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Space Transportation Technology

Tiny Ion Engine Runs On Water 103

Posted by timothy
from the instant-ice-tea-doubles-the-range dept.
symbolset writes "Discovery News is covering a project by two engineers from the University of Michigan to pair cubesats with tiny ion engines for inexpensive interplanetary exploration. The tiny plasma drive called the CubeSat Ambipolar Thruster (CAT) will ionize water and use it as propellant with power provided by solar cells. In addition to scaling down the size of ion engines they hope to bring down the whole cost of development and launch to under $200,000."
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Tiny Ion Engine Runs On Water

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  • by Anonymous Coward on Sunday July 14, 2013 @05:13PM (#44279667)
    n/t
    • by Anonymous Coward on Sunday July 14, 2013 @05:43PM (#44279863)

      That answer is just as dumb.

      It runs on both.

      It always needs a propellant and a energy source.

      • Re: (Score:2, Insightful)

        by Anonymous Coward
        The propellant used is incidental, as evidenced by the ion drives that run on xenon, for example. The difference here is that the engine can use something easily found in space, i.e. water. It's no small achievement, but the headline is disingenuous to say the least.
        • by K. S. Kyosuke (729550) on Sunday July 14, 2013 @05:52PM (#44279917)

          The propellant used is incidental, as evidenced by the ion drives that run on xenon, for example.

          Actually, there are *very* good reasons for why specific kinds of engines run on specific kinds of propellants. "Incidental" is hardly the word I'd use.

          • by fisted (2295862)
            Now that your post is +5 Informative, would you mind adding some information regarding those ,,*very* good reasons''?
            • Re: (Score:3, Informative)

              by Anonymous Coward
              Ease of ionization, mass to charge ratio (something favoring both being xenon), cost, size and ease of storage, scalability of storage (two things apparently favored by water over xenon), long term impact on accelerating grids, ...
        • Re: (Score:1, Interesting)

          by Anonymous Coward
          Can you define "easily found" as regards to water in space? Are you telling me there's a 5 gallon jug of pure water just waiting to be used as propellant? Is there also a canister of xenon? That's also found in space.
            • by interval1066 (668936) on Sunday July 14, 2013 @06:25PM (#44280149) Homepage Journal
              You'd think that the Fremen with all their technology would find a way to scoop it up and funnel it down to Arrakis then.
              • by Anonymous Coward
                Dune is at best soft sci-fi.
                • by cellocgw (617879)

                  Dune is at best soft sci-fi.

                  Well of course it is, duh! Sand is soft. You want hard SciFi, try Podkayne of Mars. Ooops, not *that* kind of hard?

              • by Noughmad (1044096)

                Arrakis used to have plenty of water, unfortunately all those damn Fremen kept collecting it and hiding it in caves.

              • You'd think that the Fremen with all their technology would find a way to scoop it up and funnel it down to Arrakis then.

                This is a common trope in SF: You take an advanced planet X and resource Y and say that Y is rare there. There are two alternatives. Either the natives completely ignore the masses of resource Y right over their heads, or they skip them completely and go interstellar to find something that could more easily be obtained locally.

        • by The Cat (19816) *

          So let me ask you the real question on everyone's mind: When you go to a party where there are a lot of attractive women, do you announce your arrival with something like "Hi everyone! I'm a gigantic dick!"

    • Water is the fuel, sunlight is merely a power source. The solar arrays could be replaced with whatever power source you want - RTG, fission reactor, Li-ion battery, etc.

      • by icebike (68054)

        Water is the fuel, sunlight is merely a power source. The solar arrays could be replaced with whatever power source you want - RTG, fission reactor, Li-ion battery, etc.

        A fuel, by definition, supplies power. Water supplies none. Therefore it is not a fuel.

        Water is merely a propellant.

        You don't get to use the word "merely" in relation to a power source. That's totally backwards.

        • by Anonymous Coward

          Propellants often react or change in some way to provide energy. They don't have to, and technically propellant is correct here, but I'd avoid the whole thing by going with "reaction mass"...

      • It runs on water about as much as a steam engine does.

