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."

pun intended

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.

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Yeah, but the automatic only has four speeds.

point missed

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) [wikipedia.org] I am surprised that they have just come up with this. Hell, I an surprised I hadn't come up with this.

DS1 had something like this

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 mu

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Is there anyone else that finds something poetic about Roland's summaries?

But Americans can only drive automatics! ;-)

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)

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Will the Russian spaceships leak oil and break down every few kilometres

In Soviet Russia rockets still launch you.

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But when I've been in the USA, people only drive cars with automatic gearboxes!

The Border Patrol does tend to prefer them, but there are a great many people not affiliated with Immigration and Customs Enforcement.

Re:But Americans can only drive automatics! ;-)

Our women control us - I can't have a car with a stick shift because then my wife can't drive it :(

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?

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Our women control us - I can't have a car with a stick shift because then my wife can't drive it :(

That is the #1 reason to buy a stick shift, at least when it comes to friends wanting to borrow your car. It gives you the perfect way to say "No, you mo

yeah, but can it go into reverse?

That's what I wanna know...

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Can a motorbike go in reverse? They work in the same way.

Is a Honda Goldwing a motorbike?

Xyz

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!

Amazing Technology

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

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.

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The analogy was probably come up with by the PR department at the university. I had a similar experience with a project I did for my PhD work. We were using execution replay to efficiently do a forensic post-mortem analysis. The PR department called my

And now for something completely different...

I read the summary, and thought I understood it.

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 par

aerospike engine

The problem you were pondering is not solved by a transmission. It's solved this way...

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.

Re:Uhm

Not only is the cars analogy poor, it's also wrong. At least as per the summary: It is the maximum exhaust velocity that is fifth gear. Specific Impulse is directly related to the exhaust velocity.

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.

Say what?

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.

Re:Say what?

IANAAE either, but I read about them in a book; anyhow, none of your (1) and (2) applies. First of all, the proposed "new" engine is not one engine but two very well known and used engines. One is a chemical rocket that oxidizes (burns) the fuel, and the released chemical energy accelerates the molecules of gas and propels the vehicle. Another is an ion drive where an external energy source is used to accelerate molecules of gas. Since this external energy is solar batteries, you can accelerate a molecule to a very high speed, and so get a lot of bang from a given quantity of the reaction mass.

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.

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I remember listening to a satellite designer in 1990 who spoke of ion engines as if they were already in most satellites - he was talking about opimising another generation of the things to get a longer life.

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Except there's nothing at all new about the idea. EVERY ion propelled spacecraft (and there have been a few) has used this combination of chemical rocket boosters to get into orbit, then ion drives to go from there.

Stupid summary, incoherent article and u

They Avoided the P Word Again

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?

Soooo... it's another VASIMR?

Aside from the fact that the Variable Specific Impulse Magnetoplasma Rocket [adastrarocket.com] 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...

Old News

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

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...

Not *physical* limits

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

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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...

...except for the amount of fuel you carry.

Remember, kids, there

Maybe ...

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.

Misleading.

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

Clarification of 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 [gatech.edu] is slightly less misleading than the various summaries derived from it.

Can someone buy this Roland guy some books

It's good to be enthusiastic but a little better to be able to describe what you are writing about.

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I think we've all bought Roland quite enough.

Really misleading.

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 [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!

Engineer > Capt'n, the engines canna take it anymore!

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.. :D

Living in New Jersey, fighting villains from afar.

You gotta find first gear in your giant robot car!

More efficient - 4 "gears"

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.

Nooooooooo

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!

Concept already in use

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.

Roland Piquepaille: the next John Katz?

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?

Re:Solar?

In *SPACE* you need very little. Ion drives work fine.

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TFA is pretty badly written. What they mean is that the satellite can now carry 40% less fuel because its motor is more efficient. Since you are carrying less fuel, you now have more room for other stuff, or you might be able to use a smaller launch vehicl

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Lower fuel consumption in space = less fuel required onboard = lower launch weight = lower launch cost.

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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

Re:Solar?

Well, didn't the voyager spacecrafts have solar power too?

There is very little sunlight where Voyager probes [wikipedia.org] were supposed to go:

Voyager probes are powered by three radioisotope thermoelectric generators, which have far outlasted their originally intended lifespan, and are now expected to continue to generate enough power to keep communicating with Earth until at least around the year 2020.

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.

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It would be a stretch, but consider 1st tops out ~35-40 mph. 5th is usable starting at around 30-35 mph. So in theory, you could shift directly from 1st to 5th.

As for reverse...gravity takes care of that.

Grump

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It would be a stretch, but consider 1st tops out ~35-40 mph.

40mph in 1st gear? Boys, boys, boys, we obviously don't drive the same vehicle [europe-machinery.de]...

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Where are geras 2-4?

Considering that both TFAs couldn't even decide whether this advancement relates to launch vehicles, LEO satellites, or deep space probes... I think we can safely overlook the confusion over the number of totally inapplicable mechani

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There have been proposals to use jet engines in the first stage as reusable boosters. The problem is that a rocket wants to get out of the atmosphere as fast as possible to minimise drag, which is fundamentally incompatible with using the air to reduce the