The whole point of implementing A* on Curiosity was to give it some navigation autonomy. The time delay in getting sensor data back to earth, coming up with a motion plan, then sending the plan back to be executed imposes tight limits on how fast the rover can drive, what kinds of terrain it can cover, and ultimately how much science can be done. Local autonomy for basic "go over to than weird-looking rock" tasks is a major improvement.

You could A* your way around the whole planet by using an Earth based computation but only if you knew where every rock was.

There must be some equation of motion in space robots that combines terrain difficulty, robot speed, round trip time to Earth, and how far ahead you’d need to be able to see.

Curiosity moves about as fast as a Roomba. The ping is (min/avg/max) 10’/24’/40’. Ergo, it needs to be able to see X yards ahead of itself to plan A* from Earth, requiring a camera boom Y feet tall producing images with Z megapixels of resolution.

I wonder what X, Y and Z are.

Some very rough numbers, if you want plans valid until you see the results and travel at a good speed:

- You want a travel speed of 0.5 m/s - Worst-case round trip time from command to result is 40 minutes, or 2400 seconds - Max distance covered is 1200 meters - Assume you can drive over any rock 10cm or less in size (the rover can do better, but at a reduced speed)

So you need to scan an area 1200m x 1200m, with range accuracy of, say, +/-5cm. Forget the camera boom height, or the time it might take to scan and process, there's no sensor that will give you that kind of accuracy. The stereo baseline would be huge, and leave you entirely at the mercy of whatever texture or not a given part of the martian surface has to offer. LIDAR is OK if you definition of "long range sensing" is larger objects at 200m. The time cost for shipping back all the raw data for processing would kill performance as well, and if you wanted to process it locally the compute requirements would be just as high as doing the planning locally as well.

Onboard, or at least much closer,compute is the only way forward in autonomy. Honestly, the best bet on improving local compute would be to send a robot bulldozer, some C4, a rack full of milspec servers, and a big RTG. Blow a nice crater, push the servers to the bottom, and bury them in dirt for shielding. If you get really lucky, you could find some old cave or lava tube.

That's more or less what they used to do with Sojourner, only with humans setting out the way points rather than A* . It never managed to get more than 10 meters from its lander though, I assume this was partly driven by the limitations on a human's patience in operating a slow vehicle with 28 minute feedback loop.

One drawback of the remote A* approach is that you end up using more energy as the rover would have to be constantly communicating with its onboard antenna. Its relay satellites are only in range for a limited period each day. Fine grained maneuvers (like drive around that big rock to get to this small rock) would also prove difficult because of likely errors in the rover's inertial-navigation system.

https://en.wikipedia.org/wiki/Sojourner_(rover)

Does curiosity really move that fast? Roomba is maybe 2 mph. I thought curiosity was closer to 0.1 mph

His or her estimate seems wildly off. I had the same response because my Roomba moves fast!

Some quick googling says-

Curiosity max speed equals 0.08699 mph.

Roomba equals a foot per second which is 0.682 mph.

Off by about 7.82x.

Thanks: my estimate of Roomba slowness was way off. I’ve only ever seen them on TV.

I remember once hearing that Curiosity, flat out, could do 1km a day.

Random but I highly recommend the new "mapping" type roombas. Best thing I bought all year.

With what kind of processing power did the recent Change'5 probe did the autonomous docking manoeuvre in lunar orbit..

Also it seems to be doing sometype of image processing to identify a suitable landing spot and guiding on to that point.

I was thinking, instead of that, what if you had a separate isolated tiny computer on spacecraft, that was powered by its solar panels (so there's no electrical wiring, or other connection to it), and have its own radio. And this separate computer could use the latest bleeding-edge CPU, and be encased in a radiation-hardened shell. It would use its radio to talk to the slower main computer, and do math really fast locally, and if need be, beam the results to Earth, or to a nearby orbiting satellite.

Unfortunately there isn't really any practical way to have a radiation hardened shell that is sufficiently effective. Eg. 5cm of aluminium stops only 30% of the galactic radiation. (Heavier elements (e.g. gold) are scattered by incoming particles causing incoming heavy ions which cause even more damage.)

So practically it would still experience significant radiation.

But having the main compute for Mars remain in orbit with the relay isn't a bad idea.

Shannon limit implies a linear relation between bit rate and transmit power. The only way to get fast enough transfer would be to spend tons of the power budget on radio

For Mars, at least, that would be tens of minutes round trip because of the speed of light.

It works for some things, but for pathfinding it isn’t a great fit.

The other issue is bandwidth between the craft and Earth, which is quite limited.

Maybe there would be benefits to a “orbiting datacenter” around Mars carrying a bunch of rad-hardened compute? I assume NASA has considered this and decided it would be a bad idea.