×

Welcome to the Slashdot Beta site -- learn more here. Use the link in the footer or click here to return to the Classic version of Slashdot.

Thank you!

Before you choose to head back to the Classic look of the site, we'd appreciate it if you share your thoughts on the Beta; your feedback is what drives our ongoing development.

Beta is different and we value you taking the time to try it out. Please take a look at the changes we've made in Beta and  learn more about it. Thanks for reading, and for making the site better!

New Ion Engine Enters Space Race

Soulskill posted about 6 years ago | from the cool-now-where-are-my-ramjets-and-warp-drives dept.

Space 168

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

cancel ×
This is a preview of your comment

No Comment Title Entered

Anonymous Coward 1 minute ago

No Comment Entered

168 comments

why xenon? (2, Interesting)

Justabit (651314) | about 6 years ago | (#23112790)

Wouldn't a heavier material like lead be more efficient at mass transfere and therefor thrust?

Re:why xenon? (-1, Flamebait)

Anonymous Coward | about 6 years ago | (#23112814)

We could always burn niggers for fuel. We can get amazing thrust and solve most of the world's crime all in one fell swoop.

Re:why xenon? (-1, Flamebait)

Anonymous Coward | about 6 years ago | (#23112834)

Racists like you would burn well, except you're too full of shit.

Re:why xenon? (-1, Flamebait)

Anonymous Coward | about 6 years ago | (#23112880)

Wow I'm amazed your nigger brain was able to learn how to use a computer. I guess you can be left behind to help scrub the toilets. The Mexicans have been slacking at that job lately.

Re:why xenon? (-1, Flamebait)

Anonymous Coward | about 6 years ago | (#23113036)

Wow, I'm amazed your mom lets you stay up this late. Didn't she ever teach you not to be such an asshole or is she a dumb-ass like you are too?

Re:why xenon? (0, Offtopic)

calebt3 (1098475) | about 6 years ago | (#23113054)

"Late" is a matter of perspective [xkcd.com] .

Anyways, it is 7:25 PM in the Pacific Time Zone right now.

Re:why xenon? (0)

Anonymous Coward | about 6 years ago | (#23113250)

Um, I think this [penny-arcade.com] is the link you're looking for.

Re:why xenon? (-1, Troll)

Anonymous Coward | about 6 years ago | (#23113082)

7:30 is late? Since when? Is this some nigger thing that I'm not understanding?

Re:why xenon? (-1, Offtopic)

Anonymous Coward | about 6 years ago | (#23113202)

Do you really think you're making an impact with your racist statements? You're just convincing the rest of the world of your own idiocy.

Re:why xenon? (3, Informative)

Anonymous Coward | about 6 years ago | (#23112926)

Wouldn't a heavier material like lead be more efficient at mass transfere and therefor thrust?
Mass has nothing to do with it. The only thing that matters is charge. If you put H+ or Xe+ in a constant electric field they will will both have the same kinetic energy once they exit (hence, something that has a 1 e charge put across a 1 V potential will have 1 eV of kinetic energy on exit). Xenon is useful because you can strip a lot of electrons off of an atom to make a highly charged ion. It is also easy to store and ionize.

Re:why xenon? (5, Insightful)

doctor_nation (924358) | about 6 years ago | (#23113112)

No, mass is important. The fact that xenon is so massive is exactly why it's used- that and the fact that it has a very low ionization potential. The only better material is mercury, but they stopped using that several years ago for obvious reasons.

Re:why xenon? (5, Informative)

evanbd (210358) | about 6 years ago | (#23113342)

It's more complicated than that. To good approximation, ion engines add energy, not momentum or velocity, to the particles they accelerate. So heavier ions leave slower, resulting in lower Isp. Thus, Xenon has relatively low Isp. However, it has the huge advantage of being easy to ionize, a gas, and nontoxic (mercury manages the first two but not the third (at ion engine pressures it's a gas), and adds the downside of tending to dissolve the engine too much).

