WEBVTT FILE 1 00:00:00.000 --> 00:00:02.700 [music] 2 00:00:02.700 --> 00:00:03.633 Following MOLA, 3 00:00:03.633 --> 00:00:06.633 in some ways, we were in demand to consider 4 00:00:06.633 --> 00:00:11.066 whether we could provide a laser altimeter to another mission. 5 00:00:11.400 --> 00:00:13.266 A few missions, actually. 6 00:00:13.266 --> 00:00:16.700 It was no longer a question of if lidar could work, 7 00:00:16.700 --> 00:00:19.366 but where else it could work? 8 00:00:19.366 --> 00:00:23.033 But as the opportunities to test the limits of lidar arose, 9 00:00:23.033 --> 00:00:24.866 so did the challenges ahead. 10 00:00:24.900 --> 00:00:33.000 [music] 11 00:00:33.000 --> 00:00:37.033 The Goddard team quickly began to see the evolution of lidar missions, 12 00:00:37.033 --> 00:00:41.233 building on the successes of new frontiers mapped by MOLA. 13 00:00:41.233 --> 00:00:44.133 We've measured the changes, the seasonal changes 14 00:00:44.133 --> 00:00:45.800 in the Mars icecaps, 15 00:00:45.800 --> 00:00:47.866 both the North Pole and South Pole. 16 00:00:48.200 --> 00:00:49.400 We've measured the volumes. 17 00:00:49.400 --> 00:00:51.700 We've measured the mass that's involved in it. 18 00:00:51.700 --> 00:00:53.033 We now have a density. 19 00:00:53.033 --> 00:00:55.833 So now we know the kind of processes that-- 20 00:00:55.833 --> 00:00:57.366 Dave Smith invited me 21 00:00:57.366 --> 00:01:01.266 to be on the MOLA Altimetry Science Team. 22 00:01:01.766 --> 00:01:05.366 And that was because of my experience with using 23 00:01:05.900 --> 00:01:07.466 altimetry over 24 00:01:07.466 --> 00:01:10.466 land rather than ocean processes. 25 00:01:10.600 --> 00:01:15.300 Zwally was an obvious choice to study the Martian ice caps for MOLA, 26 00:01:15.300 --> 00:01:19.200 given his decades of expertise with our own polar regions 27 00:01:19.200 --> 00:01:24.500 studying the ice sheets of Greenland and Antarctica through the 1970s and 80s. 28 00:01:24.500 --> 00:01:27.533 And then as we went into the eighties, 29 00:01:27.533 --> 00:01:29.933 NASA was sort of the beginning 30 00:01:29.933 --> 00:01:32.833 of the development of the Earth Observations Program. 31 00:01:33.000 --> 00:01:36.900 So the Earth Observing System, I think, will be the first effort 32 00:01:36.900 --> 00:01:39.900 targeted at looking at the whole Earth system 33 00:01:39.900 --> 00:01:41.266 as a system, 34 00:01:41.466 --> 00:01:44.600 rather than just the little components that make it up. 35 00:01:44.933 --> 00:01:49.400 Somewhere along then I teamed up with Jim Abshire. 36 00:01:49.633 --> 00:01:53.766 Jay had been pushing for a long time for a dedicated ice 37 00:01:53.766 --> 00:01:57.266 altimetry mission, which turned into ICESat-1. 38 00:01:57.466 --> 00:02:00.333 Designing ICESat-1 marked a major leap 39 00:02:00.333 --> 00:02:04.266 in what lidar needed to do and how challenging it would be to do it. 40 00:02:04.400 --> 00:02:08.900 To measure the changing ice sheets, the lidar had to be far more precise, 41 00:02:08.900 --> 00:02:12.733 cover the same tracks season to season, and it needed more power 42 00:02:12.733 --> 00:02:14.900 and a larger instrument, 43 00:02:14.900 --> 00:02:17.100 which meant much more time to build. 44 00:02:17.633 --> 00:02:20.166 We built a simulator for ICESat-1 45 00:02:20.166 --> 00:02:22.066 that allowed us to sort of 46 00:02:22.066 --> 00:02:23.966 figure out how precise it could be, 47 00:02:23.966 --> 00:02:27.000 how we would process the waveform data coming back, 48 00:02:27.000 --> 00:02:28.600 how we would track the surface. 49 00:02:28.600 --> 00:02:30.300 This algorithm 50 00:02:30.300 --> 00:02:32.033 was much more complicated 51 00:02:32.033 --> 00:02:34.300 than anything I had ever worked on before. 