Events of October 24, 2012
Is it really November already? After Columbus Day, everything just seemed to whiz by to me in a blur of midterms, essays, and hurricanes ... but I was able to take some time out to travel across the river to MIT for an appointment I'd made several weeks before.
Back in January, I talked about all of the events I was looking forward to this year in space and astronomy news, starting with the twin GRAIL probes entering orbit around the moon on New Year's Eve and New Year's Day. The mission certainly didn't disappoint--my father and I were huddled around the computer watching the live animation of the probes' movements, provided by the excellent Eyes on the Solar System program, watching the "distance" and speed figures shrink, and listening to the communications chatter from the control room. When the GRAILs were safely in their orbits, we celebrated.
A few weeks later, I found myself in a rather unenviable position, out getting lunch at the Student Union without my laptop just minutes before the press conference announcing the winners of the contest to name the probes that had been held for schoolchildren across the country. I got the press conference up on my smartphone, but without headphones, I couldn't hear a thing in the noisy cafeteria! I hurried downstairs and found a quiet spot in a room that wasn't in use, just in time to hear the announcement.
The winning class held up cards, revealing their chosen names letter-by-letter, cheerleader-style:
"What does that spell? EBB and FLOW!"
Like most of the space fans watching, I approved of the names--since the probes were mapping the moon's gravity, and the moon's gravity creates tides on Earth, the tidal theme was very appropriate. The names were opposite, but connected, perfect for twin spacecraft, and in addition--they just sounded kind of cute!
Back in September, when I went to hear Dr. Charles Elachi speak, I ran into Maria Zuber, the top scientist on the GRAIL mission, and asked her if it would be possible to meet up and do an interview for my blog at some point in the future. The 24th was the first day she was available, as her work keeps her pretty busy (as you'll see), so I packed my tape recorder and caught a cab to MIT. After a little trouble finding the building, we sat down and started to talk...
Me: I feel bad that I wasn't able to interview you last time [we first corresponded last fall, when the GRAIL probes were launched], but now the mission has actually been going on, so I'm sure you'll have more to talk about.
Maria Zuber (MZ): Well, some people like to talk about what they hope they're going to do. I tend--when I have something, that's when I'm ready to talk. (laughs)
Me: So this is more comfortable for you?
MZ: Well, it is, yeah, because I've never been one to toot my horn unless there's something to toot about. So when you hear from me, we've got the stuff.
Me: Okay, so why don't you start off by stating your name and what you do?
MZ: Okay--Maria Zuber, I'm a Professor of Geophysics at MIT, and I'm the Principal Investigator on the GRAIL mission. That stands for Gravity Recovery And Interior Laboratory. The mission launched last September 10th--successfully, thank goodness. When the Apollo missions went to the moon, they went on a three-day trajectory to get to the moon. And what we decided to do was something called a low-energy trajectory. So we went out to the Earth-Sun Lagrange Point, which is the place where gravity--
Me: It's canceled out.
MZ: — yeah, gravity vanishes, it's balanced between the Earth-Moon system and the Sun. And the reason that we did that is that we were able to use very little fuel to get into lunar orbit. So we launched [both spacecraft] on a single rocket and then each spacecraft only had to slow down by 190 meters per second to get captured by the moon's gravity. And so, that meant we could launch two spacecraft on a single rocket rather than using two rockets, and so we actually saved 150 million dollars by going to the moon in three months instead of three days. That was a very clever thing by our mission design team.
Me: How does that compare to the looping that the LRO [Lunar Reconnaissance Orbiter] did, the LRO and LCROSS missions? I remember that they went very far away from the Earth and moon and then came back in.
MZ: They got into a big, looping orbit around the moon. This is a much lower one. Essentially, we went into a parking orbit around the Earth and just gave the spacecraft a little nudge to get them going towards the Lagrange Point.
Me: Because it's space.
Me: [In the microgravity of space] things just keep going where they're pushed.
MZ: Yes. The way that you get into orbit around a planet is that you slow down enough so that the gravity field of the planet can capture you. So to only have to slow down 190 meters per second is pretty good. We could have a nice small fuel tank.
Me: I think it's incredible that we know orbital mechanics well enough now to do all of these different things, these maneuvers, and to have so many different ways to do these things based on the mechanical and mission requirements.
