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Comment by Out_of_Characte | Hacker News Reader

Single points of failure are inevitable. engineers could always make a copy of the entire design but that would double the costs and you would still be left with unknown points of failure that the telescope double would have.

The solar shield is like rolling out five layers of tightly packed tinfoil from several points without tearing. Claiming that you would do away with single points of failure if you were the one designing it is too easy to say on HN

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Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.

I'm not arguing you could completely go away with single points of failure when designing a spacecraft while being limited by the payload mass and volume. But the whole JWST unfolding sequence looks like a way too risky gamble to me. Maybe, it was worthwhile to sacrifice some of the scientific payload mass to add more redundancies into the solar shield design and increase the chances the telescope would be able to reach the beginning of its observation process.

There's also the whole "what if we could avoid mass and volume constraints" tangent, that was discussed in the yesterday's Starship article, but it's more of a theoretical consideration for now.

Honestly, I thought the same about the whole Perseverance landing sequence on Mars. But now it's done, and the rover is running around doing its thing.

So, what I learned is that single points of failure on initial deployment -- which by definition only has to run once -- is a drastically different cost vs risk calculation than something that happens during normal operations.

The unfolding sequence looked complicated to me, too, and then I remembered I am just a guy online.

You are right that a magical rocket could solve many of NASAs problems (just launch ten Webbs and use the ones that don't work as sunshades for the rest!) but I think NASA is being pretty practical in not waiting for one to be invented.

>entire design but that would double the costs

What was the original budget for JWST? Where's it at now? From your assessment and the numbers, it sounds like there's not just double but triple redundancy now.

In 1996 when it was a proposed idea the estimated cost was 500 million USD and the proposed launch was 2007. But the design kept getting more and more lofty and the project got more and more complex. The initial estimate was a bit off, it has cost about 9.6 billion USD so far.

Still though, if everything works and we learn more about the universe, I think it'll have been worth it.

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