WEBVTT FILE 1 00:00:00.010 --> 00:00:04.030 Indistinct radio voices 2 00:00:04.050 --> 00:00:08.110 Indistinct radio voices, beeping 3 00:00:08.130 --> 00:00:12.140 Music 4 00:00:12.160 --> 00:00:16.180 Music, beeping 5 00:00:16.200 --> 00:00:20.320 Music 6 00:00:20.340 --> 00:00:24.350 Music, beeping 7 00:00:24.370 --> 00:00:28.440 Radio voice: reduction wheels still at idle, thruster duty cycle is 8 00:00:28.460 --> 00:00:32.460 consistent with expected values. Copy all. Calculate total burn duration. 9 00:00:32.480 --> 00:00:36.520 Estimated burn duration is 17 thruster seconds. 10 00:00:36.540 --> 00:00:40.670 Copy. Julie McEnery: I heard about the potential collision on Thursday 11 00:00:40.690 --> 00:00:44.720 evening. I thought 'oh, that's, that's odd, 12 00:00:44.740 --> 00:00:48.790 but let's not panic just yet.' And then we get an update on Friday, 13 00:00:48.810 --> 00:00:52.890 and it looks worse. Oh, my heart sank. 14 00:00:52.910 --> 00:00:56.920 So we then continued over the weekend, and it just, 15 00:00:56.940 --> 00:01:00.950 didn't get better. Eric Stoneking: There are all kinds 16 00:01:00.970 --> 00:01:05.060 of things orbiting the Earth. Obviously the active spacecraft that we're still 17 00:01:05.080 --> 00:01:09.080 using. But also expired spacecraft, many of them still 18 00:01:09.100 --> 00:01:13.120 on orbit. And then there are old parts 19 00:01:13.140 --> 00:01:17.170 and then real debris, down to flecks of paint. 20 00:01:17.190 --> 00:01:21.270 If you see a piece of debris far enough in advance, 21 00:01:21.290 --> 00:01:25.300 you can decide to alter your orbit to make sure that 22 00:01:25.320 --> 00:01:29.360 your orbit and its orbit don't intersect--that there isn't a collision. 23 00:01:29.380 --> 00:01:33.380 Julie: Fermi is a special kind of telescope, designed 24 00:01:33.400 --> 00:01:37.450 to make observations of the universe in the highest energy form of light--in gamma 25 00:01:37.470 --> 00:01:41.470 rays. Fermi sees gamma rays from supermassive black holes, 26 00:01:41.490 --> 00:01:45.510 gamma rays from the remnants of stars that have exploded at the end their 27 00:01:45.530 --> 00:01:49.630 life. But we also see gamma rays from flares from the sun. 28 00:01:49.650 --> 00:01:53.660 We get a very different picture, and thus a much deeper understanding of what you're 29 00:01:53.680 --> 00:01:57.750 looking at. Eric: Late March of 2012 we got a call 30 00:01:57.770 --> 00:02:01.820 from the Department of Defense. There was a defunct Russian 31 00:02:01.840 --> 00:02:05.970 satellite in an orbit that would intersect Fermi's orbit in about a week. 32 00:02:05.990 --> 00:02:10.000 It wasn't that they knew they were going to hit, it was that they didn't know that they weren't 33 00:02:10.020 --> 00:02:14.030 going to hit. So that was something we had to be concerned about. Julie: Those two spacecraft 34 00:02:14.050 --> 00:02:18.080 were occupying the same space within 30 milliseconds of each other. 35 00:02:18.100 --> 00:02:22.160 That's why this was scary. Eric: These are objects, several tons 36 00:02:22.180 --> 00:02:26.190 each, as wide as a small airplane, traveling 20 37 00:02:26.210 --> 00:02:30.230 times faster than a bullet. The Fermi mission would be over; the spacecraft 38 00:02:30.250 --> 00:02:34.290 almost certainly would not survive that. The basics 39 00:02:34.310 --> 00:02:38.370 of the collision avoidance maneuver is we just use our thrusters 40 00:02:38.390 --> 00:02:42.380 to alter our orbit a slight amount just to provide a little bit of 41 00:02:42.400 --> 00:02:46.440 separation between ourselves and the other piece of space debris. 42 00:02:46.460 --> 00:02:50.450 Julie: We hadn't ever used the propulsion system before, 43 00:02:50.470 --> 00:02:54.500 and using something for the first time was going 44 00:02:54.520 --> 00:02:58.620 to be a major decision. We had to decide 45 00:02:58.640 --> 00:03:02.640 of the two disasters that could happen-- 46 00:03:02.660 --> 00:03:06.800 a collision with another satellite, or a fatal failure 47 00:03:06.820 --> 00:03:10.830 with the propulsion system--what decision is most defendable. And we concluded 48 00:03:10.850 --> 00:03:14.930 that we really needed to proceed with the burn. Radio voice: Latch valves 49 00:03:14.950 --> 00:03:18.970 open, line pressure rising. Copy. Eric: Normally the 50 00:03:18.990 --> 00:03:22.990 spacecraft is orbiting the Earth, looking at the sky, so 51 00:03:23.010 --> 00:03:27.040 in preparation for the maneuver, it changes its 52 00:03:27.060 --> 00:03:31.100 attitude, parks its solar arrays, and its high- 53 00:03:31.120 --> 00:03:35.130 gain antenna to be out of the way of the thrusters. The maneuver itself is just 54 00:03:35.150 --> 00:03:39.210 fire all thrusters for one second. And then after that's done 55 00:03:39.230 --> 00:03:43.260 then the spacecraft goes back to normal science. Radio voice: Primary burn complete, verified one second maneuver. 56 00:03:43.280 --> 00:03:47.290 Copy, maneuver complete. Julie: It was 57 00:03:47.310 --> 00:03:51.380 a huge relief, a huge weight off my 58 00:03:51.400 --> 00:03:55.390 chest. Having done the maneuver, and avoided a 59 00:03:55.410 --> 00:03:59.510 collision means we continue operating. So continue doing the the great 60 00:03:59.530 --> 00:04:03.530 science that we have been doing over the past four-and-a-half years. 61 00:04:03.550 --> 00:04:07.560 Music. Beeping 62 00:04:07.580 --> 00:04:19.139 Beeping.