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NASA Space Science

NASA's Ion Thruster Sets Continuous Operation Record 165

Posted by Soulskill
from the burnin-out-its-fuse-up-there-alone dept.
cylonlover writes "NASA's Evolutionary Xenon Thruster (NEXT) ion engine has set a new world record by clocking 43,000 hours of continuous operation at NASA's Glenn Research Center's Electric Propulsion Laboratory. The seven-kilowatt thruster is intended to propel future NASA deep space probes on missions where chemical rockets aren't a practical option. The NEXT is one of NASA's latest generation of engines. With a power output of seven kilowatts, it's over twice as powerful as the ones used aboard the unmanned Dawn space probe, yet it is simpler in design, lighter and more efficient, and is also designed for very high endurance. Its current record of 43,000 hours is the equivalent of nearly five years of continuous operation while consuming only 770 kg (1697.5 lbs) of xenon propellant. The NEXT engine (PDF) would provide 30 million newton-seconds of total impulse to a spacecraft. What this means in simple terms is that the NEXT engine can make a spacecraft go (eventually) very far and very fast."
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NASA's Ion Thruster Sets Continuous Operation Record

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  • by MyLongNickName (822545) on Friday December 28, 2012 @10:03AM (#42410597) Journal

    This ion thruster placed on Voyager 1 would have taken it up to 37 km/s over 5 years compared to the 17km/s it is going now. Not part of my calculations is that Voyager 1 would have been slightly lighter due to the reduced fuel load. i don't have exact enough numbers to do the calc, but it would have likely been in the low 40's km/s.

    • by MyLongNickName (822545) on Friday December 28, 2012 @10:16AM (#42410647) Journal

      Just realized how careless I was. My calcs assume acceleration from propulsion only. Voyager 1 took up much less fuel but is going at a pretty good clip due to gravitational assists. So the comparison is not apples-to-apples. Voyager 1 has used about 80 kg of mass to get to its current speed, but a good part of that was due to energy from being placed in orbit and from a slingshot around Jupiter.

    • by necro81 (917438)
      Also not included in your calcs is the velocity "lost" due to escaping from the sun's gravity well. Still, it's a hell of a lot faster.

      Only problem is coming up with a multi-kilowatt electrical source that far out in space. Voyager's RTGs were only a few hundred watts, I believe.
      • by Rich0 (548339) on Friday December 28, 2012 @11:06AM (#42410927) Homepage

        Agreed. You can get a lot of energy from solar in the inner solar system, but ion engines are about long durations, and you're not going to be spending that much time in the inner solar system. I guess you could launch it towards the sun and do a slingshot around it. That will let you pick up a lot more velocity due to spending more time where your panels are effective, but it obviously adds a lot more distance to your trip as well.

        You could just use a much larger RTG, or perhaps even a reactor. Not sure how that works out in terms of mass trade-off vs just using a conventional rocket.

        • by Anonymous Coward on Friday December 28, 2012 @11:20AM (#42410995)

          You would think that launching towards the sun would help; so did I. After hours of playing Kerbal Space Program, I've learned that in order to even get to the sun, you have to negate then Earth's velocity in order to fall close enough to the sun to get a boost, and you'd have to get pretty close to get a boost. Not sure if the time and energy expended doing a sun flyby (not to mention having to add extra solar shielding) would provide enough of an advantage for extra-solar trips.

          Even gravitational boosts from other planets are tricky. You have to make sure you're coming from behind in order to get a boost since it allows you to fall into the planet while it's still traveling away from you, giving you more speed longer. If you intercept in front of it, the planet basically stops you in your tracks and pulls your towards itself, killing your momentum.

