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.