1 00:00:00,000 --> 00:00:04,000 When you look at NASA's James Webb Space Telescope you can't help but 2 00:00:04,000 --> 00:00:08,000 see the huge gold mirrors. 3 00:00:08,000 --> 00:00:12,000 But that gold is really only on the surface the rest of the mirrors 4 00:00:12,000 --> 00:00:16,000 mirrors are made out of a metal called beryllium. 5 00:00:16,000 --> 00:00:20,000 Why does Webb have beryllium Mirrors. Elements of Webb 6 00:00:20,000 --> 00:00:24,000 Let's head to the shop that worked on these mirrors to get a better idea about why 7 00:00:24,000 --> 00:00:28,000 why this metal is so remarkable. 8 00:00:28,000 --> 00:00:32,000 music 9 00:00:32,000 --> 00:00:36,000 I’ll just follow the noises. 10 00:00:36,000 --> 00:00:40,000 Engineers chose beryllium for 3 major reasons. 11 00:00:40,000 --> 00:00:44,000 It is super lightweight. 12 00:00:44,000 --> 00:00:48,000 It is the second lightest of all the metals and only two thirds the weight 13 00:00:48,000 --> 00:00:52,000 aluminum. It's super strong. 14 00:00:52,000 --> 00:00:56,000 Beryllium is 6 times stiffer than steel. 15 00:00:56,000 --> 00:01:00,000 Each of these cantilevered weights are the same 16 00:01:00,000 --> 00:01:04,000 except for the type of metal. They are the same length, the same weight 17 00:01:04,000 --> 00:01:08,000 and size. Look at what happens when they are lifted 18 00:01:08,000 --> 00:01:12,000 and released at the same time. The beryllium wiggles with less intensity 19 00:01:12,000 --> 00:01:16,000 and stops moving first. That is because it is far 20 00:01:16,000 --> 00:01:20,000 stiffer than the other two. So it can also hold its shape 21 00:01:20,000 --> 00:01:24,000 over really broad range of temperatures, and that's especially important in the colds ones. 22 00:01:24,000 --> 00:01:28,000 I measured these identical aluminum and beryllium mirrors, 23 00:01:28,000 --> 00:01:32,000 and left them in some dry ice for a while. Science. 24 00:01:32,000 --> 00:01:36,000 I admit, that my measuring technique could used some work 25 00:01:36,000 --> 00:01:40,000 But the aluminum shrunk more than the beryllium. 26 00:01:40,000 --> 00:01:44,000 Materials tend to change in shape, volume, and density 27 00:01:44,000 --> 00:01:48,000 in response to temperature. When something is heated up, 28 00:01:48,000 --> 00:01:52,000 the molecules begin to vibrate more and separate, a little. The amount the material 29 00:01:52,000 --> 00:01:56,000 changes is predictable and is based on its 30 00:01:56,000 --> 00:02:00,000 coefficient of thermal expansion. So beryllium it stops shrinking and changing 31 00:02:00,000 --> 00:02:04,000 its size when it cools below 100 Kelvin. 32 00:02:04,000 --> 00:02:08,000 So the mirrors we see are a little too large on Earth 33 00:02:08,000 --> 00:02:12,000 and will be the exact size they need to be once they are out in space. 34 00:02:12,000 --> 00:02:16,000 music 35 00:02:16,000 --> 00:02:20,000 Beryllium is obviously an incredible material. 36 00:02:20,000 --> 00:02:24,000 But everything does have its nuances. 37 00:02:24,000 --> 00:02:28,000 So, why isn’t beryllium used more often? 38 00:02:28,000 --> 00:02:32,000 Machining beryllium requires extreme care. If you think about it, 39 00:02:32,000 --> 00:02:36,000 beryllium is actually a powder 40 00:02:36,000 --> 00:02:40,000 that is pressed together and requires 41 00:02:40,000 --> 00:02:44,000 very very light cuts. Any small mistake it would crack, 42 00:02:44,000 --> 00:02:48,000 and there would probably be a piece that would fall off. 43 00:02:48,000 --> 00:02:52,000 And you've lost a part that can be worth anywhere between 44 00:02:52,000 --> 00:02:56,000 between \$1,800.00 to \$2,000.00 a pound. 45 00:02:56,000 --> 00:03:00,000 Under the wrong circumstances, beryllium may be fragile, and it's fairly expensive. 46 00:03:00,000 --> 00:03:04,000 But it holds its shape well, is very stiff and most 47 00:03:04,000 --> 00:03:08,000 most importantly it's light weight. Rockets need a lot of fuel 48 00:03:08,000 --> 00:03:12,000 for each pound of payload, so any weight saving measures 49 00:03:12,000 --> 00:03:17,460 are really really worth it. 50 00:03:17,460 --> 00:03:17,461 music