NASA's Fermi telescope dodges a 3,100-pound bullet

Evasive actions had to be taken to ensure the spacecraft wouldn't end in a massive collision high above Earth.

An artist's rendering of the Fermi telescope in orbit. Screenshot by Eric Mack/CNET

The near miss that happened with a high-tech telescope orbiting the Earth last month was so dramatic that I have to assume Hollywood thrill makers will soon be calling up NASA project scientist Julie McEnery to get all the details and begin determining how feasible it is to jam Ben Affleck or Morgan Freeman into the story line.

McEnery works with NASA's Fermi Gamma-ray Space Telescope, which has the mission of mapping the highest-energy light in the universe. On March 29, McEnery learned that Fermi and a dead Russian spy satellite, Cosmos 1805, were speeding toward the same point in space on nearly perpendicular orbits. They would miss being in that same place at the same time by only 30 milliseconds, likely passing within about 700 feet of each other.

"My immediate reaction was, 'Whoa, this is different from anything we've seen before!'" McEnery recalled in NASA's official account of the story.

McEnery first received warning of Fermi's expected visitor only a week beforehand. A collision with the 3,100-pound Cosmos 1805 would release as much energy as two and a half tons of high explosives and destroy both satellites. Is that you calling, Mr. Bruckheimer?

NASA's rendition of the original courses of the two spacecraft. Screenshot by Eric Mack/CNET

Now, 700 feet might seem like plenty of clearance for an old piece of Russian space junk to pass by and simply wave at Fermi rather than going for the potentially disastrous high-five. But when you're a space telescope traveling at 27,000 miles per hour, you can obviously cover a lot of ground in 30 milliseconds, and predicting the paths of wayward satellites is not always as precise as such high speeds demand.

Four years ago, another dead Russian satellite was forecast to pass within 1,900 feet of the functioning Iridium 33 communications satellite. Nothing has been heard from Iridium 33 since the predicted time of closest approach. Clouds of debris on radar soon confirmed the first known collision between two satellites.

"It was clear we had to be ready to move Fermi out of the way, and that's when I alerted our Flight Dynamics Team that we were planning a maneuver," McEnery said.

The only tool at the Fermi team's disposal were thrusters designed for use at the end of the satellite's life to take it out of orbit -- and the way of other satellites, ironically -- to burn up in the atmosphere. Adding to the high stakes was the fact that those thrusters had never been tested, because a malfunction like a propellant leak or explosion could prematurely end Fermi's mission.

On Tuesday, April 3, the threat of collision remained. It was time to perform an evasive maneuver and fire the thrusters.

Fermi paused its scanning of the heavens and shifted into a defensive position to protect its antenna from the impending exhaust.

Then Fermi fired all its thrusters for just one second.

That was all it took. You can cover a lot of ground at 27,000 miles per hour, but at that speed you can also greatly alter a trajectory by side-stepping just a little bit of ground, or space, rather. Fermi would now miss Cosmos 1805 by a comfortable margin of 6 miles.

"A huge weight was lifted," McEnery said. "I felt like I'd lost 20 pounds."

And it was all accomplished without having to send a single super-attractive hero type into space to save the world. Sorry, Hollywood, maybe this story of another quiet victory for the nerds behind the screens isn't for you after all -- unless that dude with the mohawk was involved.

Meanwhile, you can check out this short film that NASA produced about Fermi's saga:

 

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