Perseverance rover uses same PowerPC chipset found in 1998 G3 iMac

Crazy. Just put 10 complete systems in some radiation shielding.

> The CPUs used in space applications typically lag ~20 years

This. Worked in physics department in the 90s that built satellites, and all the chips were late 70s or early 80s chips. Programming them was "fun".

Fun fact, a friend of mine bought and old mac, installed linux, and used it to do profiling for some code he wanted to fly. Great way to quickly find the problem areas!

Those old macs run Ubuntu just fine :)

Once you have a rad-hard CPU, what do you do for the RAM, some super ECC?

RAD750 usage is confirmed in https://mars.nasa.gov/mars2020/spacecraft/rover/brains/

Also worth mentioning that chips from 20 years ago are built on old fabrication technology, with ginormous transistor sizes (compared to modern CPUs). The RAD750 has a 150nm to 250nm minimum feature sizes, a Ryzen Zen 3 chip has a feature size of 7nm, two orders of magnitude smaller!

Feature size is super important in radiation exposed environments because resistance to bit flips from a stray proton (or other charged particles flying around in space) is inversely proportional to the size of your transistors. So small transistors mean they’re more likely to be activated by stray charged particles causing all kinds of interesting and exciting problems (which you don’t want to be debugging from one end of a 12 light minute comms channel).

If RAD750 came out in 2001 that means it was only ~5 years behind. Which raises the question of why isn't there a RAD-A72 now.

Many of my clients in aerospace are still designing in PPC parts in 2021.

Aren't these Motorola-lineage architectures specifically good at doing lockstep computation? I.e. there are a bunch processors executing identical instructions and comparing the outputs?

If I can get a Linux distro to boot into a shell on it, I can do work on it. It'll probably be nicer than vim over ssh still.

The first version of the rPI was pretty close in specs to computers from that time and it works fine - though the G3 mac shipped with way less RAM by default. The first gen rPI on my desk even boots into a usable desktop.

There's a lot of bloat in modern software, such as browsers, but most is in the form of code/features that are rarely used.

Maybe someday we'll see electron versions that can be stripped to stuff you actually need.

It's not obsolete if it's running the apps that you need.

I've done embedded work on MCUs with less horsepower than you probably have in your headphones.

Sure it's not going to run windows 10, but it'll reliably control that device until the mechanical parts wear down. Same applies here, where the advantage of huge transistors means much greater resistance to cosmic rays, and a 20 year old design means all the bugs and quirks are well understood.

The latest and greatest is nice, but not always the right choice for the problem at hand when you have the option of custom firmware and you aren't connected to a hostile internet.

I keep some old computers running as a hobby, and you'd be surprised at how well they still run if you stick Linux on them.

It's only obsolete if it doesn't have the features you need.

Which, in this case, include radiation resistance, which is much harder, if not impossible, to achieve with modern chips with very tiny transistors. Large transistors can much more easily shrug it off.

The old chip is not just "good enough". It's the only thing that works.

This. I worked on satellite control systems in that time frame on these exact boards (OSE and VxWorks); at the time they were considered incredibly powerful for space applications. It was quite the step up from other embedded systems.

Ingenuity is also basically disposable. If it has a complete failure there is no critical mission tasks that are blocked or interrupted. When the device is basically a bonus-time test with a fixed weight limit then you can take a lot more risks to pack more into that weight if you accept a reasonably high probability of failure.

And the camera system uses an Intel processor running Linux and FFmpeg

It also reboots itself quite regularly because they're worried about radiation failures.

I remember reading that it only takes a couple milliseconds to reboot so they're not worried about it moving very far while they do.

There's some surprisingly powerful rad-hardened ARM cpus out there. I'm surprised they didn't go in that direction.

The older stuff uses bigger(size) transistors, which are inherently more robust against a cosmic ray causing a bit flip, and thus easier to make radiation hardend versions.

Space qualified processors are very expensive to develop and produce. They are optimized for use in space and manufactured on an entirely different process than commercial chips. All of this is to ensure reliability in the harsh environment of space. Due to these development and fabrication costs, it's worth it to keep using the same processor as long as it is capable of doing the needed computations. The current RAD750[0] has been used since 2005 and will likely continue to be used for some time.

[0] https://en.wikipedia.org/wiki/RAD750

It's not weight, it's because they're proven and reliable. You don't want to risk the success of the mission on unproven hardware.

For secondary purposes they have no problem running more modern silicon. E.g. the Ingenuity helicopter, as a last-minute addition (and secondary mission) uses much newer hardware and software: https://spectrum.ieee.org/automaton/aerospace/robotic-explor...

