Chapter 3: Take the Next Steps
Narration: Lauren Ward
Transcript:
00:00:02:21 - 00:00:03:19
Following MOLA,
00:00:03:19 - 00:00:06:10
in some ways, we were in demand to consider
00:00:06:19 - 00:00:11:02
whether we could provide a laser altimeter to another mission.
00:00:11:12 - 00:00:13:08
A few missions, actually.
00:00:13:08 - 00:00:15:24
It was no longer a question of if
00:00:15:24 - 00:00:18:23
lidar could work, but where else it could work?
00:00:19:11 - 00:00:22:24
But as the opportunities to test the limits of light out arose,
00:00:23:01 - 00:00:32:07
so did the challenges ahead.
00:00:33:00 - 00:00:37:01
The Goddard team quickly began to see the evolution of lidar missions.,
00:00:37:01 - 00:00:40:23
building on the successes of new frontiers mapped by MOLA.
00:00:41:07 - 00:00:44:04
We've measured the changes, the seasonal changes
00:00:44:04 - 00:00:47:21
in the Mars icecaps, both the North Pole and the South Pole.
00:00:48:06 - 00:00:49:12
We've measured the volumes.
00:00:49:12 - 00:00:51:17
We've measured the mass that's involved in it.
00:00:51:21 - 00:00:53:01
We now have a density.
00:00:53:01 - 00:00:57:11
So now we know the kind of processes that-- Dave Smith invited me
00:00:57:11 - 00:01:01:08
to be on the MOLA Altimetry Science Team.
00:01:01:23 - 00:01:04:25
And that was because of my experience with using
00:01:05:27 - 00:01:07:14
altimetry over
00:01:07:14 - 00:01:10:14
land rather than ocean processes.
00:01:10:18 - 00:01:14:25
Zwally was an obvious choice to study the Martian ice caps for MOLA,
00:01:15:09 - 00:01:18:21
given his decades of expertize with our own polar regions
00:01:19:06 - 00:01:24:06
studying the ice sheets of Greenland and Antarctica through the 1970s and 80s.
00:01:24:15 - 00:01:26:26
And then as we went into the eighties,
00:01:27:16 - 00:01:29:28
NASA was was sort of the beginning
00:01:29:28 - 00:01:32:25
of the development of the Earth Observations Program.
00:01:33:00 - 00:01:36:23
So the Earth Observing System, I think, will be the first effort
00:01:36:27 - 00:01:41:01
targeted at looking at the whole Earth system as a system
00:01:41:14 - 00:01:44:06
rather than just the little components that make it up.
00:01:44:28 - 00:01:49:12
Somewhere along then I teamed up with Jim Abshire.
00:01:49:19 - 00:01:53:23
Jay had been pushing for a long time for a dedicated ice
00:01:53:23 - 00:01:56:25
altimetry mission, which turned into ICESat-1.
00:01:57:14 - 00:02:00:10
Designing ICESat-1 marked a major leap
00:02:00:10 - 00:02:04:08
in what lidar needed to do and how challenging it would be to do it.
00:02:04:12 - 00:02:08:15
To measure the changing ice sheets, the lidar had to be far more precise,
00:02:08:27 - 00:02:12:22
cover the same tracks season to season, and it needed more power
00:02:12:22 - 00:02:16:26
and a larger instrument, which meant much more time to build.
00:02:17:19 - 00:02:22:02
We built a simulator for ICESat-1 that allowed us to sort of
00:02:22:02 - 00:02:25:04
figure out how precise it could be, how we would process
00:02:25:04 - 00:02:28:18
the waveform data coming back, how we would track the surface.
00:02:28:18 - 00:02:34:09
This algorithm was much more complicated than anything I had ever worked on before.
00:02:34:15 - 00:02:38:09
But all this meant essentially for for the ICESat mission,
00:02:38:09 - 00:02:43:21
you needed a much more advanced version of MOLA and Mars.
00:02:43:21 - 00:02:47:15
We really didn't know what was there until we got the measurements.
00:02:47:15 - 00:02:49:06
So we were doing discovery.
00:02:49:06 - 00:02:52:18
On Earth, we have to make quantitative measurements about what's happening.
00:02:52:28 - 00:02:56:14
Four, three, two, one,
00:02:57:18 - 00:02:59:20
and we have ignition and liftoff
00:02:59:20 - 00:03:04:01
for NASA's ICESat and CHIPSat spacecraft looking at stars and ice.
00:03:05:03 - 00:03:07:06
But after we'd worked on GLAS
00:03:07:06 - 00:03:10:29
at that point, more than a decade and had already launched them, usually
00:03:11:00 - 00:03:12:20
it's like, okay, now we're going to be able
00:03:12:20 - 00:03:16:11
to enjoy the data coming down and what can we see in the data?
00:03:17:03 - 00:03:20:17
But there was much more, what is this mystery we're seeing?
00:03:20:17 - 00:03:22:18
Why is the laser energy going down?
00:03:22:25 - 00:03:26:07
Things were not working the way we expected them to,
00:03:26:07 - 00:03:28:19
and there were mysteries and we weren't expecting
00:03:28:21 - 00:03:31:20
after MOLA particularly to have mysteries at that point.
