Mars Rovers Celebrate Their 1000th Sol On Mars

Cherita Chen writes, "Yesterday NASA, Cornell University, and the USGS celebrated the Mars Exploration Rovers' 1000th Sol on the Red Planet. The first rover to land, Spirit, reached the 1000 Sol mark a few weeks ago while the planet was in Solar conjunction. 'Opportunity,' Spirit's twin, and the second lander to make the bounce to Mars, celebrated the milestone yesterday while sitting atop Victoria Crater on the other side of Mars. Both Rovers are still operational (though Spirit is limping) and are sending back valuable data. Not bad for what was slated to be a '90 Sol' mission."

Comments

Usual x10 engineering factor

[RichMan]

Can we say it is due to the usual x10 engineering safety margin?

90 sol * 10 -> 900. Sort of close to 1000%.

The engineers would have looked at MTBF (mean time between failures) of the components and probably designed for at least a 99% survivability to 90 sol. This might factor down to a 90% survivability to 900 sol depending on the failure curves for the parts. So the the probability of two surviving that long would be 0.9 * 0.9 = 0.81 or 81% chance.

Re:Usual x10 engineering factor

[imsabbel]

Spacecraft dont use x10 engineering safty margins.
They dont even use 50% margines.

If they did, they would never be able to lift of the ground.

Re:Usual x10 engineering factor

[Vellmont]

Can we say it is due to the usual x10 engineering safety margin?

I don't know. How many other rovers have been deployed in the Martian environment that we can get data back from to determine component lifetimes? I only know of one, and it was a much smaller rover.

I find it pretty amazing that these machines have worked as long as they have. I can't imagine it's an easy job to design a rover to last as long as it has without really being able to test the thing in the environment it's going to be in. Sure you can simulate parts of the environment, but I doubt you can simulate them all at the same time with all the parts working together.

Many people seem to pooh-pooh the survivability of these things because they just assume they were over-engineered. I'm sure they were over-engineered, but the amazing thing is that they were over-engineered in the right way, and pretty cheaply too (820 million to get them to Mars and the first 90 days of operation).

The predictions

[Kjella]

Not bad for what was slated to be a "90 Sol" mission."

The predictions was probably made as some sort of "average", but the odds it'd last exactly 90 days was slim. I'd say the odds of not landing properly at all, or immobilized shortly sfter landing was fairly significant. It's like a computer surviving burn-in or a person surviving infant mortality (though they are much lower in recent year), then they're likely to live significantly well past average. Plus some luck with whirlwinds clearing the solar panels, I guess.

Re:Silly Jargon

[exp(pi*sqrt(163))]

I just hope they never have probes on Mars and Venus at the same time because calling both types of day 'sol' will be confusing (though admittedly Venus is a little different). The length of the Martian day is a property of Mars, not of the Sun. It should have a name that reflects it's Martianness.

NASA Propaganda

[edbarbar]

> Not bad for what was slated to be a '90 Sol'

They intentionally underestimate the operational duration of the equipment to continually "WOW" the public. "Undercommit, overdeliver."

Something Engineers need to do to when scheduling their projects.