MZ: For the mechanical design of our mission, we were just so fortunate to have really, really good mission designers. These two spacecraft together have so far done 55 propulsive maneuvers since they were launched, which is (laughs) — a lot! Most spacecraft will do just a handful. We've done 55 in the course of about a year. When a spacecraft first gets into orbit, it will often do just a big elliptical orbit, which is what LRO did around the moon, and then you do a burn, to take energy out of the orbit, and that brings the orbit down to the point we want to map at.
We did eight burns per spacecraft, to bring these spacecraft down to their lower orbits, and then we had to do a bunch of tiny burns to line them up. We could have done big burns, but by doing these little burns, it built in some resiliency, because we could miss any given one and it wasn't critical, we could make it up the next time if we missed one. We didn't miss any, but because we were doing it so slowly, we could assess very accurately what our orbit was. We didn't waste any fuel, we could do it extremely precisely by doing all of these little burns.
Personally, I've been very involved in every aspect of the mission, so I either go out to Lockheed, where they operate the spacecraft, or to JPL, where they run the mission, or I'm on the phone with them while all of this is going on, so during our extended mission right now, I'm on the phone three-to-five hours a day, either doing maneuvers or planning maneuvers or assessing maneuvers. And I think to myself, "Was it really a good idea to do this?" (Laughs)
But it was! It was! It's taken a lot of time, but we're getting absolutely the most out of this mission that we can.
Me: What have you learned so far from these probes?
MZ: Well, I have to be careful about what I say here, because we have three papers in review in Science [magazine] and they're embargoed, so I can't talk to the press about results too much yet. Although, I'll be happy to talk to you about results in a couple of months. (Smiles)
Me: Oh, sure, sure, I understand. I just meant vaguely.
MZ: Well, I can tell you generally what we've done in terms of gravity field research, and then I'll tell you what we're doing right now. We haven't produced our best [map of the moon's] gravity field yet, but so far we've produced the best gravity field map for any planetary body in the solar system, and the best one that there will be for any known time to come.
This is because we can go low. In the primary mission, the two spacecraft--it's probably worth stopping to explain that these two spacecraft measure gravity by measuring the distance change between them. So that's the reason we need two spacecraft. The way we normally track the gravity field of planets is to track one spacecraft in orbit around that planet from Earth, but we don't see the back side of the moon from Earth, so we have to have two spacecraft that can track each other like that.
We orbited at an average altitude of 55 kilometers above the moon, and you can't do that with Earth, because the atmospheric drag doesn't allow you to orbit at that distance.
Me: 55 kilometers up isn't even space! [The Kármán Line, the edge of Earth's atmosphere and the beginning of space, is defined as 100 kilometers, or 62 miles, above sea level. This means that from my dorm room here in Boston, outer space is actually closer than Cape Cod. Something to think about.]
MZ: Right, you have to be at at least 200 kilometers to orbit the Earth, often higher. In the primary mission, we produced a gravity field map with a spatial resolution size on the surface of 13 kilometers, which is pretty amazing for a global model. And right now, we're in an extended mission that's going to end in December. We have learned the gravity field well enough that in the extended mission, we can operate at an even lower altitude.
I asked my mission designers, "How low can we go and still map safely?" We're currently mapping the moon at half that altitude, so 22-and-a-half kilometers average altitude above the moon. Last week, we got within 7.6 kilometers of the moon. So while the average altitude is 22-and-a-half kilometers, the orbit goes elliptical very quickly because the moon's gravity field is so bumpy, especially when you get down low. You get bounced all over the place by the gravity field. So the high point of the orbit is about 28 kilometers and the low point was 7.6. And it will get lower as the course of the mission goes on. [Astute aerospace fans will have noted that 28 kilometers is not only far short of the Kármán Line but actually lower than Felix Baumgartner's recent stratospheric skydive.]
So the fact that you can orbit around a planet--
MZ: --with two spacecraft flying in precise formation and measure the distance changes between them to better than a tenth of a micron per second, which is about the same as a human blood cell. We can do that extremely precisely, and we do it five times per second.
Me: When they're at that lowest point now, if you were on the surface of the moon, would they be visible overhead?
MZ: Oh, hmmm, well, let's see... so the two spacecraft are about the size of an apartment-sized washer and dryer, so they're small. So when they're at 7 kilometers, that's about the height that commercial airplanes fly on Earth. So you probably couldn't see each one of them, but they're getting close to the size you could see.
At the very, very end of the mission, I have further challenged my engineering team to see if we can go lower, and we're in the process of planning that. The goal here was to get enough gravity information at as low an altitude as we could, so that we could study the mass distribution inside the planet. By flying really low, we can measure very small mass variations. On Earth, if you wanted to measure similar things, you would have to fly over with an airplane or tow similar equipment on the ground.
