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To MARS with MER - MER the Mission

Adam Steltzner
Mars Exploration Rovers EDL Lead Mechanical Engineer
NASA Jet Propulsion Laboratory

"December 12, 2002"

P2K: The parachute's solved, your job's done, right?

Adam Steltzner: Almost. We're entering the phase of the mission now where we just have to tell the story, get the story out that we are in good shape, so that all the various people who have to sign off on allowing us to launch will sign off and allow us to launch.

P2K: What has happened since we met last? Have you been on the road just as much as ever?

Adam Steltzner: Pretty much just as much as ever. My daughter was born at the beginning of October, so I took a couple weeks off there. But other than that it's been the same basic "road trip" life that I've been doing for the last couple of years. We had, since we've last spoken, we've had a very successful airbag test series with our flight design. That test series was designed, the tests were set up to establish what the performance of the airbags would be on Mars, and the result from that is the performance is looking great. We have outstripped our expectations on the airbag performance. Check that box, we've got a set of airbags, we can do the job. In fact, you can see them packed in here, mockups of them, packed up in against the flight lander.

Since then, also, since we last spoke, we had a very successful parachute test and we've narrowed in on the precise parachute build that we're using and we've seen excellent strength behavior out of the parachute. Remember, that was what we were struggling with. We were struggling to get a parachute that was strong enough for us. And the parachute that we've come to, the design we've come to, has performed flawlessly in its tests up at Ames. And those were the big hurdles that we had left. And so, we just had a review last week in which we told that story, the story of the airbags and the story of the parachutes, and got the word out to headquarters and the management personnel, exactly how good we are doing with respect to those two very critical subsystems.

P2K: The airbag has been a bit of a problem from Plum Brook on (i.e. the October 2001 tests.)

Adam Steltzner: Yes. As the design of the spacecraft progressed, the spacecraft got heavier. And in order to enter this heavy spacecraft and get it safely to the surface of Mars, the parachute got bigger. When the parachute got bigger, we had to look at ways of making it more structurally efficient, to pack enough parachute inside the volume that we had available to us.

In Hartford (CT, at Pioneer Aerospace), (JPL videographer) John (Beck) caught up with us looking at the results of the initial testing associated with that bigger parachute, and what we found was the parachute, although it was big enough, it wasn't strong enough, and we saw the damage that those initial tests that we conducted out in May demonstrated to us. And that was very alarming. We were one year out and we had a parachute that wasn't strong enough.

So over the intervening eight months or so we just really turned the crank on modifying the parachute design, not the parachute shape, but the structure of the parachute design, to meet the needs that we have.

P2K: What was your reaction when you saw the first test in the wind tunnel?

Adam Steltzner: When we went into the wind tunnel we took a slew of different designs. Actually, all told, there were five different parachute configurations that we took into the tunnel, one of which was our flight configuration, others of which were variations on the flight configuration using different fabrics.

What surprised us was that some of those fabrics that were, imporous, that did not allow any air to flow through the fabric, resulted in parachutes that would not open. They would come to a partially inflated condition and stall there. This was very alarming to us, initially at least, because we were concerned that even though these tests were subsonic tests, with a high density, low Earth atmosphere, we were concerned that that behavior might indicate inflation problems in our supersonic, Martian atmosphere parachute inflation.

In the intervening time we've done a suite of other tests and some research that has led us to realize that those inflation problems that those non-flight configurations had up at Ames are not indicative of the inflation we will see on Mars with our flight parachute.

But there were a few weeks, actually two months, there, that were quite distressing to us, and it all started with that first test in Ames where we had that parachute come to this partially inflated configuration and just sit there, wallow in the wind tunnel for minutes on end without fully inflating, and it was a shock to us then. But we've since realized that it's not a harbinger of doom for the flight parachute.

P2K: Steve's (Squyres) adjectives were "terrifying, appalling, horrible." What were your adjectives as you saw that? What were you feeling?

Adam Steltzner: Shocking, baffling, a sense of dismay. You know, the problem that we had was that we knew that the tests we were conducting up at Ames were not indicative of the parachute's inflation performance at Mars. They were indicative of the strength performance of the parachute, but not of the inflation, how or whether it will inflate. We knew that. That said, we didn't want to have to face an inflation issue in the Ames tests, and we did not expect to face an inflation issue in the Ames tests, so that first test went off and we just looked at that with amazement and despair. It was quite despairing because there was a concern that our capacity to keep the world comfortable with our progress and allow ourselves an unfettered work environment to make it to the completion of the project might be in jeopardy.