          • by Immerman (2627577) on Friday December 28, 2012 @03:35PM (#42412891)

            Umm, no. Maximum energy gain for a gravitational assist is a slingshot maneuver where you narrowly miss a head on collision with the planet, you will then be whipped around on a parabolic path and depart in the opposite direction with twice the planet's velocity added to your own. The "gravitational tugboat" maneuver you describe is great for minor boosts and course corrections, but is unlikely to be used for speed unless a slingshot maneuver is incompatible with reaching the desired destination.
            http://en.wikipedia.org/wiki/Gravity_assist [wikipedia.org]

            As for a solar slingshot, yeah it's pretty pointless for in-system travel - it's hard to get close (not to mention survive the passing), and since it's basically the "stationary point" for the solar system you can't steal much speed from it, so once you reach your starting distance you'll have roughly* the same velocity as when you started with. Unless you just want to briefly go really fast for some reason, or are on an interstellar vessel seeking a gravity assist on your way to somewhere else in the galaxy, the sun is pretty useless for gravity boosts.

            * You won't leave a solar slingshot with exactly the same velocity because the sun itself is orbiting the solar-system's barycenter, typically between about 1/2 and 1 solar-diameter from the sun's center and constantly moving as the orbiting of the outer planets shift the system's center of mass. So there will be some velocity transfer, just not enough to be actually useful.

          • by khallow (566160)
            Launching from near the Sun helps, if you have high thrust engines (for example, chemical, a amazingly efficient solar sail, nuclear propulsion, etc). The cause is the Oberth effect [slashdot.org] where you can get a huge boost from thrusting in a deep gravity well (cues jokes please) as long as you result in a trajectory that achieves escape velocity. It's primarily because you aren't pulling all that propellant out with you.

            Unfortunately, current generation electric propulsion isn't high thrust to weight and hence, c
        • You'd get solar energy by going close to the sun, but no "slingshot" - the slingshot trick relies on the fact that the planets are moving in their orbits. In fact the technique slightly reduces the planet's orbital velocity - the energy has to come from somewhere! But because the sun is stationary (with respect to the solar system, of course) there's no advantage to be gained.
          • by Rich0 (548339)

            Yup, realized that. I was referring only to spending more time in the inner solar system - as long as your thrust was directed along your velocity vector any speed you pick up on the way towards the sun will translate directly into speed on the way out.

      • Only problem is coming up with a multi-kilowatt electrical source that far out in space.

        Purely a political problem. Suitable and inexpensive reactor designs have existed for decades.

      • Also not included in your calcs is the velocity "lost" due to escaping from the sun's gravity well.

        The funny thing is that higher initial speed (or, more on the note of continuous acceleration, comparatively short acceleration deep inside the gravity well) actually diminishes the effects of the speed loss. Do the math yourself. If you accelerate to the local parabolic speed, your speed in the infinity is going to be zero. If you accelerate to local parabolic speed plus, say, 3 km/s, your speed in the infinity is going to be significantly higher than those 3 km/s. You don't even need to integrate anything

      • Re: (Score:3, Interesting)

        by cheesybagel (670288)

        Only problem is coming up with a multi-kilowatt electrical source that far out in space

        SAFE-30 [wikipedia.org] nuclear reactor. In fact the Jupiter Icy Moons Orbiter [wikipedia.org] (JIMO) was planned to use nuclear-electric propulsion to explore the moons of Jupiter but it was cancelled. Another possibility if you want to stay in the inner planets i.e. not go further than Mars is to use a gigantic solar panel array. The 8 ISS solar arrays generate 84 kW.

  • Ion thrusters (Score:4, Interesting)

    by P-niiice (1703362) on Friday December 28, 2012 @10:05AM (#42410607)
    The simple concept that we now have "Ion Thrusters" is extremely cool to me. Only "Warp Drive" would be cooler, be we have a ways to go there.
  • by Anonymous Coward

    while consuming only 770 kg (1697.5 lbs) of xenon propellant.

    Last I heard, xenon was a gas, and that sure sounds like an awful lot of it - how much is left (on our planet)?

    • by dr.Flake (601029)

      My first thought as well.

      Wikipedia's first hit:

      "Extraction of a liter of xenon from the atmosphere requires 220 watt-hours of energy.[52] Worldwide production of xenon in 1998 was estimated at 5,000–7,000 m3"

      Sounds like we have some scaling issues before this engine puts us on mars on a regular basis.

      • What I don't understand is why you would measure "production" of a gas as a unit of volume. And if you're going to do that, why wouldn't you include the pressure as well? Doesn't this tell us basically nothing, or is there some sort of standard I don't know about?

