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There have been several proposals to develop Air-Launched rockets, like what Virgin Orbit or Pegasus rocket doing.

All of the concepts are released from aircrafts in a Sub-Sonic velocity (0.7 to 0.8 Mach), why this particular velocity was chosen? What would change if they choose to launch it in super-sonic velocity?

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  • $\begingroup$ There are not many aircrafts able to fly at high altitude with heavy payload at supersonic speed. For air launch of rockets the vertical speed component would help to leave the atmosphere as fast as possible but you would need an aircraft able to climb nearly vertical at high speed and altitude. $\endgroup$ – Uwe Sep 29 '18 at 23:38
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    $\begingroup$ You may want to have a look at the posts by user Muze space.stackexchange.com/users/18879/muze, you seem to be thinking similar thoughts and while it's ok to ask similar questions it helps if you read existing answers first and use them to shape your questions. $\endgroup$ – GremlinWranger Sep 30 '18 at 0:01
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Much the same reason as no current commercial aircraft is supersonic, drag/cost climbs substantially and the aerodynamics becomes much more complex given the need to take off subsonic and fly supersonic. Notably This drone gives an example of the challenges and constraints of getting an external payload above mach one and separating it cleanly. the listed 5000kg weight also suggests how much bigger the launch platform would have to be (Pegasus is ~20000kg).

There are limited gains for doing this, going from 200 m/s to mach2 / 600 m/s is only a small fraction of the needed final velocity of 7400 m/s. So your overall rocket size shrinks by a small amount while the size and complexity of your launch platform climbs massively.

The current air launch platforms make sense because they use cheap(ish) and reliable aircraft to launch from, and have the ferry range to find clear weather/safe ground track for a launch to avoid scrubs due weather or obstacles (for customers where not hitting launch windows causes costs in some way).

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