Some of the early surface gravity measurements on Earth were taken by the army as they trudged around with a hand-held gravimeter, and they were measuring that kind of thing. By doing it from orbit, you can measure much more precisely than you can by dragging something around in the field.
Me: I'm an archeological remote sensing major, so this is very, very relevant. I think it's really great that there are techniques and technologies that are developed for one branch of science that are so transferable to others. And it's so useful, to be able to apply that to other fields and to other questions that you might have in the future.
MZ: One of the really exciting things about this is that in the Earth Sciences, we study the interior of the planets using geophysical techniques. We do seismology, we do magnetics, we do gravity, and that kind of information is usually at a much larger scale than when we study the surface. People go out and do fieldwork, they lug equipment around, and by getting these measurements at low-altitude, we can map at high-resolution and the geophysics is really entering the realm of geology.
In fact, we gave an update on the data we're collecting at a lunar meeting this week, and Jack Schmidt, the astronaut from Apollo 17, he was--
Me: A geologist who was on the moon.
MZ: -- he was the only geologist who walked on the surface of the moon. And he said, "Hey, we collected some surface gravity data at the Apollo 17 landing site, we should compare our data to your data from orbit!" (laughs) And I said, "You know what, we could do that now." It makes sense to do this now, so that's something that we're really looking forward to doing.
Me: Do you think that there would be changes over forty years? Or would that only be on a planet that was geologically active?
MZ: The moon is not geologically active. I would not expect to see changes, but one thing I would say is, never say never. There could be changes on the moon, they would be very tiny, so there are moonquakes that occur every month. The moon raises tides on the Earth and we see the results on Earth, but the Earth raises tides on the solid moon, and that produces moonquakes.
So we consider the moon to be a geologically inactive planet, but recent orbiters have detected that there's a monthly water cycle on the moon. There's a micron-thick layer of hydroxyl that gets activated when the sun shines on it and the molecules bounce around and then when the Sun goes down, they drop to the surface. So with remote sensing in orbit, you would see a very, very tiny signal of water on the surface that disappears when the Sun is shining on it. So we think of the moon as being inactive, but there are some things that change.
So one of the things that has been exciting about studying the moon is the discovery of water, particularly in the Polar Regions. And we're down low enough that we can actually try to look for subsurface ice signatures in some of the polar craters. If there's enough water there, we would see something unusual in those craters.
That'll be something that we're looking for, but it takes very long to process this data.
Me: I know that on Earth, they've used gravity data to find places where there is water underground. With the GRACE mission, they did that.
MZ: Sure. The GRACE mission on Earth, which is also a dual-spacecraft mission, looks at river discharge and aquifers. You can actually see water replenishing in the aquifer during the rainy season and being discharged in the dry season. We don't think the moon has nearly that much water, so we wouldn't expect to see changes in ice content, but what we would be looking for is anomalously low densities in polar craters that are much different than similar craters away from the poles.
Me: What would you say so far has been the most exciting or the best thing that has happened, the most exciting experience so far in the course of the GRAIL mission?
MZ: Let's see ... there's no doubt that the biggest adrenaline rush was the launch. There's nothing like launching your own rocket, no matter what experience you have, it's hard to beat launching your own rocket. I guess my marriage and the birth of my children and the launch of my rocket, those are the defining experiences in my life.
MZ: Of course, family always first, but rocket launches are right up there. And having the two spacecraft get into orbit.
What's very interesting, and this is a little bit hard to describe, is that these spacecraft, they're machines. You start with some aluminum, you start with circuit boards, you put all the stuff together, you wire it up, you put software on it, and it's something that you create. And what's amazing is that you send it to this faraway place, and it does what you tell it to do.
It's very hard to explain. You built it, of course it does what you tell it to do, but what I liken it to is when you fly in an airplane. I love to fly in airplanes. Whenever I take off in an airplane, its amazing to me, I think it's amazing to me. I think it's amazing that an airplane can fly. And I know exactly why an airplane should fly, lift plus thrust is greater than load plus drag, the plane takes off. But to me, it's just a wonderful thing to me whenever an airplane takes off.
So the fact that you can send these machines far, far away and you tell them what to do and they do what you tell them, perfectly, is to me, I just can't even describe what a thrill it is. And when the data comes down, I look at the raw data all the time, it's coming down on my computer right now. You look at this data that nobody's ever seen before, so there's a period in my life every day where I look at what we have, and I have information in front of me that nobody in the history of humanity has ever seen before.
