JOE PALCA, host:
From NPR News, this is SCIENCE FRIDAY. I'm Joe Palca. Up next, the latest on the Mars rovers, the gift that keeps on giving to NASA.
The rovers Spirit and Opportunity landed in, what, January, 2004, and were intended to operate for 90 days. Oh boy, did they like saying that, 90 days. And now, we're almost six years into the mission, and they're still sending back data from the Martian surface.
Well, last spring, Spirit, which is the one - one of the rovers, the first one to land, actually, ran into a bit of a problem. The rover was driving along, and it hit a little bit of a crunchy surface of Mars, didn't really look like anything different, but it was like one of those hard, crunchy things you sometimes get, like thin ice on a pond, and it broke through, and what was underneath wasn't water, of course. It was this slippery, sandy stuff. But fear not. NASA is working - is not just sitting idly by. It's working on a way to free Spirit. I mean, the new mission has a logo. What would you guess? Free Spirit.
So joining me now to talk about the efforts to free the rover is John Callas. He's project manager for the Mars rover exploration - Mars exploration rover, sorry, at NASA's Jet Propulsion Laboratory in Pasadena. Welcome to SCIENCE FRIDAY, John Callas.
Mr. JOHN CALLAS (Project Manager, Mars Exploration Rover, Jet Propulsion Laboratory, NASA): Thank you very much.
PALCA: And if you want to join this conversation, the number is 1-800-989-8255, 1-800-989-TALK. Okay, so did I describe that properly: It was driving along, and it sort of cracked through a crusty thing and fell into this softy-sandy thing?
Mr. CALLAS: Yes, essentially. Spirit is the rover that lost the functionality in its right front wheel about three years ago. So it had compromised mobility. So for the past three years, it's had difficulty driving, and we drive it mostly backwards.
PALCA: We should remind people that there are six wheels altogether. So you've got - and they all are powered, right? So you can push - you know, motors on all the wheels.
Mr. CALLAS: That's right. We can drive all the wheels. But Spirit has only five driving wheels, and it has to drag that one sixth wheel. This is kind of like a grocery store shopping cart, where one of the wheels is jammed, and you try to push it.
PALCA: You can do it, but it's harder.
Mr. CALLAS: That's right, and so as it drives, it has a tendency to dig up the terrain more, and it has more difficulty getting over terrain. And we moved into this area that looked benign to us. It looked safe. It looked like terrain that we've driven on before, and the rover broke through this crust into this loose, soft material underneath and has been trapped there for the past six months. And we're now just trying to get the rover unstuck from this location.
PALCA: So how do - okay, so it's on Mars, and it's sitting there, and it's got some - you can take pictures, and you can look around and see where you're sitting, but how do you figure out here on Earth what you can do up on Mars?
Mr. CALLAS: Well, that's the challenge. You know, unfortunately, we can't send - call AAA and have them go to Mars to get the rover unstuck. So we have to bring Mars down to Earth, and what we've done at JPL in Pasadena is to create a Mars environment. We built a big sandbox. We filled it with material that exhibits the characteristics of this loose, fine material on Mars. And then we have an engineering rover, which is virtually identical to the two rovers on Mars. It's often the lesser-known third sibling. And we stuck it in this sandbox, and we've been doing experiments for the past six months and seeing if there's a way we can get the rover unstuck. And it's an exceedingly difficult problem.
PALCA: Okay, so you began the process of sending Spirit a series of commands, what, about two weeks ago now, that were going to be used to try to begin the process of getting out. What's happened?
Mr. CALLAS: That's right. We started about two weeks ago, and it has been really hard. We haven't gotten going yet. What has happened is the right rear wheel has started to exhibit problems. We haven't had trouble with that wheel before, but now it's stalling on us, which means that we try to drive it, and it jams up, and then the rover says uh oh, there's a problem. So it stops. And we've been doing some investigation of that wheel, and it keeps exhibiting this problem. And we don't know the source of the problem, whether it is something outside the rover like a rock jammed in the wheel or whether it's a problem with the motor or gearbox itself.
Remember, these pieces of hardware are well past warranty. I mean, they were designed for only three months of operation on the surface of Mars and, you know, almost six years now. So there's some suspicion that we might have a problem with that wheel.
PALCA: Right, right. And just to bring it up and get it out of the way because I know - people always ask me around the newsroom, but explain to people why you can't ask the Opportunity rover to come over and give it a pull out.
Mr. CALLAS: Well, we'd love to do that, but Opportunity is a long way away. It's almost exactly on the other side of the planet from Spirit. So it's 12 Martian time zones away. So it would take, you know, about 10,000 kilometers' worth of driving to get there.
PALCA: And this thing - I mean, that's the other thing people need to understand is these rovers, while they roll around, they're not going much faster than a tortoise.
Mr. CALLAS: That's right. They only move about as fast as a turtle crawling along the ground. So it's slow and steady with these rovers.
PALCA: Okay. If you have a question for John Callas about the rovers, give us a call. Our number is 800-989-8255, that's 800-989-TALK, or you can send a tweet to @scifri, and we'll get your call or your question that way.
So people have said, you know - I mean, everybody has experience with being stuck someplace. I mean, you can't rock the rovers or get them back and forth. I mean, why is Mars so much harder than getting stuck on Earth?
Mr. CALLAS: Well, a number of reasons: First of all, it's not like any experience you've had here on the ground. It's not like getting stuck in the snow or in the mud. And again, as you mentioned, the rovers move very slowly. So you can't rock them back and forth and use momentum.
