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PaperclipPerfector  5mo ago (text post)   3396 thread views

Friday Fun Thread for June 7, 2024

Be advised: this thread is not for serious in-depth discussion of weighty topics (we have a link for that), this thread is not for anything Culture War related. This thread is for Fun. You got jokes? Share 'em. You got silly questions? Ask 'em.

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and the revolutionary impact of reusability being a house of cards.

..uhh, what?

Their record for flying the 1st stage booster is doing so 21 times. How's that not impressive?

I feel like "Impressive" is a motte-and-bailey. Musk regularly makes entire series of predictions and promises, and people give him an amount of praise I'd consider valid, if he actually managed to fulfill said promises. But since he hasn't we retreat to acting like the things he accomplished are what earned him the amount of praise he's getting. I heard, on several occasions that "rapid reusability" means rockets turned around as fast, and as often as airplanes. When I see that, I'll be writing my apology letter to Daddy Musk.

I guess I fundamentally disagree with this view because it's anti-aspirational. The aspirational goal is aircraft-like rapid reuse, and yes, that goal has not been achieved. But the actual accomplishment of slightly-less-rapidly reusable boosters good for at least tens of flights is still way more than anyone else has achieved, worthy of great praise, and should not be diminished! I'd much rather over-praise a company that delivers on 25% of its extremely aspirational goals than one that delivers 90% of unambitious goals.

how much maintenance was required between those flights, and how much did that maintenance cost?

Musk claims that for them, refurbishment cost is ~10% of mfg cost of a booster. If you have a gigabrain theory how it's actually not cheap and SpaceX is borrowing money to sell launches at an artificially low price, I'd surely love to hear about it.

Note that their mfg cost is also a lot lower than for other companies.

Also it seems launching 1 kg to LEO, which used to cost $25k in the Apollo era is now down to $1200 if done by SpaceX.

If BFR which costs $100 million to build each( I refuse to use 'starship', they can go fuck themselves with that name) ends up equally reusable, cost of launching 150 tons to LEO is going to go down to cca 15 million $. (I assume $5 million covers the fuel cost handily especially in Texas). Musk is more optimistic about BFR reusability due to improvements such as no soot anymore but there's the heat shield on upper stage and all that too so who knows.

Meanwhile, in comparable dollars in 1960s, cost of launching a similar amount of mass was cca 1.2 billion $.

If it works out, one could launch an entire aircraft carrier sized ship, in chunks, for less than it costs to build one today. ($12 billion, launch cost 9 billion$).

Pretty funny - we could actually start building space battleships soon. The nuclear salt-water rocket propulsion that would give them range to Pluto and back one tank fairly fast are doable, and if your exhaust has a speed of 66 km/s there's no risk of it spiraling down into Earth atmo anyway.

Musk claims that for them, refurbishment cost is ~10% of mfg cost of a booster. If you have a gigabrain theory how it's actually not cheap and SpaceX is borrowing money to sell launches at an artificially low price, I'd surely love to hear about it.

Naw, just looking for numbers to sanity-check the claim of reusability. 10% refurbishment sounds like extremely good savings.

I think we're going to need to build some things off-planet before battleships are worth having to defend those things, but I'm definately rooting for Musk on this one.

The nuclear salt-water rocket propulsion that would give them range to Pluto and back one tank fairly fast are doable

"When Chernobyl reached peak x power during its explosion it was about 350 gigawatts for a fraction of a second. This is 700 gigawatts continuously, right, it's a non-stop Chernobyl going on."

are doable

Well, maybe? For obvious reasons we'll never get the EPA to approve a ground test, and I'd be a bit leery about LEO too, which leaves us just hoping that Zubrin's paper was solid.

Of course, the 66 km/s exhaust version was his conservative design; the really speculative version upgrades the uranium enrichment level from "20%" to "weapons grade" and bumps up the yield, to get the delta-V to a few percent of the speed of light. YOLO, right?

Either way, while I'm generally a big fan of the SpaceX "get hardware flying so if it breaks you learn more faster" strategy, I think I'd be cool with taking things more slowly before assembling a 200,000 megaton hopefully-not-a-bomb in orbit.

"When Chernobyl reached peak x power during its explosion it was about 350 gigawatts for a fraction of a second. This is 700 gigawatts continuously, right, it's a non-stop Chernobyl going on."

Chernobyl also released radiation from reactions that have taken place in the months before, so it's not really a good approximation of harm that'd be caused by using nuclear saltwater rockets for space launches.

It is, however, in essence similar to Orion launches, and the radiation release there was found to not be particularly bad by the engineers worrying about it. I'm not sure what approaches they used, but if they were using LNTR and got a figure of "may give 1 person cancer" then it's probably not a big deal.

In any case, it's one of those questions that can't be answered without a good simulation.

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