- A dead NASA telescope and an old US Air Force satellite have up to a 1-in-10 chance of crashing in space above Pittsburgh on Wednesday evening.
- Experts called the odds "dangerous" and "alarming," since a head-on collision could produce nearly 300,000 chunks of debris that would threaten other spacecraft.
- LeoLabs, a company that tracks satellites and space debris, calculated that the two objects could pass dangerously close to each other — as close as 12 meters, or 39 feet.
- NASA said the Air Force, which tracks satellites for the government, had not notified it of any potential collision.
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Two satellites might collide in space on Wednesday evening when their orbits cross paths 560 miles above Pittsburgh.
The larger object is an old space telescope called the Infrared Astronomical Satellite, or IRAS, a joint mission between NASA, the Netherlands, and the UK that ran out of fuel and died in November 1983. The other is a gravitational experiment called GGSE-4 that the US Air Force launched in May 1967.
The satellites will pass dangerously close to each other 25 seconds before 6:40 p.m. ET, according to LeoLabs, a company that uses radar to track satellites and debris in space.
LeoLabs calculated that the two objects could come within 12 meters, or 39 feet, of each other. The group described the data as "alarming"on Twitter.
On Wednesday morning, LeoLabs calculated a 1-in-20 chance of a collision, higher than its initial estimate of 1 in 100. The revision took into account that GGSE-4 has a 59-foot boom extending from its main body and that trackers don't know whether the boom is facing IRAS.
Experts at The Aerospace Corporation ran their own simulation on Tuesday and found a 1-in-10 chance of a crash.
Roger Thompson, a senior engineering specialist at The Aerospace Corporation, confirmed LeoLabs' other calculations, saying the satellites could come within 15 to 30 meters of each other.
"This is one of the closest that we have ever seen," Thompson told Business Insider. "LeoLabs has pointed out a very dangerous conjunction."
The US Air Force, which tracks satellites for the government, has not notified NASA of any potential satellite collision, the space agency told Business Insider in an email.
If the satellites collide, they could break apart and create a cloud of debris orbiting Earth that could threaten other satellites and the International Space Station. If such orbital junk were to get too plentiful and out of control, it could cut off our access to space for hundreds of years.
Because IRAS is quite large, a collision would be dangerous, according to both satellite-tracking companies. LeoLabs said that space telescope is 11.8 feet long and 10.5 feet wide. Both satellites are moving quickly: 14.7 kilometers per second, or 9.1 miles per second.
"Anytime you have a high-velocity collision like that it's serious, because the energy of the collision is so high that the debris gets spread into other orbits," Thompson said.
Thompson calculated that a head-on collision would produce about 290,000 chunks of debris that are at least 1 centimeter wide, the size that experts consider dangerous.
If the satellites crash, he added, observers on the ground in Pittsburgh would likely see a bright flash in the sky, like a shooting star.
While a 5% to 10% chance of a hit may seem low, NASA routinely moves the International Space Station when the orbiting laboratory faces a 0.001% (1-in-100,000) chance or greater of a collision with an object.
But these two satellites can't be controlled, Ted Muelhaupt, who leads The Aerospace Corporation's satellite system analysis, told Business Insider.
"Nobody can do a thing about this, no matter how well we're tracking it, because these are both dead objects," he said.
Thompson and Muelhaupt said the probability of a collision would probably change as the satellites continue to approach each other.
More space junk raises the risk of more dangerous collisions
Over 100 million bits of junk surround Earth, from abandoned satellites, spacecraft that broke apart, and other missions. Each piece of that debris, no matter how small, travels at speeds high enough to inflict catastrophic damage to vital equipment. A hit could kill astronauts on a spacecraft.
Each collision makes the problem worse, since it fragments satellites or debris into smaller pieces.
"Each time there's a big collision, it's a big change in the [low-Earth orbit] environment," LeoLabs CEO Dan Ceperley previously told Business Insider.
In 2007, China tested an anti-satellite missile by blowing up one of its own weather satellites. Two years later, an American spacecraft accidentally collided with a Russian one. Those two events alone increased the amount of large debris in low-Earth orbit by about 70%.
"Because of that, now there's sort of a debris belt," Ceperley said.
India also generated thousands of bits of debris last March when it blew up a spacecraft in a test of an anti-satellite missile.
If the space-junk problem gets extreme, a disastrous chain of collisions could spiral out of control and surround Earth in an impassable field of debris. This possibility is known as a Kessler event, after Donald J. Kessler, who worked for NASA's Johnson Space Center and calculated in a 1978 paper that it could take hundreds of years for such debris to clear up enough to make spaceflight safe again.
"It is a long-term effect that takes place over decades and centuries," Muelhaupt said. "Anything that makes a lot of debris is going to increase that risk."
If the two satellites collide head-on, half of the cloud of debris would shoot up away from Earth, and the other half would spread into lower orbits among other satellites and the space station, Thompson said. At first, it would be a cylinder-shaped field of debris that would be dangerous to pass through. After a few days, he said, the debris cloud would spread out.
Collisions in space are becoming more likely as more satellites fill the sky. Companies like SpaceX, Amazon, OneWeb, and perhaps even Apple plan to launch tens of thousands of satellites this decade to form internet-providing "megaconstellations."
In September, the European Space Agency had to maneuver one of its spacecraft at the last minute to avoid colliding with a SpaceX satellite. The chance of that crash was 1 in 1,000.
What's more, there is no system in place to remove older satellites like IRAS from orbit as they die.
"Events like this highlight the need for responsible, timely deorbiting of satellites for space sustainability moving forward,"LeoLabs tweeted.
Pulling dead satellites out of orbit could prevent crashes
The Federal Communications Commission, which licenses private companies' satellite launches, is considering new regulations to address the issue of space debris.
But right now there is no silver bullet for the many metal chunks rocketing around Earth, or for the swarms of dead satellites that threaten to create more debris.
One solution, however, is a cleanup mission proposed by the ESA to capture one of the agency's defunct satellites in a net, drag it into Earth's atmosphere, and burn it there. Private companies — including Tethers Unlimited, TriSept Corp., and a Boeing subsidiary called Millennium Space Systems — have explored similar concepts for larger-scale space cleanup.
Those companies could one day use LeoLabs' data to identify high-risk satellites, track them down, and pull them out of orbit to reduce the chance of space collisions creating clouds of debris.
"A lot of the risk comes from this small debris, all this stuff that's never been tracked before. Nobody's got a good solution to clean that up," Ceperley previously told Business Insider. "Let's make sure we don't make more of it."
Dave Mosher contributed reporting for this story.