Hacker News Reader

Comment by rbanffy | Hacker News Reader

This is one of the reasons SpaceX uses supercooled fuel and oxydizer (and one of the reasons for going methalox in the first place) - the tanks self-pressurize, so they can skip the Helium system.

Pumps are still good because you really don't want the tanks to pressurize at the same pressure as the combustion chamber. If you do, you'll see a rapid disassembly, but your claim on it being unscheduled will be questioned.

View on HN

This is completely, completely wrong. Really honestly confused nonesense. Supercooling lowers the ullage pressure, if anything increasing the need to pressurise (self or otherwise), because the self pressurisiation (the vapour pressure) is lower. So you have to do additional work to feed the pumps. The only reason to supercool is to increase the density. Your comment is quite incorrect.

I really appreciate your expertise and that you're taking the time to correct the sometimes overeager amateurs in this thread. But can I suggest you tone down the unnecessary invectives? It's true that there ought to be some social penalty paid when people give confident wrong answers -- it's a pet peeve of mine -- but I think it's sufficient to just say something like "Your comment is incorrect. Here's why, in detail. Please don't project so much false confidence next time." That still stings for the other person to hear, as it should, but it leaves them much more likely to want to learn more. And it's much less likely to escalate into a fight that distracts from the main subject.

All fair, valid and noted. It’s the eve of Opportunity’s demise, and i worked on mars EDL, and the infinite tide of javascripters making statesmanly-yet-quite-mistaken proclamations on physics can feel quite disrespectful to the actual engineers who work on this stuff now, worked on the stuff on both sides in the cold war, and everyone back to goddard, tchiolkovsky and moore. But you are right. More whisky and no more HN.

Reply on news.ycombinator.com