*Question about horizontal air launches.* That's a tricky one. Well, I think it's important to keep in mind that the payload to orbit advantage from an air launch is negligible. I think this audience understands that, but most people don't, because it seems like, well, you're high up there and so surely that's good and you're going at, say, 0.7 or 0.8 Mach and you've got some speed and altitude, you can use a higher expansion ratio on the nozzle, doesn't all that add up to a meaningful improvement in payload to orbit?
The answer is no, it does not, unfortunately. It's quite a small improvement. It's maybe a 5% improvement in payload to orbit, something like that, and then you've got this humungous plane to deal with. Which is just like have a stage. From SpaceX's standpoint, would it make more sense to have a gigantic plane or to increase the size of the first stage by five percent? Uhh, I'll take option two. And then, once you get beyond a certain scale, you just can't make the plane big enough.
When you drop the vehicle, the rocket, you have the slight problem that you're not going the right direction. If you look at what Orbital Sciences did with Pegasus, they have a delta wing to do the turn maneuver but then you've got this big wing that's added a bunch of mass and you've able to mostly, but not entirely, convert your horizontal velocity into vertical velocity, or mostly vertical velocity, and the net is really not great. So, Orbital, for example, is an interesting example. They started off with the Pegasus as an air launch vehicle and then ultimately did not do any air launch vehicles.
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