Indistinct radio voices Indistinct radio voices, beeping Music Music, beeping Music Music, beeping Radio voice: reduction wheels still at idle, thruster duty cycle is consistent with expected values. Copy all. Calculate total burn duration. Estimated burn duration is 17 thruster seconds. Copy. Julie McEnery: I heard about the potential collision on Thursday evening. I thought 'oh, that's, that's odd, but let's not panic just yet.' And then we get an update on Friday, and it looks worse. Oh, my heart sank. So we then continued over the weekend, and it just, didn't get better. Eric Stoneking: There are all kinds of things orbiting the Earth. Obviously the active spacecraft that we're still using. But also expired spacecraft, many of them still on orbit. And then there are old parts and then real debris, down to flecks of paint. If you see a piece of debris far enough in advance, you can decide to alter your orbit to make sure that your orbit and its orbit don't intersect--that there isn't a collision. Julie: Fermi is a special kind of telescope, designed to make observations of the universe in the highest energy form of light--in gamma rays. Fermi sees gamma rays from supermassive black holes, gamma rays from the remnants of stars that have exploded at the end their life. But we also see gamma rays from flares from the sun. We get a very different picture, and thus a much deeper understanding of what you're looking at. Eric: Late March of 2012 we got a call from the Department of Defense. There was a defunct Russian satellite in an orbit that would intersect Fermi's orbit in about a week. It wasn't that they knew they were going to hit, it was that they didn't know that they weren't going to hit. So that was something we had to be concerned about. Julie: Those two spacecraft were occupying the same space within 30 milliseconds of each other. That's why this was scary. Eric: These are objects, several tons each, as wide as a small airplane, traveling 20 times faster than a bullet. The Fermi mission would be over; the spacecraft almost certainly would not survive that. The basics of the collision avoidance maneuver is we just use our thrusters to alter our orbit a slight amount just to provide a little bit of separation between ourselves and the other piece of space debris. Julie: We hadn't ever used the propulsion system before, and using something for the first time was going to be a major decision. We had to decide of the two disasters that could happen-- a collision with another satellite, or a fatal failure with the propulsion system--what decision is most defendable. And we concluded that we really needed to proceed with the burn. Radio voice: Latch valves open, line pressure rising. Copy. Eric: Normally the spacecraft is orbiting the Earth, looking at the sky, so in preparation for the maneuver, it changes its attitude, parks its solar arrays, and its high- gain antenna to be out of the way of the thrusters. The maneuver itself is just fire all thrusters for one second. And then after that's done then the spacecraft goes back to normal science. Radio voice: Primary burn complete, verified one second maneuver. Copy, maneuver complete. Julie: It was a huge relief, a huge weight off my chest. Having done the maneuver, and avoided a collision means we continue operating. So continue doing the the great science that we have been doing over the past four-and-a-half years. Music. Beeping Beeping.