Comment by wolverine876 | Hacker News Reader

Comment by wolverine876 | Hacker News Reader

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Hey - thank you! I really appreciate hearing from someone who actually knows what they are talking about.

I know nothing about the helicopter in particular but as I pointed out, NASA seems to very frequently underestimates longevity and performance (not a crime at all and maybe politically wise); I can't remember when they've overestimated. Forget my impressions in prior posts - how and why does that actually happen?

> tech demo ... precarious ... not much engineering experience

Also, while I've taken the opportunity of spare resources to do experiments (though not usually on Mars), I'm careful about timing and appearances - I don't want to embarass my team or partners with a failure that's visible to outsiders who wouldn't understand it was an experiment, and would think we just failed at our jobs.

Everything NASA does seems to be on a very public stage, interpreted by endless outsiders (like on HN :) ). The whole world watched the helicopter's first flight. How can someone approve the helicopter, and promotion of its flight, and risk the world saying, for the next decade, 'that crazy helicopter embarassment shows we need to rein in NASA', blah blah blah? NASA's reputation is very important to humanity.

Thanks for sharing what you know. You guys do amazing things; people are so jaded that they don't realize how incredible it is.

For very expensive projects like mars landers, it's imperative that everything is very reliable. If the mission plan is 5 flights, that means the systems need to be reliable enough that there's a 99.9% chance that it will successfully complete those five flights. But that also means that there's, say, a 98% chance that it can successfully complete 20 flights and maybe a 80% chance that it could complete over 50 flights. So these extended missions are really a consequence of building things to complete the primary mission as effectively as possible.

As I tried to clarify above, the helicopter was a tech demo ($90M) and not subject to the same risk rules as “very expensive projects like mars landers” (Perseverance: $2.4B). Your first sentence is trying to equate them.

Heli was on board the lander but it was not subject to the same risk constraints.

I think your probabilistic risk assessment has something going for it, but not all risk would scale that way.

I’m surprised at the self assurance of some of these comments!

One key differentiator is if the mission is competed or directed.

Directed (in essence) means that the National Academies (NAS) decadal survey recommended that specific mission. (They specify the what but not too much about the how.) A directed mission is assigned to an implementing center (JPL , GSFC, etc.) And they build it to accomplish their best interpretation of the NAS DS guidance.

Sometimes this can be expensive, more expensive than the NAS expected (JWST). And sometimes the imperative to make it work to accomplish the “down from the NAS” guidance, with near 100% certainty, in a novel environment will result in over performance like you noted.

The noteworthy directed missions are mostly large flagship missions.

The other category is cost capped competed missions. (VERITAS is a recent one, so was New Horizons, but they exist in astrophysics and earth science as well as planetary; see for example https://en.m.wikipedia.org/wiki/New_Frontiers_program). “Tell us what you can build to accomplish some portion of the following high level science goals in $300M or less”

Over engineering is not really possible under those conditions! You will be competing against the absolute best concepts and teams in existence. So the budget is really squeezed.

These two mission types are complementary in the obvious way. The flagships push engineering capacity way forward, and the competed missions have a lot of innovative concepts within a cost cap.

There are also pure tech demonstrations (often piggybacking like the helicopter did) and certain other categories but the competed/directed split is primary.

Thank you, that deepens my understanding quite a bit. Either way, directed or competed, NASA missions hardly ever fail - very impressive in itself.

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