00:03:31:24 - 00:03:35:08
One of these unexpected mysteries came down to the wire.
00:03:35:08 - 00:03:36:24
Several wires actually.
00:03:36:24 - 00:03:39:25
What happened on GLAS was the laser diodes
00:03:39:27 - 00:03:43:22
had had gold bond wires and indium solder.
00:03:44:02 - 00:03:45:16
If you bring these two metals together,
00:03:45:16 - 00:03:49:05
even though they're not reactive, they do combine to form gold indide.
00:03:49:21 - 00:03:54:05
The gold indide ate away at the wires, leading to added thermal stress
00:03:54:18 - 00:03:57:01
and eventually the failure of the first laser.
00:03:57:13 - 00:04:00:13
And the second and third lasers were degrading as well.
00:04:00:22 - 00:04:02:24
Tough decisions were ahead.
00:04:02:24 - 00:04:04:00
When these missions operate,
00:04:04:00 - 00:04:07:12
there's a lot riding on the mission and you don't want to make any mistakes.
00:04:07:27 - 00:04:11:07
You want to optimize things as best you can.
00:04:11:17 - 00:04:15:15
The question was, given that we would have so much lifetime
00:04:15:15 - 00:04:20:13
expectancy from the lasers, well, the scientific decision was
00:04:21:00 - 00:04:24:19
the best way to use that was to operate for a period
00:04:24:23 - 00:04:27:20
of about a month and do that three times a year.
00:04:28:15 - 00:04:32:07
That decision paid off when ICESat showed dramatic change in land
00:04:32:07 - 00:04:36:18
ice around Greenland, and it also proved that lidar could be used to measure
00:04:36:18 - 00:04:41:28
something called sea ice freeboard, a major breakthrough in determining sea
00:04:41:28 - 00:04:43:04
ice thickness
00:04:43:04 - 00:04:47:08
and an essential science goal for the future of ice-measuring satellites.
00:04:47:18 - 00:04:50:16
Even though the ICESat project required much
00:04:50:16 - 00:04:54:15
more care and feeding, it really laid the groundwork
00:04:54:15 - 00:05:00:04
for all the subsequent missions that Goddard has has flown.
00:05:01:09 - 00:05:02:03
Around the same
00:05:02:03 - 00:05:06:10
time that ICESat was developed, Goddard was tasked with designing a laser
00:05:06:10 - 00:05:09:19
for measuring a place far from any icy poles.
00:05:10:23 - 00:05:14:29
Sean Solomon was the PI of Messenger, and he said,
00:05:14:29 - 00:05:18:13
You know, I've been asked to PI a mission to Mercury.
00:05:18:26 - 00:05:21:01
I really want a laser altimeter on board.
00:05:21:09 - 00:05:23:03
Can you make one that will work there?
00:05:23:03 - 00:05:27:09
So the short answer seemed to be, yeah, I don't see why not, but there will be
00:05:27:09 - 00:05:30:09
extreme thermal circumstances that we'd have to worry about.
00:05:30:10 - 00:05:32:08
That was a really tough one because you fly in close
00:05:32:08 - 00:05:36:21
to the 800-degree planet and then, you know, you have a 12-hour orbit.
00:05:37:02 - 00:05:42:15
The temperature changes by tens of degrees in in a few minutes.
00:05:42:18 - 00:05:47:14
It had to always shield itself from the Sun constantly,
00:05:47:14 - 00:05:51:27
which meant that in orbit it was often at a very high angle.
00:05:52:08 - 00:05:55:19
It was a challenge to try to continually figure out where
00:05:55:19 - 00:05:57:13
the surface of Mercury was.
00:05:57:13 - 00:06:01:16
And then they wanted to be small, much smaller than a MOLA.
00:06:01:16 - 00:06:05:11
I think it's up to a quarter or fifth of the size.
00:06:05:12 - 00:06:09:19
But I remember the manager who was running it for us at the time
00:06:09:28 - 00:06:15:27
kind of said, you realize I I've thinned every wire in this electronic package
00:06:16:04 - 00:06:19:24
so thin that you better not look at it twice because it might break.
00:06:19:24 - 00:06:22:27
But that's the level we had to go to get within the seven kilograms.
00:06:24:09 - 00:06:28:03
And MLA was the laser altimeter that we proposed,
00:06:28:09 - 00:06:31:26
and this was really pushed the limits
00:06:31:26 - 00:06:34:03
of what we could reasonably expect to do.
00:06:35:29 - 00:06:38:20
Despite the extreme environmental gantlet,
00:06:39:05 - 00:06:43:11
the Mercury Laser Altimeter kept on collecting data for four years,
00:06:43:24 - 00:06:48:20
right up until the very end, when MESSENGER crashed into Mercury in 2015.
00:06:49:08 - 00:06:52:19
But before that, it captured historic views of the planet's
00:06:52:19 - 00:06:55:01
topography.
00:06:56:21 - 00:07:00:17
It is time for America to take the next steps.
