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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."
Is the plan to try to get these into space? CNN is reporting another reusable rocket powered vehicle that will be able to do this.
-Sean
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.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"uhhh. Yeah. A rocket carries it's own fuel and oxygen supply. A jet, even one without moving parts, just supplies one of the components. That's why things like the bussard ramjet, even though they only operate in space, are called jets; they gather the fuel from interstellar space.
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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.
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.
Don't Bogart the fish sticks
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;
Some jets do, some don't. Pulse jets and ram jets don't use a turbine -- the turbine is used to suck in and compress air for combustion. Ram and pulse jets use their forward motion through the air to do this (so they need a push to get started). Jets work on the action-reaction principle too.
thus they pull themselves through the air in a way similar to a boat propeller (or, for that matter, an airplane propeller).
One particular type of jet, the turbofan, works this way (partly). Take a regular turbojet and mount a honking big ducted fan on the same shaft as the turbine. Runs a bit quieter and more efficiently than a pure turbojet, but limits your top speed (subsonic).
Jet engines cannot work in space.
Well, they could if you carried a great big tank of compressed air along -- but that'd be kind of silly. The tank would be heavy and the mass of all that nitrogen is unwanted.
-- Alastair
No. Ramjets don't have compressors.
The difference is that a jet engine uses oxygen from the atmosphere as one of its fuels. Rockets carry all their fuel(s) with them.
Its good to see progress from some of the small launch vehicle companies, especially after the failure of Rotary Rocket.
The actual success here, though, is perhaps not as revolutionary as it first appears. The DC-X had a similarly reusable and relightable rocket even though it was in a more conventional vertical 'rocket ship' design.
Getting cheaper access to space is the key to broader space tourism and proper space industires. Other companies trying this include Pioneer Rocketplane, Armadillo Aerospace, JP Areospace and TGV Rockets to name but a few. There's even a UK outfit, Bristol Spaceplanes,
and the European Space Agency is beginning to think in this direction too, according to CNN.
All the companies are small and desperately in need of money if anyone wants to invest. Its probably less risky than Worldcom!
Another useful resource is the Space Access Society. Indeed they've argued that the whole X-33 mess was in fact Lockheed-Martin protecting their lucrative disposable launcher market by messing up the project. Sadly, NASA seems to have been complicit in this.
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.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"Also that weird non-ducted turbofan that had the vanes mounted on the outside. (Did that ever make it into commercial production?)
Two words: Bussard ramjet. (Not that I think it can work, but, hey, it's fun to think about.-- ;-)
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Rocket engines are much more powerful, lighter, and more efficient (bizarely enough.)
You're correct on the powerful and lighter part. But rockets are far less efficient in the atmosphere than jets. Rockets get a maximum specific impulse of 500, while jets can get 5,000.
Jets are inherently more efficient because they don't need oxidiser and most of the working mass is air.
If you don't understand any of my sayings, come to me in private and I shall take you in my German mouth.
Actually, pulsejets don't need forward speed to start. A pulsejet is a combustion chamber with one-way reed valves on the front end. All you do is spray fuel into the combustion chamber and ignite. The fuel explodes. The pressure causes the front reed valves to close, therefore making the explosion blow out the back only, creating thrust.
This happens at many hundreds of times a second, each time the reed valves opening to admit new air and the fuel gets sprayed in. Pulsejets are simple but inneficient and very, very, very loud. They sound somwhat like a two cycle engine with 100 more decibels.
Ramjets are just basically tubes where fuel is burned under compression from moving air. Ramjets need to be going at least a few hundred miles per hour to work well. The plus side is that ramjets are very efficient and can travel very fast, up to mach five. (The limit for turbojets is about mach 2.5. The SR 71 accomplished mach 3 by turning off it's turbines and only using the afterburner, basically turning it into a ramjet)
A ramjet can only get to Mach 5-7 because the air needs to be slowed down to subsonic speeds. This is usualy accomplished with a supersonic conical diffuser, which slows and compresses the air. (Compressed air is slowed down at supersonic speeds) After mach 6, the engine encounters severe aerodynamic problems when slowing down the air.
For speeds from Mach 5-30, you need a Scramjet, or supersonic combustion ramjet. These burn fuel travelling through the engine at supersonic speeds. They are fast and efficient like ramjets. But they have to be going mach 4 to start working.
So a dream aircraft would be one that has combo ramjet-scramjet engine with a retractable reed-valve cover for to convert it to a pulsejet. Such a craft could gain altitude, then go into a dive, getting to low supersonic speeds where the ramjet would begin to work, accelerating it to scramjet speeds.
Such a craft would be able to fly into orbit without the need for rockets.
If you don't understand any of my sayings, come to me in private and I shall take you in my German mouth.
Actually, pulsejets don't need forward speed to start.
Yeah, I know, but figured the details would get in the way of my original message. The details you give are incomplete. A pulsejet still needs a source of incoming air to start -- a blower will do it -- and will only continue to run when the blower is removed if (a) the pulsejet is in forward motion, or (b) the reed valves and length of the pulse jet are tuned to each other such that the partial vacuum in the jet after the detonation pulse sucks the reed valves open without sucking the exhaust back into the jet.
That's another reason the things are so damn loud: they have run at the resonant frequency of the pipe.
As for flying to orbit without rockets, the drag penalty of flying through the air to get your oxidizer, even with a scramjet (so you don't have to accelerate the mass of air -- of which 80% is useless mass (nitrogen) -- to the speed of the vehicle), isn't worth the benefit. It's easier to just carry a tank of LOX with you and get above the atmosphere as fast as possible.
-- Alastair
Fuel mass efficiency is better with a jet engine, I'll grant you.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"Space, while being close to a vacuum is not a perfect vacuum. There are about 5 molecules per cubic meter, or something similar, and many seem to be simple molecules like methane or hydrogen.
Technically, if you are going fast enough these should form a pressure wave just like in atmosphere. The difference is you have to be going MUCH faster (perhaps relativistic speeds, you can probably calculate it) to acheive the same pressure.
the other difference is that jet engines use the oxygen in the air for combustion. There isn't oxygen in space and far as I have read. However of the molecules free-floating in space, Hydrogen seems to be abundant. If the aforementioned speed is obtainable via some other means, could it be possible to carry oxygen for the purpose of running the chemical combustion of the engine, or would the energy necessary to maintain the speed be more than the engine can put out?
- Sig