so just how intelligent can we make our space probes, revisited

August 18, 2012 — 5 Comments

circuit boards

Once upon a time I wrote a post about the sacrifices in intelligence our rovers have to make to be able to travel to other worlds and why these sacrifices are necessary. Basically, we can build very smart bots here on Earth because we can give them a big energy supply for faster, more complex, and more energy demanding computation. On Mars, however, this big energy supply will be a big liability since it will have to take away from a rover’s ability to move or its overall mission time. I’m still pretty confident in my earlier assessment, but some stories spreading around pop sci blogs made me realize that there was a AI-hobbling factor forgotten that wasn’t addressed; cosmic rays. As rovers explore Mars, they’re bombarded with radiation that easily penetrates through the red planet’ thin atmosphere. To give Curiosity the best possible tools to explore the Martian surface, it was given a very powerful setup, at least by spacecraft standards.

BAE Systems’ RAD750 chips provide it with a blazing dual 200 MHz processors and 256 MB of DRAM as well as an entire 2 GB of flash memory. Again, this is blazing only in the world of space travel since these are pretty much the specs for a low end smartphone, and even that probably has a dual core 1 GHz CPU. But the low end smartphone probably can’t withstand a massive radioactive bombardment without going haywire. The problem is the DRAM, or the memory the computer uses to keep all the things it needs to run. When hit by cosmic rays, it goes through something called a bit flip. Ordinarily, for us, this is no big deal because the vast majority of the memory our devices use is taken up by some background process, usually one with enough temporary variables that can absorb the hit before being cleared out of a register in a matter of nanoseconds. This means we either don’t care, or don’t notice, and that’s just fine for those rare cases when a stray particle flips a bit or two. Hell, we lose entire packets when we send them around the internet with certain protocols and that’s a lot more than a bit, but life goes on.

For rovers on other worlds, this is a much, much bigger issue. Not only are the bit flips a lot more frequent since they’re being showered by energetic particles, there’s a lot less margin for error since their setups are a lot more lean. Were a particle case a most significant bit to flip while a small array of bytes is telling the rover how to move, the consequences could be disastrous. The value for 0×00 [00000000] could turn into 0×80 [10000000] and instead of telling the wheel motors to stop, the byte stream just gave it the command to apply 50% power to each wheel, driving it into a ditch, or right off a cliff. And this is why the RAD750 chip is made to only tolerate a single bit flip per year, about twice during the entire Curiosity mission. Were the scenario I just outlined happen, the chip would auto-correct the stream to keep 0×00 as it was when assigned. Rovers go on their merry way, JPL is not living in fear of cosmic rays giving Curiosity a mind of its own, and we get great high rez pictures from the surface of another planet. Win, win, win, right?

Yes, but the auto-correction and the radiation hardening necessitates some tradeoff. It makes the chip more expensive, or consume a little more power, or slows down the CPU cycles, all of which could be used to make rovers smarter and more autonomous. Though dumbing them down a little is a small sacrifice for making sure they’re a lot less likely to randomly drive off a cliff unless you have the budget to build a much bigger robot, launch it on a much more powerful rocket, and devise a way for it to land safely tens if not hundreds of millions of miles from home. Don’t get me wrong, Curiosity’s dual cores and an RTG will make it a lot smarter than previous rovers, but it’s hardly an E-Einstein and unless we find a way to double or triple the size of our Martian rovers, or create artificial magnetospheres for our spacecraft, it’s going to be fairly close to the peak of the kind of intelligence we can get in an interplanetary robot for the next decade or so. Actually, considering that just testing and certifying a new radiation-hardened chip can take that long, that may be an optimistic assessment.

And this is why ultimately, we have to go to other worlds ourselves if we want to do high impact science quickly and efficiently. Robots are safer, they’re cheaper, and they don’t want hazard pay, true. But ultimately, humans are going to be much better explorers than the rovers and probes they send. Not only do they have the necessary brainpower to deal with challenging alien environments without a 34 minute delay between actions, they also have the will and interest to try new things and fit in an experiment or two that can’t be crammed into a rover’s schedule but can teach us something new and exciting as well. And this is not to mention the medical benefits we’d reap from getting humans ready to walk on other worlds and the possible wonders it could do for surgeries, physical therapy, and regenerative treatments as all these technologies and ideas are forces to come together, compete, and produce a roadmap that can be empirically tested and proven by a real mission…

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  • Brett

    . . . Or, you could just put the smarter computer in a more shielded “mother” ship in orbit around the planet/moon, where it could also draw upon plentiful solar power if it’s within the orbit of Mars. That smarter computer could then remotely control the “dumber” probe in real-time. In fact, you could have it control multiple probes around the planet, provided you have some other satellites in orbit to relay the signals.

