Chapter 3: Take the Next Steps
Narration: Lauren Ward
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in some ways, we were in demand to consider
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whether we could provide a laser altimeter to another mission.
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A few missions, actually.
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It was no longer a question of if
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lidar could work, but where else it could work?
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But as the opportunities to test the limits of light out arose,
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so did the challenges ahead.
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The Goddard team quickly began to see the evolution of lidar missions.,
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building on the successes of new frontiers mapped by MOLA.
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We've measured the changes, the seasonal changes
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in the Mars icecaps, both the North Pole and the South Pole.
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We've measured the volumes.
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We've measured the mass that's involved in it.
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We now have a density.
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So now we know the kind of processes that-- Dave Smith invited me
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to be on the MOLA Altimetry Science Team.
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And that was because of my experience with using
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land rather than ocean processes.
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Zwally was an obvious choice to study the Martian ice caps for MOLA,
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given his decades of expertize with our own polar regions
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studying the ice sheets of Greenland and Antarctica through the 1970s and 80s.
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And then as we went into the eighties,
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NASA was was sort of the beginning
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of the development of the Earth Observations Program.
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So the Earth Observing System, I think, will be the first effort
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targeted at looking at the whole Earth system as a system
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rather than just the little components that make it up.
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Somewhere along then I teamed up with Jim Abshire.
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Jay had been pushing for a long time for a dedicated ice
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altimetry mission, which turned into ICESat-1.
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Designing ICESat-1 marked a major leap
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in what lidar needed to do and how challenging it would be to do it.
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To measure the changing ice sheets, the lidar had to be far more precise,
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cover the same tracks season to season, and it needed more power
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and a larger instrument, which meant much more time to build.
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We built a simulator for ICESat-1 that allowed us to sort of
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figure out how precise it could be, how we would process
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the waveform data coming back, how we would track the surface.
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This algorithm was much more complicated than anything I had ever worked on before.
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But all this meant essentially for for the ICESat mission,
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you needed a much more advanced version of MOLA and Mars.
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We really didn't know what was there until we got the measurements.
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So we were doing discovery.
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On Earth, we have to make quantitative measurements about what's happening.
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Four, three, two, one,
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and we have ignition and liftoff
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for NASA's ICESat and CHIPSat spacecraft looking at stars and ice.
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But after we'd worked on GLAS
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at that point, more than a decade and had already launched them, usually
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it's like, okay, now we're going to be able
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to enjoy the data coming down and what can we see in the data?
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But there was much more, what is this mystery we're seeing?
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Why is the laser energy going down?
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Things were not working the way we expected them to,
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and there were mysteries and we weren't expecting
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after MOLA particularly to have mysteries at that point.
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One of these unexpected mysteries came down to the wire.
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Several wires actually.
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What happened on GLAS was the laser diodes
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had had gold bond wires and indium solder.
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If you bring these two metals together,
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even though they're not reactive, they do combine to form gold indide.
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The gold indide ate away at the wires, leading to added thermal stress
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and eventually the failure of the first laser.
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And the second and third lasers were degrading as well.
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Tough decisions were ahead.
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When these missions operate,
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there's a lot riding on the mission and you don't want to make any mistakes.
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You want to optimize things as best you can.
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The question was, given that we would have so much lifetime
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expectancy from the lasers, well, the scientific decision was
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the best way to use that was to operate for a period
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of about a month and do that three times a year.
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That decision paid off when ICESat showed dramatic change in land
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ice around Greenland, and it also proved that lidar could be used to measure
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something called sea ice freeboard, a major breakthrough in determining sea
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and an essential science goal for the future of ice-measuring satellites.
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Even though the ICESat project required much
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more care and feeding, it really laid the groundwork
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for all the subsequent missions that Goddard has has flown.
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Around the same
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time that ICESat was developed, Goddard was tasked with designing a laser
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for measuring a place far from any icy poles.