However, for most ion engine applications, Isp isn't the primary concern -- thrust is. Ion engines easily manage more Isp than they need, but the solar cells to power them are heavy. It would be simpler and produce a shorter flight time to lower the Isp, not to mention reducing the delta-v required (orbital transfers using very long burns, as with ion engines, pay a penalty in delta-v for doing some of their burn higher in the gravity well than they have to; this can be as much as 50% iirc).

In short, Xenon is chosen because it's easy to work with and not too expensive; the heavy mass is a plus in many applications, but the reasons are more complicated than most people realize.

Re:why xenon? (2, Funny)

RobertM1968 (951074) | about 6 years ago | (#23113820)

Hmmm... I think I really need to re-watch my episodes of Star Trek TOS... I know they covered the whole Ion Engine thing in one of them... THEN I can come back and comment intelligently on this topic.

Re:why xenon? (5, Informative)

Anonymous Coward | about 6 years ago | (#23113138)

No, the only thing that matters is momentum. If you shine a 3 MW laser out the back of the spacecraft for 1 s it is only going change the momentum of the spacecraft by 3 MJ/c = 0.01 kg*m/s. If you toss a 145 g baseball out the back of your spacecraft at 30 m/s (KE of baseball = 130.5 J) you will gain 4.35 kg*m/s of momentum, 435 times what the laser would do.

In the case above p = sqrt(2m * E). While E is a function of charge alone, the momentum is a function of both mass and kinetic energy. But it is a sqrt so you need to take into account your ion charge and its mass. A +16 charge is only twice as good as a +4 charge and 16 u is only twice as good as 4 u. Once you take this into account you will find that the difference between Xenon's 131.3 u mass and lead's 207.2 u mass is not as significant as other factors (like ease of use or ease of ionization).

Re:why xenon? (1)

Anonymous Coward | about 6 years ago | (#23113172)

If you toss a 145 g baseball out the back of your spacecraft at 30 m/s (KE of baseball = 130.5 J)
Whoops, I failed to divide by 2. s/130.5/65.25/

Re:why xenon? (1, Insightful)

Anonymous Coward | about 6 years ago | (#23113596)

You also don't appear to be a fan of significant figures.

Re:why xenon? (5, Funny)

Nullav (1053766) | about 6 years ago | (#23113368)

So...you're proposing that we propel spacecraft with baseballs?

Re:why xenon? (4, Insightful)

jollyreaper (513215) | about 6 years ago | (#23113766)

So...you're proposing that we propel spacecraft with baseballs?
No, we're propelling our baseballs with spacecraft, depending on your frame of reference.

Re:why xenon? (0)

Anonymous Coward | about 6 years ago | (#23114790)

I know a few pitchers you can start with.

Yer both wrong/right (4, Interesting)

starglider29a (719559) | about 6 years ago | (#23113424)

The only thing that matters is VELOCITY, not momentum. Mass flow RATE. At least if the test is "efficiency". That is what we (rocket scientists) call "Specific Impulse" (Isp). When you do the Delta-V equation, it's only

DeltaV = Isp*ln (m1 - m2) if memory serves. If not, someone will fix it for me. Nothing about momentum. The difference in mass is the only factor for a given propellant/engine combo

Whatever you can get out of the poopchute the fastest is the most efficient. Without speaking of the ionization process, hydrogen is prolly the best, being the lightest, BUT it's density is so low that the mass to contain it lowers the return. Recall that Clarke's Discovery had ammonia instead of hydrogen as Sakharov propellant, because it was denser (smaller, lighter tanks). And thus, it didn't leak out after 9 years (2010 - 2001)

Xenon is probably an optimum of mass and density. Plus whatever they said about ionization.

Re:Yer both wrong/right (4, Informative)

evanbd (210358) | about 6 years ago | (#23113962)

That's ln(m1/m2); units analysis is sufficient to show your version is wrong (you can't take the log of a quantity with units in it).

