Web extra: Steven Squyres talks about roving on Mars
- By Florence Olsen
- Jan 31, 2008
Steven Squyres, professor of astronomy at Cornell University, is principal investigator for the Mars Exploration Rover Project. The mission of the Mars rovers, Spirit and Opportunity, was supposed to last 90 days. However, the robots’ endurance — more than 1,442 days at the time of this interview — has surprised everyone. Federal Computer Week Managing Editor Florence Olsen interviewed Squyres Jan. 23 about the Mars mission. FCW
: How has your relationship with Spirit and Opportunity evolved during the past four years, and how would you describe that relationship in terms of your feelings for the rovers? SQUYRES
: That’s an interesting question. Actually, the relationship with the rovers began much earlier than four years ago. I was there when they were born. They had many parents. It’s funny — we tried to make them as identical as we could, for very good reasons. First of all, if you intentionally make them different, then you’ve got to learn how to operate two different machines. Second is if you make them different, you’ve got two different designs you’ve got to come up with and test, and that takes more time and more money. There are also obvious benefits when you’re in the development phase. Say, if a part breaks or fails, you can take a piece off one rover and put it on the other. So it makes sense to try to make them identical.
As with any machine that complex, however, you can’t quite get them exactly identical. Even when they were babies, they were different from one another. The way it worked out, we built Spirit first. Then Opportunity came along later. As you put one of these things together and you start to use it and start to test it, you learn where the weak points are in the design. The first time you test almost anything, it’s bound to fail. It’s very rare for a test to be right the first time. Spirit was kind of a problem child from the start. In most of the tests, we encountered problems on Spirit first. We’d go and fix them. Then we’d make the same fixes on Opportunity. So when it came time for Opportunity to undergo the same test, we would generally find that things went better.
Since the rovers got to Mars, their personalities have diverged considerably. They are much, much more different from one another now than they were when we first landed. It’s been a combination of things. One is that they landed at very different places — the terrain, the topography, the geology — is very different at the two sites, and so we’ve used them in rather different ways. Spirit landed in a rugged, mountainous, difficult-to-drive-around-on place. It landed in a place where the rocks are very hard, so when you try to grind into them with our rock grinding tool, the rock abrasion tool — we call it the RAT — things wear out more quickly. Spirit faced a rather different set of challenges than Opportunity, which landed where the terrain is very smooth and flat and the rocks are very soft. Opportunity kind of had an easier job all the way through. So we used them rather differently. Of course, what’s happened is we designed these things to last for 90 days. And today is day — let me check for you — today is day 1,442 of our 90-day mission. These things have been up there for a long time.
What’s happened is things have started to break. Pieces have started to fail on both rovers, but of course you don’t have the same failures on both rovers. One thing will break on one rover. A different thing will break on the other rover, so they’ve become more and more different from one another. Some things you can’t fix. You can’t go up there with a screwdriver. So some things break, and you learn to live with it. They’re two very different vehicles to operate today.
As far as our relationship with them, it’s a natural tendency to project attributes onto machines and to identify with them. And we feel that. It’s a little silly maybe, but it’s natural and we just go with it. When they do something good, we’re proud, and when they do something wrong, we get a little angry with them. And when they get into trouble, we worry. We feel all of these things. The worst part, of course, is going to be when the mission finally ends — when they die — and I don’t know what that’s going to feel like. I think it’s going to feel pretty bad. But they’ve lasted so long and they’ve done so much. They’ve had far richer and more productive lives than anyone, including those of us who created them, could have ever hoped for. So it’ll be an honorable death, but it will be a tough day. FCW
: If NASA develops a new breed of rovers, what characteristics would you want them to have? SQUYRES
: That’s actually happening. There’s a rover mission called the Mars Science Laboratory mission. It’s going to launch in 2009. What it does is build on what we have learned. So it has many of the capabilities that you would want to add to what we were able to carry with us on the first rover mission. For example, we’ve been able to do a lot in terms of reading the geologic record and helping to understand whether conditions would have once been suitable for life. But one thing that we can’t do is look for organic molecules. We can’t look for organic material. The instruments we have — they don’t do that. We focus on rocks and minerals. The next rover is going to carry instrumentation that will enable us to look for organic molecules.