    • by The Cat (19816) *

      There's one in every FUCKING thread.

  • by tloh (451585) on Sunday July 14, 2013 @05:19PM (#44279699)

    .....but more practically: how much thrust/impulse/whatever would you be able squeeze out of an amount of water that can be carried by a tiny cubesat? The article implicitly compares it favorably to current Xenon/Krypton based systems, but made no effort to explain why. Any slashdoter willing to work out the math?

    • by K. S. Kyosuke (729550) on Sunday July 14, 2013 @05:43PM (#44279869)
      I'd be also interested in knowing that. Xenon really is the almost ideal propellant: low ionization energy, heavy ions, completely inert, good density... Water might be slightly nasty, especially if the oxygen ions will come into contact with something reactive. But I do hope that these guys pull it off. I've been a space propulsion junkie since the age of ten or so. Stuff like this makes me tickled pink.
      • by M0HCN (2981905) on Sunday July 14, 2013 @06:15PM (#44280095)

        Thats true, but the issue in a cubesat is going to be all about total propellant mass fraction (The fraction of the vehicle mass at launch made of of stuff you can sling out the back at high speed), so while Xe is a better reaction mass if you have the space for the tank, it may well be that in this particular use case the higher storage density (and thus the ability to fit more of it into a tiny tank) actually trumps the heavier ion.

        Space propulsion is all about propellant mass fraction and exhaust velocity, as those two numbers define how much delta V you can get out of your available fuel.

        The problem with light ions in this situation is that the momentum transferred is simply the product of exhaust mass and exhaust velocity, the energy required to produce that exhaust velocity is 1/2 mv^2, thus a heavier ion travelling more slowly requires less energy input to the accelerator for a given amount of momentum transfer then a light ion moving fast.

        However if you have surplus electrical power, and are not too concerned about producing large accelerations (even by ion drive standards), and can solve the corrosion and thermal management problems, it might actually be a reasonable tradeoff.

        All space propulsion is tradeoffs between energy/reaction mass/specific impulse/acceleration, there are no really right answers here, and having another validated tool in the box is always going to be useful.

        • by symbolset (646467) * on Sunday July 14, 2013 @08:46PM (#44280815) Journal
          Exhaust velocity is 20,000 Km/hr and propellant is half the mass of the craft so it should be on the order of Dawn Mission's 10,000 KPH delta V. If it works at all. These ion engines can theoretically run on a wide variety of propellants like xenon, argon or iodine but since water is so common in space it would be nice if it were effective. Ultimately that means one might refuel in transit, or we might shoot fuel at one with a rail gun. Further out there is less solar energy for the solar cells but we can laser illuminate them. Radio is a problem because of power laws, but space to space laser comm fixes that, with satellite to ground radio relays.
          • by Teancum (67324)

            Further out there is less solar energy for the solar cells but we can laser illuminate them.

            Solar energy production only really becomes an issue when you get beyond Mars.... about the orbit of Jupiter or so (perhaps a little closer to the Sun depending on your solar array size and efficiency). There is still a whole lot of Solar System much closer that can be used for all kinds of activities, including 99.9% of all satellites that are currently in use or for that matter have ever been used. Exploration of the outer Solar System definitely requires some alternate energy sources, but that isn't go

            • by symbolset (646467) * on Monday July 15, 2013 @01:21AM (#44281859) Journal
              The main asteroid belt is beyond Mars, but it's also the closest space that water ice can remain on a body after all these billions of years. Ceres is a gift. It is a fuel depot for interplanetary exploration. It is a potential habitat. It is a gateway to the stars. 200 quadrillion metric tons of water in a low-g environment close enough to the sun for solar cells to work. What more could you ask for? Somebody to exploit it for you? Just wait and they'll come along but they will charge market rates for the effort and then some margin.
              • by real-modo (1460457) on Monday July 15, 2013 @03:43AM (#44282217)

                It is a potential habitat. It is a gateway to the stars.

                ...and here you reveal your true colours.

                Ceres is not a potential habitat.

