NASA's Ion Thruster Sets Continuous Operation Record

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NASA's Ion Thruster Sets Continuous Operation Record

Posted by Soulskill on Friday December 28, 2012 @01:54AM 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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If I am doing the math right by MyLongNickName · 2012-12-28 02:03 · Score: 4, Interesting

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.

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1. Re:If I am doing the math right by MyLongNickName · 2012-12-28 02:16 · Score: 4, Informative
  
  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.
  
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2. Re:If I am doing the math right by necro81 · 2012-12-28 02:19 · Score: 2
  
  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.
3. Re:If I am doing the math right by Anonymous Coward · 2012-12-28 02:38 · Score: 0
  
  Sweet, that's 0.000133 the speed the light! If we strap 100 of these together (assuming good scaling) we can finallly achieve 1% of c -- which, is not supposed to occur ... darn... where is that nifty reference that predicts when humanity will achieve such goals?
4. Re:If I am doing the math right by Rich0 · 2012-12-28 03:06 · Score: 4, Interesting
  
  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.
5. Re:If I am doing the math right by Anonymous Coward · 2012-12-28 03:20 · Score: 4, Informative
  
  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.
6. Re:If I am doing the math right by Impy+the+Impiuos+Imp · 2012-12-28 04:15 · Score: 1, Interesting
  
  > I guess you could launch it towards the sun and do a slingshot around it.
  No, too much energy! That will make it go faster than is possible in normal space, i.e. faster than the speed of light, and thus throw it back in time.
  Previous to this discovery, only the mysterious energies released in a warp core cold start implosion could make you go faster than light while still in normal space.
  
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7. Re:If I am doing the math right by Bengie · 2012-12-28 04:51 · Score: 1
  
  I am curious as to why we're not supposed to achieve 1% of c. I thought the whole purpose of using an ion-thruster was to potentially achieve relativistic speeds, which you can't do with chemical rockets.
  
  Mind my laymen's explanation, which could be completely wrong. My understanding was that chemical rockets have a maxed velocity because the energy departed from burning fuel is based on the the relatively slow speed that the matter leaves the rocket based on the temperature of exhaust. Ion-thrusters shoot ionic matter out the back-end at much higher speeds, much like a particle accelerator, but slightly lower power right now.
8. Re:If I am doing the math right by OakDragon · 2012-12-28 05:08 · Score: 1
  
  Sorry, I'm replying to negate my accidental Overrated mod... meant to be : Funny+1 :)
  
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9. Re:If I am doing the math right by CapOblivious2010 · 2012-12-28 05:09 · Score: 1
  
  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.
10. Re:If I am doing the math right by Impy+the+Impiuos+Imp · 2012-12-28 05:16 · Score: 1
  
  Thanks! I was wondering what kinds of asses mod down humor. -1 lame, maybe, but on principle? =D
  
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11. Re:If I am doing the math right by Guspaz · 2012-12-28 05:33 · Score: 2
  
  The exhaust velocity on an ion thruster is nowhere near that of a partical accelerator. According to a 1996 NASA document I found, the exhaust velocity of an ion thruster is 31.5 kilometers per second, while particle accelerators are very close to the speed of light. The speed record is 0.999999999976c, which is roughly ten thousand times faster than the ion thruster exhaust velocity. That's not to say that thruster exhaust velocity is the speed limit, since the thruster exhaust velocity is relative to the thruster, not the third party observer measuring the speed of the spacecraft.
  At some point, though, you're going to be getting hit pretty hard by interstellar particles. Even in diffuse regions, you get a particle density of 10^-4 particles per cubic centimeter, so if we assume a spacecraft with a surface area of 10,000 square centimeters (one square meter) traveling at 3000 kilometers per second, you're going to be hit by (if my math holds up), 300 million particles per second travelling at a rather high speed, although that's not actually that much energy. I don't know enough to say if that would cause a problem.
12. Re:If I am doing the math right by John+Hasler · 2012-12-28 05:43 · Score: 1
  
  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.
  
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13. Re:If I am doing the math right by K.+S.+Kyosuke · 2012-12-28 06:01 · Score: 1
  
  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, it's a simple matter of total (potential + kinetic) mechanical energy preservation, and as you surely recall, there is a squaring in the 1/2*v^2*m term.
  
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14. Re:If I am doing the math right by Immerman · 2012-12-28 07:35 · Score: 4, Informative
  
  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
  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.
  
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15. Re:If I am doing the math right by JWSmythe · 2012-12-28 08:08 · Score: 1
  
  Ya, I did that once. Then I found out the shitty part.
  Sure, you can go blazing around the sun like doing your own recreation of the big bang, and zing back 1000 years. You can't go forward using the same method.
  It'll only be another 1960 years until I'm born. You people won't have found how to leave this miserable rock for a couple hundred more years. That whole "whee, we're just outside the atmosphere" thing and "oohh, we have a RC car on the next planet", while quaint, doesn't even begin to give you a clue of what's out there.
  What's worse is, if you go to your space agencies and tell them exactly how to make interstellar vehicles, they just laugh. Definitely don't try to tell them that you came from the future. They'll start quizzing you on who will win some sports event next year, or who a national leader will be next voting cycle. Hell if I know who your next figurehead leader will be. I bet you can't tell me who yours was 2000 years ago either.
  
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16. Re:If I am doing the math right by cheesybagel · 2012-12-28 08:33 · Score: 3, Interesting
  
  Only problem is coming up with a multi-kilowatt electrical source that far out in space
  SAFE-30 nuclear reactor. In fact the Jupiter Icy Moons Orbiter (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.
17. Re:If I am doing the math right by cheesybagel · 2012-12-28 08:43 · Score: 1
  
  I bet a cathode ray tube electron has relativistic velocities.
18. Re:If I am doing the math right by wagnerrp · 2012-12-28 09:41 · Score: 1
  
  It all comes down to conservation of momentum. You throw stuff out the back, and to conserve momentum, you go faster. Eventually, you're going to run out of stuff to throw out the back (fuel), so the faster you throw it (specific impulse), the higher your final velocity will be. You could theoretically reach relativistic velocities using chemical rockets, but your payload fraction would approach zero. We use staging on rockets to cheat this limitation, in a sense, as we discard otherwise dead mass as we accelerate, making the remaining fuel more effective.
19. Re:If I am doing the math right by khallow · 2012-12-28 09:46 · Score: 1
  
  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 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, can't really exploit the Oberth effect very well.
20. Re:If I am doing the math right by Anonymous Coward · 2012-12-28 11:47 · Score: 1
  
