Slashdot Mirror
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."
So they have designed a new space rocket which works as it has a five-gear transmission system.
That must make for some pretty awesome burnouts.
The theory of relativity doesn't work right in Arkansas.
I dont get how _solar_ energy can be used to propel a rocket. I mean, rocket engines need enormous amounts of thrust, so how can solar cells provide the kick?
This should lead to a new space speed record. The simplicity is beautiful, and having paid attention to ion drive since Deep Space One (pun intended) I am surprised that they have just come up with this. Hell, I an surprised I hadn't come up with this. As far as I can tell this baby is beautiful in its simplicity.
FairTax baby!
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)
That's what I wanna know...
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!
For a car, this would be analogous to staying in first gear all the time. So they have designed a new space rocket which works as if it has a five-gear transmission system.
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?
- I voted for Nintendo and against Bush
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.
12,5 gears it will use 100% less fuel.
less fuel for rocket means more fuel for us drivers meaning the price for fuel will be cheaper right?
What about the payload of xenon that has to be carried for the ion drive to spew out the ions? This takes up a lot of space and has to be factored into weight calculations as much as fuel does. Xenon is just a different type of "fuel", so having something run on this is not unlike saying that something is better because it uses liquid fuel as opposed to solid.
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)
That was a totally useless article, designed for page hits alone. Wise up, editors!
Solar energy can't deliver more than 0.01% of the energy required for launch, and you can't expect an ion engine to contribute anything significant when on the ground, even if it's made 100% efficient by constantly trimming its fields. The whole concept is just nonsense.
And the gears analogy is nonsense too --- there just aren't any here. At best they have two engines, an ordinary unspecified one for launch and an unspecified ion engine once in space. The whole thing is unspecified and meaningless as described, doh.
AND THERE ARE NO 5 GEARS!!!!
Slightly OT. Has anyone made a multi stage rocket where the lower stages use air instead of carrying their oxygen with them? I know about http://en.wikipedia.org/wiki/HOTOL, I was wondering about vertical launched rockets.
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...
TFA talks about the rocket switching from first to 5th. I suppose If I were switching out of first at mach 3 I'd forego 2nd to 4th as well, but where are the other in-between gears?
What about reverse?
It is dangerous to be right when the government is wrong.
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...
recommended tag: incoherent
when the rocket reaches outer space, the computer puts it in 5th gear. The article isn't clear on whether there is a reverse gear ;-)
A reverse gear could be useful for reusable satellites.
Linux Help
for all things on Linux
You have to read between the lines because of the military secrecy but it sounds like they just made some improvements on ion drives. While using ion drives in space is common sense it doesn't really do anything to help the real problem of it still taking stupid amounts of reaction mass to get into space in the first place.
This article is very poorly written. The gearing they are describing is for an ion propulsion system to be used once in space. not the actual rockets that get you out of the atmosphere. The reduced fuel they talk about is not reduced rocket fuel, but reduced propellant gas for the ion engine.
Poorly titled post, and a poorly written article.
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.
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, so you will still get stuff spraying out sideways. What you would need is an impracticably huge bell shape so the gases thin out to the Knudsden regime before bounding specularly off the walls. However, you could steer the heavy positive ions backwards with a magnetic field pointing out of the back of the engine, perhaps backed up by additional coils once you are in space. It would be a bit like the hydrogen scoop on a Bussard ramjet, only not as big, and backwards.
Then I read the 'explanation'. Meh.
that that is is that that is not is not
It's good to be enthusiastic but a little better to be able to describe what you are writing about.
This project isn't about *physical* limits.
It's about *cost* limits, both monetary and pay-load.
Fuel engine can accelerate as much we want (at least as you said, within relativistic limits). But to do so, I needs a lot of fuel.
The whole idea that a lot of scientist have, including this project, is to use fuel engine only for take off, when a lot of energy is needed to overcome gravity and lift the ship, and then switch to a ion engine that can both :
- be powered by solar pannels, thus not needing as much fuel, and leaving more space/weight for pay-load.
- can be throttled to provide the exact needed thrust.
Use the heavy but powerful fuel-engine for take-off, then the light and manoeuvrable ion engine for outer-space flight.
"Sufficiently advanced satire is indistinguishable from reality." - [Tips: 1DrYakQDKCQ6y52z6QbnkxHXAocMZJE61o ]
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..
She can smoke the clutch on anything.
Other than this text, there is no discernible information contained in this sig.
You gotta find first gear in your giant robot car!
My God , It's full of Ions . . .
We are Dead Stars looking back Up at the Sky
Hydrogen balloon to about 30 miles. Rocket to low earth orbit. Solar sails to anywhere in the inner solar system. Nuclear-powered ion engine further out.
Contribute to civilization: ari.aynrand.org/donate
If you class the mothership and the exoatmospheric craft as just componenet parts of a coherent system, the old x-15 and the kinetic ASAT missile and now spaceship one used air breathers for the "first stage" of a two stage system.
I think maybe this might work, a 5 stage complete system, airbreathers at two places in the launch stack, where they might work the best.
