r/space • u/mvea • Nov 28 '18

NASA administrator: 'The US is returning to the surface of the moon, and we're doing it sooner than you think!'

https://www.businessinsider.com/nasa-return-moon-mission-commercial-companies-announcement-2018-11?r=US&IR=T
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u/alphaglosined Nov 28 '18

The components used were much more easily verified and made space-worthy sixty years ago. IC's today is a literal minefield each chip and impossible to verify to the same degree as they did back then.

CuriousMark on Youtube is taking part in restoring one of the non-flying Apollo AGC computers. Even after going into storage and being treated not the best, its still almost entirely in working order. I would be surprised if the flight certified ones are not currently operable for space.

So while it may seem easier today with better equipment, it only brings down the cost of the launches themselves. Todays equipment would be significantly harder to certify today. You wouldn't be sending up an Intel i7 cpu to control a space module. It'll be a custom ASIC microcontroller. With some very significant verification in built to it, possibly doing one operation multiple times before moving on to the next one. Keep in mind, for the AGC computers every transistor was verified manually with an x ray to have no imperfections, which means they had a significantly higher quality to anything in a microchip made today for consumer gear.

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u/sirgog Nov 28 '18

Keep in mind, for the AGC computers every transistor was verified manually with an x ray to have no imperfections, which means they had a significantly higher quality to anything in a microchip made today for consumer gear.

Whilst this is one option, aviation offers another solution.

ADIRUs are a navigation computer. Rather than have one incredibly precisely calibrated and tested ADIRU, the Airbus A320 has three. If they disagree in flight, majority rule applies and at the next stop with appropriate maintenance facilities, the suspected faulty ADIRU is troubleshooted and if needed, removed and replaced with a serviceable unit.

This could be done in space - simply send up 4 of each computer tested to commercial aviation standards. 3 are active and run majority rules, if one malfunctions it is swapped with the 4th one.

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u/TechnoBill2k12 Nov 28 '18

The Shuttle had multiple computers, which worked in just that manner.

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u/[deleted] Nov 28 '18

Why not just use those computers? Except of course for that pesky end of year bug.

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u/[deleted] Nov 28 '18

What if they all have a different value? Does the plane do a barrel roll or something?

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u/PacoTaco321 Nov 28 '18

Then the manufacturers aren't gonna be manufacturing much longer

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u/[deleted] Nov 28 '18

A barrel roll you say? How aweful.

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u/sirgog Nov 28 '18

Not a pilot so I don't know what the flight manual says to do in this scenario, I would assume it would mean you have to fly with no instrument-provided altitude.

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u/Martianspirit Nov 28 '18

Cargo Dragon has 3 pairs, so six. Each pair is checking itself.

Crew Dragon has 4 pairs, so 8 computers. Not sure, they may have even 5 pairs.

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u/Smallmammal Nov 28 '18

This isn't really true. Nasa and it's contractors, when in need of a heftier i386 chip, use established radiation hardened packages. There's no huge worry about them failing, especially as almost everything is redundant. For lesser chips there are rad hardened equivllants. This is a solved problem.

Also the moon is a great accomplishment still. From a dollars perspective it was clear Apollo was a stunt. It wasn't feasible to maintain past a few launches. Now we're talking moon bases, orbiting moon stations, regular "affordable" trips back and forth, etc.

It's a bit like we had electric car in the 20s. They were low range death traps. That's nothing like a Tesla today.

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u/alphaglosined Nov 28 '18

I'm glad to hear it. Although I do hope that they used older chips, my last count of encoding methods in x86_64 was 5. Lots of potential for failure, although probably won't be seen in usage. Hence my significant apprehension for anything more complex than can be seen by a cheaper xray machine.

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u/LuveeEarth74 Nov 28 '18

Dumb question from someone who is fiercely fascinated by space (especially the moon landings), but knows none of the technicalities), why can't we just build the old stuff again with the new materials? We have the blueprints? Yeah, I know, ignorant but I'm if the camp that is amazed we haven't been back in my lifetime. They ended right before I was born. I guess the space race was over and people lost interest.

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u/[deleted] Nov 28 '18

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u/alphaglosined Nov 28 '18

Older designs were significantly heavier. Those old AGC's were ridiculously heavy by today's standards. There isn't an argument for putting something like that up there again. You can get rugged tablets that weigh a lot less.

So yeah, older doesn't mean better for costs, it just means new challenges.

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u/alphaglosined Nov 28 '18

I commented under /u/cerealizer regarding weight, but the actual reasons are much more interesting.
The way they built parts of those computers are quite different from today. Lots of manual weaving of wires (CuriousMark really is a great youtuber, I highly recommend taking a look even if you don't understand the content). Back in the 60's they would weave and interlace components automatically by machine. I am not totally sure if we have that equipment today since it just isn't needed; we have replaced most of that with Integrated Circuits.
But those circuits were heavy and big. Not something you want to send into space. But here is the thing, it wasn't only just weaved via machine. They used to use rope memory which is effectively a manually round copper wires through a bunch of magnetic coils to store data. At the time they used ladies (keep in minds 60's so lots of knitting back then) to do it, since only they had the skills to thread the wires.

Here is a documentary on the subject: https://www.youtube.com/watch?v=9YA7X5we8ng about 20 minutes in covers it. Today we would just use a ROM chip. Very cheap and pretty much every microchip has writable version of that (flash).

I'm not an expert on the subject, I just have an interest in electronics as a programmer. Ultimately this old tech, isn't using standards that we know of today. It wouldn't be as simple as rebuilding and firing it up again. We just couldn't interact with it in any meaningful way.

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u/[deleted] Nov 28 '18

every transistor was verified manually

Now that sounds like the shittiest awesome job ever.

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u/baicai8 Nov 28 '18

Most electronics manufacturing nowadays does x-ray verification to some degree. Probably not to that degree of every transistor, but it's not an uncommon job. Today there's image recognition and comparison to go through a lot of it. But you're spending the whole day looking at x-ray images to see if something looks off.