Typically when unknown events happen a lot of "help" comes in from the outside and it's not unusual for that help to be more of a hindrance than a help. So we were a little concerned that we would get so much "help" from the outside that we would be hog-tied and unable to complete our job.

P2K: How many successful tests of the parachute have you now had?

Adam Steltzner: We've had eleven successful tests of the parachute. The parachute on Mars has to handle about sixteen to seventeen thousand pounds of load, of force, when it opens up. We have taken a parachute and we have opened it up at just shy of thirty thousand pounds, repacked it and opened it again at twenty-five thousand pounds. The parachute's not designed to be used in those multiple inflations, but that process we've used to demonstrate the incredible strength margins and strength capacity that our flight design has. So we've had an excellent set of tests up at Ames. We're not done. We will go back with the actual flight build, the set of parachutes that were built for flight, and we'll do our final qualification tests.But all of the testing that we've done thus far at Ames says it has very low risk. We're just going to go in and confirm that the parachutes we're actually putting on the spacecraft are identical to the ones that we tested at Ames a couple months ago.

P2K: Have you had a budget problem in doing the number of tests that you want to do?

Adam Steltzner: No. The parachute and the airbag... for these mission-critical subsystems, the money is there to do the job right, and we've had all of the financial support that we needed to get the number of parachute tests done that we felt we had to do to prove to ourselves that we were flying the right parachute and that it would behave correctly on Mars.

P2K: Since we're lucky enough to be right here, could you show me on that flight rover, even though we can't see it in detail, where are the EDL bits...?

Adam Steltzner: Certainly I will.

Most obviously on the outside here, this silver piece that you see is one of the four airbags. The lander is a tetrahedron, a four-sided pyramidal kind of solid structure, and on each of the four faces, the base and on each of the three sides, there is an airbag lobe. They're connected to one another through a set of vents; this vent is opened here and you can see inside of it. The airbags are what cushions our final impact with the surface of Mars.

Working backward, I'll walk you backward through the flight sequence. So the last thing we do is hit Mars, and so we use the airbags, which is the first thing you see, the most exterior piece of the spacecraft; that's what we use to get that job done. Stuffed inside, shown right here, okay, is the tether that tethers the lander, which has the rover on the inside and the airbags on the outside; this bridle here connects the lander with the backshell.

The backshell we used as protection as we entered the atmosphere. That was the aft, or rear protective shield, when we were entering the atmosphere. Not shown here would be the heatshield.

So as we come into the Martian atmosphere there's a heatshield and a backshell which wrap around the lander. And during entry, descent, and landing - EDL - we go through a sequence of events that gradually open up the spacecraft, kind of through a transformer type of sequence, and we execute the different pieces of EDL.

Adam Steltzner: The heatshield's not shown. This is the backshell. Inside the backshell and the heatshield is the lander.

So I'm actually going to take you the right way. First thing that happens in EDL, not shown, is a parachute pops out of the backshell. I'm sorry. Let me back up.

The first thing that happens as we come into the atmosphere, the heatshield ablates away the energy, most all, like ninety-nine point five percent of the energy, kinetic energy that we have when we hit Mars, is dissipated through burning of the Martian atmosphere and the heatshield's ablative thermal protection system. After that's occurred, we open up a parachute, which you can't see but it's stuffed inside of that backshell. The parachute then slows us down and takes off about point four five, or almost all, of the remaining energy that we have to dissipate before we run into the Martian atmosphere.

After we're successfully on the parachute, we jettison the heatshield and drop the lander below the backshell on this bridle that you see here. After we've done that, here in what's called the terminal descent configuration, and we're approaching the surface quite quickly, still.

Inside of the backshell there are three large solid rocket motors. And those rocket motors fire just prior to us hitting the surface. Almost at the same time we've inflated the airbags on the lander, which is now tethered below the backshell. We shoot off the rockets, cut the bridle, and the inflated airbags protecting the lander impact the surface and absorb our final bits of energy until we come to a rest.

Then the lander opens up and exposes the rover, which is within.

P2K: How many of these pieces that you've just described have you personally been working on the past couple of years?

Adam Steltzner: Every one but the rover.

So the heatshield, the parachute, the bridle, the rocket motors, the airbags. All of those.

All of those, for all of those subsystems, or rather for the collection of those subsystems, each one of which has had at least one engineer from JPL working on it, but for that collection I have kind of "Mother Goosed" the overall performance and production and success of it.

