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Space Technology

New Ion Engine Enters Space Race 168

Posted by Soulskill
from the cool-now-where-are-my-ramjets-and-warp-drives dept.
Bibek Paudel brings us a BBC report on the development and testing of an new ion engine by a security firm named Qinetiq. The engine will be used in an ESA spacecraft tasked with mapping the Earth's gravitational field from orbit. Only a handful of ion drives have been used for space missions before, some of which we have discussed. Quoting: "Cryogenic pumps can be heard in the background, whistling away like tiny steam engines. Using helium gas as a coolant, they can bring down the temperature in the vacuum chamber to an incredibly chilly 20 Kelvin (-253C). The pressure, meanwhile, can drop to a millionth of an atmosphere. Ion engines ... make use of the fact that a current flowing across a magnetic field creates an electric field directed sideways to the current. This is used to accelerate a beam of ions (charged atoms) of xenon away from the spacecraft, thereby providing thrust."
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New Ion Engine Enters Space Race

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  • by TFer_Atvar (857303) on Thursday April 17, 2008 @08:46PM (#23112792) Homepage
    I'll have to keep an ion this.
    • by jd (1658)
      You only need the merest whisper of an ion propulsion system story and Slashdot users will go atom with puns.
  • bad idea (Score:3, Insightful)

    by ILuvRamen (1026668) on Thursday April 17, 2008 @08:48PM (#23112804)
    Xenon isn't exactly in great supply. I think they might want to rethink that and design it with a more common material. But sweet that they're finally testing an actual ion drive.
    • Re:bad idea (Score:5, Informative)

      by wizardforce (1005805) on Thursday April 17, 2008 @08:55PM (#23112852) Journal

      Xenon isn't exactly in great supply
      Xenon is present in our atmosphere at roughly 1 part in 180 million and so its cost is about 1 dollar per gram. considering it costs about 25 dollars a gram to launch things into orbit, Xenon isn't that bad when you consider that just a fraction of the fuel is required for the same thrust as chemical fuels. It is used because it is more easily ionized than the higher "inert" gases, is relatively un-reactive and is more easily utilized in the engine, as it is already a gas.
      • Re:bad idea (Score:5, Informative)

        by morgan_greywolf (835522) * on Thursday April 17, 2008 @09:14PM (#23112970) Homepage Journal
        Xenon is apparently plentiful enough to be in most of many so-called "neon" signs: The gas that's in "neon" signage isn't always neon -- different gases are used, including argon, krypton and xenon. Neon gives a reddish-orange glow. If it's more blueish, it's probably krypton or xenon.
        • Re:bad idea (Score:5, Informative)

          by Anonymous Coward on Friday April 18, 2008 @12:42AM (#23114132)
          for bluish signs it is actually argon with a touch of mercury. argon on its own is a dim purple color which is too dim to see with other lighting, but is really neat in a very dim room. the added drop of mercury causes the chemical to fluoresce bright blue. All other colors are by putting a phosphor coating on the inside of the tubes, which emits different colors when excited by the argon-mercury mixture. Neon is only used for the classic tomato orange color, or the deep red or purple which is done with different colored glass tubing. Krypton and xenon can also be excited to emit light, but they require more energy than is commercially viable, and are rather dim.
      • If xenon is an inert gas, will any inert gas do?

    • Re:bad idea (Score:4, Informative)

      by actionbastard (1206160) on Thursday April 17, 2008 @09:37PM (#23113122)
      Xenon is used because it is the heaviest of noble gases.

      You'd best bone up on your Newtonian physics.
      • Re: (Score:3, Insightful)

        by CastrTroy (595695)
        What about Radon. According to my periodic table [wikipedia.org] Radon would be the heaviest noble gas. Not countijng Ununoctium of course, but that's a synthetic element.
        • Re:bad idea (Score:5, Informative)

          by evanbd (210358) on Friday April 18, 2008 @12:14AM (#23114000)

          The 3.8 day half-life might cause some difficulty. Not to mention that the short half-life implies a high radiation output. Generally, it's a good thing not to have your propellant tanks glow on their own.

          Besides, $6000 per milliliter is expensive, even by aerospace standards.