Our rovers are solar-powered. And that has worked OK, but there’s a big drawback with solar power, and that is it doesn’t work when the sun’s not shining. So we can’t charge the batteries at night. We have trouble when we get dust on the solar cells. Mars is a very dusty place, and dust settles from the atmosphere and coats the rovers’ solar arrays, and we are at the mercy of the winds. We have to wait for a gust of wind that will dust off the solar arrays. On the next rover mission — the one that’s flying in 2009 — power is not supplied by solar cells. It’s powered by plutonium. We’ve got a nuclear power source that supplies a steady, reliable source of power. Another thing is this next vehicle is bigger. The larger a rover is, the easier it is to drive over rocks. A field of obstacles that Spirit and Opportunity might have a tough time picking their way through, this thing can just go monster-trucking right over it. So it’ll be able to cover greater distances, get more done and so forth. It will arrive at Mars in 2010. It will build on these missions and benefit from lessons that we’ve learned. FCW
: How have the rovers survived in extreme conditions that you had not expected them to endure for so long? SQUYRES
: There were three things that enabled the rovers to survive far longer than we had expected and to get through the winter. One is that we just built good hardware. We tested the living daylights out of these things, and we built really good stuff, and we’re proud of that. But that alone doesn’t account of it. I never — even though I had a lot of confidence in the hardware — never expected them to last this long. There were a few other things that really helped. One that we already touched on were these wind gusts. We thought correctly that we would see dust build up on the solar arrays. What we didn’t count on was that gusts of wind would periodically clean the solar arrays off. When that happens, it’s like taking the vehicle to a car wash. It just cleans it off, and power goes way up again. It’s h ppened three times to Spirit, and it’s happened repeatedly to Opportunity. So that was just good luck. We can’t contribute it to anything other than just Mars being good to us. It’s exploration. You don’t know what you’re going to get.
The other thing that has been enormously beneficial — this has been particularly important for Spirit, because Spirit lies fairly deep in the Southern hemisphere at a fairly high latitude on Mars in the wintertime. What happens is the sun gets lower in the Northern sky. You’d like to have some mechanism that you can use to crank up the solar array so the sun would be shining more directly on them. And, of course, we don’t have the ability to do that. But what we can do is drive the rover onto a north-facing slope. As long as there is topography, as long as there are hills, mountains, craters and so forth, we can drive the vehicle onto a steep slope that faces north and tilt the solar arrays toward the sun and use that trick to survive the winter. We’ve survived two Martian winters with Spirit, and we’re now beginning our third Martian winter. And in each of those winters we’ve operated because we had this topography, these slopes to work with. That has been allowing us to survive the very harsh wintertime conditions. FCW
: Would you be as interested in studying Mars and Europa if it weren’t for evidence that water existed on Mars and that Europa contains an ocean that might support life? SQUYRES
: I would still be interested because I like planetary exploration in general. I’m interested in Venus. I’m interested in Mercury. But it’s the former or maybe current presence of water on those objects that makes them special. And that is what has caused me in my career to focus largely on those two objects. They have greater potential as an abode for life than most of the other planets, which have far harsher conditions. FCW
: Establishing decision-making procedures that will lead to good decisions is a constant challenge for federal executives. Is it a challenging aspect of your work as principal investigator for the Mars mission? SQUYRES
: Oh, you betcha. I’ve got two priceless rovers on the surface of another world doing something that’s never been done before. I’ve got 170 scientists on my team with 170 different opinions about what the rovers should do. And we have to come to a consensus every day. We can’t program these rovers a week in advance, a month in advance. Every day you have to decide what to do because when you drive, each day you’re someplace new, and you’ve got to figure out, "OK, what do we do on Mars today?" You can’t plan a week ahead. So what happens is each day for each rover, a team of scientists and engineers — a typical number might be two dozen scientists and a dozen engineers — come together, and in a matter of a few hours it is the job of that team each day to look at what happened on Mars yesterday and decide what is going to happen on Mars today. You have to come to consensus, and there have been two factors that have enabled us as a team to do a pretty good job of actually reaching a consensus. One is the rovers have lasted so long. If you think the rovers are only going to last a few months, there’s an enormous amount of pressure to get things done. Everyone wants to see that their thing gets done. If the rovers are going to last for years, then there’s a certain kind of horse-trading that can go on. "OK, we’ll do your thing this week if you promise that we can do my thing next week." That goes on all the time. As long as you have confidence the vehicles are going to last, you can use that to your advantage.
