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Space Technology

Fuel Efficient Five-Gear Rocket Engine Designed 122

Posted by Zonk
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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Fuel Efficient Five-Gear Rocket Engine Designed

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  • by User 956 (568564) on Saturday February 24, 2007 @04:38AM (#18132754) Homepage
    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.
    • by anagama (611277)
      Yeah, but the automatic only has four speeds.
    • point missed (Score:3, Insightful)

      by sporkme (983186) *
      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. As far as I can tell this baby is beautiful in its simplicity.
      • 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
        • Been here long? Any article posted by Ronald P is generally quite lame and in many cases he mis-states the facts. He does it to get hits on his webpage not to share useful info. Many many people here have complained the editors favor him for some reason. I too RTFA and found it to be very misleading after tracking it back to the source. I used to work at NASA (2X in fact) and know a bit about rocket engines! The ion drive idea isn't new, this throttling isn't either. IIRC, DS-1 has a version of it and there
          • by Baron_Yam (643147)
            Have I missed some configuration option for blocking articles submitted by a particular source?

            I'd be OK with blocking all of Pipsqueak's submissions.
        • by Rei (128717)
          Amen. That bothered me, too. I don't expect people who post articles about space on slashdot or people who write articles about space to necessarily understand the difference between, say, a Hall effect thruster and an ion drive. But I do expect them to at least understand the difference between a chemical booster and an ion drive. For God's sake, it's not like this is a difficult concept.
    • by sporkme (983186) *

      it has a five-gear transmission system
      We have never received any transmissions from space. Now we are going to send up a five-speed? As-if.
  • 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?
    • Re:Solar? (Score:5, Interesting)

      by bky1701 (979071) on Saturday February 24, 2007 @04:51AM (#18132810) Homepage
      In *SPACE* you need very little. Ion drives work fine.
      • by Prune (557140)
        That may be, but TFA is talking about "lower launch costs".
        • Re: (Score:3, Informative)

          by MightyYar (622222)
          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 vehicle to carry the smaller satellite. Obviously this would reduce launch costs.
        • Re: (Score:3, Insightful)

          by jacksonj04 (800021)
          Lower fuel consumption in space = less fuel required onboard = lower launch weight = lower launch cost.
    • Re: (Score:3, Informative)

      by SirLoadALot (991302)
      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.
    • by kraemate (1065878)
      Well, didn't the voyager spacecrafts have solar power too? So, whats the new technology in this "five-gear" rocket engine? Sounds like a no-brainer to me : use conventional rocket engines to escape earth, and then switch to solar/ion drives.
      • Re:Solar? (Score:5, Informative)

        by tftp (111690) on Saturday February 24, 2007 @05:24AM (#18132932) Homepage
        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.

        • This isn't some amazing new leap in technology - It's just using current technology in a much more efficient manner. FTFA:

          Georgia Tech's significant improvement to existing xenon propulsion systems is a new electric and magnetic field design that helps better control the exhaust particles, Walker said. Ground control units can then exercise this control remotely to conserve fuel.

          To tell the truth, I'm glad to see so many stories recently that talk about increased efficiency in anything we do. The less ene

    • by sjasja (694035)
      The summary unnecessarily confuses things. It starts talking about launcher engines, while the real subject is an in-space low-thrust ion engine.

      Ion engines run for months on end at low thrust but high efficiency, so the acceleration adds up when you are going, say, from one planet to another. They are not useful for launching anything to orbit.
    • Here is the article of the Tech page: http://www.gatech.edu/news-room/release.php?id=128 1 [gatech.edu]
  • by fantomas (94850) on Saturday February 24, 2007 @04:50AM (#18132802)
    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)

    • Re: (Score:3, Funny)

      by dbIII (701233)

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

      In Soviet Russia rockets still launch you.