        • Re: (Score:3, Informative)

          by davolfman (1245316)
          Radon has this annoying tendency to emit alpha radiation. Alpha radiation does nasty things to any materials it contacts by embedding helium nuclei in their structure. That and it has a half life of less than 4 days so it's not really suitable for any sort of long term use, and if you're using an ion drive you've already chose to do things the long, efficient way.
          • Re: (Score:3, Interesting)

            by CastrTroy (595695)
            I'm not saying it would be better suited to the purpose. All I was refuting was the fact that Xenon is the heaviest noble gas. I don't think Radon would be the best thing to use, but that doesn't disprove that fact that there are heavier noble gases than Xenon.
          • Re: (Score:2, Interesting)

            by Anonymous Coward

            Radon has this annoying tendency to emit alpha radiation. Alpha radiation does nasty things to any materials it contacts by embedding helium nuclei in their structure.
            OTOH, you don't heave to spend any energy to ionize Radon, as it readily ionizes itself. Just keep high positive potential on the walls of the chamber (tank) to fend of alpha particles.
    • Re: (Score:3, Insightful)

      by doctor_nation (924358)
      It is expensive, but it has great performance compared to almost all other materials (the one better is mercury...). Sure, you can use other materials, but the efficiency drops like a rock. I think the use of Krypton or Argon is being looked at for some thrusters (maybe not ion thrusters). Oh, and ion thrusters have been around since the 60's, and Hall thrusters before that (made by the Russians). They've flown on a lot of missions already- this one isn't at all remarkable to be honest. Deep Space 1 wa
    • There have been very similar drives for at least 30 years. This is just a new model. I spent all day in a meeting discussing control system issues related to the use of a very similar engine on our spacecraft.

            Xenon is a good propellant since it's easy to ionize.

                Brett

       
    • Re: (Score:3, Interesting)

      by v1 (525388)
      sort of what I was wondering. I suppose there's no escaping physics though, you have to use something for fuel. (ok "fuel" is a bad word for it, how about "mass"?) I was hoping ion drives could run without losing mass, but that's the only fundamental way to accelerate something in a vacuum isn't it? by throwing mass overboard, preferably at high speed? (the high speed part being what the ion drive specializes in)

      I suppose the only way around this would be a solar sail, or perhaps such a thing powered by
    • by rilister (316428)
      I'll pass by most of that comment, but you might be interested to know that, amongst many others, NASA's Deep Space 1 probe is in space right now using an (older design of) ion drive.

      It uses Xenon atoms

      http://en.wikipedia.org/wiki/Ion_engine#Deep_Space_1 [wikipedia.org]
  • by OldFish (1229566) on Thursday April 17, 2008 @08:57PM (#23112864)
    As long as the ion drive has to carry all the mass it'll ever use it will never be useful for seriously long trips. It would need to vacuum up stray particles as a mass source for that. But it's mildly interesting anyway.
    • by bagboy (630125) <neo AT arctic DOT net> on Thursday April 17, 2008 @09:06PM (#23112912)
      couldn't they just tie a Roomba to the back of the space craft?
      • Re: (Score:2, Funny)

        by JustOK (667959)
        It would be better on the front, but, still, it wouldn't really get into all four corners of space.
      • Measuring magnetic fields with an ion generator nearby sounds a bit disturbing. They better turn it off while making measurements.

        You've got to say these obvious things because the space boffins seem to forget now and then.

        • Measuring magnetic fields with an ion generator nearby sounds a bit disturbing. They better turn it off while making measurements.

          You've got to say these obvious things because the space boffins seem to forget now and then.

          Why? Magnetic field measurements are very common on plasma experiments, which can have similar or even more severe environments than this ion engine. Turning the plasma/ions off kind of defeats the purpose of most such measurements.
      • by fractoid (1076465)
        Yes, but... actually, "Roomba Ramjet" sounds a lot cooler than "Bussard Ramjet", you may be on to something. Stick the roomba on the front, though, to clean up all that pesky space debris!
    • by evanbd (210358)
      What kind of mission delta-v did you have in mind, exactly? Some of the modern nuclear engine proposals can get single-stage delta-v over 1% c (nuclear salt water rocket and fission fragment rocket, for example). There is some debate about whether going even that fast in interstellar space is feasible, I believe. Besides, modern analysis indicates that there isn't enough hydrogen in the local neighborhood for Bussard's proposal to work, even if you manage to build a functioning fusion reactor for it.
      • Re: (Score:3, Interesting)

        by Lord Apathy (584315)

        indicates that there isn't enough hydrogen in the local neighborhood

        I've heard this before, this and there are many other reasons that don't make a pure Bussard ramjet possible. A few years ago I came across these guys. [ibiblio.org] While I don't know how realistic their ship but one thing that did catch my eye was this. [ibiblio.org]

        I was especially fascinated by how they address the fuel problem. They created something called an acceleration track. The idea is that fuel is launched before the ship is in packages. The ship would over take each fuel and supply package as it left the system.

