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To MARS with MER - MER the Mission

Stacy Weinstein
Test Engineer
NASA Jet Propulsion Laboratory

P2K: What is your job on this mission?

Stacy Weinstein: My job is to do testing for the entry, descent and landing system, which means I get to work with airbag drop tests, rocket drop tests, parachute drop tests, and make sure that the capabilities we are sending to Mars work here first the way we envision them.

P2K: The lab did it before with Pathfinder so it knows perfectly well how to do this. There's no real problem in doing this is there?

Stacy Weinstein: Well... it's not quite the same as Pathfinder. First of all, we are landing in a different season, in a different time of day, which means we've got a lot less dense of an atmosphere, which means we are going to be falling faster, and we are heavier. We are a lot heavier this time on entry, descent and landing (EDL) than we were on Pathfinder, so those two things combined mean that we have to go back and recheck our airbags for heavier masses and potentially faster velocities. We have to size up the rockets, so basically we have to rebuild the rockets. We have to build new rockets that weren't there for Pathfinder. Because of concerns about winds there are a lot of things that ripple through the whole system, and before you know it you're changing almost everything or modifying almost everything. So we have to go back and retest and make sure that our designs are going to work in this new environment.

P2K: What are the deal breakers about landing on Mars with a mission like the Mars Exploration Rovers?

Stacy Weinstein: Well the deal breakers are things like impact velocity: how fast are we going to hit the surface. We've got an airbag system that was tried on Pathfinder, but we're going to a new location, we're landing more mass (ed. "weight"), we're landing in a spot that is different. We've only been to three spots on Mars before - Viking and the Pathfinder spots. So those are just three samples of the whole planet. Is the rest of the planet the same? What about inclinations (ed. meaning "slopes"), once the bags hit and we bounce and we roll for a while. Are we going to roll down a really steep incline? Or is it going to be a long, sloping grade? What's it going to be like? Are the bags going to hold up? Then there's issues of the parachute and descent rate... What kind of atmosphere are we going to have there when we arrive? We have data, obviously, but there are still kind of wide error bars on that, and so we have to bound our descent rates, and the timing of everything in the sequence-when things are going to happen - and we have to have enough knowledge, and enough robustness in the software to make sure that we can accommodate what happens if we are coming in too fast. What happens if we are coming in too slow, what about effects on the heat shield? If we are coming in at too steep of an angle things might get too hot. Stuff like that. So there are quite a few "deal breakers," but I guess in my mind I'd focus on the airbags.

P2K: How complicated is a mission like this in comparison to the many other missions that you've been on - flyby missions, and other kinds of missions? Just how difficult is this?

Stacy Weinstein: This is fairly difficult. We are landing on another planet. A flyby... you fly by and maybe you fly by a little too high, or a little too low, but as long as you get into orbit, or as long as you cruise by and you can take some pictures you are going to get something.

Here if we don't make it through entry, descent and landing we don't get anything. So from my point of view in the mission it's a very challenging kind of high-pressure implementation that we are using, coming down through an atmosphere, trying to make sure that all the timing is right, and that we survive. Survive in good condition, and then we have to get the rover out and let it do its job.

P2K: Here we are on 9/26/01. What do you have to do in the next two months to make things work?

Stacy Weinstein: We have three drop tests coming up. Starting Monday we are going to be dropping the airbags over at NASA Plum Brook Facility over in Sandusky, Ohio. This will be the first time we've dropped the rovers' airbags. Everything we've dropped so far has been leftover Pathfinder airbags, so these are in brand new condition. So we've got that going on.

Also starting in December we will be dropping radar, which is very similar to Pathfinder's however, we are coming in at a different speed, and we have a higher altitude capability to do some radar characterization drop tests. That will happen at China Lake Naval Air Weapons Center. Starting in December.

Starting in January we're going to do some drop tests of our three-body system. The parachute, backshell, deployed bridle, and lander, with live motors perturbing the backshell. Leading up to some more complicated tests where we use our lateral motors, the TIRS motors, as well as the RAD motors for descent. Those will also be at China Lake.

Those I think are the big three things on our plate right now.

P2K: Do you test to see how well things work, or do you test to see how things go wrong?

Stacy Weinstein: Hopefully in every test nothing goes wrong, but things always go wrong. We look for robustness. We look for nominal performance. We look for margins... How far can we take this before the system breaks... before we fall off a cliff performance wise. So we are looking for all that stuff.

P2K: Who goes to these tests?

Stacy Weinstein: First and foremost are the contractors or the personnel, technicians working the test... putting together the hardware, the people doing instrumentation, that sort of thing. I go to the tests. Other people from JPL go to the tests that need to understand what's going on. They need to get the data, so they need a sense of what's happening during the test so they can correlate their data when they get it. But probably just a handful of JPLers compared to all the other people that are working on the test.

P2K: How many different systems are there on board the mission?

Stacy Weinstein: In the entry, descent and landing part of the mission there's the parachute, the heat shield, aeroshell, we have a backshell, we have the RAD motors, the TIRS motors, we have an IMU which gives us rates so that we can fire some of our logic, we have a radar, we have a bridle, and of course, we have a lander and airbags. We have airbag retraction motors and lander petal opening motors, and then there is the rover inside.

Aside from entry, descent and landing and the surface operations we also have the cruise stage and the launch vehicle.

P2K: Does everything have to work perfectly for the mission to work?

Stacy Weinstein: Not everything has to work perfectly for the mission to work and return good data, but there are a couple of things that are "critical path", that if they don't work we get nothing. For instance, if the airbags didn't work chances are we're not going to get anything. If the bridle doesn't deploy well, chances are we're not going to get anything. If the RAD motors don't fire chances are we're not going to get anything. There are other things that can be "graceful degradations", for instance an instrument slightly out of calibration, and maybe we can figure that out on the ground. Things like that that we can deal with over the long period once the rover's on the surface.

