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disabled

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is

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thursday evening i thought oh that's

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that's odd

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um

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but let's not panic just yet and then we

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got an update on friday

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and it looks worse

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oh my heart sank

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um

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and it just you know didn't get better

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there are all kinds of things orbiting

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the earth

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obviously the active spacecraft that

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we're still using but also

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expired spacecraft many of them still on

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orbit and then there are

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old parts and then real debris down to

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flecks of paint

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if you see

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a piece of debris far enough in advance

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you can decide to alter your orbit to

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make sure that your orbit and its orbit

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don't intersect that there isn't a

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collision

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fermi is a special kind of telescope

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designed to make observations of the

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universe in the highest energy form of

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light in gamma rays

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fermi sees gamma rays from supermassive

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black holes gamma rays from the remnants

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of stars that exploded at the end of

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their life but we also see gamma rays

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from flares from the sun

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we get a very different picture and thus

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a much deeper understanding of what

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you're looking at

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late march of 2012

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we got a call from the department of

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defense

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there was a defunct russian satellite in

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an orbit that would intersect fermi's

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orbit in about a week it isn't that they

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knew they were going to hit it was that

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they didn't know that they weren't going

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to hit so that's something we had to be

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concerned about

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those two spacecraft were occupying the

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same space within 30 milliseconds of

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each other that's why this was scary

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these are objects several tons each as

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wide as a small airplane traveling 20

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times faster than a bullet the fermi

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mission would be over the spacecraft

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almost certainly would not survive that

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the basics of the collision avoidance

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maneuver is we just use our thrusters to

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alter orbit slight amount just to

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provide a little bit of separation

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between ourselves and the other piece of

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we hadn't ever used the propulsion

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system before

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and using something for the first time

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was going to be a major decision

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we had to decide

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of the two disasters that could happen

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the collision with another satellite

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or a fatal failure with a propulsion

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system what decision is most defendable

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and we concluded that we really needed

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to proceed with the burn

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latch valves open brine pressure rising

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normally the the spacecraft is

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orbiting the earth looking at the sky

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so

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in preparation for the maneuver it

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changes its attitude

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parks its solar arrays

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and its high gain antenna to be out of

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the way of the thrusters the the

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maneuver itself is just fire all

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thrusters for one second

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and then after that's done then the

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spacecraft goes back to normal science

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one second maneuver

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copy

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maneuver complete

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it was a huge relief a huge

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weight off my of my chest

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having done the maneuver and avoided a

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collision means we continue operating so

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continue doing the great science that we