4

I'm reading conflicting things on the timing of the pitchover. When exactly does it start?

Many people write that it's almost immediately after launch, as soon as it's practical. Once the rocket clears the launch tower, say.

Others write that it's much later. The Kerbal Space Program is just a game, but it seems common wisdom there to start your gravity turn at 10 km of altitude. Start higher, and you lose fuel to gravity losses. Start lower and you lose fuel to air drag.

I'm specifically curious about the Falcon 9 rockets. Sure, every mission is different, but at least on average, when is pitchover done? Even better than pitchover start time would be the altitude at which it is done.

Thanks!

  • Some launchers even start angled ad the launch pad. – SE - stop firing the good guys Dec 16 '20 at 20:27
  • For Saturn V it's in the graph from your previous question https://space.stackexchange.com/q/49141/6944 – Organic Marble Dec 16 '20 at 20:31
  • Shuttle started pitching at the end of its vertical rise phase - ~ 350 ft altitude - as part of the roll maneuver. – Organic Marble Dec 16 '20 at 20:39
  • Thanks, all. Any numbers on the Falcon 9? –  Dec 16 '20 at 20:43
  • 2
    Too lazy to write an answer, but Flight Club does educated-guess simulations of launches including Falcon 9, and generates many data plots. The "Elevation" plot is what you're looking for; it shows a 2-degree pitchover at T+15 seconds for this particular mission and a more significant turn beginning at T+25 seconds. – Russell Borogove Dec 16 '20 at 20:52
  • Thanks, Russel! That's a good starting point :) –  Dec 16 '20 at 20:54
  • 1
    @RussellBorogove, any idea how they got the drag coefficient plot? This would be useful to me, but I'm wondering if I can trust. Thanks! –  Dec 16 '20 at 21:01
  • 1
    No idea, but Flight Club creator @DeclanMurphy occasionally appears here. – Russell Borogove Dec 16 '20 at 21:35
  • No throttle back shown on this launch... Wondering if they truly skipped it or if it just wasn't captured in the data? –  Dec 16 '20 at 21:45
  • @Alex after checking out answers to Does anyone know how the Flight Club website simulates Falcon 9 launches? maybe you can just post a new question asking exactly those questions about drag coefficients and throttle-backs. – uhoh Dec 16 '20 at 22:08
  • Oh, bummer, that's not actual flight data, it's just simulation data. Sure, they get parts of the flight right, but as a simulation, they would have to guess parameters, and that's not trivial work. It's neat to see the results they get, but I don't think those are numbers to blindly trust. They aren't actual flight data. –  Dec 16 '20 at 22:17
  • @Alex the answer is: it depends – Topcode Dec 16 '20 at 22:24
  • @Topcode, of course it depends, does anyone doubt it? But just because "it depends" doesn't mean you can't give meaningful useful metrics for it. All things everywhere "depend". The shape and size of an apple each "depends," but you can say it's approximately spherical approximately 3 in across. This is the sort of answer that would be useful. Saying something depends is to say nothing at all. –  Dec 16 '20 at 22:42
  • KSP received wisdom is full of untested assumptions, plausible guesses, and relics of older game engines physics models –  Dec 17 '20 at 00:46
  • Agreed, as I said, KSP is just a game, and it seems self-evident that you don't use games to engineer rocket launches. Nevertheless, the game is based on physics principles, and, with conflicting info out there on the timing of the pitchover, it is suggestive of how one is actually done. If a KSP gamer gets best launch performance by starting the pitchover at 10 km high, and if the game is based on physics principles, you start to wonder if in fact real launches might start pitchover miles high. The game is suggestive, that's all. No one is taking KSP for a source of truth. –  Dec 17 '20 at 04:55
  • I wish people would stop commenting on the obvious. Yes, things "depend." No, a game is not a reliable source of truth. Yes, in the lack of clear info on a topic, a game based on sound physics is suggestive of how things might be done. Let's please not waste time stating the obvious or saying what amounts to nothing at all. We're all smarter than that. –  Dec 17 '20 at 04:57

0 Answers0