00:07:01:12 - 00:07:04:10
Beginning no later than 2008,
00:07:04:10 - 00:07:08:25
we will send a series of robotic missions to the lunar surface to research
00:07:09:09 - 00:07:13:05
and prepare for future human exploration.
00:07:13:24 - 00:07:17:07
And then one day, the President, I think it was George Bush, suddenly
00:07:17:07 - 00:07:18:26
decided, we're going to go back to the Moon.
00:07:18:26 - 00:07:21:01
Well, all of a sudden, okay!
00:07:21:01 - 00:07:25:20
We've been thinking of putting the lidar around the Moon for a long time, actually.
00:07:26:05 - 00:07:30:14
And I really wanted to have a crack at doing a good one--instrument--for for
00:07:31:15 - 00:07:32:05
the Moon.
00:07:32:05 - 00:07:35:25
I mean, my interest was in gravity and topography, two things
00:07:35:25 - 00:07:38:16
that need to come together to measure the structure of a planet.
00:07:39:23 - 00:07:43:06
And then all of a sudden, we got a call from Headquarters.
00:07:43:06 - 00:07:48:23
Can you design the lidar around the Moon to map the Moon, to map the topography?
00:07:49:02 - 00:07:52:23
And so the instruments were chosen from proposals
00:07:52:23 - 00:07:56:09
based on the ability to help select sites
00:07:56:15 - 00:08:00:28
and determine the the safety of landing in particular sites on the Moon.
00:08:01:07 - 00:08:05:21
The lidar would be the Lunar Orbiter Laser Altimeter, or LOLA,
00:08:06:03 - 00:08:08:21
and it marked another leap into laser altimetry.
00:08:08:23 - 00:08:11:21
We also came up with the idea
00:08:11:21 - 00:08:13:21
of having multiple beams.
00:08:14:03 - 00:08:17:21
We managed to put five beams on the surface, and that kind of
00:08:17:21 - 00:08:20:29
changed the the observational strategy, if you know what I mean.
00:08:21:06 - 00:08:24:01
Five parallel beams.
00:08:28:18 - 00:08:29:03
But after
00:08:29:03 - 00:08:31:25
launch, LOLA was suspiciously silent.
00:08:32:13 - 00:08:34:23
When LOLA started, I think that was just devastating.
00:08:34:27 - 00:08:39:11
We didn't get any measurement at nighttime when we first turned on.
00:08:39:11 - 00:08:43:14
So it was quite a shock, and it was the first lidar that didn't work
00:08:44:16 - 00:08:46:11
at the initial turn on.
00:08:46:11 - 00:08:49:02
The people that are heavily involved in the instrument development,
00:08:49:07 - 00:08:52:23
you're pulled back in if there's surprises that occur.
00:08:52:24 - 00:08:55:07
On LOLA, the blankets were all tied
00:08:55:07 - 00:08:58:11
tightly to the beam expander and the telescope and this Germanium
00:08:58:11 - 00:09:02:02
black Kapton, which we didn't test with was was very strong.
00:09:02:07 - 00:09:04:13
And then we caused a misalignment.
00:09:04:24 - 00:09:08:21
I remember we discussed whether we wanted to check the alignment
00:09:08:21 - 00:09:12:15
at spacecraft level, and I, you know, we just decided not to do it.
00:09:12:16 - 00:09:15:06
I think that was my fault because we could have.
00:09:16:07 - 00:09:17:00
We started in the
00:09:17:00 - 00:09:19:13
worst possible orbit for that failure mechanism,
00:09:20:00 - 00:09:23:13
and so we we were out of alignment and we had no signal at all.
00:09:23:13 - 00:09:26:12
And it was just it was a it was a tough couple of weeks.
00:09:27:01 - 00:09:27:14
Yeah.
00:09:27:14 - 00:09:31:11
It is a lessons learned for life for me.
00:09:31:15 - 00:09:34:28
Couple of weeks later, we noticed a little blip at the South Pole.
00:09:35:18 - 00:09:39:13
And so we had some hope.
00:09:39:13 - 00:09:42:17
And it eventually just, you know, as the orbit progressed,
00:09:42:25 - 00:09:46:01
the signal kept getting stronger and stronger on the daylight side.
00:09:46:10 - 00:09:50:12
Despite a bumpy start, in time LOLA and the Lunar Reconnaissance
00:09:50:12 - 00:09:54:01
Orbiter mission became revolutionary in mapping our Moon.
00:09:54:11 - 00:09:57:17
And it turned out to be exceptional in terms of
00:09:57:24 - 00:10:02:21
describing the topography of the Moon as a result of LOLA, I think largely,
00:10:03:00 - 00:10:06:20
if not the others as well, the doubts about whether a laser altimeter,
00:10:06:20 - 00:10:10:14
for example, could last--age limits, lifetime
00:10:10:14 - 00:10:15:22
limits--on the laser altimeter were dispelled.
00:10:16:25 - 00:10:17:13
The shape of
00:10:17:13 - 00:10:20:29
what we build, live, work, study, operate on,
00:10:20:29 - 00:10:25:07
whether it be on the Earth, the Moon, Mars, wherever we're going, matters.