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.