said Ray Williamson, executive director of the Secure World Foundation, an organization dedicated to the peaceful use of outer space. "The shape of the structure is not perfectly spherical, so when it heats up and starts to break up, it will break into odd pieces. Once it begins to break up, then they can get a better sense of where this is roughly going to hit."

Scientists at NASA's Orbital Debris Program Office estimate that at least 26 large pieces of the bus-size satellite will endure the scorching heat of re-entry. Approximately 1,170 pounds (532 kilograms) of material are expected to reach the ground, NASA officials said.

These pieces of debris will likely be scattered over a 500-mile (804-kilometer) long path. But agency officials have been quick to stress that there is very little chance that satellite chunks will smash intotowns or cities. [Amateur Astronomer Photographs Doomed Satellite]

Instead, it's much more likely that the debris will fall over water or remote, uninhabited areas, NASA officials said.

"There's always a concern," Matney said. "But, populated areas are a small fraction of the Earth's surface. Much of the Earth's surface has either no people or very few people. We believe that the risk is very modest."

Odds of human injury very low

For comparison, when NASA's space shuttle Columbia tragically broke apart during re-entry in 2003, debris from the 100-ton spacecraft was scattered across Texas, but did not damage any structures or injure any people.

"When [Columbia] came back, as the shuttle heated up, it broke into pieces — some of them very large, and some very small," Williamson said. "Even then, there was difficulty in trying to find the pieces that were spread over such a large area. It was such an unpopulated area that it was very difficult to locate all the pieces, even though they knew from videos pretty much precisely the track that it followed across the atmosphere."

 

NASA has calculated the odds of anyone anywhere in the world being hit by a piece of the UARS satellite at 1in3,200. But, the chance that you personally will get hit is much more remote, on the order of 1inseveral trillion, Williamson said.

Still, if anyone happens to stumble upon a piece of the defunct satellite on the ground, agency officials stress that for safety and legal reasons, it is best to leave the material where it is, and alert the authorities.

"If you find something you think may be a piece of UARS, do not touch it," NASA officials said. "Contact a local law enforcement official for assistance."

- Photos: Space Debris Images & Cleanup Concepts

- Video: Crashing Satellite's Debris Region Predicted: 500 Miles of Possibilities

- Worst Space Debris Events of All Time

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6.5-Ton Defunct Satellite Falling to Earth Faster Than Expected, NASA Says

NASA space junk experts have refined the forecast for the anticipated death plunge of a giant satellite, with the U.S. space agency now predicting the 6 1/2-ton climate probe will plummet to Earth around Sept. 23, a day earlier than previously reported.

The defunct bus-size spacecraft is NASA's Upper Atmospheric Research Satellite (UARS), which launched in 1991 and was shut down in 2005 after completing its mission. The satellite was expected to fall to Earth sometime this year, with experts initially pegging a weeks-long window between late September and early October, then narrowing it to the last week of this month.

That window, NASA now says, has been trimmed to just three days.

"Re-entry is expected Sept. 23, plus or minus a day. The re-entry of UARS is advancing because of a sharp increase in solar activity since the beginning of this week," NASA officials wrote in a status update today (Sept. 16). The projection is a day earlier than a previous forecast released by NASA yesterday.

NASA spokeswoman Beth Dickey confirmed with SPACE.com earlier today that the reason UARS is expected to fall early in its re-entry window is because of the sharp uptick in solar activity. Solar effects from the sun can create an extra drag on satellites in space because they can heat the Earth's atmosphere, causing it to expand, agency officials have said. [Photos: Space Debris & Cleanup Concepts]

Where will UARS fall?

But exactly where the UARS spacecraft will fall is still unknown.

NASA expects at least 26 large pieces of the massive satellite to survive the scorching temperatures of re-entry and reach Earth's surface. Titanium pieces and onboard tanks could be among that debris, but the UARS satellite carries no toxic propellant (NASA used up all the fuel in 2005).

The debris is expected to fall over a swath of Earth about 500 miles (804 kilometers) long, NASA officials said. [Video: Where Could UARS Satellite Debris Fall?]

There is a 1-in-3,200 chance of satellite debris hitting a person on the ground, odds that NASA says are extremely remote. Outside experts agree.

"Look at how much of Earth is covered with water," Victoria Samson, the Washington Office Director of the Secure World Foundation, an organization dedicated to the peaceful use of outer space, told SPACE.com this week. "There's a really good chance it's going to go straight into the ocean."

Constant satellite watch

NASA officials expect the UARS satellite to fall over a region somewhere between the latitudes of northern Canada and southern South America, which leaves a vast swath of the world open as a possible re-entry point. About 75 percent of the Earth's surface is covered in water, which makes an ocean splashdown likely, NASA and experts have said.

NASA and the Joint Space Operations Center of U.S. Strategic Command at Vandenberg Air Force Base, Calif., are keeping a close watch on the falling satellite, but will only be able to pinpoint its actual crash zone to within about 6,000 miles (10,000 km) about two hours before re-entry.

As of Thursday, the UARS satellite was flying in an orbit of between 143 and 158 miles (230 to 255 km) above Earth. That orbit is dropping lower each day, NASA officials said. [Infographic: NASA's Falling UARS Satellite Explained]

NASA has advised the public not to touch any debris that may reach the surface, should it be discovered. Instead, the space agency says that anyone who finds satellite debris should contact their local law enforcement agency.

The $750 million UARS mission was designed to measure ozone and other chemical compounds found in Earth's ozone layer in order to better understand how the upper atmosphere affects our planet. It also recorded wind speeds and temperatures in the stratosphere, as well as the energy Earth received from the sun.

To follow NASA's UARS satellite updates, click here.

  *   Worst Space Debris Events of All Time
  *   Fear of Ozone Loss Launched UARS Satellite
  *   Falling Space Junk: The Facts About NASA's Doomed UARS Satellite

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