Why is Opportunity lasting so long?

[Frida Space]

Hi everyone. Today I have a question that might be stupid, but, even if I've been following space exploration everyday for a couple of years now, I had never thought of. In fact, I didn't come up with it, a friend of mine did. So, the question is why is the Opportunity rover lasting so long on Mars? Sure, a lot of space probes have exceeded their warranty dates. However, rovers are very different. The wheel system, for example, was designed to last only 90 days, and now, 3953 Sols later, it's apparently doing better than Curiosity's wheels. My question is why? Did the engineers back then think that the martian surface was much more hazardous than it actually turned out to be? However, my question doesn't refer just to the wheels, but to the entire rover itself. I'm not even sure whether or not there's a precise answer(s), but either way thank you to anyone that will reply.

[epoca]

That's a good question. I'm not really sure I can help you with it though.

[PB666]

That's a good question. I'm not really sure I can help you with it though.

I think that they thought that in 90 days the solar panels would be covered with dust and there would be inadequate energy to proceed. But the occasional martian breeze actually removed dust and kept it going. I don't know why the wheel system has lasted so much longer, the longevity may have been based on catastrophic risk that either never materialized or that they managed, with experience, to circumvent.

[sgt_flyer]

Well, nasa researched the cause of curiosity's wheel damages - the big punctures were done by pointy rocks they never encountered with the other rovers

http://www.planetary.org/blogs/emily-lakdawalla/2014/08190630-curiosity-wheel-damage.html

This kind of pointy rocks combined with Curiosity's sheer weight (900kg vs 150kg for opportunity) doesn't help, as you have much more weight on each wheel. It's normally not a problem, because curiosity's wheels are much larger, but when all the weight on a wheel is focused on a pointy rock instead of evenly on ground, that creates a hole

Edited March 8, 2015 by sgt_flyer

[Redjoker]

I can't help you with the wheels, but I believe one of the reasons it has exceeded its expected life is the solar panels. NASA believed that the solar panels would slowly be coated in martian dust and cease to work, however a light wind would blow off the dust every once in a while. I could be wrong though.

[SargeRho]

The mars exploration rovers had to survive a much rougher landing than curiosity, bouncing around on airbags for a while, so they're probably build a bit tougher.

[Drunken Hobo]

I believe a number of the instruments have broken over the years, but the main drive is still going strong.

I suppose the simple answer is that it was built properly. Extremely high tolerances in building the thing, combined with some built-in redundancy (Spirit managed to drag a broken wheel for years before eventually giving up). It's not too complex a design and of course it's driven incredibly slowly. It took 10 years to cover the same distance Lunokhod 2 managed in a few months. There's a reason tortoises live so long.

[Brethern]

It's allot better for Someone to guarantee something for only 90 days and have it last three years then have something guaranteed for three years and it last only 90 days.

[Frida Space]

Well, nasa researched the cause of curiosity's wheel damages - the big punctures were done by pointy rocks they never encountered with the other rovers

This kind of pointy rocks combined with Curiosity's sheer weight (900kg vs 150kg for opportunity) doesn't help, as you have much more weight on each wheel. It's normally not a problem, because curiosity's wheels are much larger, but when all the weight on a wheel is focused on a pointy rock instead of evenly on ground, that creates a hole

Thanks for the link. So I'm guessing they overstimated the wheel-damage risk for Opportunity and understimated it for Curiosity? Curiosity's wheels do look much more fragile (that's probably because they wanted to make them as light as possible, but now it's a big problem for the rover. I remember sometime last year they had to change the rover's path plan to avoid further damage).

The mars exploration rovers had to survive a much rougher landing than curiosity, bouncing around on airbags for a while, so they're probably build a bit tougher.

That makes sense, but the question still stands. If they built Opportunity and Spirit a bit tougher, then why did they think they wouldn't last long? From what others have posted here, it appears they probably didn't think that the martian wind would blow off dust from the panels so often.

Thanks everyone! The Science Labs are an awesome place.

[SargeRho]

Yeah, they figured the panels would be too dust-covered within 90 days for it to keep operating.

I believe a number of the instruments have broken over the years, but the main drive is still going strong.

I suppose the simple answer is that it was built properly. Extremely high tolerances in building the thing, combined with some built-in redundancy (Spirit managed to drag a broken wheel for years before eventually giving up). It's not too complex a design and of course it's driven incredibly slowly. It took 10 years to cover the same distance Lunokhod 2 managed in a few months. There's a reason tortoises live so long.

There is not a whole lot of redundancy on those rovers. They have one processor, one power supply, etc. Any of those break, the rover's dead. The rovers themselves are the redundancy.

[Bill Phil]

Margins?

[Drunken Hobo]

There is not a whole lot of redundancy on those rovers. They have one processor, one power supply, etc. Any of those break, the rover's dead. The rovers themselves are the redundancy.

Well, they sent two near-identical rovers. I'd say that's pretty good redundancy.

[Frida Space]

Margins?

That's not my question. My question is if (and if yes, what) did the scientists/engineers back then think would have caused the rovers to die so soon (if not in 90 days, in a year or so presumably, definitely not in 6-7 years like Spirit or 11 and counting for Opportunity). From what people have written so far, it appears that NASA could have overstimated the surface hazards (or that it did an excellent job in avoiding them once on the surface, unlike it seems to be doing with Curiosity) and that it could have underestimated the effects of winds "cleaning" the solar panels. Sure, margins and construction have definitely played a major role in allowing the rovers to live so long, but I don't think it's just those two things.

