Air Launching Rockets:The Possibilities of the A380?

[Shawnzyoo]

in light of the recent failure of the cosmos-1 booster rockets
has there been any real thought to using planes as carriers for unmanned rockets to around 45,000 ft?
i.e. white knight carrying the X-43 or SpaceShipOne
or possibly a much MUCH bigger plane...like Airbus A-380??

 

[Q_Goest]

There's a company called "Orbital Sciences Corporation" that builds and launches the Pegasus rocket which gets into the air strapped under an L1011. They used to use a B-52 when they were just starting out about 15 years ago, but have become more commercialized since then I suppose.
http://www.orbital.com/SpaceLaunch/Pegasus/

Intuitively it seems like a good idea, you get some altitude and velocity to start out with and thereby decrease the amount of fuel / increase the amount of payload as if the aircraft is some kind of booster. But a quick look at the math shows there isn't much benefit. A satalite in low Earth orbit is moving around 17,000 miles/hr at an altitude of between 250 and 900 miles. Let's use 500 miles as LOE for the sake of discussion.

If you add together the potential and kinetic energy of a kilogram in low Earth orbit it comes to about 37,000,000 Joules (rounded off).

Compare that to a kilogram strapped to an aircraft flying at 39,000 ft and moving along at 600 miles/hr. That same kilogram only has 150,000 joules of energy. That's only about 0.4% of the total energy it needs to get to LEO. There's some minor advantage to it being above the atmosphere, but that's not much additional advantage.

So in short, launching something off an aircraft gives you virtually no benefit in reaching orbit, the altitude is way too low and the speed is a tiny fraction of what's needed. True, a higher speed version at much higher altitude would help improve that, but the benefit is more one of being able to skirt around legal and political issues of launching something from an established launch facility.