The problem is that in chemical rocketry, Isp and density Isp matter, but in ion engines energy efficiency matters too. Raising the Isp raises the mass efficiency, but at high Isp the energy efficiency drops. Since the solar cells and power electronics are heavy, energy efficiency matters. For most current applications, ion engines have more Isp than they need, even with xenon. Besides, excessively long burn times add a delta-v penalty for doing too much of the burn high in the gravity well.

Re:Yer both wrong/right (1)

starglider29a (719559) | about 6 years ago | (#23114086)

Thanks for the correction. These days, I'm doing more with ASP than ISP. In fact, ISP now means something else.

Re:why xenon? (1)

zippthorne (748122) | about 6 years ago | (#23113826)

Ah, but how many baseballs can you carry on your spacecraft?

What about photons? ..
there are many kinds of efficiency. You must always remember to be most efficient with the thing you have the least of.

Re:why xenon? (3, Informative)

mk_is_here (912747) | about 6 years ago | (#23113070)

From wikipedia [wikipedia.org] :
Xenon is the preferred fuel 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 fuel the engine. The inert nature of xenon makes it environmentally friendly and less corrosive to an ion engine than other fuels such as mercury or caesium. Xenon was first used for satellite ion engines during the 1970s. It was later employed as a propellant for Europe's SMART-1 spacecraft[16] and for the three ion propulsion engines on NASA's Dawn Spacecraft.

Re:why xenon? (4, Informative)

zippthorne (748122) | about 6 years ago | (#23113228)

Smaller molecular weight typically preferred for space thrusters, due to the higher exhaust velocities for similar amounts of energy or momentum imparted. p=mv and E=mv^2 and all.

Which in turn means higher specific impulse.

Which in turn means greater delta-v budget for the same mass.

The price for pushing fewer molecules at higher speeds? Lower thrust at the same power level. But if you've got "unlimited" energy (solar) or "nearly unlimited" (RTG), you can take afford to take the time.

In fact, there are transfers calculated that take less time, despite taking longer to get up to speed, due to the greater delta-v.

Since double-ionzation is much more difficult than single ionization, different atoms have different work functions, and there is a limit to the electric field you can practically achieve, charge:mass ratio is a design constraint.

Re:why xenon? (3, Informative)

Manhigh (148034) | about 6 years ago | (#23113632)

When it comes to ion propellant, the important figure of merit is the ratio of ionization energy to atomic weight. For each unit of energy spent creating an ion, you want a relatively heavy ion to propel for some "oomph." Historically, mercury and argon have also been used, though they are less efficient (and in mercury simply undesirable).

oh yea (-1, Troll)

Anonymous Coward | about 6 years ago | (#23112796)

anal sex won't do anything but make your dick stink

bad idea (2, Insightful)

ILuvRamen (1026668) | about 6 years ago | (#23112804)

Xenon isn't exactly in great supply. I think they might want to rethink that and design it with a more common material. But sweet that they're finally testing an actual ion drive.

Re:bad idea (5, Informative)

wizardforce (1005805) | about 6 years ago | (#23112852)

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

Re:bad idea (5, Informative)

morgan_greywolf (835522) | about 6 years ago | (#23112970)

Xenon is apparently plentiful enough to be in most of many so-called "neon" signs: The gas that's in "neon" signage isn't always neon -- different gases are used, including argon, krypton and xenon. Neon gives a reddish-orange glow. If it's more blueish, it's probably krypton or xenon.

Re:bad idea (5, Informative)

Anonymous Coward | about 6 years ago | (#23114132)

for bluish signs it is actually argon with a touch of mercury. argon on its own is a dim purple color which is too dim to see with other lighting, but is really neat in a very dim room. the added drop of mercury causes the chemical to fluoresce bright blue. All other colors are by putting a phosphor coating on the inside of the tubes, which emits different colors when excited by the argon-mercury mixture. Neon is only used for the classic tomato orange color, or the deep red or purple which is done with different colored glass tubing. Krypton and xenon can also be excited to emit light, but they require more energy than is commercially viable, and are rather dim.