                Assume you can develop a shelter with adequate shielding from cosmic rays and solar storms, adequate insulation, pressure containment, etc. (Despite the fact that we don't know what "adequate" is, or exactly what's in "etc".) And assume you can transport inhabitants there, all the while keeeping them healthy. Fine. One teeny little failure in one annoying little subsystem, lasting a mere minute, and every inhabitant is dead. What are the odds of zero operation failures in a lifetime? Never happened in any city here on Earth. Or even any inhabited building.

                Another thing. If you could build machines reliable enough to transport people safely around the solar system (and you actually wanted to have people live off Earth), why would you bother with a habitat on an asteroid? Stick with what works: the spaceship. Iain Banks had this right.

                Ceres is not a gateway to the stars.

                Nothing is. The stars are too far away. You'll never live long enough to learn anything from sending a physical mass to any star with Earth-like, habitable zone planets; your city won't exist long enough. Your civilization likely won't last long enough. (The Fermi paradox is no paradox at all. It's a demonstration of how far apart stars are, and how hostile and unrewarding the intervening space is...and perhaps of the rationality of other intelligent life.)

                So what are we left with? Ceres is a potentially useful source of reaction mass/propellant, if anyone ever discovers a valid reason to send physical masses past geosynchronous orbit. (I'll believe mining asteroids could be profitable when I discover a pressing ubiqitous and essential materials problem for which all solutions require one particular element, and the element is both in short supply here on Earth and abundant on an asteroid near Ceres. To date, though, there are substitutes and alternatives for pretty much everything that might start to get short in the next century, so don't hold your breath.)

                I can see a point to mini ion drives. They're potentially handy for sending things out to geosynchronous orbit and doing stuff there and in LEO. And I can see a point to operating telescopes with good resolving power out "in space". But I can't see why they'd need to be very far away from Earth. And even for purposes of scientific experimentation, I can't see a point to sending physical mass much past the outer part of the Oort cloud.

                If you want to get a semi-knowledgeable public interested in this stuff, don't use words and phrases like 'habitat', 'gateway to the stars' or 'profit' when talking about this stuff. They scream "space cadet".

                • by tlambert (566799)

                  It is a potential habitat. It is a gateway to the stars.

                  ...and here you reveal your true colours.

                  Ceres is not a potential habitat.

                  Assume you can develop a shelter with adequate shielding from cosmic rays and solar storms, adequate insulation, pressure containment, etc. (Despite the fact that we don't know what "adequate" is, or exactly what's in "etc".) And assume you can transport inhabitants there, all the while keeeping them healthy. Fine.

                  You mean like a buttload of water? Or this? http://tech.slashdot.org/story/08/11/04/171242/experimental-magnetic-shield-against-cosmic-rays [slashdot.org]

                • by symbolset (646467) *

                  Like tlambert said, I'm pretty sure that 500km of water is an adequate radiation shield. I wasn't even discussing human habitation anyway - we can get the water off without ever setting foot there but of course eventually we will when we can get there quick enough to not kill the passengers.

                  As for my civilization, I've high hopes and like you, low bets.

                  I think I'll leave the rest of your psychosis alone. I'm sure it makes sense to you. Maybe you should share it with an interested professional. I could

                • by tibman (623933)

                  When i think of life-support i always think about submarines and the ISS. Subs go down for months at a time and failure is very news worthy. I don't see why a habitat cannot be built on Ceres. The ISS would die without constant resupply though. There is no environment to work with there : / Solar power is about the only thing they get.

              • by Teancum (67324)

                That somebody is likely going to be Planetary Resources, or some other similar company who is going to get involved with asteroid mining. I would suspect that when Rio Tinto gets involved is when you will see serious money being put on the line for asteroid mining (they make IBM seem like a small start-up company). Rio Tinto also has the cash reserves necessary to build a mining colony in space if necessary, and certainly have mining operations in some rather inhospitable locations around the world. Movi

                • by symbolset (646467) *

                  Asteroids which come near Earth are Planetary Resources' focus. They hope to capture one and exploit its minerals. That is an easy mission: catch what comes to you. Some of these Near Earth Asteroids still contain some captured water content, but an asteroid that has frequented Earth's orbit for a long time will not have them in great pure degree because those boil off - so a great deal of energy and technology must be spent to convert fractions of rock to water. Far more than would be spent to just go