52 00:02:34.500 --> 00:02:38.300 But all this meant essentially for for the ICESat mission, 53 00:02:38.300 --> 00:02:42.466 you needed a much more advanced version of MOLA. 54 00:02:43.000 --> 00:02:43.700 On Mars, 55 00:02:43.700 --> 00:02:47.500 we really didn't know what was there until we got the measurements. 56 00:02:47.500 --> 00:02:49.200 So we were doing discovery. 57 00:02:49.200 --> 00:02:52.600 On Earth, we have to make quantitative measurements about what's happening. 58 00:02:52.933 --> 00:02:56.466 Four, three, two, one, 59 00:02:57.600 --> 00:02:59.666 and we have ignition and liftoff 60 00:02:59.666 --> 00:03:04.433 for NASA's ICESat and CHIPSat spacecraft looking at stars and ice. 61 00:03:05.100 --> 00:03:07.200 But after we'd worked on GLAS 62 00:03:07.200 --> 00:03:09.466 at that point, more than a decade, 63 00:03:09.466 --> 00:03:10.600 and it had already launched, 64 00:03:10.600 --> 00:03:12.666 and usually it's like, okay, now we're going to be able 65 00:03:12.666 --> 00:03:14.633 to enjoy the data coming down, 66 00:03:14.633 --> 00:03:16.366 and what can we see in the data? 67 00:03:17.100 --> 00:03:20.566 But there was much more, what is this mystery we're seeing? 68 00:03:20.566 --> 00:03:22.600 Why is the laser energy going down? 69 00:03:22.833 --> 00:03:26.233 Things were not working the way we expected them to, 70 00:03:26.233 --> 00:03:28.700 and there were mysteries, and we weren't expecting-- 71 00:03:28.700 --> 00:03:31.800 after MOLA particularly-- to have mysteries at that point. 72 00:03:31.800 --> 00:03:35.533 One of these unexpected mysteries came down to the wire. 73 00:03:35.533 --> 00:03:37.600 Several wires actually. 74 00:03:37.600 --> 00:03:39.900 What happened on GLAS was the laser diodes 75 00:03:39.900 --> 00:03:44.000 had gold bond wires and indium solder. 76 00:03:44.066 --> 00:03:45.533 If you bring these two metals together, 77 00:03:45.533 --> 00:03:49.466 even though they're not reactive, they do combine to form gold indide. 78 00:03:49.700 --> 00:03:54.600 The gold indide ate away at the wires, leading to added thermal stress 79 00:03:54.600 --> 00:03:57.433 and eventually the failure of the first laser. 80 00:03:57.433 --> 00:04:00.733 And the second and third lasers were degrading as well. 81 00:04:00.733 --> 00:04:02.800 Tough decisions were ahead. 82 00:04:02.800 --> 00:04:04.000 When these missions operate, 83 00:04:04.000 --> 00:04:05.566 there's a lot riding on the missions. 84 00:04:05.566 --> 00:04:07.900 You don't want to make any mistakes. 85 00:04:07.900 --> 00:04:11.333 You want to optimize things as best you can. 86 00:04:11.566 --> 00:04:14.833 The question was, given that we would have so much 87 00:04:14.833 --> 00:04:18.233 lifetime expectancy from the lasers, 88 00:04:18.233 --> 00:04:21.000 well, the scientific decision was 89 00:04:21.000 --> 00:04:24.766 the best way to use that was to operate for periods 90 00:04:24.766 --> 00:04:28.233 of about a month and do that three times a year. 91 00:04:28.500 --> 00:04:32.500 That decision paid off when ICESat showed dramatic change in land ice 92 00:04:32.500 --> 00:04:36.600 around Greenland, and it also proved that lidar could be used to measure 93 00:04:36.600 --> 00:04:39.666 something called sea ice freeboard, 94 00:04:39.666 --> 00:04:43.133 a major breakthrough in determining sea ice thickness 95 00:04:43.133 --> 00:04:47.600 and an essential science goal for the future of ice-measuring satellites. 96 00:04:47.600 --> 00:04:50.533 Even though the ICESat project required much 97 00:04:50.533 --> 00:04:54.500 more care and feeding, it really laid the groundwork 98 00:04:54.500 --> 00:04:58.766 for all the subsequent missions that Goddard has has flown. 99 00:04:58.766 --> 00:05:01.300 [music] 100 00:05:01.300 --> 00:05:03.800 Around the same time that ICESat was developed, 101 00:05:03.800 --> 00:05:06.333 Goddard was tasked with designing a laser 102 00:05:06.333 --> 00:05:10.000 for measuring a place far from any icy poles. 