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Fuel Efficient Five-Gear Rocket Engine Designed
Posted by
Zonk
on Sat Feb 24, 2007 05:36 AM
from the next-they-need-to-make-a-death-ray-for-peaceful-purposes dept.
from the next-they-need-to-make-a-death-ray-for-peaceful-purposes dept.
Roland Piquepaille writes "Georgia Tech researchers have had a brilliant idea. Rocket engines used today to launch satellites run at maximum exhaust velocity until they reach orbit. For a car, this would be analog to stay all the time in first gear. So they have designed a new space rocket which works as it has a five-gear transmission system. This rocket engine uses 40 percent less fuel than current ones by running on solar power while in space and by fine-tuning exhaust velocity. But as it was designed with funds from the U.S. Air Force, military applications will be ready before civilian ones. Here is how this new rocket engine works."
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pun intended (Score:3, Funny)
That must make for some pretty awesome burnouts.
point missed (Score:3, Insightful)
Re: (Score:3, Insightful)
But Americans can only drive automatics! ;-) (Score:4, Funny)
(ducks and grins)
Re: (Score:3, Funny)
In Soviet Russia rockets still launch you.
Re:But Americans can only drive automatics! ;-) (Score:5, Funny)
I guess if I bought a cool enough car she might learn. But then it's chicken and egg - how can I get this cool car without using a lot of our money, which I'd need permission to spend on a car that she can't drive?
Parent
Xyz (Score:5, Informative)
For all the rest: Beware beware! This is a Roland post! Last link goes to his page!
Amazing Technology (Score:3, Insightful)
40% less fuel usage means less fuel needed to get into space, meaning a lighter rock; saving even more fuel. This will also drastically reduce the cost of getting into orbit as well, meaning more satellite based technology in the near future. This is an all around good thing.
I do wonder if this technology will go the route of the automobile or the bicycle. Staying at five gears or heading for twenty-one?
Uhm (Score:5, Insightful)
Apart from the fact that no technical details are described about this new technology, and that "gears" makes no sense at all in a rocket, and thus the comparison got tiring even the first time they used it, the authors of the article couldn't even make up their mind about what this invention is intended for. In the heading they talk about rockets for launching satellites, but everywhere else in the article, they talk about "satellite engines" used in orbit, which are apparently some form of improved ion-drive, completely useless for launch vehicles.
This is just silly. To illustrate how silly it is, we could just as well have an article about how a new toaster will use multiple stages to toast, just like rocket engines have multiple stages to orbit. This can potentially lead to up to 40% reduced cost of toasting toast, and potentially, making toast in deep space more of a reality, as well as in other energy-starved places. Then we can include a drawing of a hairdryer to "explain" it, and continue to explain that while commercial applications are a few years off, the new toaster will soon be ready to used for military infrared signalling.
And now for something completely different... (Score:3, Interesting)
A conventional rocket motor chucks out lots of hot, ionized gas. In the lower atmosphere, this comes out as a long, thin flame. As the atmosphere gets thinner, the gas can fly out sideways. You have the paraboloidal bells at the base of the rocket with try an convert this sideways motion of the plasma into downward motion, so you get as much forward momentum as you can. However, the gas in the bells is colliding with itself as much as with the engine walls,
aerospike engine (Score:4, Informative)
Aerospike Engines (how they work) [aerospaceweb.org]
Aerospike Engine (history) [wikipedia.org]
Linear Aerospike Engine (see the "efficient at all altitudes" section) [nasa.gov]
Rocket engines [nasa.gov] are more efficient (see: specific impulse [wikipedia.org])when the exhaust velocity of the escaping gas is higher. The shape of the bell of the "traditional" rocket nozle is static and thus operates at maximium efficiency at a particular altitude. The linear aerospike engine makes one side of it's bell continuously variable -- by using the air as one side of the nozle and taking advantage of the changing atmospheric pressure as the rocket ascends. The rocket engine will then have a continuously variable, uh, "transmission", to borrow the terminology of this discussion which beats a five-speed hands down. : )
The article summary, the RP/ZDNet press release rehash, and indeed the original press release itself are all very poorly written.
Parent
Re:Uhm (Score:5, Informative)
But, KE = mv^2 (or P=rho*v^2 in this case) The power available (photovoltaic, chemical, nuclear-electric, etc.) is relatively constant, so the density of the exhaust gasses (and therefore the thrust since it goes like momentum T={mass flow rate}*v) goes way down at higher exhaust velocities.
High-thrust, low impulse would be "first gear" and only needed for launch. It is the maximum flow rate, and obviously uses up propellant like nobody's business. Orbital transfers would use the "fifth gear" mode as once in orbit, there is no atmosphere to rise out of before turning tangentially to the ground, the energy source (solar power) is relatively unlimited over time, and continuous thrust is even more efficient than even the ever useful hohmann transfer.
There are maximally energy efficient thrust modes between max flow and max velocity depending on orbital velocity, but with a continuous source of energy, the life limiting factor is actually propellant, and since it's not easy to resupply to a spacecraft, it's usually better to be miserly with the thing you can't replace and run all the time in high-Isp (specific impulse) mode.
AND the engine's not even new. It's not even a completed version of a recent project like VASIMR. It's a Hall thruster, which impressive though they are, are mature enough to have actually flown already. Not to mention that it will probably never be capable of the kind of thrust needed for launch.
Parent
Say what? (Score:5, Interesting)
1. high-thrust mode is hugely less efficient than low-thrust mode, or
2. there is a considerable fuel cost to starting and/or stopping the motor.