  Part of gravity assist is also to use the temporary boost in velocity to increase the bang for the buck from the engines. While you're on the fast part of the slingshot it pays off to get as much power out as possible because you get huge gains in kinetic energy that way. This comes courtesy of the fact that Delta Ek = Work = Force * Distance, so if you're travelling at a good clip, your distance in this equation is proportionately larger.
  So, a slingshot around the sun isn't as pointless as it sounds. By putting a craft on an elongated eliptical orbit around the sun, one could fire the engines when the craft approaches perihelion, and shut them off to conserve fuel afterwards. After making enough trips around, you'll gain considerably more kinetic energy than you'd get otherwise. At that point you'd either have to fire engines at aphelion or use a planet as a slingshot to deorbit the sun.
21. Re:If I am doing the math right by Rich0 · 2012-12-28 13:11 · Score: 1
  
  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.
22. Re:If I am doing the math right by Anonymous Coward · 2012-12-28 16:48 · Score: 0
  
  And you might win that bet. Given a 25KV cathode potential, your electrons would be hitting the screen at around .25c, I believe.
23. Re:If I am doing the math right by Immerman · 2012-12-28 17:52 · Score: 1
  
  Huh, I hadn't thought of that. That could make a solar slingshot useful for interstellar launches at least, assuming we could shield against the massive radiation of a near solar approach. Actually getting there shouldn't be too difficult, a partial slingshot around a convenient planet to eliminate virtually all angular momentum and drop like a rock into a very close approach. Of course given the much higher return velocity it'd probably be extremely difficult to recover the energy thus discarded, but with a sufficiently close approach and powerful enough engines that might be an acceptable loss. Certainly worth considering for an interstellar launch, especially of something massive like a world-ship.
  
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24. Re:If I am doing the math right by Anonymous Coward · 2012-12-28 20:19 · Score: 0
  
  Exactly. I'm trying to repair my force-vector repulsor which burned out a coil but everytime I try and explain what I need, they just laugh and walk away. Now I'm stuck here because they prefer that electrons travel along metal wires instead of a vacuum! Idiots.
25. Re:If I am doing the math right by Anonymous Coward · 2012-12-29 04:34 · Score: 0
  
  At some point, though, you're going to be getting hit pretty hard by interstellar particles
  Yep, even in the vacuum of space there's still drag - if you're going fast enough.
  A true vacuum doesn't really exist in nature, although you can get close in places such as between galaxies.
26. Re:If I am doing the math right by Anonymous Coward · 2012-12-29 04:57 · Score: 0
  
  All I wanted was an IBM 5100, and everybody thought I was pulling some kind of prank. We got the problem solved without it anyways.
27. Re:If I am doing the math right by Anarchduke · 2012-12-29 06:09 · Score: 1
  
  Caesar Augustus.
  
  --
  who prays for Satan? Who in 18 centuries has had the humanity to pray for the 1 sinner that needed it most? ~Mark Twain
28. Re:If I am doing the math right by JWSmythe · 2012-12-30 02:54 · Score: 1
  
  I'd give you mine, but I'm pretty sure it's in a eccentric orbit around Sol. Somewhere around the orbits of Sol 6 and Sol 9 (Saturn and Pluto, in Earth terms). All the odds of hitting one of their little probes, and I managed to hit two on the last trip. I won't admit which ones, since they'll probably try to sue me.
  If they ever do manage to find my repulsors or the part of the hull they were attached to, I believe one is still stuck in the side. If you get there first, can you give the crew who are probably floating around it, a proper space funeral?
  We were lucky to even land. We followed this massive radio signal at 60.886ÂN, 101.894ÂE, assuming it was a landing beacon, Well, at least no one saw us come in. The atmospheric shock wave was pretty significant though.
  
  --
  Serious? Seriousness is well above my pay grade.
Given that we aren't actually simpletons... by Anonymous Coward · 2012-12-28 02:03 · Score: 0

... it might have been nice to know how far and how fast.
1. Re:Given that we aren't actually simpletons... by MyLongNickName · 2012-12-28 02:09 · Score: 1
  
  Most likely this thing was not aboard any ship or probe or any other object in outer space. This thing is being developed, so it is likely attached to some instruments in a lab where they can monitor it continually and make sure there aren't any problems. Likely they shut it down periodically to look for any problems, signs of breakdown or other signs that this cannot be scaled up for any reason.
  So how far and how fast are irrelevant. There are enough numbers in the summary that you can do your own calculation on any object you like.
  
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2. Re:Given that we aren't actually simpletons... by Anonymous Coward · 2012-12-28 02:20 · Score: 0
  
  Apparently you are.
3. Re:Given that we aren't actually simpletons... by craznar · 2012-12-28 02:25 · Score: 5, Funny
  
  My calculations would say it probably went at a speed of around 0km/second, placing it now around 0km from Earth after 5 years.
  
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4. Re:Given that we aren't actually simpletons... by avgjoe62 · 2012-12-28 02:34 · Score: 4, Funny
  
  Check your maths. My calculations place it about .001 km from Earth...
  
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5. Re:Given that we aren't actually simpletons... by Anonymous Coward · 2012-12-28 03:06 · Score: 5, Insightful
  
  Likely they shut it down periodically to look for any problems, signs of breakdown or other signs that this cannot be scaled up for any reason.
  .
  Not. It was 43,000 hours of continuous operation.
6. Re:Given that we aren't actually simpletons... by Desler · 2012-12-28 04:05 · Score: 2
  
  If they shut them down how could it be claimed to be continuous operation? You do know that continuous means "uninterrupted", right?
7. Re:Given that we aren't actually simpletons... by Aaden42 · 2012-12-28 04:13 · Score: 4, Funny
  
  Maybe they mean "continuous" operation the way ISP's mean "unlimited" bandwidth?
8. Re:Given that we aren't actually simpletons... by Anonymous Coward · 2012-12-28 04:28 · Score: 0
  
  Good job repeating what the guy above you said an hour ago. Mod parent down, "redundant"
9. Re:Given that we aren't actually simpletons... by Anonymous Coward · 2012-12-28 04:29 · Score: 0
  
  Except that the unlimited never meant "unlimited bandwidth". That issomething invented by idiots. The term has always meant unlimited connection time. It was to differentiate from earlier dialup times where your billing plan usually cost per minute of service or had hard limits to how much uptime alloted to you vefore overage charges.
10. Re:Given that we aren't actually simpletons... by Desler · 2012-12-28 04:33 · Score: 1
  
  Repeat:
  "To utter in dulication of another's utterance".
  Which my post wasn't. Fail.
11. Re:Given that we aren't actually simpletons... by Anonymous Coward · 2012-12-28 05:02 · Score: 0
  
  Yes it was. I pointed out that the OP missed the "continuous" in the title. You did the same thing. Quit being stupid.
12. Re:Given that we aren't actually simpletons... by JWSmythe · 2012-12-28 05:04 · Score: 1
  
  My maths are 0.00074295 km from the Earth. :)
  
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13. Re:Given that we aren't actually simpletons... by Anonymous Coward · 2012-12-28 05:08 · Score: 1
  
  Tse.Tse. It's underground, you both got the sign wrong.
14. Re:Given that we aren't actually simpletons... by HiThere · 2012-12-28 07:01 · Score: 1
  
  Yes. But it was on a test stand, so that *IF* problems developed, they could shut it down to fix the problem. Think of it as a debugging run.
  