    • Re: (Score:2, Funny)

      by Anonymous Coward
      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.
    • by MightyYar (622222) on Saturday February 24, 2007 @08:54AM (#18133608)
      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?
      • 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 moron, you'll only wreck it or get me a parking ticket" without actually saying it and being impolite. Instead, you just say, "Wow, I didn't know you could drive stick," and then they say, "Oh damn, I forgot about that. Hmm, I wonder if Bob would let me borr

    • by maxume (22995)
      There aren't really any good reasons to put a manual in a SUV.
      • by Bertie (87778)
        I'd say the last thing you want if you're doing some serious bogtrotting is for your vehicle to be hunting up and down the gears till it finds one that sticks. Modern automatic transmissions are smart, but people are smarter.

        Oh, hang on - they never get taken off road, do they? You're quite right. Carry on.
    • No, that's only the soccer moms in their suburban assault vehicles. There are still some of us in the U.S. driving sticks -- automatics are against my religion :)
  • That's what I wanna know...
  • Xyz (Score:5, Informative)

    by Anonymous Coward on Saturday February 24, 2007 @04:51AM (#18132808)
    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!
    • by EotB (964562)
      Damn, wish I had of known that before I gave him my hard earned ad revenue.
  • Amazing Technology (Score:3, Insightful)

    by Bellum Aeternus (891584) on Saturday February 24, 2007 @04:55AM (#18132826)

    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?

    • by b4stard (893180)

      40% less fuel usage means less fuel needed to get into space, meaning a lighter rock; saving even more fuel.
      Borderline perpetuum mobile. :)
    • I would say the aim would be to have a system that doesn't have set "gears" but rather adapts fluidly to the need required.
      For a car, this would be analog to not having gears and staying all the time at most fuel efficient rev-count.
  • Uhm (Score:5, Insightful)

    by joto (134244) on Saturday February 24, 2007 @05:05AM (#18132860)

    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.

    • recommended tag: incoherent
    • by martyros (588782)

      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 advisor, and after a long discussion, came up with the analogy of a "security camera". This was in the University's press release, which got copied to all the major news outlets. It was even used in an interview the BBC did with my advisor.

      The analogy w

    • 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 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,

      • by trout007 (975317)
        From what I understand there are two things that make a rocket go. The pressure at the output of the engine bell and the conservation of momentum of the exhaust. I think the momentum is a much larget portion so to be more efficient you want higher exhaust velocity and lower pressure. Also you want to have the exhaust gasses expand well in the bell. Too narrow a bell and they are underexpanded and too large and it gets heavy and it can delaminate. That is why staging rockets is a good idea you can fine
      • aerospike engine (Score:4, Informative)

        by Gary W. Longsine (124661) on Saturday February 24, 2007 @11:27AM (#18134394) Homepage Journal
        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.
        • by jd (1658)
          Thanks for those references. Of course, most of this is redundant, as the military already have a program on hypersonic scramjets. Use a jet first-stage, essentially the same method as used by the X-Prize winner, and you can get far greater efficiency than from a rocket alone. (Basically the design proposed by the Advanced Rocket Launch Assist - ARLA - system.) The problem is starting off, but the military have long-ago been using turbine-assisted ramjets to solve that problem.

          The idea behind assisted ram

    • Re:Uhm (Score:5, Informative)

      by zippthorne (748122) on Saturday February 24, 2007 @10:00AM (#18133890) Journal
      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.
    • by daiichi (888740)
      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.

      I too had an issue at first with the article--but then I saw at least one point: if a satellites maneuvering fuel can be reduced, there is less mass that needs to

    • by DsNchNtD (1065188)
      I think the article is using the term 'satellite' to mean the vehicle that is now in space. When going up it needs all the power it can get, but once it is up there it doesn't need to use the heavy fuels for immediate impulse and can instead rely on slower ion propulsion methods which consume very little fuel. In a sense, they are using the gears of an engine as a metaphor for the ability to control how much propellant in the vehicle (gas in a car) is used to move. You need a lot less gas to go from 30-40
  • 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?
  • Say what? (Score:5, Interesting)

    by ottffssent (18387) on Saturday February 24, 2007 @05:19AM (#18132914)
    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? (Score:5, Informative)

      by tftp (111690) on Saturday February 24, 2007 @05:43AM (#18132984) Homepage
      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.