P2K: "Graceful degradation" is such a nice phrase. What does graceful degradation mean?

Stacy Weinstein: Graceful degradation means that over time there's degradation in an instrument or system. For instance, on Pathfinder the rover would speak to the lander who would then communicate back with us on Earth, and the telecommunications system on the rover and the lander had to stay in sync. Because of temperatures and other factors, these things would drift a little bit every day and then we would have to resync them. So that's a kind of graceful degradation and eventually things got to the point where the rover and lander couldn't talk any more.

P2K: What do you guys use as a phrase for the opposite of graceful degradation?

Stacy Weinstein: There are many phrases... "single point failure"... something that we can't recover from. This fails, and the mission is over.

P2K: One of the things that I thought was so amazing about the Pathfinder folks is that they said well, Gee, by the time we were just about to land we couldn't think of a single test that we said we wanted to do that we didn't have time to do. That we didn't have money to do, even though they were scrimping and saving for money. Are there going to be things that you will launch and cruise and land that you want to test that you won't have time to test?

Stacy Weinstein: That's a possibility. Right now we are working on an incompressible test flow, which means that we won't launch unless we do these certain tests, and then there are other tests that, well, we could still do these after launch, it will possibly affect our decision on how to set the software. What kind of tolerance to set. Right now, the way the schedule is there's nothing that we're not going to get to do that we would have liked to do.

P2K: What is it that you like about this kind of high pressure, high-risk career? What's fun about having to work this hard and think this hard?

Stacy Weinstein: Dropping airbags... dropping rockets... having hardware to play with, there's a challenge just trying to get things done. The nice thing is that there's a light at the end of the tunnel. There's a launch date and it's coming right up. It's in May of 2003, and we're racing for that and we know that that's the finish line. Mars isn't going to wait for us. We don't get to slip two months or four months. We've got to get it done by then, and that's a big challenge. What's also fun is working with all these great people. Everybody I work with is just so wonderful and so intelligent. It's a high-energy situation.

P2K: What prepared you for this at school or at home, or what made you say that this is the kind of thing that you would like to end up doing? Did you think this was the kind of thing you were going to be doing when you went through college or through high school?

Stacy Weinstein: When I was a little girl my father sat me in front of the TV and said watch this, you are going to remember this some day. And it was the Apollo mission that eventually landed men on the Moon. I didn't get to see the landing, but I did get to see the launch. I was hooked on space since then and I've had other ambitions and things I kind of wanted to do, but I keep coming back to space no matter what I do. So when I was in fifth grade I was writing little creative stories about being a rocket designer and stuff like that and so I just always knew that someday - hoped someday - that I'd be doing stuff like this.

P2K: Are you an engineer or systems engineer?

Stacy Weinstein: I'm an engineer, specifically systems engineer. Before I was doing systems work I was doing orbital mechanics, mission design, trajectories that kind of thing. So I migrated over into the systems area to get my hands on the hardware, rather than just sit behind a computer and be thinking about trajectories all day.

P2K: How similar is working with inflating airbags, and pyrotechnics, and exploding rockets as opposed to what you did in college? Were the courses there abstract or were they practical?

Stacy Weinstein: Oh, they were very abstract. The courses we had were very abstract. Luckily when I went to school there were some opportunities to get your hands on, but I was an aerospace engineer. If you're a mechanical engineer you can build little cars and gears and wheels and stuff like that. Electrical engineers get to build circuits. Computer scientists get to build compilers. We didn't get to build much other than in simulations. Once in a while we get to go into a wind tunnel and put an airfoil in there and measure some stuff, but there was just no training to prepare me for what we're doing now. It's all on the job.

P2K: I get the sense you like things that are supposed to explode that do explode like rockets going off at the right time. What's so much fun about doing those kinds of tests?

Stacy Weinstein: Well I don't like to see things explode when they're not supposed to, but I do like to see... Well, how can you explain it? I mean it is exciting, it's just exciting to see stuff drop, and to see stuff inflate and go off and bounce and move. I mean it's motion. It's more fun sometimes, many times than sitting in your office working on the computer and reading the latest e-mail. It's exciting stuff, and you don't get to do that very often. There are some people that make a career out of it, but not me... not most of us here at JPL. And so this is an exciting opportunity.

P2K: Is Mars a kick itself... the red planet? Or is it the technical challenge that gets you going?

Stacy Weinstein: Both. There's so much we can do at Mars. People talked about if we were going to set up colonies in space, or send humans to have some sort of space-based laboratory where would we go. Would we go to the Moon? Would we go to Mars? Nobody thinks about going to Venus or Mercury. It is just inhospitable there. Jupiter, there's no place to land. Anything out past Jupiter is too far away. So we're pretty much left with the Moon and Mars. The Moon is easy to get to, but there's no atmosphere and very little water. Mars we know has an atmosphere. We don't know if there's water there yet. We do know that there is an icecap at one of the poles, but gravity's kind of close (to Earth's. Ed.) Atmosphere, we can work with that. There are a lot of things we can do we can make fuel out of the atmosphere. There is soil we could possibly grow stuff with, or at least use it as a growing medium and do some hydroponics. I mean there are things we can do there to establish even a presence and keep moving forward the exploration of space. That's a lot of why Mars is so exciting. Also the geology... it's so close to us orbitwise. Why did we get all the life? Why did we get the oceans and the soil and the animals and plants and Mars didn't? Did Mars ever have that? We don't know. And those are questions that are just so riveting... so exciting... and anything that we can do to work on the path of getting those answers I think is very exciting too.