WEBVTT Kind: captions Language: en 1 00:00:00.099 --> 00:00:02.429 Today’s guest video is from Amy at Vintage Space, 2 00:00:02.429 --> 00:00:05.020 who has brought along one of the greatest 3 00:00:05.020 --> 00:00:07.700 and also the tiniest props that I have ever seen 4 00:00:07.700 --> 00:00:09.470 Amy, it’s all yours. 5 00:00:09.470 --> 00:00:12.160 One of the benefits to being a professional space history nerd 6 00:00:12.160 --> 00:00:16.160 is you get to add some amazing artefacts to your private collection. 7 00:00:16.160 --> 00:00:21.080 My latest addition is this tiny piece of Kapton foil from Apollo 11. 8 00:00:21.080 --> 00:00:26.320 This tiny piece of foil went to the moon and came back through the earth’s atmosphere 9 00:00:26.320 --> 00:00:30.250 to be put on to this piece of paper, so I can hang it on my wall. 10 00:00:30.250 --> 00:00:33.760 But if you look closely at the piece, you’ll notice that it’s sort of silvery 11 00:00:33.760 --> 00:00:37.030 and it looks like it’s been scratched off and there’s gold underneath. 12 00:00:37.030 --> 00:00:39.780 So, what’s going on with this piece of foil? 13 00:00:39.780 --> 00:00:42.600 What exactly was that silvery stuff? 14 00:00:42.600 --> 00:00:46.679 And the larger question is, why does the Apollo spacecraft look white when it launches, 15 00:00:46.679 --> 00:00:47.839 silver when it’s around the moon, 16 00:00:47.839 --> 00:00:50.350 and a dirty gold once it’s come back to earth? 17 00:00:50.350 --> 00:00:54.299 Well, it’s all part of the thermal protection system. 18 00:00:54.299 --> 00:00:58.140 Thermal protection was a huge engineering challenge for the men and woman who designed 19 00:00:58.140 --> 00:01:00.160 and built the Apollo spacecraft. 20 00:01:00.160 --> 00:01:03.350 Not only was the vehicle going to be flying through the vacuum of space 21 00:01:03.350 --> 00:01:06.149 where it would be exposed to raw, unfiltered sunlight 22 00:01:06.149 --> 00:01:10.910 and also in the shadow behind the moon, where there would be no light hitting it at all: 23 00:01:10.910 --> 00:01:15.490 it also had to return through the earth’s atmosphere at lunar re-entry speeds. 24 00:01:15.490 --> 00:01:19.700 This is an insanely fast re-entry through the earth’s atmosphere. 25 00:01:19.700 --> 00:01:20.950 In the case of Apollo, 26 00:01:20.950 --> 00:01:30.810 this re-entry speed was 24,677 miles per hour or 36,194 feet per second. 27 00:01:30.810 --> 00:01:36.530 That translated to a heat during re-entry of over 4,000 degrees Fahrenheit. 28 00:01:36.530 --> 00:01:39.240 That meant the Apollo spacecraft was going to need 29 00:01:39.240 --> 00:01:41.440 a very specific thermal protection system 30 00:01:41.440 --> 00:01:44.560 to not only get the spacecraft through the earth’s atmosphere in one piece, 31 00:01:44.560 --> 00:01:47.470 but to protect the three astronauts inside it. 32 00:01:47.470 --> 00:01:51.479 The thermal protection system actually involved a number of different elements. 33 00:01:51.479 --> 00:01:53.499 First was the boost protective cover. 34 00:01:53.499 --> 00:01:56.130 This is the white covering that fits over the command module 35 00:01:56.130 --> 00:01:59.720 that you see as being white when the spacecraft has made it to its launch vehicle 36 00:01:59.720 --> 00:02:02.200 on the launch pad, ready to go to the moon. 37 00:02:02.200 --> 00:02:06.540 This protected the spacecraft from the heat associated with launching through the atmosphere, 38 00:02:06.549 --> 00:02:08.110 but it didn’t last very long. 39 00:02:08.110 --> 00:02:10.740 The boost protective cover was separated from the spacecraft 40 00:02:10.740 --> 00:02:14.720 when the launch escape tower jettisoned 200 seconds after launch. 41 00:02:14.720 --> 00:02:18.490 Once the boost protective cover was clear, the spacecraft looked silver. 42 00:02:18.490 --> 00:02:23.090 That’s because the entire Apollo command module was covered with a pressure sensitive 43 00:02:23.090 --> 00:02:24.920 Kapton polyimide tape. 44 00:02:24.920 --> 00:02:28.970 This tape was made of coded aluminium and oxidized silicon monoxide. 