3 ms·
Look at this analysis of the Falcon 9 flight profile, in particular the graph at the bottom right: https://www.reddit.com/r/spacex/comments/6303ko/falcon_9_full
by fdej 9y ago
Look at this analysis of the Falcon 9 flight profile, in particular the graph at the bottom right: https://www.reddit.com/r/spacex/comments/6303ko/falcon_9_full_thrust_flight_analysis/ https://www.reddit.com/r/spacex/comments/6303ko/falcon_9_ful...
The majority of the horizontal delta-V is produced in the second stage. The job of the first stage is to a large extent just to lift the second stage out of the densest part of the atmosphere, to minimize drag for the second stage. A plane can do the same thing, and possibly more cheaply in certain scenarios (well, that has to be Allen's plan anyway).
- mikeash 9y agoKeep in mind that it's not just a matter of getting the second stage up high, but giving it enough vertical velocity so that it can reach orbital speed before it falls back into the atmosphere. If you could magically drop the second stage off at its separation altitude but with zero vertical speed, it wouldn't be able to reach orbit. An airplane won't provide much vertical speed, if any, so it's not really doing the same job. Still, just letting the rocket start up high is a big advantage.