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  I think we've pushed this "anyone can grow up to be president" thing too far.
15. Re:Given that we aren't actually simpletons... by JWSmythe · 2012-12-28 08:12 · Score: 1
  
  Ahhh, I remember when AT&T Worldnet screwed that up for everyone. They gave "unlimited" and would periodically bump their users offline. Those of us who had our machines automatically reconnect and notify us of our new IP were apparently a pain. "Unlimited" became "Unlimited, yet limited to x hours per month" and if you did stay connected all month, it was something like a $5,000 charge for the extra time, even if you barely transferred anything.
  I almost preferred the per minute billing. I couldn't get back to my home machine that way though.
  
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Ion thrusters by P-niiice · 2012-12-28 02:05 · Score: 3, Interesting

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.
1. Re:Ion thrusters by flyingfsck · 2012-12-28 02:17 · Score: 3, Informative
  
  Ion thrusters are in wide use on satellites for many years already. This is merely an improved version.
  
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2. Re:Ion thrusters by Lincolnshire+Poacher · 2012-12-28 02:22 · Score: 4, Informative
  
  The simple concept that we now have "Ion Thrusters" is extremely cool to me.
  OK, brace yourself for techno-orgasm.
  The first recorded successful firing of ion thrusters in space was onboard the Soviet Zond 2 probe. 8th December 1965.
  Yes, fifty years ago.
  That particular installation was experimental, but ion engines were widely used in subsequent Soviet probes. Mainly developed at the Kurchatov Institute.
3. Re:Ion thrusters by Narishma · 2012-12-28 02:31 · Score: 1
  
  Only "Now"? They've been in use for decades in various probes and satellites...
  
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  Mada mada dane.
4. Re:Ion thrusters by renoX · 2012-12-28 02:48 · Score: 1
  
  > The first recorded successful firing of ion thrusters in space was onboard the Soviet Zond 2 probe. 8th December 1965.
  Thanks for the information, I knew that it was Russians who worked first in this field, but I didn't know that this was *that* early.
  As there was discussion about Voyager 1, it's interesting to remind ourself that it was launched in 1977..
5. Re:Ion thrusters by Anonymous Coward · 2012-12-28 03:30 · Score: 0
  
  The simple concept that we now have "Ion Thrusters" is extremely cool to me.
  Why? Because it sounds cool, huh. Do you even know how they work? Do you know what an Ion is? Are you just impressed because of that one Star Trek episode where they say the aliens have an "Ion Drive" which is centuries ahead of Star Fleet? Hint: That was just technobabble. In reality these engines are just repelling charged particles of gas. You can get your own Ion Generator for less than $100 on Ebay. Search: "Air Purifier".
6. Re:Ion thrusters by ArsonSmith · 2012-12-28 04:03 · Score: 4, Funny
  
  And first put on a small one man fighter called the Twin Ion Engine fighter in 1977.
  
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7. Re:Ion thrusters by Anonymous Coward · 2012-12-28 04:25 · Score: 1
  
  It's going to be a while on "Warp Drive". They're working on a detection device for the required field now. It's called the "White-Juday Warp Field Interferometer". I don't think anyone has a clue as to how to alter space, but at least they will be able to detect any changes. Let the testing commence!
8. Re:Ion thrusters by Anonymous Coward · 2012-12-28 04:30 · Score: 0
  
  I thought it was cool because Star Wars has TIE Fighters. Of course as a kid I thought it was named that way because it looked like a bow tie and not Twin Ion Engine Fighter.
9. Re:Ion thrusters by Rob+the+Bold · 2012-12-28 05:06 · Score: 4, Funny
  
  And first put on a small one man fighter called the Twin Ion Engine fighter in 1977.
  But it was short range only, and couldn't operate far from base.
  
  --
  I am not a crackpot.
10. Re:Ion thrusters by Anonymous Coward · 2012-12-28 06:16 · Score: 0
  
  or moon.. wait, that's no moon....
11. Re: Ion thrusters by Anonymous Coward · 2012-12-28 06:41 · Score: 0
  
  Wow way to be a pompous Debbie Downer. Do you feel better about yourself now that you've demeaned someone else?
12. Re:Ion thrusters by Provocateur · 2012-12-28 07:46 · Score: 2
  
  Warp Drive? It's only around the corner once you've reached Orbital Science See?
  
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13. Re:Ion thrusters by demonlapin · 2012-12-28 08:58 · Score: 1
  
  I've got a bad feeling about this...
14. Re:Ion thrusters by ArsonSmith · 2012-12-28 09:46 · Score: 2
  
  Unless it had gotten lost, been part of a convoy or something.
  
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  Paying taxes to buy civilization is like paying a hooker to buy love.
15. Re:Ion thrusters by Anonymous Coward · 2012-12-28 10:06 · Score: 0
  
  Unless it was part of a convoy and got lost...
16. Re:Ion thrusters by Anonymous Coward · 2012-12-28 21:39 · Score: 0
  
  Guess this was the old record which was broken http://en.wikipedia.org/wiki/SMART-1
17. Re:Ion thrusters by Anonymous Coward · 2012-12-29 03:24 · Score: 0
  
  Forget calling it Ion Thrusters, they used the word impulse in the description, that gives us free reign to call them
  Impulse Drive.
Um, they used what? by Anonymous Coward · 2012-12-28 02:09 · Score: 1

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)?
1. Re:Um, they used what? by dr.Flake · 2012-12-28 02:19 · Score: 1
  
  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.
  
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2. Re:Um, they used what? by JoeSchmoe999 · 2012-12-28 02:25 · Score: 1
  
  Approximately 1/2 trillion kilograms give or take
  
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3. Re:Um, they used what? by Anonymous Coward · 2012-12-28 02:28 · Score: 0
  
  Wolfram alpha says that the "volume of 770kg of xenon" is 131,000 liters (34,500 gallons). Unfortunately it doesn't know the answer to "volume xenon on earth"...
  I'm not entirely sure the 34,500 gallon answer is right either (i didn't spend the time to re-verify by pV = nRT -- I think that's it) and I didn't immediately find at what pressure they keep this stuff at -- I was wondering about the storage-space aspect of this myself.
4. Re:Um, they used what? by Anonymous Coward · 2012-12-28 02:33 · Score: 5, Informative
  
  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 87Â±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)
5. Re:Um, they used what? by necro81 · 2012-12-28 02:46 · Score: 3, Informative
  
  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 (at STP), or about 35,000 kg. (This reference 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.
6. Re:Um, they used what? by O('_')O_Bush · 2012-12-28 02:48 · Score: 4, Informative
  
  More importantly, some Xenon isotopes are common byproducts of our current fission reactors.
  