        • by compro01 (777531) on Friday December 28, 2012 @10:54AM (#42410843)

          is there some sort of standard I don't know about?

          Yes. Standard temperature and pressure [wikipedia.org].

          the IUPAC's definition is a temperature of 273.15 Kelvin (0 C) and a pressure of 100 kilopascals, though there's a bunch of other standards to choose from.

        • by jo_ham (604554)

          If a pressure is not given, assume STP. At least, according to IUPAC. Though like many unit cock ups in the past, assumptions can get you in all sorts of trouble. however if it was given in m^3 then it's going to be reasonably safe to assume STP, then you just use the ideal gas law to work out quantity - Xenon is reasonably close to one.

      • by davydagger (2566757) on Friday December 28, 2012 @11:03AM (#42410909)
        "220 watt-hours of energy."

        Less power than running a dungeon in world of warcraft using a decent gaming rig. doubly so, if you run dual cards.

        total power usage of gaming rig under load - ~400 watts

        Time to run a dungeon - between 45 min - 1 1/12 hours.

        300 - 600 watt hours
      • by Hadlock (143607)

        Xenon doesn't have a whole lot of uses here on earth. It's an inert (noble) gas. Ion engines aren't terribly useful for moving living beings around as they wouldn't accelerate an object (and it's life support systems) out of LEO and to Mars before the occupants either starved or died of cancer. Chemical rockets aren't as efficient, but at least they can get you to Mars in under 9 months. A very loose analogy would be crossing the Atlantic in an open 8' rowboat vs flying across in a jet powered 747.

    • by Anonymous Coward on Friday December 28, 2012 @10:33AM (#42410723)

      lots and lots and lots. just expensive to separate as it is widely distributed.
      Xenon is a trace gas in Earth's atmosphere, occurring at 87±1 parts per billion (nL/L)

      (wikipedia is fun)

      being heavy it doesn't escape the atmosphere.
      It is very dense as a liquid, stores compactly, and can used as a heatsink for the engine.

      for fun:
      770kg of xenon is 130641 L at STP
      it is 252 L at xenon boiling point (as liquid)
      it is also ~2% of total xenon production (in 1998)

    • by necro81 (917438) on Friday December 28, 2012 @10:46AM (#42410791) Journal
      Unlike helium, which is so tenuous it escapes the atmosphere, xenon is a relatively heavy gas that sticks around. It's not particularly abundant (less than 100 parts per billion in the atmosphere) but it can be pretty easily separated out. According to wikipedia's references, annual xenon production is 5000-7000 m^3 [wikipedia.org] (at STP), or about 35,000 kg. (This reference [bgcspecgas.com] estimates 9000 m^3/yr, or 53,000 kg.) So 770 kg used in one multi-year experiment isn't such a big deal. When it is used in various applications, it tends to return to the atmosphere, from whence it can be separated again.
    • by O('_')O_Bush (1162487) on Friday December 28, 2012 @10:48AM (#42410805)
      More importantly, some Xenon isotopes are common byproducts of our current fission reactors.
    • by compro01 (777531)

      Xenon makes up about 87 parts per billion of the Earth's atmosphere.

      The dry mass of the Earth's atmosphere is approximately 5.14 quadrillion tonnes.

      That comes to about 447 million tonnes of Xenon.

      Xenon is also a waste product from nuclear fission.

    • by Rockoon (1252108) on Friday December 28, 2012 @10:53AM (#42410837)

      Last I heard, xenon was a gas, and that sure sounds like an awful lot of it - how much is left (on our planet)?

      Seriously man.. 770kg shouldnt sound like "an awful lot of it" when you are asking about how much we have "on our planet." You do know how massive the atmosphere is, right?

      Extracting a liter of xenon from the atmosphere requires 798000 joules of energy, and 770 kg of xenon is 131804 liters. So thats 104388768000 joules of energy.

      (yes, I am shooting for "oh noes big number")

      Thats equivalent to under 3 minutes of output of the typical (average American) coal plant that puts out 667MW.