      • There is some debate about whether going even that fast in interstellar space is feasible

        It seems to me that the faster a spacecraft travels, the more damage is done when a random chunk of whatever collides with the spacecraft. Outside of comet tails and meteor showers, I am not sure there are that many random chunks of matter in space but travelling at 1% of the speed of light when you hit a speck of sand, for example, must be a bad thing. Has this been quantified? Would a steel plate at the front of
        • by evanbd (210358)
          The right shield is probably a very thin shield, well in advance of the craft, and then a heavy shield -- the dust spec explodes on contact with the thin shield, and then has some time to disperse before hitting the actual armor. Note that a 1mg dust spec at 1% c has the energy content of 1kg of TNT. The armor should be doable, but it's not trivial -- and as you get much faster, it gets *really* nontrivial.
    • You're both right.

      http://en.wikipedia.org/wiki/Bussard_ramjet [wikipedia.org]

      http://en.wikipedia.org/wiki/Tales_of_Known_Space [wikipedia.org]

      There are a lot of unanswered questions about this technology, but I'd quote AC Clarke at you if someone says it's impossible.

    • by Nyeerrmm (940927) on Thursday April 17, 2008 @09:29PM (#23113076)
      It depends on how long you mean. Its certainly still a long way from being able to run an interstellar mission, but for an interplanetary mission it provides a lot of benefits. Lower mass and faster travel times are the primary ones; even though its low thrust its constant thrust so it can build up, particularly on longer missions (think to Jupiter rather than the moon).

      Also, the one problem I see with the idea of 'vacuuming' space, beyond the obvious engineering problems, is that in order to use them in a system you'd lose more momentum than you'd gain, at least using engine technology of this sort. Imagine it from the spacecrafts point of reference, all the very rarefied gas is coming towards it at the speed the spacecraft is traveling in the inertial frame. As it captures the gas, it has to slow it down to stationary, and then speed it up and send it back out; in doing so unless the exhaust velocity is faster than the spacecraft velocity, you're going to lose momentum rather than gain it.

      Now if you could come up with a way to ionize the gas as it passes and use magnetic fields to accelerate it further (like a swimmer or an air-breathing engine) that would certainly be interesting.
      • Re: (Score:3, Interesting)

        by evanbd (210358)
        The drag problem isn't that clear cut. The reference frame isn't "spacecraft velocity" in any sense you'd normally think of it -- it's the solar wind, at ~500,000 km/s. In interstellar space it slows enough that fusion engines could easily have a higher exhaust speed, up to several % c spacecraft velocity. The problem becomes one of collecting enough hydrogen, and getting it to fuse. In-system, though, you can use the solar wind drag to your advantage, at least if you want to head outbound. Wikipedia [wikipedia.org] h
        • by delt0r (999393)
          The speed of light is 300,000 km/s. So i think your figure on the solar wind velocity might just be off a tad.
      • by Hucko (998827)
        So you are saying, it would make a great brake?... now if only we can get approach the speed of light...
    • The mass of the fuel and the mass of the engine are pretty much meaningless - what kills ion engines is generally the mass of the power supply.
    • by bug (8519)
      An ion drive, along with most forms of propulsion, would indeed run out of juice for the reasons that you mentioned. If you want to keep the peddle to the floor during your trip across the stars, then you might want this instead:

      http://en.wikipedia.org/wiki/Bussard_ramjet

      A system like that would take a helluva beating. I'm a bit skeptical.
    • As long as the steam engine has to carry all the mass it'll ever use it will never be useful for seriously long trips. It would need to stop frequently for more coal and water as a power source for that. But it's mildly interesting anyway.

      Moral of the story: you have to start somewhere.
  • Ooo (Score:3, Informative)

    by dreamchaser (49529) on Thursday April 17, 2008 @09:06PM (#23112910) Homepage Journal
    TIE Fighter's, anyone? (Twin Ion Engine, for those of you who are not true geeks)
  • by Ungrounded Lightning (62228) on Thursday April 17, 2008 @09:22PM (#23113030) Journal
    Ion engines ... make use of the fact that a current flowing across a magnetic field creates an electric field directed sideways to the current.