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7. Re:Um, they used what? by 19thNervousBreakdown · 2012-12-28 02:48 · Score: 1
  
  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?
  
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8. Re:Um, they used what? by compro01 · 2012-12-28 02:48 · Score: 2
  
  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.
  
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9. Re:Um, they used what? by Rockoon · 2012-12-28 02:53 · Score: 3, Interesting
  
  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.
  
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10. Re:Um, they used what? by compro01 · 2012-12-28 02:54 · Score: 3, Informative
  
  is there some sort of standard I don't know about?
  Yes. Standard temperature and pressure.
  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.
  
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11. Re:Um, they used what? by RevDisk · 2012-12-28 03:00 · Score: 1
  
  Xenon in atmosphere is 1 part per 11.5 million, and our atmosphere is about 5×10^18 kg. So rough guess is about 400,000,000,000 kg of xenon is left. Which is only about 240 million units of that amount of propellant. Happy news is that it's quite plentiful on Jupiter.
12. Re:Um, they used what? by RevDisk · 2012-12-28 03:03 · Score: 1
  
  520 million units, rather. Friggin English/metric. Sorry about that. Again, very rough estimated.
13. Re:Um, they used what? by davydagger · 2012-12-28 03:03 · Score: 4, Informative
  
  "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
14. Re:Um, they used what? by Anonymous Coward · 2012-12-28 03:15 · Score: 1, Interesting
  
  That's about a $1 Million dollars worth of Xenon. Now, if they used mono-isotopic Xenon, they could improve the efficiency probably by a factor of two, which would cut way down on launch and carrying costs. But Xe-136, if it could be gathered in that amount, would cost over a Billion.
  As long as I'm throwing millions and billions around, I should point out that the quantity of Xenon available is in the range of millions to billions of Kilograms. It's just difficult and expensive to purify. Unless we let an improperly run Nuclear Reactor make it for us. All the hot isotopes decay away rapidly, into chemically separable daughters, which leaves an enriched Xe-136 feedstock.
  (My numbers may be way off; It's been a few years since I worked in those fields. If Xenon looks expensive... I once had to guard and supervise the purification of four grams of Calcium-48. It was, theoretically at least, (We were the only people on Earth using it.), worth about $1 Million a _gram_.)
15. Re:Um, they used what? by Anonymous Coward · 2012-12-28 03:32 · Score: 0
  
  Shouldn't be hard to switch to something else when we ru out of Xenon.
16. Re:Um, they used what? by 50000BTU_barbecue · 2012-12-28 04:03 · Score: 1
  
  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.
  
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17. Re:Um, they used what? by jo_ham · 2012-12-28 04:34 · Score: 2
  
  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.
18. Re:Um, they used what? by jo_ham · 2012-12-28 04:41 · Score: 2
  
  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, despite its low partial pressure.
19. Re:Um, they used what? by Anonymous Coward · 2012-12-28 04:58 · Score: 1
  
  And every molecule of xenon used in this experiment... went back into the atmosphere.
20. Re:Um, they used what? by Anonymous Coward · 2012-12-28 05:22 · Score: 0
  
  Probably was recycled.
21. Re: Um, they used what? by JoeRobe · 2012-12-28 06:46 · Score: 1
  
  Why would isotopic purification increase the efficiency by a factor of 2?
  
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  The best way to predict the future is to invent it.
22. Re:Um, they used what? by HiThere · 2012-12-28 07:16 · Score: 3, Informative
  
  For the engine they probably store it as a liquid. Significantly below the transition point. On Earth that's not much of a problem, and in space not much of one either...unless you get near the sun. 165K seems to be cool enough.
  Quote from Wikipedia:
  
  Xenon is the preferred propellant for ion propulsion of spacecraft because of its low ionization potential per atomic weight, and its ability to be stored as a liquid at near room temperature (under high pressure) yet be easily converted back into a gas to
  
  Note, however, that ion engines can theoretically work with any atom. Personally, I think they should be designed to use some common heavy element, like iron, and to accelerate the ions maximally. This, however, is an eventual design goal, not something to aim for in the next decade or so.
  
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23. Re:Um, they used what? by Anonymous Coward · 2012-12-28 08:00 · Score: 0
  
  I prefer the Transamerican Union of Pure and Applied Chemistry bit either way, no Biggie.
24. Re:Um, they used what? by Sardaukar86 · 2012-12-28 10:13 · Score: 1
  I know little about the topic so was wondering if someone might comment on whether a concept might be currently possible or likely to be possible within a decade or so. It seems to me we have a (theoretical) propulsion for Solar sailcraft that works on the principle of directing concentrated energy beams from the Earth to a collector on the spacecraft itself.
  I'm also assuming the following, which may or may not be correct:
  
  o Ion engines need a store of reaction mass and the electricity to run their grid, however the electrical needs are fairly modest as you point out.
  o Tuned microwave beams are capable of effectively moving electricity from source to destination
  o Technology is at the stage where a sat could be tracked across the visible sky and accurately targeted by an energy beam
  If the above isn't too wildly inaccurate, I am wondering if this might allow us to design satellites that carry no power source of their own; onboard fuel and solar panels give way to banks of capacitors and stored reaction mass for the ion thruster. Would this allow us to leave satellites in orbit for much greater periods of time, powering it from the ground this way?
  Would it even be worth it given how cheap sat-to-space deployment is becoming?
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25. Re: Um, they used what? by Anonymous Coward · 2012-12-28 13:28 · Score: 0
  
  "Why would isotopic purification increase the efficiency by a factor of 2?"
  Plasma optics. Mono-isotopic propellent is easier to focus precisely, with much less loss from other isotopic ions banging away on the chamber walls or focussing elements, not only losing potential propellant force, but also for allowing lighter components; high energy ions have a nasty habit of eroding whatever they hit.
  An intriguing proposal is a few kilograms of Radium-226, which alpha-decays to Radon 222, which would be a most excellent propellent. (It's all about mass.) With a half life of 1600 years, Radium-226 is perfectly suited for long, long, term missions.
  There are certain... safety... issues with this approach, however.
26. Re:Um, they used what? by Hadlock · 2012-12-28 13:41 · Score: 1
  
  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.
  