    • One would assume since ion thrusters only work in a vacuum, that whatever test chamber they used to fire the engine also recuperates the xenon. One hopes. One further hopes that in reality only a small amount of xenon was continuously cycled between the test chamber and the engine.
      • by jo_ham (604554)

        The hassle of recovery of the gas is entirely based on cost. Helium is routinely recovered and recompressed in research labs and institutions, usually centrally because of the high cost and scarcity - the helium compressor at my university consumes 0.125 MW, by far the single biggest energy sink on the campus, when a critical volume has been recollected ready for purification and reliquification. It's still cheaper doing it this way than just buying more in.

        Xenon is relatively easy to extract from the air,

  • The nice thing is if you want a more recent update, just start calling all of the people on Slide 6. Then again, this is a four year old presentation...some have probably moved onto other positions.
  • I thought to use something as fuel in an ion thruster, it has to be able to ionize? Xenon is about as inert as it gets and really isn't useful for anything because nothing reacts with it in any way. In fact, wasn't hydrogen or something the typical fuel for an ion thruster? Can one of the hundred or so ion thruster engineers that are likely here on slashdot (lol) explain it to us?
    • Re:Xenon? (Score:4, Funny)

      by wbr1 (2538558) on Friday December 28, 2012 @11:24AM (#42411011)

      I thought to use something as fuel in an ion thruster, it has to be able to ionize? Xenon is about as inert as it gets and really isn't useful for anything because nothing reacts with it in any way. In fact, wasn't hydrogen or something the typical fuel for an ion thruster? Can one of the hundred or so ion thruster engineers that are likely here on slashdot (lol) explain it to us?

      http://en.wikipedia.org/wiki/Ion_thruster [wikipedia.org]
      http://en.wikipedia.org/wiki/Xenon [wikipedia.org]
      You figure out the rest.

    • Re:Xenon? (Score:5, Informative)

      by burisch_research (1095299) on Friday December 28, 2012 @12:43PM (#42411523)

      In a chemical sense, yes Xenon is inert and doesn't like to ionize. However, in the case of an ion thruster, the ionization is accomplished using high voltages - very easy to do.

      Xenon is preferred because it's non-toxic, comparatively easy to handle, and has a 'heavy' nucleus -- meaning that you can more easily give each atom more of a push, resulting in higher thrust. You could use ions of any atom you like, though. Hydrogen's got the lightest nucleus there is, so it's not much use, not to mention being a royal pain to handle.

      The Russians started out with, iirc, cesium and mercury thrusters. But of course these are really nasty substances and you really don't want to be around them if you can help it.

      • by tibit (1762298)

        Mercury is nasty? Given what's typically used in rocket propulsion, mercury is nothing to worry about. I still have a few grams of mercury stored for experiments, and still have a mercury thermometer or two. Why wouldn't I want to be around it? It's stored in sealed glass containers, in secure storage.

    • Re:Xenon? (Score:5, Informative)

      by jo_ham (604554) <joham999@FORTRANgmail.com minus language> on Friday December 28, 2012 @12:50PM (#42411561)

      Xenon is easy to ionise - it's a large, diffuse atom with the outer electrons far from the nucleus. It's also inert and heavy, giving you a non-toxic, non-corrosive fuel with a high mass/charge ratio; ideal for an ion thruster.

      If only it were cheaper to buy!

      It's also not true that "nothing reacts with it". The lower end of group 18 does react with strong oxidisers and you can form (and isolate) crystals of XeO4 and so on. The closest to being truly "noble" gasses are helium and neon.

    • Recall the existence of all those xenon arc bulbs in photo flash and strobe lights and the answer is obvious...
  • I just like saying it, it sounds so cool. Ion Thrusters....
  • The fact that it has a high specific impulse is good, if one were traveling though very empty space. But, the gravitational slingshots and interplanetary highways require short bursts of high energy, at very specific times, rather than high efficiency.

    Still, though, the problem which neither of these addresses, and that none of the solutions I have seen so far address, is the collision with other masses.

  • The FOCAL [centauri-dreams.org] mission might benefit from this kind of tech, seeing as it involves getting a telescope 550AUs out from the Sun and using the sun as a lens.

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