Re:bad idea (4, Informative)

actionbastard (1206160) | about 6 years ago | (#23113122)

Xenon is used because it is the heaviest of noble gases.

You'd best bone up on your Newtonian physics.

Re:bad idea (2, Insightful)

CastrTroy (595695) | about 6 years ago | (#23113306)

What about Radon. According to my periodic table [wikipedia.org] Radon would be the heaviest noble gas. Not countijng Ununoctium of course, but that's a synthetic element.

Re:bad idea (1, Insightful)

Anonymous Coward | about 6 years ago | (#23113754)

Well, Radon has some, let's say, unusual side effects, including a strange tendency to make your neon sign glow mysteriously without turning the power on....

Re:bad idea (4, Informative)

evanbd (210358) | about 6 years ago | (#23114000)

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

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

Re:bad idea (3, Informative)

davolfman (1245316) | about 6 years ago | (#23114116)

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

Re:bad idea (3, Insightful)

doctor_nation (924358) | about 6 years ago | (#23113130)

It is expensive, but it has great performance compared to almost all other materials (the one better is mercury...). Sure, you can use other materials, but the efficiency drops like a rock. I think the use of Krypton or Argon is being looked at for some thrusters (maybe not ion thrusters). Oh, and ion thrusters have been around since the 60's, and Hall thrusters before that (made by the Russians). They've flown on a lot of missions already- this one isn't at all remarkable to be honest. Deep Space 1 was a lot more impressive.

Re:bad idea (1)

Brett Buck (811747) | about 6 years ago | (#23113198)

There have been very similar drives for at least 30 years. This is just a new model. I spent all day in a meeting discussing control system issues related to the use of a very similar engine on our spacecraft.

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

          Brett

 

Re:bad idea (2, Interesting)

v1 (525388) | about 6 years ago | (#23113206)

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

I suppose the only way around this would be a solar sail, or perhaps such a thing powered by some sort of a beam (of mass, energy, or a combination of the two) from the origin.

Cool but... (1, Informative)

Fluffeh (1273756) | about 6 years ago | (#23112856)

As cool as it is, these engines are pushing the xenon gas out at over 40,000m/s, they still only push out 40kg (http://news.bbc.co.uk/2/hi/science/nature/7346789.stm)if the stuff before the fuel runs out. As much as I am all for cool new space stuff, I am also a fan of manga and sci-fi. Some of these guys should watch more Star Trek - we need THOSE sort of engines powering our experiments.

Re:Cool but... (3, Informative)

Nyeerrmm (940927) | about 6 years ago | (#23112994)

Any kind of rocket propulsion will inherently have these limits. Whether its a chemical rocket at 3000m/s with lots of thrust, an ion thruster (which aren't that uncommon, not sure why the article says it is) with 30000m/s and fractions of newtons, or something advanced like VASMIR with high exit velocities and relatively high thrust (and large power requirements), you run into the basic problem that you have to carry all your fuel with you, and the thrust you get out of it is limited by the velocity of the fuel, for which the power requirements increase my v^2 (E=1/2 m v^2).

The only ways I can see to get away from this rather immutable law of nature is to use something like solar sails, which are cool but have a lot of engineering work still needing to be done, or designing a whole new kind of physics that lets us warp space to our needs. I'm pretty sure thats how even the impulse engines work on Star Trek, since if it wasn't, the Enterprise would probably have to be mostly fuel tanks. Of course if you're working on those physics, good luck, I hope you figure out.

Re:Cool but... (1)

evanbd (210358) | about 6 years ago | (#23112998)

Alas, the energy requirements are tough. About the only option is some form of nuclear propulsion -- though there are a number of interesting varieties of nuclear. The original Orion [wikipedia.org] concept is an interesting one -- I've been reading some of the original cost estimates (pdf [nasa.gov] ), and they get quite interesting -- $3.30 per kg for a Jupiter mission, assuming reasonable costs for the plutonium. (Not 2008 dollars, and I don't know what the actual price of plutonium is these days.)