      • by dbIII (701233)
        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.
      • by ceoyoyo (59147)
        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 unoriginal idea. I guess Roland couldn't find anything good but needed his weekend ad money.
      • by ottffssent (18387)
        See, now that makes sense!

        I count two engines and no gears in your description though, so I don't think it's what the article is talking about.

        I'm not certain of that however, because even the Georgia Tech article repeatedly talks about this engine being useful during takeoff. The initial claims could be simply bad phrasings of something true: less mass needed for maneuvering == less fuel on the launchpad == more space for payload. But then it says "Satellites using the Georgia Tech engine to blast off ca
    • #1 is true, #2 is not. Hall thrusters (which is what the article is talking about) can be run in a high-thrust, low-efficiency mode, or a low-thrust, high-efficiency mode. The problem to date has been that the design is locked in to one or the other. What they've done is make a tuneable Hall thruster with a variable thrust and efficiency. This is actually pretty impressive considering how difficult it is just to tune a magnetic field for one operating point, let alone a few. And then to be able to shif
  • by pln2bz (449850) * on Saturday February 24, 2007 @05:33AM (#18132960)
    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?
    • by Jerf (17166)
      "Big words" like "plasma" scare folk. Look! Six! As you all know, we can only read words of five or less. More and we just get scared.

      I hope that last word didn't blow your stack, but when you need a "big word", you need a "big word".

      (Wow, this is hard. How did he manage this [muppetlabs.com]? It would take me a year, I swear, and I used five, not just four.)
  • by cbhacking (979169) <.moc.oohay. .ta. ... isiurc_tuo_neeb.> on Saturday February 24, 2007 @05:38AM (#18132972) Homepage Journal
    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...
    • by radtea (464814)
      Satellites using the Georgia Tech engine to blast off can carry more payload thanks to the mass freed up by the smaller amount of fuel needed for the trip into orbit.

      It's impossible to tell for sure from the lies and confusion in the article, but it seems like it may be optimized for station-keeping while at the same time being useful for the final orbital insertion or orbital transfer burn.

      But what would a "science journalist" be doing without writing an article that was full of ridiculous contradictions,
  • Old News (Score:3, Informative)

    by zaydana (729943) on Saturday February 24, 2007 @05:44AM (#18132990)

    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)

    by PopeOptimusPrime (875888) on Saturday February 24, 2007 @05:52AM (#18133008)
    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...
    • 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 fu
    • by autophile (640621)

      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 aren't any gas stations in space!

      --Rob

  • 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.
  • 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.
  • by Tx (96709) on Saturday February 24, 2007 @07:03AM (#18133204) Journal
    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.
  • I think this quote from the press release I found at the Georgia Tech news page [gatech.edu] explains things more clearly than the two links in the article do:

    [Georgia] Tech's significant improvement to existing xenon propulsion systems is a new electric and magnetic field design that helps better control the exhaust particles, Walker said. Ground control units can then exercise this control remotely to conserve fuel.

    So they've improved the degree to which one can regulate the output of conventional ion thrusters. Better thrust control means better fuel efficiency, so you need less fuel to do the same work as before.

  • It's good to be enthusiastic but a little better to be able to describe what you are writing about.
  • Really misleading. (Score:5, Insightful)

    by Alex Belits (437) * on Saturday February 24, 2007 @07:59AM (#18133422) Homepage
    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! (Score:3, Funny)

    by StarfishOne (756076) on Saturday February 24, 2007 @08:28AM (#18133522)
    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

  • She can smoke the clutch on anything.
  • You gotta find first gear in your giant robot car!
  • 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.
  • 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!
  • Couple of points to consider with rockets taking off from earth.
    1. Air friction;
    2. Limits due to occupants.

    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

  • by amightywind (691887) on Saturday February 24, 2007 @10:54AM (#18134168) Journal
    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.
  • 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 achiev

  • 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.
  • Wow, I didn't know aerospace borrowed drivetrain technology from cars. I thought it was only the other way around [allpar.com].

  • by cbnewman (106449) on Sunday February 25, 2007 @02:22AM (#18141094)
    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?

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