Comment by usrusr | Hacker News Reader

Comment by usrusr | Hacker News Reader

Parent Full thread

According to von Braun's Popular Science AMA it was a safety feature:

"It is in the area of crew safety that fins come in handy. In Saturn V the booster fins are not to provide perfect aerodynamic stability under all conditions - that would take fins of excessive size. But the fins reduce the aerodynamic instability enough to make sure that the astronauts can safely abort, no matter what technical trouble may afflict their space vehicle."

( https://books.google.de/books?id=MiYDAAAAMBAJ&pg=PA184 , continued from https://books.google.de/books?id=MiYDAAAAMBAJ&pg=PA68 )

Both could be true at once, just like when bicycle helmets are worn more as a fashion statement than out of confidence in their protective value. Or maybe he was just squelching rumors.

Answering this accurately would require a lot more information about the aerodynamics of the Saturn V than I have. But I suspect it was the latter - he was justifying a design decision after the fact.

I say that because for the fins to do any good at all, boundary layer or not, the launch vehicle has to be moving at speed. I don't think a successful crew capsule abort would be likely past a couple of hundred miles per hour. If that.

> I don't think a successful crew capsule abort would be likely past a couple of hundred miles per hour. If that.

That's not true at all. Every manned space launcher has provisions for bringing the crew down safely on a suborbital trajectory if orbit can't be reached. You would hardly give up on your astronauts just because, say, some stage failed to light. It's not like with an unmanned satellite, where it either gets to orbit or crashes/burns up.

Apollo certainly had provisions for crew abort all the way to orbit, which are discussed here: https://en.wikipedia.org/wiki/Apollo_abort_modes

I agree that they had those provisions. I'm just skeptical about them working if the primary stack ACS went south. The crew capsule didn't have its own ACS, IIRC. It would have likely entered a high rate tumble shortly after an abort separation.

It would have been worth a shot, just like jumping out of a speeding car about to go over a cliff. But you probably die anyway.

Reply on news.ycombinator.com