P2K: Which one of them has given you the hardest time?

Adam Steltzner: That's a tough one. That's like asking which one of your children you like least.

I think that the parachute is the one that is the most difficult to finally put to rest, all of the elements of the parachute. Specifically, the inflation question of the parachute is one that is very difficult to completely satisfy.

If you look at what you really need to know to be absolutely, one hundred percent certain that the parachute will act as you want it to act on Mars, the only real way to do that is to put the parachute on Mars. You could spend hundreds of millions of dollars doing Earth tests and they still can't exactly duplicate the conditions on Mars. So the parachute's been a real difficulty for us.

The airbag has always been tough, but the airbag's capabilities have kind of defined our mission. But the parachute needed to perform, has needed to give us a certain performance, and making certain that we're comfortable... and that we've done a good job of proving that the parachute will meet that performance has been perhaps the toughest job.

P2K: I thought the parachute, along with the airbags, was another one of these legacies that weren't supposed to be a problem.

Adam Steltzner: That's right. That's right. Both of them started out as MPF - Mars Pathfinder - reflights. The airbags have evolved substantially, and I'm going to tell you that these airbags today are ten times better than the airbags that Pathfinder had. We've been able to take the work that I did on developing these airbags and extend it, because we have a method that we can use in Earth testing that's very satisfactory to give us a sense of the performance of the airbags.

For the parachute, the parachute is essentially the same parachute that Pathfinder flew, a little bigger, but it's had to handle higher loads and we've had to look more closely at the arguments that we used, the rationale we used to fly it in Pathfinder, and do a better job of defending that rationale.

P2K: What have you learned on the job here at JPL that they didn't tell you at engineering school and that you couldn't tell your students, what would you need to know to be a successful in this business.

Adam Steltzner: I think - it's a good question.

I would say... "expect to be surprised." That is, when you are in an academic environment, when you are teaching, or a student yourself, you tend to think of the world as being very analyzable, that you can take the world and break it into pieces, each of which is understandable, and then collect those pieces together for a total understanding. And largely that is true, but the historic process, as you go through that process in reality, in the field, in the nitty-gritty here, the number of surprises you encounter is surprising itself.

And I think that the one thing that I didn't learn in engineering school that I've certainly learned through this process is never underestimate the opportunities you will have to be surprised, and expect - Amelia Earhart said - expect the unexpected. And I think that would be what this has taught me.

P2K: It surprises me how many bits and pieces are sort of being dreamt of or modified at the very last minute. Tell me about the descent rate limiter.

Adam Steltzner: Once again, as the mission matured, it also got heavier, the spacecraft got heavier. And the pieces of the Pathfinder hardware, the legacy hardware that we had, were being stretched thinner and thinner and thinner, until variously they had to be redesigned.

We've talked about the parachute, we've talked about the airbags. One of the elements that we had to do a redesign relatively late - that is to say, relatively recently - is the descent rate limiter. The descent rate limiter sits inside of the lander here. And it is the device that limits the speed at which you play out this bridle. When we lower the lander out of the backshell, the descent rate limiter limits the rate, the speed at which the lander is released from the backshell. We were struggling to try and make the Pathfinder design work, and it was very marginal. And finally, about three months ago, we said enough. Let's think outside the box and fix this problem with a clean sheet of paper, essentially. Using the elements that we had, but reconfiguring them in a different fashion and using some very high strength materials called Zylar - actually, the material that this bridle is made out of, this bridle is made out of Zylar, which is a very high-tech, newer softgood, fabric, material. And we employed that same material for the lanyard in the descent rate limiter.

And using that material and some ingenious engineering on the part of some colleagues, we put together a descent rate limiter that is very robust. And it's been a whirlwind operation because three months from soup to nuts is a very short period of time. But the team has done an excellent job and we really have got a great performing subsystem, great performance.

P2K: Is it unusual to have as many things in the EDL system come together so late in the game?

Adam Steltzner: Not particularly. Pathfinder had some elements of the EDL system being tuned and modified quite late in the game. We did not anticipate having to do that because we really thought we were going to be able to leverage the Mars Pathfinder heritage and just refly this hardware. It was, you know, in hindsight that was... we were mistaken in assuming that, because as history evolved we could not really leverage that flight hardware. And so that's what put us in these... constantly realizing that this subsystem that had been making, had been meeting the needs, just wasn't going to meet the needs. So it's not unusual when you're creating a new system, but when we started this job we didn't think we were creating a new system. In the end, that's exactly what we have done. We've recreated a new EDL system based loosely on the Mars Pathfinder architecture but for which each piece of the puzzle has been changed fairly significantly to meet the needs of this missions.