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27. Re: Um, they used what? by Hadlock · 2012-12-28 13:46 · Score: 1
  
  If I had to guess, the isotopic version is probably missing or has an extra ion (or two or three), which makes it easier for the ion engine to accelerate it using the same power output. The mass difference is probably negilible, but you could accelerate the same mass using less power (say, 3.5kw instead of 7kw)
  
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28. Re:Um, they used what? by Anonymous Coward · 2012-12-28 14:45 · Score: 0
  
  Sardaukar86 you know what google tells you. Nothing more.
29. Re:Um, they used what? by Anonymous Coward · 2012-12-28 17:04 · Score: 0
  
  Hah. If you think plain old helium is getting expensive, try helium-3, whose only commercial source is aging thermonuclear weapons. Thousands of dollars per liter, and each liter masses something like an eighth of a gram.
30. Re: Um, they used what? by JoeRobe · 2012-12-29 02:44 · Score: 1
  
  I'm a mass spec guy, so I certainly agree that different masses will focus differently. But in the ion drive schematics I see online, I don't see where there is a focussing step. The plasma is made, then just accelerated across a planar electrostatic voltage drop. No focussing needed. I'm also not seeing a x2 increase just from a slightly better ability to focus even if that did matter.
  
  --
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If only it could use a cheaper reaction mass by Anonymous Coward · 2012-12-28 02:10 · Score: 0

xenon is a rather rare gas...
1. Re:If only it could use a cheaper reaction mass by Anonymous Coward · 2012-12-28 03:45 · Score: 1
  
  Strictly speaking, that's not correct, because a significant amount of xenon is generated during uranium fission reactions and some of that will decay to stable Xe isotopes. I don't know if that is possible to recover in commercial quantities at a reasonable price, but there are ways to do it.
2. Re:If only it could use a cheaper reaction mass by jandrese · 2012-12-28 04:10 · Score: 1
  
  Depends, if the Xenon is shot back at Earth it could re-enter the atmosphere and be ready to be extracted again.
  
  --
  
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3. Re:If only it could use a cheaper reaction mass by Immerman · 2012-12-28 07:53 · Score: 2
  
  That would be pretty pointless though - pushing directly away from the planet you're orbiting just changes your orbital eccentricity, without significantly changing your orbital energy. Meaning that when you reach the opposite side of your orbit you'll be even closer to the planet than you were before. And since you'd have to be pretty close to begin with for a significant portion of your exhaust to collide with the planet that probably means you've just executed a de-orbiting maneuver. And actually, since we're talking about a very low-thrust, very long-duration engine, what we're probably doing is just continuously cancelling out the orbital adjustment we made while on the opposite side of the planet.
  
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Cool... by Anonymous Coward · 2012-12-28 02:11 · Score: 0

Now we just need something 1000X faster to make interstellar (robotic) probes practical.
1. Re:Cool... by MyLongNickName · 2012-12-28 02:22 · Score: 3, Interesting
  
  Although acceleration is not the same as speed, AC is right. Even if you assume the probe's weight is negligible, you begin to run into issues with thrust to weight of fuel. Over the five years cited in this story, the ion thruster consisting of fuel only would get you to 75km/s, or about a 14,000 year flight to alpha centauri. Scaling up doesn't help much as the ion thruster has to accelerate a larger mass.
  
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2. Re:Cool... by bzipitidoo · 2012-12-28 03:01 · Score: 4, Informative
  
  I keep hoping, but interstellar is extremely difficult. It won't happen in our lifetimes. To get to Alpha Centauri in just 70 years requires acceleration to near 0.1c. That takes way more energy than we can currently give our probes. Thinking that a gravity assist can help significantly with that is like thinking you can make your car go significantly faster by having a person stand beside the road and blow air at your back as you pass.
  Maybe we could eventually swing something on the order of 700 years. But just 70 years is really pushing the longevity of our current designs. Plutonium doesn't last long enough. In any case, how to make a probe last 700 years is only half the problem. Keeping a project alive, relevant data fresh on current media, and people trained for such a length of time would be the other half. 700 years is an awful long time for circumstance to scuttle the project. Can NASA or any other agency last that long? Can the US?
  Barring catastrophe, we will eventually do it.
  
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3. Re:Cool... by atrain728 · 2012-12-28 03:07 · Score: 3, Interesting
  
  Doesn't sound like alot, but 75km/s would still make it the fastest man-made object in history.
4. Re:Cool... by NatasRevol · 2012-12-28 03:25 · Score: 3, Informative
  
  For a more earthly comparison, it would take about 8.6 seconds to drive across Kansas at that speed.
  http://en.wikipedia.org/wiki/Kansas
  
  --
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5. Re:Cool... by smpoole7 · 2012-12-28 03:30 · Score: 3, Interesting
  
  > Thinking that a gravity assist can help significantly ...
  http://en.wikipedia.org/wiki/Gravity_assist
  Right. Most folks, even amateur space enthusiasts like us, don't really understand the gravity "slingshot" and how it works. Some have the idea that you can just accelerate like a demon toward a given planet or moon, whip around it and somehow gain all sorts of new velocity. That's not so.
  What you will gain is part of the orbital velocity of the object that you're "slingshotting" around. Nice boost and it makes a difference -- our space probes use it all the time -- but it's not some magical means by which you can accelerate to C-fractional speeds.
  
  --
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6. Re:Cool... by Anonymous Coward · 2012-12-28 03:31 · Score: 5, Funny
  
  That's still a lot of time to spend in Kansas.
7. Re:Cool... by NatasRevol · 2012-12-28 03:41 · Score: 1
  
  But it's still a lot better than the 8.6 hours it takes to drive across it.
  
  --
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8. Re:Cool... by Megane · 2012-12-28 04:05 · Score: 4, Insightful
  
  To get to Alpha Centauri in just 70 years requires acceleration to near 0.1c.
  And then to actually stop there to land on a planet requires deceleration by nearly 0.1c.
  
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9. Re:Cool... by Impy+the+Impiuos+Imp · 2012-12-28 04:30 · Score: 2
  
  A few years of economic difficulties and some populist loudmouths talking about draconian cuts, and boom! There she goes.
  
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10. Re:Cool... by Impy+the+Impiuos+Imp · 2012-12-28 04:31 · Score: 1
  
  Bullshit!
  I send photons out my flashlight way faster than that.
  
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11. Re:Cool... by Anonymous Coward · 2012-12-28 05:41 · Score: 0
  
  nah man, just jump out as you shoot past =D
12. Re:Cool... by MachineShedFred · 2012-12-28 06:10 · Score: 3, Interesting
  
  Trying to work a project for 700 years would also inevitably land you in the position of launching something that is 300 years newer that would pass your 300 year old probe long before it got to it's destination, because propulsion tech is 300 years better.
  I mean, 700 years ago was 150 years before Copernicus created his heliocentric model of the solar system, and was lambasted for it. Now we've got probes on their way out of the solar system that he was mostly correct about.
  
