Reply to post: Re: Right Direction?

Virgin 'spaceship' pilot 'unlocked tailbooms' going through sound barrier


Re: Right Direction?

I used to think the same.

I saw images as a kid of the shuttle being transported on top of a 747; so thought why not just launch a disposable rocket stage + small lifting body return craft (say a Northrop HL-10) via a B52 or 747?. The carrier aircraft could be relatively cheap & reusable and carry the assembly to high altitudes & near mach 1, before launch rather than accelerating the rocket from zero feet and zero speed.

Turns out, it is not such a great idea in general, in particular when trying to throw tonnes of mass into space.

For a start, it does not win you very much. To make orbit you need ~mach 25 delta-v, so even if the carrier aircraft is traveling mach 1, you are only 4% there. Just carrying 5% more rocket fuel would give you similar win.

Then to hit that mach-25 you need a big rocket anyway. When you have a big (but very light) tube full of rocket fuel, the easiest way of assembling that tube of rocket fuel is having it sit vertically on the ground, rather than strapped under or over the launch aircraft & stressed to take G's horizontally and vertically.

Finally every Kg of mass you have to accelerate to orbital speed and have to bring back (especially if you have a reusable return vehicle that has wheels, wings etc) costs lots of money per Kg, so best that you dispose of as much of it as you go - i.e. a multi-stage disposable vertical launch rocket for putting stuff into orbit that you want to keep in orbit.

This is why the rocket scientists from Von Braun onwards stick to conventional rockets.

There are interesting alternatives of course; I liked the thinking behind the McDonnell Douglas DC-X, and for small payloads, something like a carrier aircraft or balloon to get a smallish (solid fuel?) rocket above the dense atmosphere might work out (i.e..nozzle design could be optimised).

Even the Skylon might fly one day, but DC-X/Skylon have never got anywhere near space and (as this accident shows), SpaceShip 2 is still a work in progress.

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