Is Mars Rover Spirit Ready For Retirement?
IRA FLATOW, host:
You're listening to SCIENCE FRIDAY from NPR News. I'm Ira Flatow. For the past five years, the Mars rovers, Spirit and Opportunity, have been sampling rocks, exploring craters and gathering temperature data well beyond their expected lifetimes of just three months. These Rovers just keep on trucking.
Well, about three years ago, one of the Spirit's front wheels broke, and with no repair shop within a hundred million miles, the hearty rover kept limping along, dragging its broken wheel, digging a gash in the dirt behind it.
And even a robot can show signs of old age, and it appears that's happening to Spirit now. Spirit is slowing down and having senior moments, suffering from what NASA calls bouts of temporary amnesia.
He's showing general signs of crankiness, refusing to wake up, obsessively rebooting itself. This is a real sign of an old computer.
So how much longer before retirement? Is the Opportunity rover soon to be the Lone Ranger of the planet? Our number, 1-800-989-8255, if you'd like to ask some of these questions yourself. You can phone in.
Let me introduce my guest, John Callas, who's the project manager for the Mars exploration rovers at NASA's Jet Propulsion Laboratory in Pasadena. Welcome to SCIENCE FRIDAY, Dr. Callas.
Dr. JOHN CALLAS (NASA): Thank you very much for having me.
FLATOW: What does that mean that it has amnesia?
Dr. CALLAS: Well, the rover takes naps each day and sleeps during the night, and so it powers up and powers down a couple of times each day, and it's supposed to store its information in non-volatile memory. This is flash memory, kind of the memory you have in your thumb drive or your digital camera.
And there's been now a few occurrences where the rover didn't do that, and so we didn't get any data, and so we call that an amnesia event because there's no memory of that information.
FLATOW: I call it a senior moment for computers.
(Soundbite of laughter)
FLATOW: How often does that happen?
Dr. CALLAS: Well, it's only happened four times. Three of those four times it happened in the last week and a half, and so that's a concern because it's a trend, and of course these rovers are getting older and the natural question is, are these age-related effects?
We have no explanation right now for what's causing this, and so we're developing some diagnostics to give us some clues as to what might be going on when these events occur or whenever they might happen again.
FLATOW: When you say it's age-related, in computer terms what does that mean?
Dr. CALLAS: Well, these rovers were designed for only a three month mission on the surface of Mars, 90 days. We are now more than 20 times past that, five years on the surface.
So these rovers have certainly lasted longer than they were designed, and so it's natural to expect that things would wear out. The most serious thing that the rovers face each day on Mars is the dramatic temperature changes. The temperatures change by over 100 degrees Celsius each day for the rovers. That's over like 150 degrees Fahrenheit.
So that's like going from the Sahara Desert to Antarctica and back again every single day without a change of clothing, and so that fatigues the rover, and that makes things break, and we've seen some things break on the rover.
FLATOW: Just the stress from the temperature? I guess things stretch and cool, and they change…
Dr. CALLAS: Exactly.
FLATOW: They - they - parts might loosen up, things like that?
Dr. CALLAS: Exactly. Solder joints crack. You know, it's much like, you know, taking a paper clip and bending it back and forth several times. Eventually the material in the paper clip fails, and the paper clip breaks.
FLATOW: When the wheel broke, I remember that. That could have been a disaster, but instead it turned out to be useful, didn't it?
Dr. CALLAS: Absolutely. I mean, this is a blessed mission. About three years ago, when the wheel failed, the wheel doesn't turn anymore and so it's locked in place. So it's kind of like one of those grocery store shopping carts where the wheel is jammed.
And so when we drive the rover, we drag that wheel, and it cuts a shallow trench, but what it's done is it's unearthed material just beneath the surface, and one of them was the presence of this material called amorphous silica.
It's basically a phase of silicon dioxide, but it forms in a hydrothermal system. So what do we mean by a hydrothermal system? We're thinking of things like a hot spring or a deep ocean volcanic vent. We know on Earth those are thriving ecosystems. So this is a smoking gun that there was a habitable environment at one time on Mars.
Now, of course, there's still a question of was there life, is there life, can we find evidence of past life? But that discovery only came about because the wheel was failed and it was dragging, and it unearthed this material that we otherwise would've just driven right by and never seen.
FLATOW: That's quite interesting. So what's - how is the other - its twin doing, the Opportunity rover? Where is that and how is it doing?
Dr. CALLAS: Well, Opportunity is almost completely on the other side of the planet from Spirit. Both rovers are fairly close to the equator, but Opportunity has been driving. It has traveled almost twice as far as Spirit has.
Opportunity's almost surpassed 16 kilometers. So that's almost 10 miles on the surface of Mars. And we're heading towards a giant crater, a crater that's about 20 kilometers in diameter, so about 12 miles across. But it's still, you know, 16 kilometers away. So we've got another 10 miles to go. And once again, these rovers, not only were they only designed to last three months on the surface, but they were only meant to go about a kilometer, about six-tenths of a mile.
Dr. CALLAS: And so we've far exceeded that with Opportunity, and now we're talking about more than doubling the distance again. So that's kind of like having your car, instead of going 100,000 miles, goes 1.6-million miles, and now we're expecting it to go 3.2-million miles.