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Sean Solomon was the PI of Messenger, and he said,
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You know, I've been asked to PI a mission to Mercury.
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I really want a laser altimeter on board.
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Can you make one that will work there?
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So the short answer seemed to be, yeah, I don't see why not, but there will be
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extreme thermal circumstances that we'd have to worry about.
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That was a really tough one because you fly in close
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to the 800-degree planet and then, you know, you have a 12-hour orbit.
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The temperature changes by tens of degrees in in a few minutes.
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It had to always shield itself from the Sun constantly,
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which meant that in orbit it was often at a very high angle.
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It was a challenge to try to continually figure out where
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the surface of Mercury was.
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And then they wanted to be small, much smaller than a MOLA.
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I think it's up to a quarter or fifth of the size.
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But I remember the manager who was running it for us at the time
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kind of said, you realize I I've thinned every wire in this electronic package
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so thin that you better not look at it twice because it might break.
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But that's the level we had to go to get within the seven kilograms.
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And MLA was the laser altimeter that we proposed,
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and this was really pushed the limits
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of what we could reasonably expect to do.
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Despite the extreme environmental gantlet,
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the Mercury Laser Altimeter kept on collecting data for four years,
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right up until the very end, when MESSENGER crashed into Mercury in 2015.
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But before that, it captured historic views of the planet's
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It is time for America to take the next steps.
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Beginning no later than 2008,
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we will send a series of robotic missions to the lunar surface to research
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and prepare for future human exploration.
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And then one day, the President, I think it was George Bush, suddenly
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decided, we're going to go back to the Moon.
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Well, all of a sudden, okay!
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We've been thinking of putting the lidar around the Moon for a long time, actually.
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And I really wanted to have a crack at doing a good one--instrument--for for
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I mean, my interest was in gravity and topography, two things
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that need to come together to measure the structure of a planet.
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And then all of a sudden, we got a call from Headquarters.
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Can you design the lidar around the Moon to map the Moon, to map the topography?
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And so the instruments were chosen from proposals
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based on the ability to help select sites
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and determine the the safety of landing in particular sites on the Moon.
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The lidar would be the Lunar Orbiter Laser Altimeter, or LOLA,
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and it marked another leap into laser altimetry.
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We also came up with the idea
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of having multiple beams.
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We managed to put five beams on the surface, and that kind of
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changed the the observational strategy, if you know what I mean.
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Five parallel beams.
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launch, LOLA was suspiciously silent.
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When LOLA started, I think that was just devastating.
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We didn't get any measurement at nighttime when we first turned on.
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So it was quite a shock, and it was the first lidar that didn't work
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at the initial turn on.
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The people that are heavily involved in the instrument development,
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you're pulled back in if there's surprises that occur.
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On LOLA, the blankets were all tied
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tightly to the beam expander and the telescope and this Germanium
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black Kapton, which we didn't test with was was very strong.
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And then we caused a misalignment.
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I remember we discussed whether we wanted to check the alignment
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at spacecraft level, and I, you know, we just decided not to do it.
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I think that was my fault because we could have.
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We started in the
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worst possible orbit for that failure mechanism,
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and so we we were out of alignment and we had no signal at all.
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And it was just it was a it was a tough couple of weeks.
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It is a lessons learned for life for me.
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Couple of weeks later, we noticed a little blip at the South Pole.
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And so we had some hope.
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And it eventually just, you know, as the orbit progressed,
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the signal kept getting stronger and stronger on the daylight side.
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Despite a bumpy start, in time LOLA and the Lunar Reconnaissance
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Orbiter mission became revolutionary in mapping our Moon.
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And it turned out to be exceptional in terms of
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describing the topography of the Moon as a result of LOLA, I think largely,
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if not the others as well, the doubts about whether a laser altimeter,
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for example, could last--age limits, lifetime
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limits--on the laser altimeter were dispelled.
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The shape of
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what we build, live, work, study, operate on,
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whether it be on the Earth, the Moon, Mars, wherever we're going, matters.