More modern interesting proposals include the nuclear salt-water rocket [wikipedia.org] and the fission fragment rocket [wikipedia.org] . Of course, neither of these is particularly well suited to in-atmosphere work, and you have to be careful where you point the exhaust (but since it's moving faster than solar escape velocity, that's a relatively simple problem).

Re:Cool but... (1)

CastrTroy (595695) | about 6 years ago | (#23113256)

Well, if you have 40 kg of fuel being propelled at 40,000 m/s out the back of the spaceship, then assuming and equal force pushing the fuel backwards pushes the spaceship forwards, this would mean that a 5000 KG spaceship would be travelling at 320 m/s, which is 1152 KM/h, which is just under Mach 1. Of course, this assumes that everything is 100% efficient.

Please feel free to correct me. I am not a physicist, and I'm probably completely wrong about this.

Still just a curiosity... (3, Insightful)

OldFish (1229566) | about 6 years ago | (#23112864)

As long as the ion drive has to carry all the mass it'll ever use it will never be useful for seriously long trips. It would need to vacuum up stray particles as a mass source for that. But it's mildly interesting anyway.

Re:Still just a curiosity... (4, Funny)

bagboy (630125) | about 6 years ago | (#23112912)

couldn't they just tie a Roomba to the back of the space craft?

Re:Still just a curiosity... (2, Funny)

JustOK (667959) | about 6 years ago | (#23113034)

It would be better on the front, but, still, it wouldn't really get into all four corners of space.

Ions and magnetic fields (1)

EmbeddedJanitor (597831) | about 6 years ago | (#23113296)

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

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

Re:Ions and magnetic fields (1)

atomicdragon (619181) | about 6 years ago | (#23113920)

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

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

Why? Magnetic field measurements are very common on plasma experiments, which can have similar or even more severe environments than this ion engine. Turning the plasma/ions off kind of defeats the purpose of most such measurements.

Re:Still just a curiosity... (1)

fractoid (1076465) | about 6 years ago | (#23114644)

Yes, but... actually, "Roomba Ramjet" sounds a lot cooler than "Bussard Ramjet", you may be on to something. Stick the roomba on the front, though, to clean up all that pesky space debris!

Re:Still just a curiosity... (1)

evanbd (210358) | about 6 years ago | (#23113050)

What kind of mission delta-v did you have in mind, exactly? Some of the modern nuclear engine proposals can get single-stage delta-v over 1% c (nuclear salt water rocket and fission fragment rocket, for example). There is some debate about whether going even that fast in interstellar space is feasible, I believe. Besides, modern analysis indicates that there isn't enough hydrogen in the local neighborhood for Bussard's proposal to work, even if you manage to build a functioning fusion reactor for it.

Re:Still just a curiosity... (2, Interesting)

Lord Apathy (584315) | about 6 years ago | (#23113918)

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

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

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

Re:Still just a curiosity... (4, Interesting)

Nyeerrmm (940927) | about 6 years ago | (#23113076)

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

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

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

Re:Still just a curiosity... (2, Interesting)

evanbd (210358) | about 6 years ago | (#23113398)

The drag problem isn't that clear cut. The reference frame isn't "spacecraft velocity" in any sense you'd normally think of it -- it's the solar wind, at ~500,000 km/s. In interstellar space it slows enough that fusion engines could easily have a higher exhaust speed, up to several % c spacecraft velocity. The problem becomes one of collecting enough hydrogen, and getting it to fuse. In-system, though, you can use the solar wind drag to your advantage, at least if you want to head outbound. Wikipedia [wikipedia.org] has a good discussion of the issues involved.