1) and so on to 5...airbreather (mothership, a normal big modified plane) to normal rocket(dropped and fired, mothership returns for landing), that dropped rocket boosts to high enough speed to go to air breather again with a scramjet, That in turn gets to high enough altitude where another normal rocket takes over for final push to get out to orbit, once in orbit, the ion engine takes over for day to day manuevering/travel
Gas-guzzling rocket motors are part of our American Way of Life. If efficiency concerns force us to change how we launch our payloads, the terrorists have won!
U.S.S. Jumpstart , "the only rocket with a clutch."
"Clutch, CLUTCH!"
"Throttle, THROTTLE!"
One of the things that limits how efficient a rocket can be is whether or not you have living things on board. If you do then you have to limit the acceleration so part of the payload isn't smeared against the back of the cabin and is still breathing when you get to where you want to go. That means that you have to spread the acceleration over a longer period of time than absolutely necessary. That in turn means you are spending fuel to lift fuel to the point where you actually throw it out the back end. It also means you are lifting everything else necessary to do the throwing. If you had a big cannon then most of your launch machinery is on the ground and stays there, the only thing winging its way upwards is what is needed to be up there. Thats one reason why unmanned missions can be more fuel efficient, higher takeoff accelerations equals less fuel used to lift more fuel higher in the air. It also means you can throw away your lift machinery faster, thats why we have multistage rockets.
The other side of the connundrum is that air resistance isn't linear. If you double your speed you get more than double the resistance. Aerodynamics can improve this somewhat but an unmanned capsule travelling from our theoretical cannon would start losing efficiency if it started off too fast. Its a min max problem to find the optimal point but I have a hunch you still get smooshed astronaut at the optimal acceleration to achieve minimum fuel costs.
The article is typical for a reporter who doesn't understand what they are writing about and is more interested in sensationalism than accuracy but the points almost gets out. Since the efficiency of the orbital maneuvering thrusters is better you can either use a smaller launch vehicle for the same mission lifetime, thereby saving fuel etc or you can use the same launch configuration and get a longer mission lifetime. The efficiencies aren't due to the launch system as implied, its due to a better payload. The same effect can happen if you have lighter, more fuel efficient electronics. Think of an original IBM 360 model 20 as compared to today's basic i386 desktop machine and the same thing happens.
You'd almost think that the thing was an integrated whole where one change somewhere effects everything else, boy thats a revelation :-)
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
I read the article carefully and looked at the diagram and it appears to me that the design is a bi-modal design. The engine either operates as a standard ("first gear") rocket engine using standard fuels, or it switches to an ionic engine ("fifth gear") that is driven by electricity and a supply of xenon gas.
If this is actually the design, this engine will not save fuel for a standard satellite launch platform, as the standard launch vehicle is jettisoned once the satellite reaches orbit. It might achieve advertised fuel savings if the last stage bi-modal engine is retained by the satellite for orbit maintenance, although how this is better than what is done now is unclear to me as I don't know anything about satellite orbital maintenance thrusters.
The ion engine must be placed upstream of the standard fueled rocket engine and it just blows the ion stream through the inoperative rocket engine and out the nozzle. How this works better than a current configuration is unclear to me, but perhaps it avoids any additional orbital maintenance thrusters and allows for changing orbits by retaining the standard rocket engine (and some standard fuel).
DS1 could turn its thrust up and down, but the specific impulse rose with increasing power. From the sketchy descriptions in TFAs, this unit can increase the specific impulse while running at constant power or perhaps even lower power. This results in much lower thrust, but stationkeeping operations require little.
<rant>
I really hate the front-page article, because it makes no distinction between the payload boost from a lighter stationkeeping system and the payload increase which would result from a more efficient booster rocket (burning chemical fuels). It also confuses the ultimate energy source for the ion system (the Sun) with the direct power source (electricity); the unit could easily run nuclear-electric, it doesn't care. This sort of nonsense makes it difficult or impossible for the naïve reader to understand the matter at hand. What's the point of putting an article on Slashdot if you're only going to make a logical mess of it? If the stuff here is going to leave people knowing less than before they read it, people shouldn't read it.
If the editors here are idiots, the readership here will slip to that level by both selection and mis- and dis-information.
</rant>
Sustainability and energy independence essay
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.
I believe this documentary provides an example of what the "Reverse" gear looks like.
What if they stall? Who're we gonna get to push start?
I am not a physicist, but last I checked, ion drives are only useful once you've broken orbit. They do not have the power to launch a craft. This silly article makes it sound like this "new" technology will improve launch efficiency somehow, but that's clearly untrue. At best, it will decrease the amount of fuel a craft needs to run through its ion engines *after* it has reached orbit, which may decrease the amount of conventional fuel needed to reach orbit. But that's about it.
how do they get and compress just oxygen from the atmosphere in general, at high speed and in-flight,in a short time period?
This is kinda difficult to understand, but its not rocket science.
Wow, I didn't know aerospace borrowed drivetrain technology from cars. I thought it was only the other way around.
OK he's not that bad, but he evidently chose to continue to post links to his blog on the slashdot main page despite numerous complaints from the community. If I accidentally click on a link to his blog one more time, my head is going to explode.
I remember that I changed some parameter when Katz was crapping up our message boards so I wouldn't have to even see his posts. Is that possible under the current incarnation of the site? How do I do it?
This rocket isn't for going into space. It's for manuevering once you're in space. It has no where near enough thrust to get a spacecraft off the ground. They're comparing it to current ion engines, not to chemical rockets.