And of course, what I want to do is analyze it and write it up so that everybody can analyze it and everybody can have it, but knowing that you're part of a group of people that has discovered something and has known something that nobody else has ever known...
Me: That's real exploration.
MZ: You never get tired of it. No matter how long I've worked on this, or how long I will work on it, I will never get over the thrill of knowing something for the first time that hasn't been known before.
Me: Do you feel a sense of having a remote presence, of feeling that it's part of you that's there, is it sort of a sense of feeling as if you are there in a way?
MZ: Absolutely. In fact, I'm on leave this semester to fly my two spacecraft, I had to go to a meeting of the faculty for something and I walked into the room, and I said, "Alright, back from the moon for an hour!" (laughs) "And then I'm going back!"
We never say, "Our spacecraft are at the moon", we always say "We're at the moon". It's something that everybody on the team feels. We're there, collecting these observations, our spacecraft are doing it for us, but there's no doubt at all that we feel like we're there with them.
Me: I suppose the corollary to asking what the best thing or most exciting thing was is to ask, what has so far been the worst part?
MZ: Oh, the worst part... well, probably the, uh, I don't know if it's the lack of sleep... well, you get over that. (laughs)
Over the course of the mission, even a mission that goes very well, you get scrutinized by a lot of review boards that are extremely critical, and they need to be critical. But even though we did incredibly well, technically, schedule, budget-wise, there were times when I felt that we weren't doing so well because of the scrutiny that we were getting.
But I'm really glad that we got that scrutiny, because if the boards hadn't been as probing as they were, we might not have been as successful as we are right now.
Me: What has been the strangest part, or the most unexpected?
MZ: So, that's actually a good question, because it ties into something that I wanted to mention. We did an education program on the mission, called--
MZ: MoonKAM. MoonKAM turned on again yesterday for the extended duration mission, because we'd had to hold off for a while because our operations were just so complex getting the spacecraft into orbit that we had to get that understood before we could start up doing the education part again.
What has amazed me is how far beyond the lesson plan the students have gone with studying the images [from MoonKAM]. We've collected over 100,000 images for students, the students targeted the images, the students uploaded the commands, and the students downloaded the pictures that they had targeted, and our colleagues at Sally Ride Science had developed activities in the classroom for students to study the images, but the students went well, well beyond what was in the activities to try to understand what was in the images.
They researched these areas themselves, we had one group of student that took an image of a crater that was 40 meters across, and they wanted to understand what that meant, so they got permission to go out on the Texas Tech football field and draw a big circle 40 meters across to be able to say, "Wow, 40 meters is actually pretty big across", even though that's a tiny crater on the moon.
There were students who, in addition to analyzing the images, read literature books about the moon, did art related to the moon, studied the moon's place in history, so it's just been incredible what an impetus this was for students. The students were just so motivated to understand these images.
When Sally Ride and I designed this experiment, we thought the students would be very interested because it was their own images of the moon, and it was just incredible how motivated they were, so we really believe we're on to something in terms of creating a really, really transformative educational experience for students.
Me: Did you have moments like that when you were young, when you got very into what was going on, and you knew that was what you wanted to do?
MZ: I've always known that I wanted to study space. I can't even begin to think what I would have done if I'd had the opportunity we've provided for these students. I built my own telescopes, I looked at the sky... you're interested in space, so you've clearly done a lot of this.
Me: I ask a lot of people this question, some people have one moment [that got them inspired] and some people don't.
MZ: There was never one single moment for me, but I am certain that we created many of these moments for the students in the MoonKAM experiment. We never expected all of them to want to grow up and work for NASA, what we wanted to do was to motivate them.
This was targeted at Middle School. Middle School is the time when students have to decide, do I take the harder math that puts me in the AP track, or do I take the easier math, and then I can't take advanced science. So why take a hard course when you can take an easier course? Well, if you can do cool stuff like that, that's a strong motivation to take the harder math. So we're hoping this inspires kids to study math and science and take classes in engineering and science in general.
This is all about us creating opportunities for us to realize that for us to advance as a society, we need scientists and engineers, but we also need informed voters, who understand complicated issues, associated with the environment, with climate, with the world around us. Who understand traffic flow, energy, medical issues, there are a lot of things going on in the world today where you have to have a pretty good understanding of science to be on top of.