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13. Re:Cool... by ThatsNotPudding · 2012-12-28 06:16 · Score: 1
  
  That's still a lot of time to spend in Kansas.
  Hoo, clever! What, no Wizard of Oz reference? Those are always so insightful.
14. Re:Cool... by qwak23 · 2012-12-28 06:25 · Score: 3, Insightful
  
  The christian church (in various forms) has been around for millenia awaiting the return of their messiah. That is quite a bit of longevity. Perhaps we should convert NASA to a religion, then there will be no problem having someone wait a few hundred years for the return of their white metallic savior.
15. Re:Cool... by geekymachoman · 2012-12-28 07:10 · Score: 1
  
  >> Barring catastrophe, we will eventually do it.
  And where did you pick that up ? On the last 50 tv shows/sci-fi movies that you looked .. ?
  You could just as easily say we're all dead. Both statements are dellusional, unfortunately influenced by above mentioned that influenced you to think this way.
  Offtopic, but relevant in some sort of abstract way: Then people wonder why media can influence people opinion (to give a green light) when it comes to bombing 20 countries in 10 years.
  And my personal opinion.. I consider you arrogant people guilty of war crimes, suffering, poverty, and everything else negative on this country. Fuck Bush and Obama what you are.
16. Re:Cool... by atrain728 · 2012-12-28 07:33 · Score: 2
  
  Through hardship to the stars! (Kansas state motto)
17. Re:Cool... by HiThere · 2012-12-28 07:40 · Score: 1
  
  I really doubt that "we", i.e., the stay-at-homes, will ever do it. The only way to have a project last for 700 years is to inspire true commitment. A colony ship might work, but but the time they got there, they wouldn't be interested in living on a planet, and this would need to be planned for. (And by planned for, I don't mean rig things to coerce them.)
  The other possibility that I see is that an AI could be designed that WOULD maintain focus for that long and longer.
  OTOH, if we don't choose to remain confined to Earth, the people will eventually be spending their lives in self-contained colony worlds. Given sufficient energy sources (independent of the sun) eventually some of them will choose to leave the area. Either political or religious disagreements would work as a reason. Speed of travel will be less important than safety, but speed of becoming "lost" might be vitally important, depending on the reason for leaving. I'm not sure they would be particularly interested in other suns, but they'd be interested in the matter that circles them...still, brown dwarfs might be just as good, or wandering planetoids. (Planets will be less desireable, because they are more difficult to extract resources from.) Note that while wandering, a high speed will be very undesireable. You want to be moving fast enough to reach new resources but not so fast that you pass them faster than you can take what you want from them. Still, suns will be areas dense in usable resources.
  This concept has been called "MacroLife". When the wandering colony encounters a rich resource, it builds a new colony or so and splits, reproducing. It probably requires controlled fusion to make it work, but it might work in a limited way with only fission power.
  
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18. Re:Cool... by RivenAleem · 2012-12-28 10:09 · Score: 1
  
  Isn't this where your Bussard collectors come in. Now, I understand that there's not likely to be a lot of Xenon in interstellar space, but it's possible that once NEXT is producing plenty of data, we can figure out how to get something working with hydrogen.
19. Re:Cool... by Hadlock · 2012-12-28 14:26 · Score: 1
  
  This is somewhat disingenuous. Physics is physics and rocket technology hasn't improved much since the Centaur (hydrogen rocket) engine in the mid-1960s because they're already getting close to the theoretical maximum energy from chemical rockets. This is sort of like saying we shouldn't develop spoons and forks at the turn of the last millennium because by 1935 we'll have developed the spork. Cutlery has been a mature technology for about two thousand years now, and you can't really improve on it. Short of FTL travel we're looking at scramjets and multigenerational probes.
  
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20. Re:Cool... by Anonymous Coward · 2012-12-28 19:53 · Score: 0
  
  The christian church (in various forms) has been around for millenia awaiting the return of their messiah. That is quite a bit of longevity. Perhaps we should convert NASA to a religion, then there will be no problem having someone wait a few hundred years for the return of their white metallic savior.
  I, for one, am willing to accept Robo-Jesus as my personal messiah-bot.
  Ooh, my captcha is "rusting." The slashdot server is a non-believer! Shun him!
21. Re:Cool... by shani · 2012-12-28 21:56 · Score: 1
  
  This is somewhat disingenuous. Physics is physics and rocket technology hasn't improved much since the Centaur (hydrogen rocket) engine in the mid-1960s because they're already getting close to the theoretical maximum energy from chemical rockets. This is sort of like saying we shouldn't develop spoons and forks at the turn of the last millennium because by 1935 we'll have developed the spork. Cutlery has been a mature technology for about two thousand years now, and you can't really improve on it. Short of FTL travel we're looking at scramjets and multigenerational probes.
  Cutlery has changed significantly, even in the 700 year period we were discussing:
  Slate article
  I'm not sure how it affects your argument, but perhaps you should try to find an example of something that hasn't changed significantly in the past 700 years.
22. Re:Cool... by Anonymous Coward · 2012-12-29 03:27 · Score: 0
  
  are you sure that the cutlery changed, or has it been the change in lifestyle of the cutlery user that changed? A fork is a adapted spoon. the wedge or scraping of food, is name changed to present a knife, now it appears we have fewer tools, and more utinsels. Just because a tool is modiied for appearence does not make it more useful, just adapeted. Changed. But its still juuuut the tool that it started as,a modified scraper rock, in the hands of a monkey, or a bird.
23. Re:Cool... by DangerousDriver · 2012-12-29 05:13 · Score: 1
  
  Isn't 0.1c a velocity?
24. Re:Cool... by MachineShedFred · 2013-01-02 00:53 · Score: 1
  
  Because new ideas never happen, right?
  There probably was once someone who said that the telephone could never be improved, because a human can only talk so fast. Then digital communications happened.
  Just because you and I can't think of it, doesn't mean it won't happen.
  
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Turn To Slide 6 For Recent Updates by bwohlgemuth · 2012-12-28 02:25 · Score: 1

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.

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Why no ion thrusters on satellites? by storkus · 2012-12-28 03:09 · Score: 1

This is a question I've wondered for years and have never seen answered: why can't chemical thrusters used on satellites (particularly in geostationary orbit) be replaced with ion ones? It seems to me that running out of fuel is the primary method of "death" for a geostationary satellite. Do station-keeping maneuvers really require that much thrust?
1. Re:Why no ion thrusters on satellites? by belthize · 2012-12-28 04:02 · Score: 3, Informative
  
  They are used on satellites. http://en.wikipedia.org/wiki/Ion_thruster#Operational_missions
Cool by maroberts · 2012-12-28 03:09 · Score: 0

Imagine 2 of these engines in a single pilot machine, equipped with lasers and with a solar panel on each side for electricity generation and to shield the body from excess solar radiation. We could call it a TIE Fighter....