The other thing, however, that has been a wonderful motivator, is hese are literally priceless assets at this point. It cost $900 million to get them up there, they are unprecedented in the history of exploration, and if we can’t come to a consensus, then they sit there on Mars and do nothing because we couldn’t get out act together back here on Earth. That’s a wonderful motivator. It’s looking at the data you have in front of you, making a set of decisions about what you should do, then acting on that decision and carrying it out on the surface of Mars. It is a challenge that we face constantly.
We have to plan on multiple time scales, too. Each day we will generate typically just one day’s worth of activities for the rover. But you’ve also got to have a long-term plan. What you’re doing that day has to make sense in the context of a plan that might extend for weeks or even months into the future. And you have to account for all the factors — the health of the vehicle, the changing season, the scientific objectives we have in front of us, the configuration of the terrain and the topography. All of that is something that you have to worry about. So we have several planning functions within the team. We have some people whose job it is to look long-term. We have other people whose job is purely tactical. We do all of that, and we’ve done it pretty well, I think. FCW
: What do you think is the greatest technical achievement of the Mars Exploration Rover Project? SQUYRES
: There are several. One obvious one is they lasted so long. I think if I had to pick a single one, it would be the fact that we have been able to cover so much ground on the surface of Mars. The mobility to travel across the surface is just fundamental to the discoveries that we have made, and is fundamental to the exploration that we do. Imagine that you’re a geologist, imagine that you’re a scientist sent to a place to explore and your job is to go a place that no one has ever been before and to figure it out, understand and report back what you’ve found. But you don’t go there and nail your boots to the ground. Mobility is fundamental to exploration. So if I had to pick one thing that’s the most important technical accomplishment, it has been the ability to travel for many kilometers on the Martian surface. FCW
: Is the Mars project also a significant policy and management achievement for NASA? SQUYRES
: Oh, absolutely, absolutely. You may realize that this mission rose from catastrophe. In 1998, there were two missions launched to Mars — a lander and an orbiter. Orbiter burned up in the Martian atmosphere because of a mix-up over English and metric units. And Lander crashed on the surface for reasons that have never been fully explained but probably had to do with an error in some of the software. Both of those missions were lost. That put an enormous amount of pressure on our mission to succeed. It would have been very easy for NASA to take the safe way out. That wasn’t what they chose to do.
What they chose to do was the most complicated Mars mission ever done. They chose to do two of them, and the reason they chose two of them was that it maximized our chances of success. And in terms of a management success story, when NASA said, "OK, here’s the money, now go," those rovers had to be on top of the rockets in Florida in about 34 months. Conventional wisdom says you need more like 48 months — about four years — so we were under enormous pressure.
We had an incredibly tight schedule. There is no way to slip your schedule. You’re schedule is literally driven by the motion of the planets around the sun. There’s nothing more fundamental than that in terms of a schedule driver. You cannot argue with Sir Isaac Newton. We had to meet that schedule with that extreme y rigorous set of constraints on us, and we did it.
We did it because of some extraordinary leadership at the Jet Propulsion Laboratory where the rovers were built, and some extraordinary leadership at NASA headquarters in Washington, where they had to make some very tough decisions about what to do about schedule and what to do about budget. The leadership on our project was exemplary. These things wouldn’t be on Mars today and still going strong if it hadn’t been for very smart, very gutsy people.