Easy Liftoff ?

Question

Why can't the first stage of liftoff for space vehicles be accomplished by reusable jet propelled launchers rather than the megalift assemblies that we are now using.? It seems that Burt Rutan has the right idea.

Answer 1

Reuseable jets are generally used for getting most suborbital and light orbital craft into the air. Look up old articles on the Scramjet test if you would like, it was an unmanned prototype aircraft using a supersonic Ramjet design that could travel at mach8-9 (with acceleration that could obliterate a person), and was taken into the air riding on the underbelly of a plane.

The problem with using the same methods for larger aircraft (such as the space shuttle) is that the shuttles weigh too much, and the engines cannot provide as much thrust as a conventional rocket can.

The boeing 747 engine provides: 66500 pounds of thrust.
A rocket? : 3.3 million pounds of thrust.

Basically you'd have to have.. 50 boeing 747 engines working together?

But the practice is definitely in use for more reasonable payloads.


Links:

http://www.boeing.com/news/releases/2006/q1/060118a_nr.html
Boeing engine thrust.

http://www.howstuffworks.com/rocket1.htm
Rocket engine thrust.

Answer 2

It takes more to lift an object that to keep it up. Therefore the main thrust used in liftoff must be enough to lift and accelerate to within 1/2 of the total thrust requirement. After that the acceleration curve begins to increase exponentially, for every foot of travel you require X of fuel depending on weight of vehicle. Our current space program has been doing this wrong for a long time. Vertical take off is most inefficient and requires more and more fuel dependent upon weight. If we lift off horizontally and use the earth's natural rotation to supplement initial motion we could get a sling shot effect and reduce fuel requirements.

Answer 3

Your launcher might have to be truly huge, depending on what size space vehicle you're working with, but I don't see anything wrong with the concept.