A dead NASA space telescope and an old Air Force satellite have a 1-in-10 chance of colliding over Pittsburgh on Wednesday, and people on the ground may see it

• A dead NASA telescope and an old Air Force satellite have a 1-in-10 chance of crashing in space above Pittsburgh, Pennsylvania, on Wednesday evening.
• Experts call 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 will pass dangerously close to one another ⁠- as close as 15 meters (50 feet) apart.
• The US Air Force, which tracks satellites for the government, has not notified NASA of any potential collision, according to the space agency.
• Visit Business Insider's homepage for more stories.

Two satellites might collide in space on Wednesday evening, when their orbits cross paths 560 miles (900 kilometers) above Pittsburgh, Pennsylvania.

The larger object is an old NASA telescope called the Infrared Astronomical Satellite (IRAS), which 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 just 25 seconds before 6:40 p.m. ET on Wednesday, according to LeoLabs, a company that uses radar to track satellites and debris in space.

LeoLabs calculated that the two objects will come within 15 to 30 meters (50 to 100 feet) of one another, a distance the group called "alarming" on Twitter.

LeoLabs calculated a 1-in-100 chance of collision, but experts at The Aerospace Corporation ran their own simulation on Tuesday and found a 1-in-10 chance. Roger Thompson, a senior engineering specialist at The Aerospace Corporation, confirmed LeoLabs's other calculations.

"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, had not notified NASA of any potential satellite collision as of Tuesday morning, the space agency told Business Insider in an email.

If the satellites collide, they could break apart and create a new cloud of debris orbiting Earth, which could then threaten other satellites and the International Space Station. If such orbital junk were ever 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 3.6 meters (11.8 feet) long and 3.2 meters (10.5 feet) wide. Both satellites are moving quickly: 14.7 kilometers (9.1 miles) per second.

"Any time 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.

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 - Thompson calculated.

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 1% 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 will probably change as the satellites approach each other, so that researchers may have more precise estimates late Wednesday morning.

More space junk raises the risk of more dangerous collisions

Over 100 million of 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 single hit could be deadly to astronauts on a spacecraft.

Each collision that occurs 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 LEO [low-Earth orbit] environment," LeoLabs CEO Dan Ceperley previously told Business Insider.

In 2009, an American spacecraft accidentally collided with a Russian one, increasing 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 in March 2019 when it blew up one of its spacecraft in an anti-satellite missile test.

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. Kessler 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," Thompson said. "Anything that makes a lot of debris is going to increase that risk."

If the two satellites collide head-on Wednesday evening, 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 new satellites this decade to form internet-providing "megaconstellations."

In September, the European Space Agency (ESA) 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, as older satellites like IRAS die, there is no system in place to remove them from orbit.

"Events like this highlight the need for responsible, timely deorbiting of satellites for space sustainability moving forward," LeoLabs tweeted about Wednesday's potential crash.

Pulling dead satellites out of orbit could prevent crashes

The Federal Communications Commission (FCC), which licenses private companies' satellite launches, is considering new regulations to address the issue of space debris.

But as of yet, there is no silver bullet for the many metal chunks rocketing around Earth, nor for the swarms of dead satellites that threaten to create more debris.

One potential solution, however, is a proposed ESA clean-up mission that aims 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 clean-up.

Those companies could one day use LeoLabs's data to identify high-risk satellites, track them down, and pull them out of orbit to reduce the chances of space collisions and the clouds of debris that they create.

"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.