[philipwhiuk]

> Chips must be “Rad-hard” - that is do more error correcting from ionizing radiation - there were entire teams at NASA dedicated to special hardware for this.

They don't do RAD hardening on chips these days, they just accept error and use redundant CPUs.

[numpad0]

There are apparently rad-hard DDR4 chips these days so this is patently false. SpaceX used to talk a lot about substituting rad-hard components with triple redundant regular x86 years ago, that's true.

I think I've also seen someone mention that the cost and power benefit of substituting rad-hard chips with garden variety wean off fast once the level of redundancy goes up, and also it can't handle deep space radiations that just kill Earthbound chips rather than partially glitching them.

[adastra22]

You are confidently incorrect. Even Starlink uses rad-hardened CPUs. Redundant error correction is only really an option on launch hardware that only spends minutes in space.

Note that on modern hardware cosmic rays permanently disable circuits, not mere bitflips.

[NitpickLawyer]

> You are confidently incorrect.

No, he's not. Dragon is using CotS, non rad-hardened CPUs. And it's rated to carry humans to space.

> AWST: So, NASA does not require SpaceX to use radiation-hardened computer systems on the Dragon?

John Muratore: No, as a matter of fact NASA doesn't require it on their own systems, either. I spent 30 years at NASA and in the Air Force doing this kind of work. My last job was chief engineer of the shuttle program at NASA, and before that as shuttle flight director. I managed flight programs and built the mission control center that we use there today.

On the space station, some areas are using rad-hardened parts and other parts use COTS parts. Most of the control of the space station occurs through laptop computers which are not radiation hardened.

> Q: So, these flight computers on Dragon – there are three on board, and that's for redundancy?

A: There are actually six computers. They operate in pairs, so there are three computer units, each of which have two computers checking on each other. The reason we have three is when operating in proximity of ISS, we have to always have two computer strings voting on something on critical actions. We have three so we can tolerate a failure and still have two voting on each other. And that has nothing to do with radiation, that has to do with ensuring that we're safe when we're flying our vehicle in the proximity of the space station.

I went into the lab earlier today, and we have 18 different processing units with computers in them. We have three main computers, but 18 units that have a computer of some kind, and all of them are triple computers – everything is three processors. So we have like 54 processors on the spacecraft. It's a highly distributed design and very fault-tolerant and very robust.

[1] - https://aviationweek.com/dragons-radiation-tolerant-design

[adastra22]

> Dragon is using CotS, non rad-hardened CPUs. And it's rated to carry humans to space.

Those are not independent facts. They put the hardware inside, behind the radiation shielding they use to keep the astronauts safe. It's why regular old IBM laptops work on the Space Station too. That kind of shielding is going to blow your mass budget if you use it on these satellites.

SpaceX, which prefers COTS components when it can use them, still went with AMD Versal chips for Starlink. Because that kind of high performance, small process node hardware doesn't last long in space otherwise (phone SoC-based cubesats in LEO never lasted more than a year, and often only a month or so).

[NitpickLawyer]

> They put the hardware inside,

Which is exactly how you'd do a hypothetical dc in space. Come on, you're arguing for the sake of arguing. CotS works. This is not an issue.

> That kind of shielding is going to blow your mass budget

SpX is already leading in upmass by a large margin. Starship improves mass to orbit. Again, this is a "solved" issue.

There are other problems in building space DCs. Rad hardening is not one of them. AI training is so fault tolerant already that this was never an issue.

[adastra22]

None of the discussed designs include radiation shielding like that. Nobody is considering doing it that way, because the math really really doesn’t work out (instead of unshielded, where it just doesn’t work out).

A cosmic ray striking a chip doesn’t cause a bitflip - it blows out the whole compute unit and permanently disables it. It is more like a hand grenade going off.

[notrealyme123]

> AI training is so fault tolerant already that this was never an issue.

Such nonsense.

[NitpickLawyer]

Between fp nondeterminism, fp arithmetic, async gradient updates, cuda nondeterminism, random network issues, random nodes failing and so on, bitflip is the last of your concerns. SGD is very robust on noise. That's why it works with such noisy data, pipelines, compute and so on. Come on! This thread is having people find the most weird hills to die on, while being completely off base.

[danparsonson]

Carrying humans to space is not the same use case as spending long periods of time in orbit.

[NitpickLawyer]

Dragon spends 6mo+ in orbit regularly. I have no idea what's happening in this thread, but it seems everyone is going insane. People don't even know what they're talking about, but they keep on bringing bad arguments. I'm out.

[danparsonson]

> Dragon spends 6mo+ in orbit regularly.

... hooked up to the ISS, with humans in attendance to fix anything that goes wrong... not doing very much.

It's akin to the difference between a boat moored up in a port, and an autonomous drone in the middle of the Pacific. Aside from that, satellites have to maneuver in orbit (to stay in the correct orbit, and increasingly to avoid other satellites). Hefting around additional kgs of shielding makes that more difficult, and costly in terms of propellant, which is very important for the lifetime of a satellite.

[elamje]

Where did you hear this?