[Scotius]

Excellent engineering

[Starwhip]

I think that they thought that in 90 days the solar panels would be covered with dust and there would be inadequate energy to proceed. But the occasional martian breeze actually removed dust and kept it going. I don't know why the wheel system has lasted so much longer, the longevity may have been based on catastrophic risk that either never materialized or that they managed, with experience, to circumvent.

I can't help you with the wheels, but I believe one of the reasons it has exceeded its expected life is the solar panels. NASA believed that the solar panels would slowly be coated in martian dust and cease to work, however a light wind would blow off the dust every once in a while. I could be wrong though.

You know a great solution to this problem? A goddamn CPU fan mounted near the front of the solar panels.

Seriously, NASA, is it so hard to get rid of a little dust?

[deadshot462]

Also remember it is not at 100% capacity today. A few of its wheels are not working so it has to drive backwards and drag wheels. The arm is stuck in a certain position. Its memory system is failing so it can't store as much data.

But I agree, Opportunity is older than most people's cars and it has had 0% hardware maintenance.

[Frida Space]

You know a great solution to this problem? A goddamn CPU fan mounted near the front of the solar panels.

Seriously, NASA, is it so hard to get rid of a little dust?

That's a good question, how to get rid of dust on solar panels. A fan is a possible theory, I wonder if someone can come up with other interesting ideas.

By the way, here is a great comparison:

- - - Updated - - -

Its memory system is failing so it can't store as much data.

Yes, it's having problem with one of its seven flash memory banks, and it often suffers amnesia events (the engineers upload comands, the software reboots itself and the rover forgets everything while trying to understand what happened). A few days ago NASA uploaded a new software which doesn't rely on the memory bank #7, which should be the bugged out one, however until a reboot the situation won't change.

[Bill Phil]

That's not my question. My question is if (and if yes, what) did the scientists/engineers back then think would have caused the rovers to die so soon (if not in 90 days, in a year or so presumably, definitely not in 6-7 years like Spirit or 11 and counting for Opportunity). From what people have written so far, it appears that NASA could have overstimated the surface hazards (or that it did an excellent job in avoiding them once on the surface, unlike it seems to be doing with Curiosity) and that it could have underestimated the effects of winds "cleaning" the solar panels. Sure, margins and construction have definitely played a major role in allowing the rovers to live so long, but I don't think it's just those two things.

If NASA had designed to operate for, say, a full year under the expected conditions, and those conditions turned out to be much less damaging, then the rover can last for many years. Add onto that the excellent engineering and attest construction, it's certain that it would last for quite some time.

If only Huygens could've lasted as long...

[Frida Space]

...and those conditions turned out to be much less damaging...

That's what I wanted to know, which conditions. Turns out they might be winds and terrain, and maybe something else we've overlooked.

If only Huygens could've lasted as long...

Or even anything more than 90 minutes

[tater]

You know a great solution to this problem? A goddamn CPU fan mounted near the front of the solar panels.

Seriously, NASA, is it so hard to get rid of a little dust?

You'd need a pretty large fan. Try it on earth, then calculate what size fan you would need if the air was only 1% as dense, but need to move similar scale-size dust particles.

[Starwhip]

You'd need a pretty large fan. Try it on earth, then calculate what size fan you would need if the air was only 1% as dense, but need to move similar scale-size dust particles.

Not a fan, exactly, more like a blower with a vent.

Or you could gently vibrate your solar panels, while angling them slightly with a servo or by design, in hopes to dislodge some of the dust.

Edited March 8, 2015 by Starwhip
What, I didn't quote that! :mad:

[bigdad84]

You'd need a pretty large fan. Try it on earth, then calculate what size fan you would need if the air was only 1% as dense, but need to move similar scale-size dust particles.

Exactly what I was thinking.... Have a ridiculously large fan on the back of a small rover.

[Nuke]

you could probibly do better with a small compressor. run the output through perforated tubes between each panel bank. trigger a solenoid valve to blow of each bank in sequence. catch is you dont have a whole lot of power to run said compressor, so it would need to compress slowly over time until you have enough pressure to blow the panels.

another more fun idea is to bring along a quad copter. just have it fly over the rover a few times. of course that might result in even more dust. you could also do some kind of mechanical wiper. there are lots of things you can do. but since it seems that mars weather is more than capable of clearing panels on its own, i dont think we need to do anything.

[Rakaydos]

Mechanical wiper would run into the problem of sandpapering the solar panels into uselessness with the martian grit.

I'd like to see a mars rover/satelite combo that runs the rover on microwave beamed power. Rectennas dont care if they're covered with a thin layer of dust, and the powersat can be repurposed to power (or help power) a followup mission.

[PB666]

If NASA had designed to operate for, say, a full year under the expected conditions, and those conditions turned out to be much less damaging, then the rover can last for many years. Add onto that the excellent engineering and attest construction, it's certain that it would last for quite some time.

If only Huygens could've lasted as long...

I think their strategy was to get information about the conditions on mars, some basic science about where to go and what to look for and then build better vessels with more comprehensive science. When the opportunity first hit mars, people had major worries about whether it was even possible. Now we know it possible and so we can invest more in the missions.

Memory is alot more dense now than it was then, and you can easily have all the redundancy you want, but as the number of communication satellites in Mars orbit increases, you also can send alot more data, which means that the mission demands increase. I think they don't really need vehicles that last more than 4 years, after that amount of time they are due for technological upgrades and new instrumentation, time for a new mission. NASA really could plop out a new mars mission every year and within 20 years have a sizable exploratory coverage of mars without ever stepping foot on mars.

Well at least Kepler's is back on line, with a much reduced information rate.