103 00:05:10.766 --> 00:05:14.966 Sean Solomon was the PI of Messenger, and he said, 104 00:05:14.966 --> 00:05:18.433 You know, I've been asked to PI a mission to Mercury. 105 00:05:18.866 --> 00:05:21.033 I really want a laser altimeter on board. 106 00:05:21.300 --> 00:05:23.100 Can you make one that will work there? 107 00:05:23.100 --> 00:05:25.133 So the short answer seemed to be, 108 00:05:25.133 --> 00:05:27.300 yeah, I don't see why not, but there will be 109 00:05:27.300 --> 00:05:30.300 extreme thermal circumstances that we'd have to worry about. 110 00:05:30.333 --> 00:05:32.266 That was a really tough one because you fly in close 111 00:05:32.266 --> 00:05:37.066 to the 800-degree planet and then, you know, you have a 12-hour orbit. 112 00:05:37.066 --> 00:05:39.566 The temperature changes by 113 00:05:39.566 --> 00:05:42.633 tens of degrees in a few minutes. 114 00:05:42.633 --> 00:05:47.466 It had to always shield itself from the Sun constantly, 115 00:05:47.466 --> 00:05:52.266 which meant that in orbit it was often at a very high angle. 116 00:05:52.266 --> 00:05:55.633 It was a challenge to try to continually figure out where 117 00:05:55.633 --> 00:05:57.433 the surface of Mercury was. 118 00:05:57.433 --> 00:05:59.166 And then they wanted to be small, 119 00:05:59.166 --> 00:06:01.533 much smaller than a MOLA. 120 00:06:01.533 --> 00:06:05.366 I think it's up to a quarter or fifth of the size. 121 00:06:05.400 --> 00:06:09.933 But I remember the manager who was running it for us at the time 122 00:06:09.933 --> 00:06:16.133 kind of said, you realize I've thinned every wire in this electronic package 123 00:06:16.133 --> 00:06:19.800 so thin that you better not look at it twice because it might break. 124 00:06:19.800 --> 00:06:23.266 But that's the level we had to go to get within the seven kilograms. 125 00:06:24.300 --> 00:06:28.300 And MLA was the laser altimeter that we proposed, 126 00:06:28.300 --> 00:06:31.866 and this was really pushed the limits 127 00:06:31.866 --> 00:06:34.366 of what we could reasonably expect to do. 128 00:06:35.966 --> 00:06:39.033 Despite the extreme environmental gauntlet, 129 00:06:39.166 --> 00:06:43.800 the Mercury Laser Altimeter kept on collecting data for four years, 130 00:06:43.800 --> 00:06:48.900 right up until the very end, when MESSENGER crashed into Mercury in 2015. 131 00:06:49.266 --> 00:06:54.200 But before that, it captured historic views of the planet's topography. 132 00:06:54.200 --> 00:06:56.700 [music] 133 00:06:56.700 --> 00:07:00.966 It is time for America to take the next steps. 134 00:07:01.400 --> 00:07:04.333 Beginning no later than 2008, 135 00:07:04.333 --> 00:07:09.300 we will send a series of robotic missions to the lunar surface to research 136 00:07:09.300 --> 00:07:13.566 and prepare for future human exploration. 137 00:07:13.800 --> 00:07:17.233 And then one day, the President, I think it was George Bush, suddenly 138 00:07:17.233 --> 00:07:18.866 decided we're going to go back to the Moon. 139 00:07:18.866 --> 00:07:20.633 Well, all of a sudden, okay! 140 00:07:20.966 --> 00:07:26.033 We've been thinking of putting the lidar around the Moon for a long time, actually. 141 00:07:26.166 --> 00:07:31.066 And I really wanted to have a crack at doing a good one--instrument--for 142 00:07:31.500 --> 00:07:32.166 the Moon. 143 00:07:32.166 --> 00:07:35.833 I mean, my interest was in gravity and topography, two things 144 00:07:35.833 --> 00:07:38.533 that need to come together to measure the structure of a planet. 145 00:07:39.766 --> 00:07:43.200 And then all of a sudden, we got a call from Headquarters. 146 00:07:43.200 --> 00:07:48.966 Can you design the lidar around the Moon to map the Moon, to map the topography? 