And for Spirit, because she only has five driving wheels, and that sixth wheel is like an anchor. So it's kind of like trying to swim a relay race with a car battery tied to your ankle. It just - it makes it very, very difficult. And then this loose, fine material, you know, it's almost quicksand-like. It just has no supporting strength, and there's nothing for the wheels to grab on to. The treads of the wheels are fully caked. So we're getting, you know, practically 100 percent slip.
PALCA: I see. Well, we have a - we actually - I forgot to mention this, but people are watching, or listening to us I guess is the right way to put it, on Second Life, and we have a question from Second Life from Benjmimulus(ph) - I hope I said that right. Could a rover still do meteorological science if you can't free it?
Mr. CALLAS: Oh, absolutely. You know, if Spirit is unable to extricate herself from this difficult situation, she will then become a Mars science lander mission. And there is a huge amount of information that we could explore with a stationary lander.
There's certainly the meteorological monitoring. We can monitor the Martian weather. But there's some very exciting things that we haven't had the time to do, because the rover's always been moving, that we'd love to do. One is to track the rover's radio signal to monitor the rotation of Mars, and that hasn't been done since Pathfinder, and Pathfinder only did it for a few months.
PALCA: Pathfinder was the smaller rover that landed in '98, right?
Mr. CALLAS: Right, and it was specifically the lander that they were tracking because what you want is something fixed to the surface of Mars, and then you monitor the radio signal very, very precisely, and that then tells you how the planet is spinning. And so you look for things like a wobble or a nutation to Mars, which tells you a lot about the interior of the planet. So it's a way of getting at the geodynamics of Mars.
The other thing we can do is use the rover's accelerometers, these are devices that monitor the rover's motion. But while it's stationary, it can look for vibrations in the Martian surface. So it's not quite as sensitive as a seismometer, but what we might be able to detect are meteor impacts into the surface of Mars.
PALCA: Okay. Well, let's invite our callers into this conversation and take a call from Todd(ph) in Madison, New Hampshire. Todd, you're on SCIENCE FRIDAY.
TODD (Caller): Yeah, I just had a quick question. Why can't they use the armature to either balance it out to help it get out, by extending it, or using it to push off, as they have it in gear slowly, pushing it and giving it momentum as you use your armature piece. Like, when I operate heavy equipment, if I get stuck, you use your crane piece to give yourself a push off as you put it in gear. And that gives you a little bit of momentum, just enough to pull you out of a ditch or out of a mud hole, stuff like that.
PALCA: I think I've got that, Todd. So this is - the rover has an arm that's still operating, and you could push the arm down and somehow use that to give you a little wobble off the mark, as it were. That's, I think, what he's talking about.
Mr. CALLAS: I have to say that is the number-one-asked question that we get�
(Soundbite of laughter)
Mr. CALLAS: �from literally around the globe. And the main reason is that there's nothing to push against. The rover is embedded in this loose, soft material, and so all the material within reach of the arm is pretty much soft, as well. So if we push with the arm, essentially what we're doing is just sticking the arm down into the soft material.
Now, we haven't ruled that out, and it's something we may still consider once we exhaust the more traditional techniques for getting the rover out. We have a whole list of exotic techniques that we might try to get the rover unstuck.
PALCA: John, I just think it's really funny that we've reached the point where we talk about traditional methods on Mars.
(Soundbite of laughter)
PALCA: That's a great image in my mind. Well, so what happens? I mean, you're moving into the Martian winter, you know, is power an issue for this project? Is there some point when you, you know, you're going to have to kind of give up because you don't have the power to drive the thing?
Mr. CALLAS: Yeah. That is a very real concern right now. Now, Spirit has survived three Martian winters, and last winter was really cold and dark and really tough for the rover but we got it through. This year, we have a better condition of the solar rays. They are not as dusty as they were last winter, but they are still continuing to get dustier. The problem is is the rover is tilted slightly to the south right now. And in the winter, the sun is going to be in the northern sky. If we cannot tilt the rover towards the north a little bit, there's a real risk that the rover won't survive this winter. And winter comes around the middle of May for Spirit.
PALCA: I see. I see. Let's take another call now and go to Bob(ph) in -Bob in Sycamore, Illinois. Bob, welcome to SCIENCE FRIDAY.
BOB (Caller): Thank you. I was just wondering if it would be possible to use the RAT to chew that leg off the way a mouse or a roach might to get out of the trap.
PALCA: Oh, okay. So you're obviously an aficionado if you know what the RAT is. John, you've got to explain to the rest of us.
Mr. CALLAS: Yes. On the end of the robotic arm, there's a device we call the rock abrasion tool, or the RAT for short. And it's essentially a little grinder and that's what we use to grind into the rocks. It's the analog of the geologist rock hammer. And the question is can we use that to chew off our leg much like a coyote will chew off its leg to get out of a trap. The answer is no. First of all, the rock abrasion tool on Spirit has since worn out its diamond-cutting piece, and it can only really brush and not grind. But even if we could, that - it would take so much grinding and cutting. I mean, I don't even think it's practical.
But cutting the wheel that is not functioning is not embedded. It's actually up on the surface of Mars, and so it slides relatively easily so that's really not what's holding us up. It's the fact that the other five wheels just don't have anything to bite against because they're in this loose material.
PALCA: Okay. John Callas, thanks very much for coming and telling us the latest and we'll certainly be hoping to hear good news in the coming weeks and months.
Mr. CALLAS: Thank you very much for your time.
PALCA: Okay. John Callas is project manager for the Mars exploration rovers at NASA's Jet Propulsion Laboratory. I'm Joe Palca and this is SCIENCE FRIDAY from NPR News. Transcript provided by NPR, Copyright NPR.
NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.