[cbanek]

(I worked at SpaceX)

Two words: flight heritage.

Successful concepts are very often reused. For example, heat shields, parachute landings, sea landings, air bags for landings on hard land, etc.

Now, let me try to explain this in something similar: cars.

Cars are all pretty much the same. They have a steering wheel, 4 tires, transmission, engine, etc. The parts all do the same thing in different cars, but we don't always use the same engine, or the same tires, or the same frame for every car.

After making cars for so long, why do car companies still have recalls?

New models of cars usually either start from scratch or start based on a different vehicle already in production (new model year). But if you're starting from scratch, you've lost all the "little fixes" that go into making a car good. Like the difference from a new model EV car to a Toyota Corolla that's been in production for basically 10 years has a very different failure/recall rate. After many years of producing the same car, you fix all the little things and get your supply chains working well.

Now back to space ships. It's the same thing. You have made a new capsule and although the concepts are the same, think about all the little things: wiring, plumbing, controls, software. These are all new and basically untested. They lack "flight heritage" (proven working in space).

For the question as why can't we make Apollo ships or Saturn V's anymore, a lot of plans and drawings were lost. Key people making decisions, testing, or even building parts on an assembly line weren't there. Companies making specialized parts folded or went under, or just stopped making those parts.

Sometimes these can be small issues. Like for the Mars Climate Orbiter there was a problem where two different companies thought they were using the same units when they were not. Or when an accelerometer was installed backward on a different ship, making the chute not deploy.

Now compare this to the Soyuz, which is more like a Toyota Corolla of space ships. It's not the fanciest or has the most space or efficiency, but it has a lot of flight heritage and operational history. And from there, you can make small changes relatively safely.

This is true for all companies making space ships. Really it comes down to how well you test things and a good helping of luck on getting it to work the first time, or fixing it quickly.

[anonzzzies]

> But if you're starting from scratch, you've lost all the "little fixes" that go into making a car good.

This is also the reason massive software rewrites often fail; you rebuild the general gist quite fast, nice code, lovely interfaces etc but it will have a trillion bugs which come from decades of adding an exception here, adding one there etc. So now you have a beautiful albeit worthless product. And often these get scrapped: I know of some tax system rewrites from mainframe to modern code that costed 10s of millions and were scrapped, multiple times for this reason.

[pie_flavor]

Joel Spolsky has an excellent writeup on this principle, explaining why it led to Netscape dying: https://www.joelonsoftware.com/2000/04/06/things-you-should-...

[bumby]

The VA has wasted hundreds of millions of dollars trying to rewrite their antiquated software.

[Bluestein]

> For the question as why can't we make Apollo ships or Saturn V's anymore, a lot of plans and drawings were lost. Key people making decisions, testing, or even building parts on an assembly line weren't there.

"Know-how rot" is a thing. Actual people involved are literally dying off, and knowledge is being lost. It could have been a peak, the Apollo program.-

[fasa99]

Welp it was a peak, the Apollo program. Actually we'd want it to not be a peak, but a stepping stone to something greater. Alas.

[bumby]

>a lot of plans and drawings were lost.

Even if the drawings are there, they are often not as good as you may hope. It’s not uncommon to have missing specs, part numbers etc. Modern engineers have to fill in the gaps and sometimes build one-off small parts when the OEM is no longer in business (or no longer interested in building small quantities of some part)

[m4rtink]

You mixed up Marce Recognisance Orbiter (still in Mars orbit) with Mars Climate Orbiter (part of Mars due to unit mixup).

[cbanek]

ah yes you are totally correct, thanks!

[dotancohen]

Though we have lost some documentation, that is not the reason that we would not build Saturn Vs or Apollo capsules anymore. Those vehicles just do not support the modem missions that we would like to do, even if we had the full specs still.

We need more mass to orbit, more time on orbit, larger spacecraft volumes, less expensive mass-to-orbit, and less toxic materials in order to do the new missions that we'd like to do.

[rendall]

I read your comment before I read the article, and it gave me context for this passage:

> After extensive tests and analyses, Boeing engineers concluded the helium leaks were the result of slightly degraded seals exposed to toxic propellants over an extended period....

> The thruster problem, testing indicated, was caused by high temperatures that, in turn, caused internal Teflon seals to deform in poppet valves, restricting the flow of fuel.

> The high temperatures, the engineers concluded, were largely the result of manual flight control tests that caused the jets to fire hundreds of times in rapid-fire fashion while the craft was oriented so those same jets were in direct sunlight for an extended period.

[dredmorbius]

Among several maddening bits from Robert Gordon's The Rise and Fall of American Growth a few years back was this passage:

> The most obvious reason why productivity remained high after World War II, despite the end of the military emergency is that technological change does not regress. People do not forget. Once progress is made, no matter under what circumstances, it is permanent.

Robert J. Gordon, The Rise and Fall of American Growth, Chapter 16, p. 550.

Emphasis in original.

The best counterexample is the apocryphal quote, since adopted by many programmers: "When I wrote that passage, there were two who understood it.—God and myself. Now, alas, God alone understands it!"

<https://quoteinvestigator.com/2013/09/24/god-knows/>

I've certainly been in that circumstance with my own code multiple times, as well as at organisations which no longer knew why, or how, certain things were done.

And people, cultures, do forget. The whole notion of "lost wisdom" or "forgotten knowdge" is legion (though unfortunately neither seems to have a Wikipedia article yet which I can conveniently cite here).

Psychology has the notion however of a "forgetting curve", based on the work of Hermann Ebbinghaus, and I'm pretty sure that there's a similar notion which applies at a cultural and/or social level:

<https://quoteinvestigator.com/2013/09/24/god-knows/>

A related concept, and one that's given me pause for thought for some time, has been what the minimum sufficient level of continuation of cultural knowledge is, especially given the distinction between explicit and tacit knowledge. The former is easy to codify and transmit via text or speech, the latter is hard to express, and requires direct experience, personal training, or otherwise greater-than-verbal or greater-than-textual instruction. "You can't learn to swim from a book" is one expression of this.[1] In a technological society which becomes ever more specialised, at what point is there no longer sufficient transmission of a concept for it to be considered still "remembered"? How many crafts today have only a single practitioner? Perhaps retired?

(I've posted previously about the art of scientific glass-blowing, which seems headed down this forgetting path.)

________________________________

Notes:

1. Though of course there are exceptions. Theodor Kaluza taught himself to swim aged thirty from a book: <https://en.wikipedia.org/wiki/Theodor_Kaluza#Personal_life>.