147 00:07:49.066 --> 00:07:52.766 And so the instruments were chosen from proposals 148 00:07:52.766 --> 00:07:56.500 based on the ability to help select sites 149 00:07:56.500 --> 00:08:01.033 and determine the the safety of landing in particular sites on the Moon. 150 00:08:01.233 --> 00:08:06.100 The lidar would be the Lunar Orbiter Laser Altimeter, or LOLA, 151 00:08:06.100 --> 00:08:08.766 and it marked another leap into laser altimetry. 152 00:08:08.766 --> 00:08:11.700 We also came up with the idea 153 00:08:11.700 --> 00:08:13.866 of having multiple beams. 154 00:08:14.100 --> 00:08:17.700 We managed to put five beams on the surface, and that kind of 155 00:08:17.700 --> 00:08:21.200 changed the observational strategy, if you know what I mean. 156 00:08:21.200 --> 00:08:23.000 Five parallel beams. 157 00:08:23.000 --> 00:08:28.600 [rocket launching] 158 00:08:28.600 --> 00:08:32.433 But after launch, LOLA was suspiciously silent. 159 00:08:32.433 --> 00:08:34.900 When LOLA started, I think that was just devastating. 160 00:08:34.900 --> 00:08:39.366 We didn't get any measurement at nighttime when we first turned on. 161 00:08:39.366 --> 00:08:44.533 So it was quite a shock, and it was the first lidar that didn't work 162 00:08:44.533 --> 00:08:46.366 at the initial turn on. 163 00:08:46.366 --> 00:08:49.233 The people that are heavily involved in the instrument development, 164 00:08:49.233 --> 00:08:52.766 you're pulled back in if there's surprises that occur. 165 00:08:52.800 --> 00:08:55.233 On LOLA, the blankets were all tied 166 00:08:55.233 --> 00:08:58.366 tightly to the beam expander and the telescope and this Germanium 167 00:08:58.366 --> 00:09:02.166 black Kapton, which we didn't test with was very strong. 168 00:09:02.233 --> 00:09:04.700 And then we caused a misalignment. 169 00:09:04.800 --> 00:09:08.700 I remember we discussed whether we wanted to check the alignment 170 00:09:08.700 --> 00:09:12.500 at spacecraft level, and I, you know, we just decided not to do it. 171 00:09:12.533 --> 00:09:15.800 I think that was my fault because we could have. 172 00:09:16.233 --> 00:09:20.000 We started in the worst possible orbit for that failure mechanism, 173 00:09:20.000 --> 00:09:23.433 and so we were out of alignment, and we had no signal at all. 174 00:09:23.433 --> 00:09:27.033 And it was just--it was a tough couple of weeks. 175 00:09:27.033 --> 00:09:27.466 Yeah. 176 00:09:27.466 --> 00:09:31.366 It is a lessons learned for life for me. 177 00:09:31.500 --> 00:09:34.933 Couple of weeks later, we noticed a little blip at the South Pole. 178 00:09:35.600 --> 00:09:37.766 And so we had some hope. 179 00:09:39.433 --> 00:09:42.833 And it eventually just, you know, as the orbit progressed, 180 00:09:42.833 --> 00:09:46.333 the signal kept getting stronger and stronger on the daylight side. 181 00:09:46.333 --> 00:09:50.400 Despite a bumpy start, in time LOLA and the Lunar Reconnaissance 182 00:09:50.400 --> 00:09:54.366 Orbiter mission became revolutionary in mapping our Moon. 183 00:09:54.366 --> 00:09:57.800 And it turned out to be exceptional in terms of 184 00:09:57.800 --> 00:10:00.233 describing the topography of the Moon. 185 00:10:00.233 --> 00:10:03.000 As a result of LOLA, I think largely, 186 00:10:03.000 --> 00:10:04.400 if not the others as well, 187 00:10:04.400 --> 00:10:06.666 the doubts about whether a laser altimeter, 188 00:10:06.666 --> 00:10:08.466 for example, could last-- 189 00:10:08.466 --> 00:10:10.800 age limits, lifetime limits 190 00:10:10.800 --> 00:10:13.000 on the laser altimeter-- 191 00:10:13.000 --> 00:10:14.233 were dispelled. 192 00:10:16.833 --> 00:10:20.966 The shape of what we build, live, work, study, operate on, 193 00:10:20.966 --> 00:10:24.833 whether it be on the Earth, the Moon, Mars, wherever we're going, 194 00:10:24.833 --> 00:10:25.600 matters.