XCOR Makes a Rocket-Powered Touch-and-Go

wronkiew writes "XCOR Aerospace made a touch-and-go with their experimental rocket powered airplane (see their announcement). The pilot was Dick Rutan, of Voyager fame. Aviation enthusiasts may be familiar with the touch-and-go, but for the uninitiated, this maneuver involves landing an airplane and then taking off again while still on the runway. Note that other rocket-powered vehicles require that the engine be dismantled before they are flown again. While their craft is not exactly a spaceship, it is good to hear of some progress in rocketplanes since the demise of the X-33."

Re:Definition of rocket?

[WolfWithoutAClause]

The main difference is that a jet engine has a rotating fan/compressor down the center. A rocket engine doesn't necessarily have a pump at all; although they usually do, but it's separate. Rocket engines are much more powerful, lighter, and more efficient (bizarely enough.)

A rocket engine consists of a combustion chamber with a nozzle attached (usually a converging/diverging nozzle called a DeLaval nozzle). Rocket engines need not have any moving parts, although in practice they usually do have some for control purposes.

Re:Definition of rocket?

[sidecut]

I'm no expert, but it's my understanding that a rocket works by expelling exhaust at a high rate of speed, which uses Newton's First Law to add momentum to the rocket as an exact reaction to the momentum of the expelled gas; i.e. the more exhaust and the faster it's expelled, the more speed is added to the rocket in the opposite direction. Rockets can work in space or in the atmosphere.

Jet engines, on the other hand, though they superficially make look like a rocket because they have very hot gases coming out from the back, actually use a turbine to push the air; thus they pull themselves through the air in a way similar to a boat propeller (or, for that matter, an airplane propeller). Jet engines cannot work in space.

Rocket engines that work in space must have a source of oxygen, perhaps in an oxydizing agent and not necessarily gaseous or liquid oxygen.

Jet engines, I believe, have the earth's atmosphere as their only source of oxygen, and so this is another reason they cannot work in space.

Re:Definition of rocket?

[Mt._Honkey]

Both work by the same (third) law. The turbine does not anything appreciable in the way of propulsion, it just compresses the incoming air so it can burn better and more explosively with the fuel. When the fuel burns with the air in a jet, it flies out of the back way fast, just like a rocket. There is a little fan in the back that powers the turbine in the front with the high speed air from the burning.

TSTO vs SSTO Re:SSTO the key to space

[WolfWithoutAClause]

SSTO will probably work. But the big question is whether it will be cheaper or not. It looks right now that the consensus is no, and TSTO (Two Stage To Orbit) is the way to go for lower cost.

However SSTO has advantages too, lower cost isn't everything. SSTO may be more reliable, because there's less to go wrong; and it may have a lower turn-around time because you don't have to reassemble the vehicles each time. But on the other hand SSTO rockets are lighter, and that means the materials can be nearer to the edge and more likely to fail. We won't know how it comes out on balance until both have been achieved and a few thousand launches are past.