What's Inside the Mars Rovers

Captain Zion writes "Space.com has a story about the hardware and software of Mars Rovers Spirit and Opportunity. Basically, they're radiation-shielded, 20MHz PowerPC machines wirh 128Mb RAM and 256Mb of flash memory, running VxWorks. I wonder if I could make a nice firewall with one of these for my home network..."

Comments

driving the rover

[QEDog]

The question that we all want to know is, how do they drive it? I imagine that they have 3 identical car cockpits, with steering wheel, brakes and gas pedal. 3 different engineers drive it, voting on their actions for redundancy. If one of them dies, or goes to the bathroom, or simply starts honking like a mad man, still the other 2 could respond.

Re:Radiation hardness

[AKAImBatman]

Vaccuum. I don't think there's any hard drive that will work in a vacuum.

By sealed, I meant "hermetically sealed". Since there's nothing living inside the case, the air can be sitting.

Radiation

As I said, shielded container. Although, someone pointed out that it wouldn't stop some of the most energetic stuff. The big question is whether a few inches of shielding would be enough to substantially reduce the radiation. We don't need it perfect, just good enough.

EMI/EMC, including Magnetic cleanliness

I didn't think that EMI would be a big problem. What would generate the interference? Hmm... perhaps a Faraday cage could be built into the casing?

Temperature range. Standard range is -34 deg C to +71, although that's usually negotiable. The less hardware you have to baby, the better.

Operating temp is 0C to 65C for microdrives. I originally stated that by sealing the device in lead, you would have a passively cooled system. (The lead would heat and bleed off the extra into space or atomosphere.) However, the more I think about it, the more I like the idea of having an active liquid or gas cooling system. This would also be built into the lead casing, and could be controlled by the computer itself. You'd need a temperature sensor inside the case, but that's not difficult or expensive.

the cost of a qualification program

Personally, I'd like to cut as much of this out as possible. "Cheaper, better, faster" remember? Probably the best way to handle this is to build the entire unit, and stress test the entire thing (Vibration, radiation, etc.). That would be cheaper than testing every component, and would give an good idea as to how sturdy shielded components are when compared to individual hardened components.

Reliability and life.

So far, Microdrives have been shown to be highly reliable and generally last. Given that flash cards are slowly destroyed by rewriting, microdrives may have a longer life time.

Here's an idea. Instead of triple redundancy, go for two microdrives and one CF card. RAID these together. Now if there truely is a failure in all drives, the CF can take over. Personally, I don't think it would be a problem, but that way you have a compromise between proven and unproven.

60 pounds is a hell of a lot. Mass is always tight, and there is no easy fix by "fueling the rocket." Would that there were!

Mass may be tight, but I find it difficult to believe that it's impossible to add 60 pounds to the craft. The craft is chosen based on the requirement for the mission, right? And the amount of fuel burned by the rocket is calculated for exact insertion into Mars orbit, right? So it's conceivable that the rocket could have extra capacity. (What are they using for interplantary missions these days? Titans?) I suppose I'd need to check the specs on the rocket.

The weight could be reduced by eliminating a computing unit. Instead, give the single unit dual processor capabilities. Both processors will attempt the same calculation in sync, which will be then checked by a simple bus controller. If the results don't match, the instruction is recalculated. That would reduce the power requirements as well. Say 30 pounds now? (Most of the weight is in lead shielding and plutonium.)

It would be interesting to be on one of these projects and have access to the mission limitations. I'm willing to bet that they could be pushed pretty far with a little creative thinking. :-)