    No it doesn't. It creates a MECHANICAL FORCE directed sideways to the current. It's the Faraday effect, which is what drives electric motors.

    It's also how you can use the Hall effect to determine whether the majority current carrier is positive or negative: The carriers are accelerated toward the same side of the conductor, so the sign of the hall voltage tells you whether you have more + or - charge carriers.

    (IIRC It's how they showed that Franklin guessed wrong when he assigned + and - to charges, leading to the sign of "classical current" and the points of arrows on semiconductor diagrams being opposite to the direction of electron flow.)
    • Re: (Score:3, Informative)

      by Anonymous Coward
      First of all, it does create an electric field, just as the summary said. I have no idea what you meant by a "MECHANICAL FORCE", since the only thing that can create a force on ions is either an electric or magnetic field-- so one of those two has to be there! Also, it is not called the "Faraday effect", that is an effect of magnetic fields on light polarization-- nothing to do with this. It's the Hall effect, which you later mention anyway.

      The reason it creates an electric field is the same as the reason t
      • by evanbd (210358)
        It all depends how you do the math. In the reference frame of the magnetic field, there is a direct force on the moving charged particle, and no electric field is present beyond what the charged particle itself creates. In the frame of the particle, the magnetic field shows up as partially an electric field, which is where the force comes from (since the particle isn't moving in its own reference frame). See special relativity and the Lorentz transformation.
  • of the NRX program. NRX (NERVA [NERVA - Nuclear Engine for Rocket Vehicle Application] Reactor-Experimental Research) was the engine that would power the spacecraft that was supposed to take us to Mars and beyond. Unfortunately it was cancelled because of 'environmental concerns' http://www.fas.org/nuke/space/kiwi.gif [fas.org].
  • by doctor_nation (924358) on Thursday April 17, 2008 @09:49PM (#23113188)
    The T5 is hardly a new thruster- it's probably been around for 10 years or more. And it's not that impressive in terms of performance for an ion thruster. More impressive ion thrusters exist, like the NSTAR thruster they used on Deep Space 1. That provided main propulsion and lasted way longer than expected, so DS1 got a lot done. Or look at the nuclear-reactor powered ion thrusters that were under development until Bush decided we were going to Mars (NEXUS and HiPEP).

    Ion thrusters (and electric propulsion) have been around since the 60s. Back then, they used mercury for propellant and they had grid voltages of 13kV. Tons of ion thrusters have flown already and are already doing stationkeeping on satellites right now.
    • Re: (Score:3, Interesting)

      by olman (127310)

      Or look at the nuclear-reactor powered ion thrusters that were under development until Bush decided we were going to Mars (NEXUS and HiPEP).
      Maybe you explain to us forehead slope challenged viewers why nuclear ion engine wouldn't be perfect for something that is going to Mars?
  • The main reason to use xenon is that you can ionize more of it due its larger size (ionization cross section), most the gas in these trusters is not ionized and is wasted. The ionization energy is insignifcant (tens of volts) compared to the expulsion voltage (tens of kilovolts).
  • Higher Efficiency? (Score:3, Interesting)

    by Doc Ruby (173196) on Friday April 18, 2008 @12:26AM (#23114064) Homepage Journal
    Are these ion engines more efficient in turning the power stored in their fuel into kinetic energy of the vehicle than the efficiency of, say, liquid fuel rockets we use to launch satellites and the Space Shuttle?
    • Re: (Score:3, Informative)

      by aXis100 (690904)
      Not so much efficiency, the main benefit is reduced weight.

      Simply put, they dont have "fuel" in the conventional sense. They use electricity (which can be sources externally or generated oboard from a nuclear source) to exject a reaction mass at high speed. Over time this reaction mass will be consumed, but get far more benefit from it that they would with normal combustible fuel.
      • by Doc Ruby (173196)
        Well, they do have conventional fuel, just not conventional for rockets, which use an unconventional fuel that's also used as the reaction mass in exhaust.

        Has anyone tried powering an ion engine vehicle with an external laser? How about a laser-driven interplanetary scoop that collects ions from interstellar space to drive as reaction mass powered by that remote laser?
    • by Urkki (668283)
      Yes, much more efficient, if by efficient you mean how much mass you need to achive certain change in velocity.