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1. Re:Cool by jandrese · 2012-12-28 04:16 · Score: 5, Funny
  
  The villainous Tie fighter pilot straps in, ready to squash the rebellion once and for all. He charges his heavy blasters, straps into the seat, and twists the knob for full throttle, feeling the exhilarating rush of a barely perceptible acceleration and the knowledge that in two or three years time he will be moving at a pretty good clip, just so long as he never has to change directions.
  
  --
  
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2. Re:Cool by Anonymous Coward · 2012-12-28 04:30 · Score: 0
  
  The only problem with this is that a dogfight above a hypothetical artificial moon would take months to conclude.
3. Re:Cool by TFAFalcon · 2012-12-28 04:40 · Score: 1
  
  Nah, we'll need to give them a bit more thrust before they become useful. Considering the fighter itself has no life support, the pilot will be dead before he gets to above walking pace if we use the current model.
4. Re:Cool by Immerman · 2012-12-28 08:14 · Score: 1
  
  Hardly, if both sides had such low-power ion-drives the defenders couldn't even get off the surface and would be sitting ducks. As long the rebels could avoid the moon's point-defense systems they could just eject annoying droids at sensitive targets until the whole place came crumbling down.
  
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Xenon? by slashmydots · 2012-12-28 03:15 · Score: 1

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?
1. Re:Xenon? by wbr1 · 2012-12-28 03:24 · Score: 3, Funny
  
  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
  http://en.wikipedia.org/wiki/Xenon
  You figure out the rest.
  
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2. Re:Xenon? by burisch_research · 2012-12-28 04:43 · Score: 4, Informative
  
  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.
  
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3. Re:Xenon? by jo_ham · 2012-12-28 04:50 · Score: 5, Informative
  
  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.
4. Re:Xenon? by neurocutie · 2012-12-28 04:57 · Score: 1
  
  Recall the existence of all those xenon arc bulbs in photo flash and strobe lights and the answer is obvious...
5. Re:Xenon? by spectral7 · 2012-12-28 05:44 · Score: 1
  
  Ion thrusters don't depend on chemical reactions. Ionization is through colliding a high-energy electron with the propellant, and then the ionized propellant is accelerated.
  Using hydrogen is pretty dumb because you're trying to generate thrust. F=ma. Hydrogen has low mass.
6. Re:Xenon? by AK+Marc · 2012-12-28 07:30 · Score: 1
  
  Hydrogen isn't that dumb if you don't have to haul around your own fuel. Scoop out the particles you run across and accelerate them out the back, even if they are "just" hydrogen.
  
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7. Re:Xenon? by tibit · 2012-12-28 08:49 · Score: 1
  
  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.
  
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8. Re:Xenon? by mike.mondy · 2012-12-28 09:52 · Score: 1
  
  Mercury is nasty? ... I still have a few grams of mercury stored for experiments ... Why wouldn't I want to be around it? It's stored in sealed glass containers, in secure storage.
  You'll become as mad as a hatter
  Apologies for ignoring your "sealed glass container".
9. Re:Xenon? by mike.mondy · 2012-12-28 09:56 · Score: 1
  
  Sorry, bad link; should have been mad as a hatter
10. Re:Xenon? by Anonymous Coward · 2012-12-28 19:49 · Score: 0
  
  The Bussard ramjet won't work. Energy losses to Bremsstrahlung radiation eat up your gains from gathering the hydrogen, making the whole scoop idea a net loss of energy.
11. Re:Xenon? by AK+Marc · 2012-12-28 23:19 · Score: 1
  
  So if I'm traveling 0.1c and scoop up hydrogen at relative rest, then shoot it out the back at .2c, I'll be slowing down?
  
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12. Re:Xenon? by Anonymous Coward · 2012-12-28 23:59 · Score: 0
  
  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.
  Think lauch gone wrong and a ton of mercury polluting a randomly selected town of Florida. It's a nasty substance.
  Versus a ton of Xenon doing no environmental damage at all.
13. Re:Xenon? by dkf · 2012-12-29 01:19 · Score: 1
  
  Versus a ton of Xenon doing no environmental damage at all.
  There's a potential hazard as all that gas will probably slump straight down (being really heavy by comparison with nitrogen and oxygen molecules) and present a risk of anoxia for every living thing in the immediate area. Yes, it would dissipate fairly quickly but the immediate vicinity would be temporarily quite hazardous. Compare with what happens when a crater lake belches carbon dioxide (admittedly in much larger quantities) that can kill substantial numbers of people. CO2 isn't as dense as Xe (which would be cold even after an explosion due to the cooling of gas expansion) so we can expect similar effects, though with even less warning as Xe is completely inert in a biological setting.
  Mind you, the best risk mitigation strategy would be to just keep everyone away from the rocket launch site which we already do. By the time you get to a kilometer away, the zone of oxygen depletion would be pretty thin; any real hazard would be mainly in any low-lying areas (e.g. watercourses) towards the site's edge where pooling could override the general dissipation due to diffusion and spreading. A sea launch, or a launch from a suitable coastal site, would probably be a good mitigation.
  
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14. Re:Xenon? by Anonymous Coward · 2012-12-29 06:09 · Score: 0
  
  Oh you could still accelerate, as long as you have fuel to add to the equation. The acceleration you can get per particle is less than what you lose when the particle hits your scoop. Thus, your ramjet needs to carry some other fuel, which makes it not a ramjet anymore, but a big, clumsy, expensive Rube Goldberg rocket.
15. Re:Xenon? by AK+Marc · 2012-12-29 07:49 · Score: 1
  
  I was talking about using the hydrogen as the fuel, but not the energy source (i.e. have a nuclear power plant for the actual ionizing). The other poster assumed I was talking about a specific implementation of hydrogen scooping, and attacked something I never said. Also, you are asserting that I'm discussing a ramjet. Again, I said no such thing. Apparently, everyone is not thinking about what I said, but what they heard about things that sound like what I said.
  