Re:Still just a curiosity... (1)

delt0r (999393) | about 6 years ago | (#23114832)

The speed of light is 300,000 km/s. So i think your figure on the solar wind velocity might just be off a tad.

Re:Still just a curiosity... (0)

Anonymous Coward | about 6 years ago | (#23114604)

Are you sure about that? My understanding regarding interplanetary missions is that most of the fuel has to be spent in getting out of Earth's gravity well, and then braking on the other side (when applicable). That sounds like something a low, constant thrust won't be able to help.

Once you're in interplanetary space, almost all of your velocity comes from the relative motion of the Earth with respect to the target. It would take order of magnitude developments in propulsion to become comparable. Is that really something our ion drive can achieve?

Re:Still just a curiosity... (0)

Anonymous Coward | about 6 years ago | (#23113394)

I think that is the whole point of an ion drive. You always need to carry all the mass on board(being that there isn't much mass in space to shoot in one direction to propel you the other-- conservation of momentum). The idea behind an ion drive is to carry much less mass and shoot it out at much higher speeds.

Re:Still just a curiosity... (1)

OldFish (1229566) | about 6 years ago | (#23114152)

well, the concept is probably doomed. The better solution is a hybrid light drive (yes, massless photons have momentum) and an ion drive that uses spent fuel as mass. Just my 2c

Re:Still just a curiosity... (1)

DerekLyons (302214) | about 6 years ago | (#23114384)

The mass of the fuel and the mass of the engine are pretty much meaningless - what kills ion engines is generally the mass of the power supply.

Ooo (3, Informative)

dreamchaser (49529) | about 6 years ago | (#23112910)

TIE Fighter's, anyone? (Twin Ion Engine, for those of you who are not true geeks)

You mean it's NOT because .... (4, Funny)

Ungrounded Lightning (62228) | about 6 years ago | (#23112982)

TIE Fighter's, anyone? (Twin Ion Engine, for those of you who are not true geeks)

You mean it's NOT because they're shaped like bow ties?

Darn!

Re:You mean it's NOT because .... (5, Funny)

coren2000 (788204) | about 6 years ago | (#23113032)

I find your lack of fashion-sense disturbing.

Re:You mean it's NOT because .... (1, Funny)

Anonymous Coward | about 6 years ago | (#23114324)

What does a Star Destroyer wear to a formal dinner? ...

A bow TIE!

Re:You mean it's NOT because .... (1)

SimonInOz (579741) | about 6 years ago | (#23114468)

TIE fighters conjures a wonderful image of two Dilberts in some sort of battle.

Evenly matched, of course.

T.I.E. (0)

Anonymous Coward | about 6 years ago | (#23112976)

In Star Wars, the name "TIE fighters" was actually an acronym for Twin Ion Engine.

So I'm wondering if this new engine makes a cool sort of tiger-roaring sound when it's running.

Cryogenic pumps can be heard in the background, whistling away like tiny steam engines.

Oh... more like a Model T, I guess. :-(

Re:T.I.E. (3, Interesting)

calebt3 (1098475) | about 6 years ago | (#23113042)

From Wikipedia [wikipedia.org] :

Sound designer Ben Burtt created the distinctive TIE fighter sound effect by combining an elephant call with a car driving on wet pavement.

No no no. Faraday effect! (4, Insightful)

Ungrounded Lightning (62228) | about 6 years ago | (#23113030)

Ion engines ... make use of the fact that a current flowing across a magnetic field creates an electric field directed sideways to the current.

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

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

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

Re:No no no. Faraday effect! (3, Informative)

Anonymous Coward | about 6 years ago | (#23113406)

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

The reason it creates an electric field is the same as the reason there is an electric field in the Hall effect. The negative ions (electrons) are much more mobile than the positive ions (charged xenon atoms), since they are much less massive-- same as in a solid, except here the positive ions are slightly mobile (not in a crystal lattice.) So, the electrons whiz away from the positive ions, causing a net electric field to form.