45 00:02:28.970 --> 00:02:32.480 The tape was applied to the entire external structure of the command module 46 00:02:32.480 --> 00:02:35.530 with the gold side down and the silver side facing out. 47 00:02:35.530 --> 00:02:36.530 That’s why, 48 00:02:36.530 --> 00:02:39.520 when you see pictures of the Apollo spacecraft in orbit around the moon, 49 00:02:39.520 --> 00:02:42.530 it looks like it’s reflecting space in a mirror. 50 00:02:42.530 --> 00:02:43.530 It’s beautiful. 51 00:02:43.530 --> 00:02:47.060 Now, when it came time for the Apollo spacecraft to re-enter the atmosphere, 52 00:02:47.060 --> 00:02:52.230 this Kapton tape wasn’t exactly enough to protect it from the searing heats of re-entry 53 00:02:52.230 --> 00:02:53.970 and it wasn’t designed to. 54 00:02:53.970 --> 00:02:54.980 The Apollo spacecraft, 55 00:02:54.980 --> 00:02:59.050 like the Mercury and Gemini vehicles before it, was a blunt body design. 56 00:02:59.050 --> 00:03:01.990 It had a rounded bottom and a conical after body, 57 00:03:01.990 --> 00:03:05.770 designed to minimize convective heating during re-entry. 58 00:03:05.770 --> 00:03:09.620 The centre of gravity in the vehicle was also offset from the axis of symmetry 59 00:03:09.620 --> 00:03:12.890 in order to generate a very small amount of lift. 60 00:03:12.890 --> 00:03:16.500 This meant that the spacecraft had a little bit of controllability during re-entry. 61 00:03:16.500 --> 00:03:20.090 So, the blunt underside of the spacecraft was taking the brunt of the heat 62 00:03:20.090 --> 00:03:23.990 and that was where the last piece of the thermal protective system was housed. 63 00:03:23.990 --> 00:03:26.520 That of course is the ablative heat shield. 64 00:03:26.520 --> 00:03:30.040 The heat shield was a honeycomb structure bonded to the stainless-steel body of the 65 00:03:30.040 --> 00:03:31.040 spacecraft 66 00:03:31.040 --> 00:03:34.870 and each little honeycomb was individually filled with an ablative material 67 00:03:34.870 --> 00:03:36.830 that would burn away as it was heated 68 00:03:36.830 --> 00:03:40.510 thus protecting the spacecraft from the worst of heat of re-entry. 69 00:03:40.510 --> 00:03:44.960 But, the heat shield and the bow shock generated by that blunt body of re-entry 70 00:03:44.960 --> 00:03:49.140 couldn’t entirely protect the outer structure of the spacecraft. 71 00:03:49.140 --> 00:03:54.520 As it went through that fireball phase of re-entry the Kapton was burned away a little bit, 72 00:03:54.520 --> 00:03:57.840 revealing the golden underside of the tape. 73 00:03:57.850 --> 00:04:01.900 But how is it that I’m able to actually own a piece of the Apollo 11 spacecraft? 74 00:04:01.900 --> 00:04:05.380 Well, it turns out that recovery crews and pretty much anybody 75 00:04:05.380 --> 00:04:07.970 who could get within arm’s reach of the spacecraft, 76 00:04:07.970 --> 00:04:10.030 and this doesn’t just go for Apollo 11, 77 00:04:10.030 --> 00:04:12.640 this applies to all the vehicles that went to the moon, 78 00:04:12.640 --> 00:04:16.660 they would reach up and just take off a tiny piece of that foil as a souvenir. 79 00:04:16.660 --> 00:04:22.520 So, even if at first glance it looks like a tiny insignificant dime-sized portion of foil, 80 00:04:22.520 --> 00:04:27.060 it’s actually amazing to think that that little dime-sized piece of foil 81 00:04:27.070 --> 00:04:30.470 helped to protect the Apollo 11 astronauts on the way to the moon 82 00:04:30.470 --> 00:04:33.819 and their re-entry back through the earth’s atmosphere. 83 00:04:33.819 --> 00:04:36.860 Go subscribe to Amy’s channel for all sorts of videos about space flight! 84 00:04:36.860 --> 00:04:41.460 I would recommend starting with her one on how the Saturn V got to the launch pad. 85 00:04:41.460 --> 00:04:45.190 Next time, we have a video about linguistics and music all in one.