FLATOW: Wow. So how long will it take to get to that?
Dr. CALLAS: It'll probably be more than a Martian year, so more than two Earth years.
FLATOW: Why do you think - and here's a question from Mark from Philadelphia, who's asking I think what's on everybody's mind, is how were the NASA engineers so far off of their estimates how long the rovers would last? I mean, they erred on the good side.
Dr. CALLAS: Well, the main reason why the rovers have lasted so long is that we've survived the Martian winters, and we didn't think the rover would survive the first winter because dust would fall on the solar arrays, cutting off the amount of power that you need, and then in the wintertime it's not only darker, but it's colder, and you actually need more power to stay warm.
Dr. CALLAS: But we've been blessed with these wind events, these wind gusts that occasionally come through and blow some of the dust off the arrays and give the rovers a new lease on life. That is a lot - it's not only to survive through the first winter but the second winter and the third winter.
FLATOW: Amazing. You know, they've been there so long that we've had paradigm shifts here on Earth in our technology: iPhones, things like that, tiny little computers. Give us an idea of what kind of computing power those rovers have.
Dr. CALLAS: Well, the rovers have a single computer that controls all the functions. It even controlled the functions when the rovers were traveling from - through interplanetary space and when they landed on the surface.
So they do a lot, but it's a single 20 megahertz processor. So it's only about one percent as powerful as your laptop computer, yet it does all this stuff for the rover. It allows it to operate autonomously on the surface, because the rovers are not joy-sticked from the ground. We can't do that because radio signals take too long to get to Mars.
So what we do is we give the rovers instructions at the beginning of the day, and then they, on their own, carry out those instructions. So they have to be self-aware. They have to take images of their surrounding, make digital maps of their environment, and then make judgments and assessments about is it safe to get to that target or how best to get to that target, and all that is done with this really tiny single processor.
FLATOW: Wow, and how big - how much memory does it have onboard in that flash memory?
Dr. CALLAS: The flash memory is only 256 megabytes. So that's probably a lot smaller than most flash drives or most digital cameras have these days.
FLATOW: And you empty that out every day and transmit it back to Earth?
Dr. CALLAS: Well, we try to empty it out every day, but they, just like in your camera, you know, you take many more pictures than you download, and I think all of us have some pictures on our own personal cameras that we haven't yet downloaded to our computer and sent off to grandma yet.
FLATOW: And how good is the link from Earth to Mars with the rovers?
Dr. CALLAS: Well, we have to communicate over interplanetary distances. So we're talking hundreds of millions of miles, and the transmitter on the rover is only about five watts of transmit power, which is not much more than a CB radio. Yet the quality of the link is probably better than most cell phones.
I mean, we've all experienced dropped calls when we're talking on our cell phone, but we rarely lose any bits when we're transmitting through deep space, talking to the rovers.
FLATOW: Now, you've set a new standard. We used to say if we could put a man on Mars - on the moon; why can't we do that - if we can put a rover on Mars and have great cell phone coverage, why can't we do that at home?
(Soundbite of laughter)
Dr. CALLAS: Exactly, yes.
FLATOW: So what's the prognosis for Spirit now? Are we going to try to test what's going on or are we just going to see a gradual decline in its ability?
Dr. CALLAS: We're trying to figure out what's causing the problem, and you know, there's always the possibility that there may be no, you know, smoking gun, there may be no specific cause that we could try to correct or mitigate. But the rover has only had, you know, a few of these upsets in the last couple of weeks. And you know, we can kind of work around that.
You know, it's much like, you know, your car doesn't always start up in the morning, but you're not about to go junk it. You know, eventually you try it a few times and it gets going, and then you can get on your way.
FLATOW: It's like hitting the old TV set or changing the rabbit ears a little bit to get better reception.
Dr. CALLAS: There's still a lot of capability in both of these rovers, and we have ways to work around, as we have for the past five years. A lot of things have failed or degraded on the rovers, and we've been successful in finding workarounds and to keep exploring, because you know, these two rovers are on the surface of another world that we've never visited before, and so the opportunity to continue exploring and continue scientific discovery is fantastic, and so we want to keep doing that.
FLATOW: And so there's no reason to believe that they have any kind of finite lifetime we can predict. They'll just keep going and going as long as they go.
Dr. CALLAS: That's right. I mean, there's no off switch on the rover. So we couldn't even turn them off if we wanted to, and as long as they can still explore, we want to keep using them.
FLATOW: It's too bad you didn't put one of those little windshield wipers to dust off the panels on this. Of course a big rover is headed on its way someday soon, we hope.
Dr. CALLAS: That's right. We have another rover in development that's even larger and more capable than these two rovers, and that will launch in 2011.
You know, if you think of these two rovers as robotic geologists, the next rover will be a robot chemist on the surface, and it'll explore the next set of questions about Mars and look for the evidence of past life or current life, look for things like organics and complex organic molecules.
FLATOW: Well, John Callas, thank you for taking time to be with us today, and good luck to your rovers.
Dr. CALLAS: Thank you very much, and my pleasure.
FLATOW: You're welcome. John Callas is the project manager for the Mars exploration rovers. That's at NASA's JPL in Pasadena, California.
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