But, you were spot on about the hall effect, and you did recall correctly about Franklin.

Re:No no no. Faraday effect! (1)

evanbd (210358) | about 6 years ago | (#23114026)

It all depends how you do the math. In the reference frame of the magnetic field, there is a direct force on the moving charged particle, and no electric field is present beyond what the charged particle itself creates. In the frame of the particle, the magnetic field shows up as partially an electric field, which is where the force comes from (since the particle isn't moving in its own reference frame). See special relativity and the Lorentz transformation.

Twin Ion Engine (0)

Anonymous Coward | about 6 years ago | (#23113104)

I'm keeping my eyes peeled for a twin ion engine

Makes me pine for the old days... (2, Interesting)

actionbastard (1206160) | about 6 years ago | (#23113166)

of the NRX program. NRX (NERVA [NERVA - Nuclear Engine for Rocket Vehicle Application] Reactor-Experimental Research) was the engine that would power the spacecraft that was supposed to take us to Mars and beyond. Unfortunately it was cancelled because of 'environmental concerns' http://www.fas.org/nuke/space/kiwi.gif [fas.org] .

Re:Makes me pine for the old days... (0)

Anonymous Coward | about 6 years ago | (#23113462)

Unfortunately it was cancelled because of 'environmental concerns' http://www.fas.org/nuke/space/kiwi.gif [fas.org] .
Don't be a dumbass. The caption on the page that photo belongs to [fas.org] reads "This KIWI-B type reactor was deliberately destroyed on January 1965 by subjecting it to a fast excursion. This test was intended to confirm theoretical models of transient behaviour."

The project was canceled because they had an intractable exhaust problem. The engine would actually emit huge amounts of uranium and carbon from the lining of the reactor during use, creating a pollution and service life problem. It's also true that nobody wanted to risk a nuclear explosion in the atmosphere over populated areas just to make space exploration cheaper, but there were plenty of other problems with the system.

Re:Makes me pine for the old days... (1)

olman (127310) | about 6 years ago | (#23114764)

The project was canceled because they had an intractable exhaust problem. The engine would actually emit huge amounts of uranium and carbon from the lining of the reactor during use, creating a pollution and service life problem. It's also true that nobody wanted to risk a nuclear explosion in the atmosphere over populated areas just to make space exploration cheaper, but there were plenty of other problems with the system.
That was 40 years ago, thought. Doesn't mean that with all the advances we've made in materials science and with applications from fusion research nuclear propulsion shouldn't be actively researched.

Good luck proposing nucular engine project for goverment funding, thought.

In any case, sans the cool orion nuclear impulse drive, I don't think any of these things would be appropriate to do heavy lifting in atmosphere. Would be good for a propulsion when you're in the orbit for much the same reasons as ion engine, except you can have proper thrust..

Spock's Brain (0)

Anonymous Coward | about 6 years ago | (#23113174)

"Brain, brain, brain, what is brain? It is controller, is it not?"

"Either it's an atomic pile a hundred miles in every direction or ... ion power."

Not news, and not impressive (5, Informative)

doctor_nation (924358) | about 6 years ago | (#23113188)

The T5 is hardly a new thruster- it's probably been around for 10 years or more. And it's not that impressive in terms of performance for an ion thruster. More impressive ion thrusters exist, like the NSTAR thruster they used on Deep Space 1. That provided main propulsion and lasted way longer than expected, so DS1 got a lot done. Or look at the nuclear-reactor powered ion thrusters that were under development until Bush decided we were going to Mars (NEXUS and HiPEP).

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

Re:Not news, and not impressive (2, Interesting)

olman (127310) | about 6 years ago | (#23114766)

Or look at the nuclear-reactor powered ion thrusters that were under development until Bush decided we were going to Mars (NEXUS and HiPEP).
Maybe you explain to us forehead slope challenged viewers why nuclear ion engine wouldn't be perfect for something that is going to Mars?