> There are some avionics components that are very tough and radiation resistant, but much of the technology is commercial grade. The processor board that we used, for instance, is a Snapdragon 801, which is manufactured by Qualcomm. It’s essentially a cell phone class processor, and the board is very small. But ironically, because it’s relatively modern technology, it’s vastly more powerful than the processors that are flying on the rover.

The Ingenuity drone also on Mars now uses a Snapdragon processor running Linux. This is not radiation hardened IIRC, but it reboots so fast that it is in control again before it hits the ground in case the computer borks due to radiation flipping bits in flight.

EDIT: Found the article again: https://spectrum.ieee.org/automaton/aerospace/robotic-explor...

I'm not sure where I got the reboot thing from, I think HN in a thread after the Perseverance landing

> Is this a good thing, or bad?

Neither. The proper question to ask: "is it the right tool for the job?" The answer here is yes. Power is a vetted architecture and has been used in critical processes for quite some time.

Just because something is old does not mean it is bad or some sort of burden.

It's not a good or bad thing. It's a process. Remote instruments (which is essentially what these missions are) don't need all that much compute to turn and face a target and acquire an image. It'd be nice to have more, but it's not strictly necessary.

Also, spacecraft a little distributed systems. There are _lots more_ processors on these things. The instruments and mechanisms all have their own processors, from what I see ... which is limited.

Don't think too hard about how Percy is self-driving on its limited compute, that will make your head hurt to think about trying to make that work.

Its the right tool for the job, so I would say its a good thing. Its a radiation hardened processor which has proven its worth in previous missions and is well known to the developers, while also providing enough computational resources to do what they need it to do.

> Is this a good thing, or bad? I've always heard the rumor that NASA computer systems for space-intended systems to be grossly out of date. However this is due to certifying that the processor, etc. can work and that process takes a long time. Just curious if anyone knows why NASA doesn't use more modern processors; is it weight?

Think of it this way: technology is not a straight-line tech tree from "less advanced" to "more advanced." It's more about tradeoffs.

So these processors might have less processing speed compared to modern consumer ones, but they're more reliable and resistant to radiation (and that's partially a consequence of the reduced speed).

They need to use radiation hardened processors. That means the chip will be in special packaging (I think ceramic), use bigger process geometries and, use redundancies in logic design within the chip. Also running at lower clock rates will reduce the chance of failure. These are not mainstream chips so they will be expensive and slow development. And lastly certification takes a lot of time and there are risks to the mission to switch from a proven technology to something new. A single glitch can end a mission that took a decade to accomplish.

> Is this a good thing, or bad?

It's the only thing that works, so it's good by definition.

Modern chips with tiny transistors can easily get fried (or make gross mistakes) because of cosmic radiation. Large transistors are much more robust.

They likely do (but with hardened hardware), as they've done previously.

https://www.extremetech.com/extreme/278160-nasa-switches-cur...

I'm pretty sure that was just a Sun/Apple thing, not a POWER thing?

Not to discount the question, because it's still interesting, but most of SpaceX's hardware doesn't leave the ionosphere.

In Mars? Nothing that I know... :P

The CRS-10 that fly to the ISS seem to use RadHArd Cortex M4 or M0, according to this ARM PR document:

https://www.arm.com/blogs/blueprint/arm-rad-hard-chips-space

https://www.voragotech.com/products-main

On 1-Aug-2017, Jinnah Hosein, who was the head of Software at SpaceX at the time, spoke to my company, Orbital Insight, in Mountain View, and I took some notes. I've never posted them anywhere, but below I'll post some unpolished bits.

WARNING: this was a lot longer and 'scattered' than I recall, apologies in advance.

DISCLAIMER: This was a casual talk and I casually took some notes, and it happened over three years ago as of this writing. In short, don't assume anything below is an accurate representation of what Jinnah said. As a long-time SpaceX fan, and as a much longer-time software engineer, I was super pumped during the whole talk, and was definitely not focused on accurate recording.

https://www.realms.org/spacex-talk-notes.html

PS: I know most of this veers way off topic, but for some reason I decided to take this opportunity to share this material.

PPS: The comment was too long to post, so you'll need to click the above link. Sorry about that. If someone would like to distill the on-topic parts into another comment, that would be fine.

SpaceX has not sent a rocket beyond the protective field of the earth so apparently the requirements are less stringent.

IIRC they use x86, just doubled just like their tesla brains.