            • by mrax (1825176)
              Actually, unmanned craft can reach outer planets by using gravity slingshots around inner planets. (Cassini probe for example) Esentially, you would first aim for Venus where you have enough solar power and use it's gravity to change course and gain some dV towards the outer planets.
              • by Teancum (67324)

                How many spacecraft have actually gone beyond the orbit of Mars? You can count them on two hands, out of tens of thousands of spacecraft that have been sent into space. Yes, unmanned spacecraft can reach the outer planets and have, but they are exceptional spacecraft that would need to be designed for that specific kind of a mission.

                I'm just saying that for 99.9% of all spacecraft that will ever be built, it isn't a problem.

        • by Nilsie (2984011)
          So i suppose Deuterium is would be an interesting candidate to regular water.
          • by Nilsie (2984011)
            To be more clear, heavy water made from Deuterium as opposed to regular Hydrygen.
      • Stuff like this makes me tickled pink.

        You're standing too close to the exhaust!

    • by mspohr (589790)

      I know it's a drag, but if you actually take the time to read the Kickstarter page, you will see that they have worked out the math. Furthermore, these are actual rocket scientists so they should be better than the average slashdotter.

      • by jd2112 (1535857)

        I know it's a drag, but if you actually take the time to read the Kickstarter page, you will see that they have worked out the math. Furthermore, these are actual rocket scientists so they should be better than the average slashdotter.

        Assuming they didn't mess up a Imperial/Metric conversion in there somewhere...

    • A cubesat is a kilogram or so. Adding a cold gas thruster with a solar panel could give it limited attitude control and not break the mass budget. I don't know how you build interplanetary telemetry and control in a kilogram so that an ion thruster can get to mars and transmit data. the solar panels necessary for a jupiter mission are massive and much more limited than a nuclear option. A big benefit of the ion engine is a reduction in the fuel that has to be lifted. And the fuel must be easy to ionize,
      • Correction:

        A cubesat is made up of one or more 10x10x10cm blocks AT LAUNCH.

        Mass is entirely dependent on how those blocks are filled up.

        Flying configuration is entirely dependent on how they're designed to pack. Quite a few of them unfold quite large solar panels and linear antennas once released into orbit - and you're not constrained to ONE block, just the block-based configuration (Many larger cubesats are made up of 3 blocks. OTOH some cubesats may disperse into a bunch of smaller devices once releas

  • by ElectroVaping (2983501) on Sunday July 14, 2013 @05:20PM (#44279711) Homepage
    Jesus could only walk on water this thing runs on water. That is no small feat...
    • by M0j0_j0j0 (1250800) on Sunday July 14, 2013 @05:43PM (#44279865)

      Ye, but can this thing turn water into wine, ye Jesus wins!

      • by Argon (6783)

        But, this does turn water into a _whine_ when expelling it but it's just that you can't hear it in space :-).

    • by sjames (1099)

      Honestly, we have no idea how big Jesus' feet were.

      • Jesus was actually a juvenile sasquatch. He had to fake his death because the hair started coming in as he reached sasquatch puberty.

    • by Whiteox (919863)

      You mean "That is no small feet" don't you?

    • by brianerst (549609)

      Come now - it's far easier to run on water than walk on water. Heck, the basilisk [wikipedia.org] can run on water. Jesus not only walked on water, but he just stood there too and helped pull another guy (Peter) out of the water when he started to sink. Granted, Peter did manage to walk on the water for a little while, so it's not just a Jesus thing...

  • by Anonymous Coward

    The submitter should be ashamed of itself.

  • by Anonymous Coward

    I am seriously impressed and wish I had more than a few cents in my bank account with which to back this.

  • by Anonymous Coward

    Summary makes no mention of the CAT [kickstarter.com] kickstarter campaign for this thing.