Hit the wayback machine Mr. Peabody (1)

zazenation (1060442) | about 6 years ago | (#23113264)

I remember back in the 60s that even Jim Kirk was impressed with "Ion Power".

It followed one of those cosmic dramatic pauses after Spock gives Jim the technical skinny on the "alien vessel" and Kirk speaks out in one of his classic redundant clarifications for the home viewer and says:

"Ion Power" in a hushed, almost reverent tone. (can't remember the name of the episode, Maybe it was the one with the Gorn ---that frog head alien with asthma that Kirk nailed with the diamond/gunpowder cannon)

I mean really, he can mix matter and anti-matter at will, modulate photons into gigawatt phaser banks and he starts going all wistful over ---
"Ion Power"?

Star Trek scripts, gotta love 'em!

Like Kirk's glaring scientific faux pas where he says the " --- the magnitude is amplified ONE to the 28th power"...

Re:Hit the wayback machine Mr. Peabody (1)

scottrocket (1065416) | about 6 years ago | (#23113704)

I believe it was "Spock's Brain", but there may well have been another episode with ion power.... (Either it was ions, Scotty surmised or a nuclear pile 100 Km in diameter - yes, you do have to love them 'Trek scripts).

You know what this means... (1)

milbournosphere (1273186) | about 6 years ago | (#23113286)

Now I can finally finish the TIE Fighter thats been in my garage all these years! Now the star destroyer, that won't be so easy....

why Xenon (1)

Jeff1946 (944062) | about 6 years ago | (#23113818)

The main reason to use xenon is that you can ionize more of it due its larger size (ionization cross section), most the gas in these trusters is not ionized and is wasted. The ionization energy is insignifcant (tens of volts) compared to the expulsion voltage (tens of kilovolts).

Higher Efficiency? (2, Interesting)

Doc Ruby (173196) | about 6 years ago | (#23114064)

Are these ion engines more efficient in turning the power stored in their fuel into kinetic energy of the vehicle than the efficiency of, say, liquid fuel rockets we use to launch satellites and the Space Shuttle?

Re:Higher Efficiency? (2, Informative)

aXis100 (690904) | about 6 years ago | (#23114438)

Not so much efficiency, the main benefit is reduced weight.

Simply put, they dont have "fuel" in the conventional sense. They use electricity (which can be sources externally or generated oboard from a nuclear source) to exject a reaction mass at high speed. Over time this reaction mass will be consumed, but get far more benefit from it that they would with normal combustible fuel.

Re:Higher Efficiency? (1)

Urkki (668283) | about 6 years ago | (#23114692)

Yes, much more efficient, if by efficient you mean how much mass you need to achive certain change in velocity.

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

So you still need something with a lot of thrust to get to a stable orbit (current option: chemical rocket; future options: nuclear rockets or laser "rockets" or space elevators). Once on stable orbit, you can use all the time you want to slowly but efficiently accelerate with an ion engine.

say what now? (1)

ILuvRamen (1026668) | about 6 years ago | (#23114382)

I thought I learned in HS that no noble gasses could be ionized because all their electron shells were already perfectly full. How can Xenon run an ion drive?

Re:say what now? (2, Interesting)

Ihlosi (895663) | about 6 years ago | (#23114776)

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



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

Re:say what now? (2, Interesting)

Ihlosi (895663) | about 6 years ago | (#23114792)

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

Load More Comments
Slashdot Account

Need an Account?

Forgot your password?

Don't worry, we never post anything without your permission.

Submission Text Formatting Tips

We support a small subset of HTML, namely these tags:

  • b
  • i
  • p
  • br
  • a
  • ol
  • ul
  • li
  • dl
  • dt
  • dd
  • em
  • strong
  • tt
  • blockquote
  • div
  • quote
  • ecode

"ecode" can be used for code snippets, for example:

<ecode>    while(1) { do_something(); } </ecode>
Sign up for Slashdot Newsletters
Create a Slashdot Account

Loading...