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16. Re:Xenon? by Anonymous Coward · 2012-12-30 05:47 · Score: 0
  
  So your idea is basically a Bussard ramjet, only worse, since you're not even going to fuse the hydrogen but just toss it out the back? The scoop without the ramjet part? Like a paddlewheel boat in space?
  That would never work! The energy losses due to Bremsstrahlung outweigh what you can get from proton-proton fusion by a factor of over a billion; a ramjet may be workable with the carbon-nitrogen-oxygen catalytic fusion process, but just catching hydrogen costs you huge amounts of momentum. Remember those particles will often be hitting your magnetic scoop at relatively high fractions of c, far faster than what you're going to get from your engine, so the incoming particles will reduce your speed far beyond what little acceleration you can get from flinging those tiny things out back with your ion engine.
17. Re:Xenon? by AK+Marc · 2013-01-01 16:25 · Score: 1
  
  You are wrong. You laugh at how little you'll gain flinging those tiny things out the back, but think that pulling them in they are going to slow you down. Are they so tiny as to not accelerate you, or so heavy that they will decelerate you? You can't have both. And the Bremsstrahlung works perpendicular to the pull, so it isn't even directly decelerating, so much smaller than the effect of accelerating them out the back. And further, you make a number of incorrect assumptions about ion drives, in that an ion drive doesn't need to greatly concentrate the particles as a fusion ramjet does. I think someone just learned a big word and says "Bremsstrahlung" every chance he gets. How cute. Billy learned a new word today.
  
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18. Re:Xenon? by Anonymous Coward · 2013-01-04 05:09 · Score: 0
  
  Let me reiterate: Those particles will often be hitting your magnetic scoop at relatively high fractions of c, far faster than what you're going to get from your engine. And yes, Bremsstrahlung works perpendicular, but if you think that makes the effect zero, maybe you should consider what perpendicular means in the context of your scoop. (I have no idea where you got the part about concentrating the particles.)
  And if we're doing the insulting e-psychiatrist bit now, I think someone just slapped two different rocketry ideas together and thinks it's clever -- but you've really just created a terrible hybrid, with none of the strengths of either design. You've got a very low impulse ion drive using one of the worst propellants available, and you're trying to use it to drive the weight of a ramjet scoop setup that's now carrying its own nuclear fuel for some reason, and yet you think you've got some kind of workable design. The length of time you'd have to run this thing to catch enough hydrogen to outweigh your scoop hardware is going to be ridiculous.
  I'm posting with a terrible head cold, and I can still see this isn't going to work.
19. Re:Xenon? by AK+Marc · 2013-01-04 07:21 · Score: 1
  
  Let me reiterate: Those particles will often be hitting your magnetic scoop at relatively high fractions of c, far faster than what you're going to get from your engine.
  
  I've constantly used 0.1c as a number for speed, so I'll continue with that here. I've also used the explicit example of traveling 0.1c and expelling the particles at 0.2c. You are telling me that 0.1c is greater than 0.5c, and that 0.2c is smaller than 0.1c.
  
  I think you are full of shit and looking for an arguement about nothing, and you are willing to lie to feel smart because you heard about "Bremsstrahlung" once, and it makes you feel smarter to work it into as many conversations as possible.
  
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20. Re:Xenon? by Anonymous Coward · 2013-01-06 07:06 · Score: 0
  
  Ah, your mistake is thinking that all particles in the interstellar medium are in some sort of cosmic rest state, and so will all be striking your vessel at exactly the speed you are travelling. This is false; the average particle close to a star will be as you expect, having been expelled from the star itself at a similar velocity to the rest of the stellar medium, but out in the vast gulf between the stars are particles who came from other stars long ago, stars with greatly different velocities. Quite a few of them will have been expelled from novas and supernovas, and thanks to the vast emptiness of space, will still be going at incredible speeds ages after the event. This is a major impediment to interstellar travel.
  Also, you'd probably do better in arguments if you didn't try to insult people and ascribe various unseemly characteristics to them. It doesn't help -- whether I'm "full of shit and looking for an argument about nothing" doesn't actually say anything about whether I'm right or wrong in this instance, so repeatedly making the accusation just makes you sound like a douchebag.
Soviet Russia by Anonymous Coward · 2012-12-28 05:19 · Score: 0

In Soviet Russia ions thrust you! ooooh, wait a minute.....
Ion Thrusters by Brad1138 · 2012-12-28 06:43 · Score: 1

I just like saying it, it sounds so cool. Ion Thrusters....

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But is it valuable? by Immerman · 2012-12-28 08:06 · Score: 1

Sure, it's not the cheapest reaction mass, but at 220 Watt-hour/liter it's not exactly terribly expensive to extract from the atmosphere, and it is well suited to ion-drive use.
What I wonder is is it actually a particularly valuable substance (usefulness as opposed to price) for anything else, or can we go ahead and use up the planet's supply* as spacecraft "fuel" in good conscience. From what I can tell it's used primarily for lighting, radiation detectors, and as a general anesthetic (How does that work? I'd expect a noble gas to be biologically inert.) All applications for which plenty of other options are available. Unlike helium which has many unique properties that make it extremely valuable and a real shame to waste in party balloons just because it's inexpensive (since helium readily escapes into space every gram we vent into the atmosphere is gone forever)
*admittedly a long-term consideration, and likely we'll have found other sources long before it's an issue

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Hydrogen stacks up really well by Immerman · 2012-12-28 08:47 · Score: 1

Actually you're probably better stripping off the electrons than trying to add them. A naive ion thruster consists of two high-voltage electrodes - the positive electrode strips off some electrons from colliding neutral atoms, which then get powerfully attracted to the negative electrode while applying an equal-but-opposite force to the thruster itself (See "lifters", a fun hovering ion-drive you can build in your garage, assuming you're competent to play with tens of thousands of volts)
The critical evaluation of the "effectiveness" of the reaction mass is the charge per mass - i.e. neutrons are "wasted" mass in the ions since they don't contribute to the accelerating force. Likewise any inner-shell (firmly attached) electrons that you fail to strip from the ions effectively neutralize the same number of protons. By that measure hydrogen is as good as it gets - it has no neutrons and its single electron is easy to strip away giving you the maximum possible charge per unit mass. The only problem with hydrogen is that it's devilishly difficult to store - as a gas it's extremely low-density, liquifying it requires high pressures or extremely low temperatures, and it's small size allows it to seep right through even even thick steel walls. It's the added mass of the container that makes it unattractive as a reaction mass. Well, that and its reactivity - something like xenon that's relatively dense and inert is much easier and safer to work with.
Your F=ma argument amounts to "which is heavier, a pound of bricks or a pound of feathers". Neither, obviously. The real question is which is it easier to carry several hundred pounds of.

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How far would it go before it ran out of fuel? by DSS11Q13 · 2012-12-28 11:52 · Score: 1

Assuming a 0 or microgravity environment, how far is "very far"?
Useful, and yet... by drwho · 2012-12-28 12:21 · Score: 1

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.
Sounds like a good delivery platform for FOCAL by Maritz · 2012-12-29 06:20 · Score: 1

The FOCAL 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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