  • And bring them back a conventional robot cold go get the sample conventional thruster put it in orbit and this thing collect it and bring it back. I will then call it wall-e
  • by Anonymous Coward on Sunday July 14, 2013 @06:54PM (#44280303)

    As has been previously mentioned, the key question of space propulsion is how much thrust can you get for a given mass of propellant? The usual measure of this is Isp, which is thrust per weight flow rate of propellant. While it seems unlikely that water will beat Xe due to having lower mass per ion, it does have several key advantages, which are not really in the article except the first one:

    1. Smaller storage tank can be used for liquid water as opposed to a gas. This is especially important if you're trying to piggyback with another satellite.
    2. Gas will leak out over time, requiring more expensive hardware to contain it. You need something able to handle the expansion and contraction associated with sunlight, plus the very high pressure. That's a lot of seals, and getting seals that won't degrade in space is not that trivial- it's a harsh environment, especially from a radiation standpoint.
    3. This is just something that occurred to me, but a large fraction of the weight on a spacecraft is a radiator, because the only way to get rid of heat in space is radiative heat transfer, which is much less efficient than convection. (and if you are generating power and thrusting, you are making heat) If you utilized the water as the working fluid in the radiator, you might be able to simplify another subsystem. I don't know if they actually did this.

    So in summary:
    It is unlikely that water produces a more efficient propulsion system, but it may well produce a simpler, cheaper, and easier to transport one.
    Disclaimer: No actual math was done for the writing of this post. If you have math to prove me wrong, please do so.

    • Say I want to fly to Saturn and land on Titan. I could build a big vehicle (think Discovery from 2001) and fit it out with a number of fission reactors and a huge array of ion engines. It would have water tanks surrounding the crew compartments for radiation shielding. The mission would include a visit to a small Saturn moon with a known source of water ice so that more reaction mass could be collected. The article doesn't have numbers for the specific impulse of these ion engines but it would certainly be

      • by symbolset (646467) *
        Once our robots start mining Ceres we will have more water on orbit than we know what to do with. Ceres has 200 quadrillion metric tons of the stuff in a convenient concentrated form and low g environment. More than all the fresh water on Earth. We might have to start worrying about free space being polluted with too much water. Argon and xenon might work better but the supply on orbit will always be rare. It would be nice if water works. That is why water is better than Xe: Eventually you might be ab
    • by c0lo (1497653)

      3. This is just something that occurred to me, but a large fraction of the weight on a spacecraft is a radiator, because the only way to get rid of heat in space is radiative heat transfer, which is much less efficient than convection. (and if you are generating power and thrusting, you are making heat) If you utilized the water as the working fluid in the radiator, you might be able to simplify another subsystem. I don't know if they actually did this.

      So in summary: It is unlikely that water produces a more efficient propulsion system, but it may well produce a simpler, cheaper, and easier to transport one. Disclaimer: No actual math was done for the writing of this post. If you have math to prove me wrong, please do so.

      Re: radiative heat transfer. I don't think that the power used by a cubesat can provide heating challenges, especially if the said cubesat is to run on solar panels (heaps of surface relative to the delivered power). So much so that keeping the water from freezing may be the actual problem (given the quite high specific heat of water/ice, it would be a pity if needed to waste energy in melting the fuel first).

  • Ok, yet another ion thruster. This time it uses water. So?

    It's no big deal, right now we have ion engines that can successfully work for years: http://www.theregister.co.uk/2013/06/28/nasa_to_shut_down_long_running_next_ion_propulsion_test/ [theregister.co.uk] We have missions that use ion thrusters to move across the Solar system: http://en.wikipedia.org/wiki/Dawn_Mission [wikipedia.org]

    Low-thrust propulsion is basically a solved problem. What is yet unsolved is getting to the LEO cheaply enough.
    • by FooAtWFU (699187)
      This solves the problem of getting to LEO cheaply enough by using a miniature, lightweight tank. That's why it's a big deal. (Or at least a medium deal.)

      And forget the interstellar-space angle for a moment, too: anyone for a decent picture of Pluto?

  • How long until we have high altitude bombers with these Tiny Ion Engines(TIE) get lasers?
  • Instead of interplanetary travel, how about using these thrusters to deorbit the cubesats at their end of life so they don't become spacejunk?

  • My dad had an engine which ran on water.
    I think it was called an outboard motor.

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