      The problem is how fast they can convert the energy of the fuel into acceleration. I think we're still a long way from an ion engine that could lift even it's own weight on Earth surface, let alone weight of an entire spacecraft of any kind. A current or foreseeable technology ion engine on the surface of Earth will just sit there, even on full power.

      So you still need something with a lot of thrust
      • by Doc Ruby (173196)
        By "efficient" I mean how much potential energy in the fuel is converted by the engine into kinetic energy of the vehicle. I suppose that a smaller reaction mass that's expended by the engine per distance means less reaction mass carried before it's expended, which means the vehicle can be less massive, therefore require less energy to move. But if the lighter vehicle is overbalanced by a less efficient energy conversion from potential in the fuel into kinetic of the vehicle, then it's not really worth it.
        • by Urkki (668283)
          Ok. The problem with that is, how do you define what "potential energy of fuel" means in ion engine. It has separate electric energy source (with nuclear fuel, or solar energy and no fuel at all), and separate propellant (like Xenon) with almost negligible mass.

          So you'd have to make a lot of assumptions (type and mass of energy source, amount of fuel on board, amount of propellant on board) to calculate efficiency like you say.

          But for any sensible assumptions, the efficiency will be much much higher than wi
          • by Doc Ruby (173196)
            Assumptions are not necessary. We're talking about a specific implementation of an ion engine, not it's theoretical efficiency.

            This new engine has a power source that has its own efficiency converting its fuel to electricity, which is the starting point. Then there is the efficiency of the ion engine itself converting that electricity to the kinetic energy of the moving vehicle. Multiply those two (fractional) efficiencies together for the total fuel efficiency of this vehicle. That's what I want to know.

            Th
  • I thought I learned in HS that no noble gasses could be ionized because all their electron shells were already perfectly full. How can Xenon run an ion drive?
    • Re: (Score:3, Interesting)

      by Ihlosi (895663)
      I thought I learned in HS that no noble gasses could be ionized because all their electron shells were already perfectly full.



      They may be harder to ionize than other substances, but it's not impossible to do so. Heck, if they could not be ionized, it would mean that they hang on to their electrons with infinite force ...

      • Re: (Score:3, Interesting)

        by Ihlosi (895663)

        ... which would also mean that you could extract infinite amounts of energy from an alpha particle (which is an ionized helium nucleus ... and energy required to remove an electron from a noble gas is infinite (i.e. a hard "cannot be ionized ever"), then adding an electron to the alpha would release infinite amounts of energy.

  • Qinetiq (Score:5, Informative)

    by julesh (229690) on Friday April 18, 2008 @04:18AM (#23114972)

    security firm named Qinetiq
    Security firm? Are people starting to forget that Qinetiq [wikipedia.org] is a privatised government agency (formally known as DERA [wikipedia.org], the Defence Evaluation and Research Agency)?
    • And lets not forget all the drama etc when the press found out how that little deal was managed and how much money the new owners made when the government woefully undervalued it (as per usal).
  • GOCE satellite (Score:5, Informative)

    by catfry (730592) on Friday April 18, 2008 @06:20AM (#23115350)
    The focus of this story is completely wrong. Ion propulsion is kinda old hat, there has been more than just 'a handful' of satellites flying with some form of it, unless your hand is really big. Granted, most of them have been as a secondary propulsion mode and for stationkeeping, but now it is also increasingly being taken up as primary probpulsion for deep space missions.
    What is really interesting is the satellite GOCE.
    Tasked with mapping out the gravitational pull of earth with very high fidelity, it needs to fly as close to the earth as possible without being dragged out of orbit by the athmosphere, and to remain stable in this very low orbit.
    For this reason this is the only satellite I know of where a major design driver was that it be aerodynamic! The ion propulsion is primarily to counteract the constant drag so the satellite maintains it's orbit, and to this end it is projected to be thrusting almost continuously.
  • "Yet despite this humble appearance, it took 20 to 30 years to develop, at a cost of tens of millions of pounds."

    Divide tens of millions of pounds by 20-30 years, and you get an annual cost of some UK engineers and their equipment. Unless, of course the figures aren't right, but I have a feeling that they are not too far out.

    I say, dash it all, buck it up you fellows! I know chaps in the RFC who are just itching to slap a couple of ion drives on their kites, what?

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