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The CPUs of Spacecraft Computers in Space

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Re: The CPUs of Spacecraft Computers in Space

#61

Post by angry_octet »

arjun-menon wrote: post #42
runeb wrote: post #37

Earlier quoted context omitted.

Could they not offload a lot of compute to ground based computers and submit results back via radio? Or are these real-time applications?

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 lo…

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.

Re: The CPUs of Spacecraft Computers in Space

#62

Post by johnwalkr »

mhh__ wrote: post #47
verberant wrote: post #3

Space flight computers in the public sector are generally 15-20 years behind the types of hardware we commonly work with on the ground, as I think this page shows. We now have pretty capable low-power SoCs and FPGAs that we've yet to see broadly leveraged for govt. space applications. SpaceX flies Starlink with Xilinx FPGAs, while NASA and DoD are still baselining new platforms on incredibly expensive (albeit rad-har…

> Starlink with Xilinx FPGAs, while NASA and DoD are still baselining new platforms on incredibly expensive (albeit rad-hard) PowerPC RAD750 and similar. Ignoring that Starlink isn't very far away, I would assume NASA stuff would also have FPGAs and ASICs on them - they aren't CPUs and aren't used like them.

It’s pretty common in space to implement a soft core CPU (or redundant ones) on a space-grade FPGA.

Re: The CPUs of Spacecraft Computers in Space

#63

Post by bryananderson »

verberant wrote: post #3

Space flight computers in the public sector are generally 15-20 years behind the types of hardware we commonly work with on the ground, as I think this page shows. We now have pretty capable low-power SoCs and FPGAs that we've yet to see broadly leveraged for govt. space applications. SpaceX flies Starlink with Xilinx FPGAs, while NASA and DoD are still baselining new platforms on incredibly expensive (albeit rad-har…

NASA has used Xilinx FPGAs on a number of missions (though still mostly smaller missions). They are doing so for precisely this reason: on-spacecraft computation for intensive tasks such as image processing.

Here’s the website for the SpaceCube platform (developed at NASA Goddard). This is a little out of date (I worked on flight software for a mission called STP-H6 which I don’t see listed here), but gives an idea of how this idea is slowly but surely gaining steam in NASA.

https://spacecube.nasa.gov/

Re: The CPUs of Spacecraft Computers in Space

#64

Post by gorgoiler »

cpgxiii wrote: post #45
runeb wrote: post #37

Earlier quoted context omitted.

Could they not offload a lot of compute to ground based computers and submit results back via radio? Or are these real-time applications?

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…

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.

Re: The CPUs of Spacecraft Computers in Space

#65

Post by throwaway189262 »

verberant wrote: post #3

Space flight computers in the public sector are generally 15-20 years behind the types of hardware we commonly work with on the ground, as I think this page shows. We now have pretty capable low-power SoCs and FPGAs that we've yet to see broadly leveraged for govt. space applications. SpaceX flies Starlink with Xilinx FPGAs, while NASA and DoD are still baselining new platforms on incredibly expensive (albeit rad-har…

The private sector has decided to put regular ground chips in spacecraft and just deal with errors using triple redundancy. Low earth orbit where most satellites hang out doesn't have much radiation anyways.

The cost savings from using regular chips is so high that I bet SpaceX will continue to use them even in deep space. Just surround them with sheilding. When a $400 desktop cpu is 500X faster than a $40,000 space rated one a couple pounds of shielding is well worth it

Re: The CPUs of Spacecraft Computers in Space

#66

Post by Rebelgecko »

verberant wrote: post #3

Space flight computers in the public sector are generally 15-20 years behind the types of hardware we commonly work with on the ground, as I think this page shows. We now have pretty capable low-power SoCs and FPGAs that we've yet to see broadly leveraged for govt. space applications. SpaceX flies Starlink with Xilinx FPGAs, while NASA and DoD are still baselining new platforms on incredibly expensive (albeit rad-har…

SpaceX doesn't have the same requirements--The radiation environment by Mercury or halfway to Jupiter is drastically different than LEO.

SpaceX missions are also a lot shorter. Having one unrecoverable latchup a week isn't a big deal if your mission is 2 weeks long. If you mission is 10 years, it starts to become a problem (especially since some radiation damage can be cumulative)

>NASA and DoD are still baselining new platforms on incredibly expensive (albeit rad-hard) PowerPC RAD750 and similar

NASA and DOD have also been sending up Xilinx and Altera boards for ages (even the non space-grade ones). However you can get rad-hard ARM CPUs that are cheaper and more powerful than the ones in a Zynq board.

Re: The CPUs of Spacecraft Computers in Space

#67

Post by throwaway189262 »

runeb wrote: post #37
cpgxiii wrote: post #15

Earlier quoted context omitted.

The RAD750 (edit - the whole RAD family, there are newer models available) remains the standard because it's the highest performance rad-hard design available, period. If you're putting an expensive satellite in orbit for 5,10 years, the cost of the processors is insignificant compared to everything else. The real problem is that we don't have good solutions for improving the performance of rad-hard designs, so we're…

Could they not offload a lot of compute to ground based computers and submit results back via radio? Or are these real-time applications?

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

Re: The CPUs of Spacecraft Computers in Space

#68

Post by throwaway189262 »

gorgoiler wrote: post #64
cpgxiii wrote: post #45

Earlier quoted context omitted.

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…

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 yar…

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

Re: The CPUs of Spacecraft Computers in Space

#69

Post by chmod775 »

throwaway189262 wrote: post #65
verberant wrote: post #3

Space flight computers in the public sector are generally 15-20 years behind the types of hardware we commonly work with on the ground, as I think this page shows. We now have pretty capable low-power SoCs and FPGAs that we've yet to see broadly leveraged for govt. space applications. SpaceX flies Starlink with Xilinx FPGAs, while NASA and DoD are still baselining new platforms on incredibly expensive (albeit rad-har…

The private sector has decided to put regular ground chips in spacecraft and just deal with errors using triple redundancy. Low earth orbit where most satellites hang out doesn't have much radiation anyways. The cost savings from using regular chips is so high that I bet SpaceX will continue to use them even in deep space. Just surround them with sheilding. When a $400 desktop cpu is 500X faster than a $40,000 space…

The kind of radiation you want to protect against is not "easily" shielded.

The effectiveness of shielding is proportional to its mass and thickness, and both are at a premium for spacecraft.

Re: The CPUs of Spacecraft Computers in Space

#70

Post by LeoPanthera »

tibbon wrote: post #36

So my watch (or maybe headphones even) is several times faster than anything that's ever run a spacecraft? (I understand why, but that this is so just blows me away)

Though true, it is important to remember that Computers Are Fast. https://computers-are-fast.github.io
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