P2K: This system is really where rubber hits the road, it's where the spacecraft hits the planet, and it's got your signature all over it. How does that make you personally feel?

Adam Steltzner: That makes me feel great. It's been, it's certainly been the high point of my career, producing, working on this essential phase of the mission. You know, I think probably everybody thinks that their piece of the mission is the most important, and I stand there right with them, and I think my piece is the most important in that EDL is where you...

We have a long history, the human species has a long history of placing robotic spacecraft in orbit for flying bodies, planets and moons and asteroids - we've done a lot. We have much less history involved in actually going to the surface of a planet. And the big problem with going to the surface of a planet, in my opinion, is the Entry, Descent and Landing problem. Showing up at a planet at about five kilometers a second, or let's call it two to three miles a second, and then slowing yourself down to something like three to ten miles an hour - doing that job is a lot of work, and to do it you interact with this unknown environment. We don't really know what the winds on Mars are like. We have some atmospheric data but we don't have solid data. And ultimately when you get done, you land on a surface that we don't know what it looks like yet, so to me it's the hardest part of the puzzle, it's been an absolutely incredible experience, very gratifying experiencing, to work on this. It is the high point of my career.

P2K: How many miles do you think you put in here on earth to get the EDL system working on Mars?

Adam Steltzner: It's funny you should mention that. I was just thinking that as I was flying back from Seattle. I've traveled somewhere between two hundred and fifty and three hundred thousand miles over the last few years putting this EDL system together. That's going around in the world ten times. I've done it all, all of it, almost all of it, inside the United States, so I've crossed the United States, well, that's about fifty times of crossing the United States. So I've been bouncing around a lot.

P2K: What do you do on the weekends? Do you have any weekends?

Adam Steltzner: I do have weekends. I used to, before I was working on the Mars Exploration Rovers mission, I used to go and do things away from home on the weekends. Since the Mars Exploration Rovers project has been going I stay at home and do laundry and relax, and sleep.

P2K: So how do you get people to share the vision? And work as hard as they've been working?

Adam Steltzner: It's surprisingly easy to get people to share this vision, the vision of going to Mars, putting a spacecraft on the surface of Mars, is fairly easy to get people excited about. It is plain exciting.

I think there is a gene that, as human beings, we all share - the "curiosity gene," the gene that has us wonder what's out there, what's around the corner. And when people, when these sub-contractors, people at other organizations around the country, have an opportunity to get involved in this, usually they are very, very, very receptive. And in the rare instances that they don't chomp at the bit immediately, if you just share with them the incredible wonderment and excitement that it means to go to Mars, they very quickly become bitten by it and overtaken by their own enthusiasm to participate.

P2K: We're standing in front of a rather large American flag. To what extent do you think that exploring Mars, exploring the solar system, is something that you're proud to contribute to the nation?

Adam Steltzner: Well, I'm going to wax philosophical here for a second - just philo-political for a second. I mentioned this gene of exploration, and I think that that, I honestly think that we physically, all of us, have that curiosity gene within our makeup of who we are, all of us, as human beings.

But I believe that also that more than any other nation, because of the history of our nation, and how we came to be, that written into the story, the mythology of America, and what it means to be an American, is this exploration, this independence, this striving to go beyond what is known. And so I'm extremely proud as an American, as a human being, to be part of the exploration of Mars and of our solar system and, to the extent that I have, to be able to support and promote the tendrils of our understanding, reaching out into the... past our current sphere of knowledge and into the unknown, expanding our understanding. I'm very proud to be part of it. I think it is a very human issue and also a very American instinct. I feel quite "American" participating in it.

P2K: All these things - the DIMES (descent imager camera) system suddenly appears out of nowhere. Is there a chance that the Mars Exploration Rovers are ...a spacecraft designed by a committee with camel-like protrusions instead of a horse-like, racehorse-like sprint to the end?

Adam Steltzner: I do completely admit to the fact that it has a little "Rube Goldberg" features to it. It's a little off. It seems like a ball of Band-aids, perhaps, and it's hard to see what the initial problem was because there are so many Band-aids. That said, it was not designed by committee. It was designed by a team, and that team worked really hard to understand the bits and pieces and how they interacted. And I'm very confident that even though it appears as many little pieces that solve this big puzzle of EDL, especially, that it works together as a coherent system and it gets us what we need - it gets us the performance we need.