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Fuel Efficient Five-Gear Rocket Engine Designed
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."
But when I've been in the USA, people only drive cars with automatic gearboxes! how will the astronauts cope with a gear stick (stick shift)? Will they need to pass another spaceship driving test? Will they need to employ more European astronauts as drivers? Will the Russian spaceships leak oil and break down every few kilometres and need roadside rescue? (umm can't think of a suitable Lada joke right now)
(ducks and grins)
For those who haven't read TFA: This is different from VASIMR. They use solar power and ion drives.
For all the rest: Beware beware! This is a Roland post! Last link goes to his page!
In *SPACE* you need very little. Ion drives work fine.
Great Intellect...
This is an ion drive. It works by using an electric field to accelerate small amounts of propellant to very high speeds. It is not useful for launching a rocket from Earth at all. But it is a very efficient way to travel in space. Acceleration is very slow, but adds up over time when there is no friction. The article is about tweaks to improve the efficiency of this type of engine.
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.
IANAAE (aerospace engineer), but obviously this is only applicable if either
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.
High-speed Road Trip (18.000KPH)
There is very little sunlight where Voyager probes 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.
It's completely impressive that people can write so many articles about plasma without directly referring to it. I see this over and over.
Is this a competition? Is there a prize?
"A man cannot begin to learn that which he thinks he already knows." --Epictetus, 1st Century A.D.
Aside from the fact that the Variable Specific Impulse Magnetoplasma Rocket is designed for long-range spacecraft rather than satellites (and I think the difference is really only one of size) exactly how is it better/different? The VASIMR may actually be more versatile, and has quite a few advantages over standard ion designs (things like being completely electrodeless and containing its plasma propellent with EM fields so as to avoid corrosion). I'm all for improved rockets, and the general concept of the ion/plasma rocket is a good one, but it sounds like duplication of effort...
There's no place I could be, since I've found Serenity...
It seems to have a similar principle to VASIMR 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.
Last time I checked, the reason IC engines use transmissions is because they're only efficient in a dreadfully small window (1000-10000 rpm). Less than 1000rpm, you're not producing enough power to overcome friction. More than 10,000 and the whole thing goes boom. This range is even smaller for diesel engines and even greater for performance engines... but for rockets it's essentially infinite. (Relativity notwithstanding) I mean, there are no physical barriers to stop you from spraying hot gases from the business end of a projectile...
Late reply, but maybe it will help somebody. The article is crap, and it's not surprising that all the other replies have misunderstood what it's about. The engine is not used for launch, it is only used for maneuvering the satellite once in orbit. It's not that it takes 40% less fuel to launch the satellite, rather that 40% less fuel needs to be carried for subsequent orbital maneuvering/adjustment due to the efficiency of this engine.
The Georgia Tech press release is slightly less misleading than the various summaries derived from it.
Oh no... it's the future.
1. In an ion engine you WANT to accelerate the propellant as fast as possible -- the satellite get the same momentum as propellant in the opposite direction, so to get best use of the same mass of propellant you should accelerate it to the maximum speed your engine allows with reasonable energy efficiency. If it's a chemical engine, the amount of energy you can use is proportional to the amount of fuel you burn, so you don't really have a choice -- from conservation of energy the maximum possible speed of escaping gas is square root of the twice energy produced by burning a unit of mass. If energy can only come from fuel, the only way to increase speed beyond that is to leave some burned fuel in the satellite yet pass its energy to the escaping gas, so even if you somehow manage to do that, you have to release burned fuel at a lower speed later, thus wasting energy, or keep it stored thus wasting energy and also increasing your mass.
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 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
Contrary to the popular belief, there indeed is no God.
Engineer > Capt'n, the engines canna take it anymore!
:D
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..
The concept is already in use with the parallel staging of the Space Shuttle. The Space Shuttle Solid Rocket Boosters are effectively a high thrust, low velocity exhaust first gear. The first gear is most effective when losses due to drag in the atmosphere are high. At sufficient height and speed, high thrust low speed exhaust is traded for lower thrust high speed exhaust when the SRB's are jettisoned and the main engines take over. This higher gear is analogous to the one described in the link.
an ill wind that blows no good
The problem you were pondering is not solved by a transmission. It's solved this way...
Aerospike Engines (how they work)
Aerospike Engine (history)
Linear Aerospike Engine (see the "efficient at all altitudes" section)
Rocket engines are more efficient (see: specific impulse)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.
If you mod me down, I shall become more powerful than you could possibly imagine.