    Humans could do the same thing, but you’d get the inevitable “Why are we paying to send humans to Mars if they’re not going to actually land there?” complaints (even though we did several “fly around the Moon missions” before Apollo 11′s landing). There’s also all the trouble and delays involved in sending humans and keeping them alive there, as well as the fact that they’d have to spend a significant chunk of their time just doing repairs and maintenance to keep themselves alive, along with the basic necessities of eating and sleeping – as with the real-life ISS crews. They could only spend a fraction of their time doing actual science, whether on Mars or in orbit around it.

  • Paul451

    Shielding against cosmic rays is nearly impossible for a space-craft. Takes a huge amount of mass. And it’s worse in orbit than on the surface. (Curiosity has a radiation detector, and apparently Mars’ limited atmosphere halved the radiation count.)

    To run a powerful enough computer to do current state-of-the-art AI, you’d need to hide the server behind 3-4 metres of water/hydrocarbon or 8-10 metres of rock/regolith/metal. (Perhaps one day we’ll have an AI server farm deeply buried on Phobos/Deimos? Control signals relayed off a network of comsats to the simpler rovers/robots on the Martian surface.)

    [Need the same kind of buried-server even more the further you go out. A Europa swim-bot, or a Titan plane-bot, needs much quicker reaction-times than a slow crawling rover on the static surface of Mars.]

  • Brett

    Shielding against cosmic rays is nearly impossible for a space-craft. Takes a huge amount of mass. And it’s worse in orbit than on the surface. (Curiosity has a radiation detector, and apparently Mars’ limited atmosphere halved the radiation count.)

    But landing on the planet imposes some stringent requirements on how massive you can make without the landings becoming progressively more difficult (just look at Curiosity). If the AI just stays in the mother ship in orbit, then the only mass penalties involved are those in launching it, accelerating it, and decelerating it. Not insignificant, mind you, but it’s easier to frontload that difficulty back on Earth.

    To run a powerful enough computer to do current state-of-the-art AI, you’d need to hide the server behind 3-4 metres of water/hydrocarbon or 8-10 metres of rock/regolith/metal. (Perhaps one day we’ll have an AI server farm deeply buried on Phobos/Deimos? Control signals relayed off a network of comsats to the simpler rovers/robots on the Martian surface.)

    You could also have the spaceship land/dock with Phobos, then have a rover pile rocks and regolith on top of the spaceship before you turn it on.

  • Paul451

    Brett,
    then have a rover pile rocks and regolith on top of the spaceship before you turn it on.

    From what I’ve read, non-radiation-hardened electronics are gradually destroyed by radiation, whether they are turned on or not. So my & your buried-on-Phobos idea wouldn’t be enough by itself. You’d still need some kind of bulk shielded Mars Cycler craft to protect the components from Earth to Mars.

    ["Mars Cycler" is a synchronous orbit between Earth and Mars that requires minimal delta-v to maintain. The idea is to put the heaviest components into a cycler orbit once, and after that, only the crew capsule (on the Earth-side of the orbit) and lander (Mars-side) need to accelerate into and brake out of the transfer orbit. The rest just keeps going back and forth. Useful if you have to lift a lot of shielding, you only lift it once, not every mission. Even better, if you can put a small 50-100m asteroid into such an orbit, you'd also have your bulk shielding (and perhaps some volatiles like fuel/water/air if you choose the right asteroid.) Core out the heart of the asteroid and place the crew modules inside, with only the docking and power/cooling modules poking out. (The mass means you can use a nuclear reactor for power and protect the crew from radiation without any additional shielding. Likewise, instant micro-meteorite protection. And a large thermal and anti-vibration mass, which should simplify module design.)

    Which, IMO, is a useful long-term goal for the US space program. Gives you a modular stepping-stone path of development from asteroid missions all the way to Mars missions, while researching the basics of asteroid mining, orbital refuelling, etc, in between. Where every step is a justifiable program in it's own right, but contributes to and enables the next step (rather than re-inventing the wheel for every single damn program.)]

  • Paul451

    (That first line was meant to be in <quote>s.)