New Ion Engine Being Tested

Dr Cool writes "A new design of spacecraft ion engine has been tested by the European Space Agency which dramatically improves performance over present thrusters and marks a major step forward in space propulsion capability. Ion engines are a form of electric propulsion and work by accelerating a beam of positively charged particles (or ions) away from the spacecraft using an electric field. ESA is currently using electric propulsion on its Moon mission, SMART-1. The new engine is over ten times more fuel efficient than the one used on SMART-1."

Re:Don't go getting any ideas

[alxkit]

http://www.news.harvard.edu/gazette/1999/02.18/lig ht.html [harvard.edu]

oh yeah?

Re:cool but

[asadodetira]

The low torque is not a big concern. In space you can rotate a spaceship any way you want by using gyroscopes.

Conservation of angular momentum says that if you turn on a gyroscope, the spaceship must start rotating in the opposite sense so the total angular momentum is the same as in the beginning. At some point you stop the gyroscope and the ship stops rotating.

YANAP...

[ArcSecond]

Think momentum, not energy.

Re:cool but

[Anonymous Coward]

Not torque in that sense, but torque as it is used in an automotive engine. A higher torque means that you can accelerate quickly from lower speeds. These are indeed a very gentle acceleration, but can achieve a very high velocity after a long time I believe these are quite energy effecient, and so can provide accelleration for pretty much the entire trip, unlike conventional thrusters which dump large amounts of fuel. Well, the Ion thrusters would at least be able to accelerate for half the trip, before they're turned around and used to decellerate for the second half (note to pedants: apply negative accelleration just sounds dumb, and it is generally understood that decellerate means to accelerate in such a manner as to reduce your velocity with respect to another object, or arbitrary "fixed" point.)

Re:Increase in the number of grids

[Nyeerrmm]

Not really, what the extra grids are doing are focusing the beams more so that they actually proceed through the grid rather than hitting it. Ions hitting the grids and causing them to collapse over time is the primary failure mode for an ion thruster, so being able to focus it more seems to allow more power to be pumped into it so that the stream is accelerated faster. I guess more grids might allow you to focus it more, but I'd guess that its a diminishing returns thing. I'm doing research with these thrusters (trying to show a particular fluid simulation, which is particularly good with parallel processing, is valid), especially for the reasons the article talks about with the testing. I think im going to try this multiple grid situation and see how it acts later.

Re:Increase in the number of grids

[Lord Crc]

Is there any reason that they couldn't just keep adding grids with varying voltages? And why are the last two voltages both low? Wouldn't it make sense to alternate them?

If you put a high-voltage grid after a low-voltage one, the ions would be repelled by it, not attracted. The voltage gradient must go in one direction: out of the thruster. I'm no scientist, but I don't think you'd gain much by adding a third couple of grids inbetween the two with a medium-voltage level. It would probably be more fruitfull to simply increase the difference between the high and low levels.

I assume the last two grids are low for the same reason the first two are high, to prevent errosion.

Re:Free Fuel?

[ichigo 2.0]

ESA is using an ion drive on the SMART-1 mission. The SMART-1 probe reached it's final destination in lunar orbit about a year ago. The engine in this news is a new improved version of the one used on the SMART-1 mission.

Also, as an European whose tax money is being spent on these ESA projects, I am slightly annoyed by the assumption that "brits" are the only ones behind ESA. The British contribution to ESA's budget is less than 14.2%, which is the portion Italy (the third biggest contributor) stands for, with the Germans (22.7%) and French (29.3%) being second and first.

Re:Old News

[angel'o'sphere]

So while the ESA is desperately trying to generate some positive press to help people forget about their recent failings the good old US of A is putting proven and effective technology into getting back to the moon.


Care to point out some of the recent failure sof ESA?

As a sidenote: the currently only ion drive propulsed moon orbiter is a european one ... From ESA not from good old US of A or NASA. And if you don't mind: its good old Europe, not good old USA ...

angel'o'sphere

Re:cool but... oranges and apples

[Jeremi]

Take the space elevator to orbit, use a little bit of conventional thrust to get out of orbit, then fire up the ion drives and eventually hop to the next planet, where your reverse the process.

Actually, in many cases you can get where you want to go with little or no thrust at all, simply by riding the elevator up past the altitude of geosynchronous orbit. The higher above that altitude you go, the greater the centrifugal force from being spun around the Earth, so it's just a matter of calculating when to let go of the elevator.

Re:Why increase grids?

[Nyeerrmm]

It's not just a question of how much thrust you get (chemical rockets are still at the top for that), its a question of specific impulse, which is basically a measure of how much propellant mass is used to attain a certain velocity change.

A chemical rocket has a specific impulse of about 300 s-400 s, while a typical ion thruster has something closer to 3000 s. This new design should be 12,000s I guess

Obviously for a larger mission than DS1 or this ESA probe, doubling them up to get more thrust is definitely a necessity, although there are limits, because each new thruster adds to the mass signficantly.

Re:cool but

[caridon20]

Even though the parrent was trying to be funny a space catapult is a sensible idea.
It would drasticly reduce the cost to throw things into space.

One idea is to put a linear acellerator on the side of mount kilimanjaro (strategic position near equator)
and use it to "kickstart" rokets. this way you can get more payload from a smaller rocket that uses less fuel. /C

Re:cool but

[DarkOx]

Well yes you could change the orientation of the craft that way. Unless you actually apply some force away from the craft you won't change the trajectory its traveling at. So all the gyroscope is going to let you do is point the craft in the direction you want and let the ion engine gradually start pussing you in that direction while you continue to travel in the old direction.

Re:210,000 m/s?!?

[deander2]

oh wait, never mind. i'm an idiot. :-P
SOL ~= 300,000 km/s, not m/s.
210,000 m/s / 300,000,000 m/s = 0.07% the speed of light
(much more believable)

Re:Charge accumulation?

[Ruie]

Does anyone know how these engines avoid accumulating a net charge over time?

They have an electron gun that shoots electrons the same way the ions go, so the net charge is close to 0.

Alleged FTL experiments

[hweimer]

"In particular, Aichmann and Nimtz have recently transmitted Mozart's 40th Symphony as frequency modulated microwaves through an 11.4 cm length of barrier wave guide at an FTL group velocity of 4.7 c, receiving audibly recognizable music from the microwave photons that survived their barrier passage. The transit time through the barrier was about 81 picoseconds and was observed to be constant for barriers with widths varying from 4.0 cm to 11.4 cm."

Nimtz is a clever PR guy but a lousy physicist. Every physics undergrad should know that both the group and phase velocity of electromagnetic waves can have arbitrary values and that this doesn't contradict special relativity. The important question is how fast information is being transmitted and for this neither the group nor the phase velocity is suitable.

Re:cool but... oranges and apples

[corngrower]

The earth already is loosing rotaional energy. Quite a bit in fact. It happens naturally. The moon has pretty much lost all its rotational energy.