If neither applies, then you would simply run the motor at high thrust for shorter periods of time, without the added expense of a low-thrust mode.
The article wasn't what you might call detail-oriented, but this is some sort of electric ion propulsion scheme, which achieves high specific impulse (~3000sec, accd. wikipedia) and so optimising for efficiency makes sense. But it's still an ion drive, so there'll be no takeoffs in its future. At least not takeoffs from anything with a gravitational well deeper than an asteroid.
So we have an article about a thing. Only the article doesn't say what it is or what it's good for. I think I'll keep getting my space news from not-ZDnet, thanks.
Re:Say what? (Score:5, Informative)
Modern satellites are inserted into orbit using kerosene or hydrogen or hydrazine, with some oxidizer (liquid oxygen for example.) These fuels contain both the energy and the reaction mass, and require nothing but a nozzle and a few pumps to work, and they are very powerful.
Once in the orbit, many satellites can be moved a little using a very limited amount of fuel that is stored in the satellite, and once used up the fuel can't be replenished. Sometimes it may be just compressed gas. It would be very useful to replace these with ion engines; the only trouble with them is that it will take a year to move a satellite from one orbit to another, since the thrust of an ion engine is measured in grams, and typically satellites weigh a ton. Try pushing your car with a feather, gently :-)
Ion engines are efficient because of throwing your precious reaction mass away at low speed it accelerates individual molecules to a very high speed, and saves the reaction mass for future use. The energy for this is provided by an external source; typically, only nuclear sources are sufficiently powerful to provide a reasonable thrust, but of course a solar panel will do as well, if you have plenty of time.
Parent
They Avoided the P Word Again (Score:4, Insightful)
Is this a competition? Is there a prize?
Soooo... it's another VASIMR? (Score:4, Interesting)
Old News (Score:3, Informative)
It seems to have a similar principle to VASIMR [wikipedia.org] engines. Basically, they can adjust the specific impulse in flight, higher specific impulse giving lower thrust but better efficiency.
Of course, the thrust that an engine like the one described would output is miniscule. It would not be useful for launch vehicles, but only for keeping satellites in orbit. That said, if you can reduce the amount of fuel a satellite uses by 40%, you can keep it up there for almost twice as long, which is never a bad thing.
nope (Score:5, Insightful)
Clarification of article (Score:5, Informative)
The Georgia Tech press release [gatech.edu] is slightly less misleading than the various summaries derived from it.
Really misleading. (Score:5, Insightful)
If your energy comes from solar panels (so it arrives if you want it or not) or a nuclear reactor (so fuel and propellant are separate), you should try to use propellant as efficiently as possible, accelerating it to the maximum speed that the engine design allows. To control the total momentum produced by the engine you can just run it for a longer or shorter time.
2. Drawing in the article makes no sense, unless it's missing something important. If electric and magnetic fields' directions are as shown (electric along the axis, magnetic along the radius), electrons' trajectories will be, depending on the initial speed, spirals around the axis of the device, or , more likely, loops returning them to the anode, not spirals around circles shown on the drawings. They would look like those spirals if those circles were magnetic field caused by the current produced by ions, but then this field should be significantly stronger than the radial magnetic field.
3. There should be something accelerating electrons, or this engine will end up charged negatively, decelerating ions that leave it until the whole process stopped with a large cloud of positive ions hanging behind it. The drawing shows cathode that supposedly emits electrons, and direction of the electric field suggests that cathode is much larger than shown of that there is another cathode, but it still doesn't show why this cathode emits electrons. It may be in a way of the stream of ions, so it's hot from being bombarded by them, or it may be an electron cannon, like in CRTs, or both, but the drawing shows neither. If the electrons going in circles are outside the engine, as opposed to how they are shown inside it, it kinda makes sense considering that ions leaving the engine produce circular magnetic field, but then the drawing misplaces it inside the cylindrical engine, where magnetic field is in a completely different direction.
See http://www.nasa.gov/centers/glenn/about/history/ip sworks.html [nasa.gov] for comparison.
4. Any ion engine can regulate the speed of its exhaust -- it's determined by electric field's strength that is in its turn determined by voltage/position of electrodes. Maybe they have invented some other way to regulate it, for example, by changing the magnetic field, but it's not what the articles claim.
5. Ion engines can't launch satellites by themselves -- even if they are used at some point, the vast majority of the energy passed to the satellite is produced by chemical engines. Ion engines can be used to adjust orbit, or to accelerate in the process of interplanetary travel, but they are useless for initial launch that requires huge amount of energy to be released over a short time. Optimizing the use of fuel for orbit adjustment may reduce the initial mass of satellite (by the amount of fuel or ion engine propellant saved over the lifetime of the satellite), what in its turn can decrease the amount of fuel used for launch.
However at the point when satellite reaches the orbit most
Capt'n! (Score:3, Funny)
Captain > Sure they can.. *presses clutch*... hey! ensign! pull that large lever over there will ya!
*ensign pulls huge lever with a lot of effort*
*clunk*
Captain > Don't they teach people at the Academy how to put a star ship transmission into overdrive anymore? Sheesh..
Concept already in use (Score:4, Informative)
Re:Solar? (Score:5, Interesting)
Parent
Re: (Score:3, Informative)
Re:Solar? (Score:5, Informative)
There is very little sunlight where Voyager probes [wikipedia.org] were supposed to go:
Sounds like a no-brainer to me : use conventional rocket engines to escape earth, and then switch to solar/ion drives.
Indeed there is little novelty in this.
Parent