Mars Rover Opportunity Turns 8

New submitter el borak writes "Never mind all the talk about the revival of the American auto industry. What may be the greatest car the U.S. has ever built is currently a tidy 78 million miles (125m km) away from this world — resting on the edge of Endeavour crater in the southern hemisphere of Mars. It was on January 25, 2004 that the rover Opportunity bounced down on Mars for a mission designed to last a minimum of three months and a maximum of just a year or two."

Re:the flipside of reliability

[Tablizer]

I think it is great that the device was design to last max a year or two, and lasted 8, but on the flipside, this means they aren't really good engineers. How can I say this? The estimates were off by 400%~800%!!! Or more!!!

Estimates were based on experience with the earlier Sojourner rover. Opportunity got lucky in that every now and then whirlwinds clean off the solar panels. This phenom was not known at the time, at least with solar panels.

And the wheels and joints have become creaky and are gradually failing. Work-arounds and adjustments to behavior have allowed it to continue. Thus, the equipment is failing, as expected. Luck and ingenuity in work-arounds should not normally be relied on for engineering duration estimates. Further, the grinder teeth have worn down and the rover is basically gumming rocks, or just brushing rocks instead of grinding.

Re:the flipside of reliability

[necro81]

The rover's aren't like the Deacon's Masterpiece [wikisource.org], where every component reaches end-of-life at exactly the same time, the mission life was dictated not by component life but environmental factors. As I understand it, the relatively short life-rating was based largely on power availability. From all previous Mars landers, it was expected that the solar panels' output would drop to useless levels within a couple months of landing. And although they surely had some ideas on how to get the rovers to survive the Martian winter, they certainly weren't going to make that a mission requirement. The mission life wasn't a matter of the rated life of the motors, or the computers, or of the fatigue life of the chassis. You couldn't have really made them cheaper and still had a usable rover: a strut with a fatigue life of only a few months' driving probably may have snapped on impact, a 1-year motor would have been more or less the same size and weight, a 1-year computer would have been identical to the computer they've got.

And, really, why would you want to shave everything down to such a short life: it's not like you could have saved much money for the taxpayer - the component cost of the rovers is only maybe 1/100th the total cost of the mission. Most of the cost is in getting the rover to Mars in the first place, followed by having a full-time staff of dozens or hundreds designing, testing, and running the thing.

Re:the flipside of reliability

[UnknowingFool]

I think it is great that the device was design to last max a year or two, and lasted 8, but on the flipside, this means they aren't really good engineers.

First of all it was engineered to guarantee to work for 3 months which was the allotted project objectives. Based on the budget and capability, this is what NASA had designed the rovers to do. Surviving for years is a bonus.

Just because they erred on the side of a good result doesn't mean the estimates are better. It means their methodology is HEAVILY padded, or if we assume +/-400~800%, they were just lucky that it didn't swing the other way. Given Phobos-Grunt, perhaps space engineering margin of error really is +/-400~800%. Although I suspect huge margins of error were thrown about in NASA>

Of course they padded their estimates and erred on the side of caution. 1) There is no way to retrieve or repair this rover. 2) NASA knew about the sticky dust from previous missions, but they didn't have omnipotence when it comes to the Mars climate. They didn't know that windstorms were capable of cleaning said dust. So you would have rather just wing it and not pad their estimates. So when the rover failed, they can tell NASA "oh well, try again in two years."

If that's the case, huge design buffers, that means they don't understand the underlying physics/materials engineer, and had to heavily overdesign, which means there is a far more efficient design out there.

I don't think you understand that there are different goals in engineering. One goal may be efficiency. The goal in this case was absolute reliability despite any unknowns the rovers may have experienced on Mars.

I'm not knocking NASA engineers, I'm just exploring how to shave down this margin so that they can make more efficient designs at lower cost that behave as expected.

Again efficiency is not as much a priority as reliability in these cases.

Building something that behaves as expected is far, far, FAR more important than building something that blows away expectations by orders of magnitude. The former is good engineering, the latter is waste, or worse, dumb luck!

The engineers never worked on the expectation that you ascribe. People outside of NASA have placed it on them. For them, the mission was successful when the rovers completed their objectives after 3 months. All these years afterwards are bonus.