Me: You said that there were students who were interested in the moon artistically and historically, how do you feel about people who have other talents and are interested in the missions, their contributions? For example, the class who named the probes? I know there are a lot of engineers who when they see artistic stuff, they don't understand it, or they say, "Oh, that's nice, but whatever", so how do you feel about other talents contributing?
MZ: Last year, for MIT's 150th anniversary, they had five institute symposia. I co-organized one on exploration, and as part of the exploration symposium, we had a storyteller come and tell stories about exploration, and we held a student competition, and we held an art exhibit, because we wanted exploration not just to be about the technology and the science.
We thought that "exploration" really should cover all aspects of endeavor--the humanities, the social sciences, all of that comes into it. We all felt the same way, to the extent that you could broaden up the participation to encompass everybody's interests. Because exploration, it's so much fun!
MZ: What could be better than discovering something? So we broaden it--everybody's good at something. Not everybody's good at math and science, although we're hoping to help people find talents in that field, but there are people with talents in literature and the arts and it's fantastic if all of these elements can be brought to bear on this problem. Artists are able to see things that I wouldn't see if I looked at something.
Me: I really do think it's incredible sometimes, when you have people with different talents who are talking about the same thing, and you have people who can make--I'm an archeologist--historical connections. I remember when the Mars rovers first landed, there was this really great article in National Geographicwhere they mentioned that each of the rovers had one arm, and they were comparing it to John Wesley Powell, who was an explorer of the Grand Canyon, who had only one arm.
Me: And they made all of these really great comparisons, and they were saying, surely the spirit of John Wesley Powell is riding with us on Mars, and I went, "That is so..."
MZ: It's great.
Me: That's a really great thought.
MZ: I hadn't seen that, but it's really good.
Me: Now, I asked you this question before, when we were at the Mars event with Dr. Elachi, and I guess I want to ask it again for the article now. You said when the probes were launched that they were like your children, and you were thinking of them as GRAIL A and GRAIL B, because that's what they were called. Now they have names, they're Ebb and Flow, do you think of them as Ebb and Flow in your head?
MZ: Yes, I do. Although for the software, we use "A" and "B", we always put "Ebb and Flow" in parentheses now, to give them names. The names have been very popular. A lot of people out there know the names. It's interesting, because the two of them were designed to be nearly identical, but they have slightly different behavior.
Me: That's just what I was going to ask.
MZ: It's very slight, in terms of battery charging levels. Slight, slight, slight differences that don't really make a difference in the performance, but it's just like you have children, and children are different, these spacecraft are different. You can sort of at this point predict what their behavior will be.
Me: I've been following them since the beginning, and I've heard people talk about the Spirit and Opportunity rovers as having personalities, because we have had so many experiences to judge by.
MZ: They behave.
MZ: I'll tell you, my spacecraft, they behave really well, it's easier to predict what they'll do than it is to predict what my friends or family will do, because people can be somewhat unpredictable!
Me: You said that you built your own telescopes when you were younger, what other projects did you do as a science enthusiast when you were younger?
MZ: When I was growing up, I lived in eastern Pennsylvania, in anthracite country. I built my own telescopes, I taught myself optics, and I ground my own lenses, I made my own eyepieces. And I spent lots, and lots, and lots of time looking up at the sky. So I knew the night sky like the back of my hand.
I did a lot of that, I did some geology, but not as much. Space was really my thing. Building equipment, too.
Me: I see you've got a LEGO box [here in your office] did you play with LEGO?
MZ: I did play with LEGO. [I follow her over to look at a LEGO model spacecraft on her desk]
Me: Ohhhhh, that's awesome!
MZ: Yeah, that's the Lunar Reconnaissance Orbiter, we have that in LEGO.
Me: Is that a kit?
MZ: Yes, I think you can probably order it online.
Me: That's incredible, can I take pictures of that later?
Me: So you still build with LEGO?
MZ: I still do, although I had an undergrad build that.
Me: I know that there's a petition to make a Curiosity LEGO set and I really hope they work that out.
MZ: They probably will.
Me: Thank you so much, I don't want to take any more of your time, I got a lot of really good data. Thank you for your time.
That night, it was clear, and the Boston University Astronomical Society had a meeting. While some of the more technically-minded students were photographing the moon with a computer-controlled telescope, I looked through its eyepiece. The view was still and crisp, with mountains and craters clearly visible. During our conversation, both Professor Zuber and I had generically referred to the moon as "a planet" because we were comparing it to planets, even though the moon is technically a satellite of the Earth, and now I understood why — the moon may not be a planet, but it is a WORLD, a real place, with its own geology and geography, a place that can be visited and studied.