Electric Ion Propulsion Engines??? Huh?

[ScienceForums]

Hey everyone, how's it goin? I have a question. I was reading this article earlier:

 

Link changed to original article

http://www.eurekalert.org/pub_releases/2009-04/esa-gei040609.php

 

It's talking about an electric ion propulsion engine. Does this really work? I mean seriously, I thought in order for something to move in space it had to have something to push against???!!!!

For real, how does electricity push anything in space? Can someone please explain this for me

 

-SCIFOR

Edited April 7, 2009 by swansont
update link

[Klaynos]

You don't need "something to push against" conventional rockets don't work like that.

 

They work by throwing mass off of the back, it's a simple conversation of momentum problem, you throw something with momentum p1 out the back you need to increase your momentum by -p1 to conserve it.

 

In this case (original source: http://www.eurekalert.org/pub_releases/2009-04/esa-gei040609.php) the thing being thrown out the back is ions.

[Sisyphus]

Indeed. Ion engines are so efficient because the ions are ejected at extremely high velocity, meaning you can get more momentum while using less mass of fuel.

[SH3RL0CK]

Indeed. Ion engines are so efficient because the ions are ejected at extremely high velocity, meaning you can get more momentum while using less mass of fuel.

 

And having to use less mass of fuel means you don't have to carry as much with you in the first place (which further increases the effectiveness of the fuel you are carrying).

[insane_alien]

but the force you get isn't exactly spectacular. your looking at a few centimeters per second per hour max.

[Sisyphus]

Right, right. It's not a replacement for conventional rockets for stuff like taking off from the surface or close maneuvering. But for long trips, slow and steady does indeed win the race.

[insane_alien]

Right, right. It's not a replacement for conventional rockets for stuff like taking off from the surface or close maneuvering. But for long trips, slow and steady does indeed win the race.

 

unless you want your crew to survive the trip. taking a few years to get to mars is all fine for a probe but it would be pretty crap for an astronaut especially as conditions aren't going to be much better on mars.

[Sisyphus]

unless you want your crew to survive the trip. taking a few years to get to mars is all fine for a probe but it would be pretty crap for an astronaut especially as conditions aren't going to be much better on mars.

 

From the Wikipedia article on Mars colonization, emphasis added:

 

Mars requires less energy per unit mass (delta V) to reach from Earth than any planet except Venus. Using a Hohmann transfer orbit, a trip to Mars requires approximately nine months in space. Modified transfer trajectories that cut the travel time down to seven or six months in space are possible with incrementally higher amounts of energy and fuel compared to a Hohmann transfer orbit, and are in standard use for robotic Mars missions. Shortening the travel time below about six months requires higher delta-v and an exponentially increasing amount of fuel, and is not feasible with chemical rockets, but could become feasible with advanced spacecraft propulsion technologies not in current use, such as VASIMR,[2] and nuclear rockets, the latter of which could potentially cut the trip time down to about two weeks.[3] Another vibrant possibility would be constant-acceleration technologies such as solar sails or ion drives which would permit passage times at close approaches on the order of several weeks[/b']. Both of these are in our current stable of techniques and we could readily obtain a constant acceleration of 0.1g.

 

The point being that small, constant acceleration tends to get you where you're going a lot faster. Chemical rockets have a lot of thrust, but they can only fire for a few minutes (as opposed to months for ion propulsion), and you pretty much just have to coast the whole way and make minor adjustments when necessary.

[cameron marical]

unless you want your crew to survive the trip. taking a few years to get to mars is all fine for a probe but it would be pretty crap for an astronaut especially as conditions aren't going to be much better on mars

 

I beleive that I mentioned this in another thread:

 

Would about 2-4 meters of a solid dense material around the outside of the spaceship not block out most If not all space radiation? Therefore, the astronauts,{though crippled by weaker hearts and near hollow bones, wich back on earth wont get you very far}, could live in space and make it to mars, right?

[swansont]

Sure — that's comparable to, or greater than, reactor shielding. I think the issue is the cost of putting that into space and propelling it. More mass means less acceleration per unit thrust.

[cameron marical]

What about hollowing out a relatively small asteroid? Though that would not take care of the propulsion problem.

 

What about electricly charging the outside of a spacecraft and keeping a constant supply of electricity to it{Solar powered of course}? If i understand right, electrons take care of protons. Why would this not work?

 

Thanks for the reply.

[Moontanman]

Even in space solar power is limited, solar power is not enough for a space craft that contains humans. Even our unmanned probes are severely limited by the limits of solar power. That is why thermal nuclear power is added to most complex space craft. IE plutonium heat generated power. To generate a positive electric charge to repel the solar wind would take far more than the available solar power but it is doable with nuclear power. Fortunately in space you do not need to shield the entire reactor. The crew can live in the shadow of a small shield when the reactor is powered up or tow an unshielded reactor far behind the space craft on a tether.

[Green Xenon]

Even in space solar power is limited, solar power is not enough for a space craft that contains humans. Even our unmanned probes are severely limited by the limits of solar power. That is why thermal nuclear power is added to most complex space craft. IE plutonium heat generated power. To generate a positive electric charge to repel the solar wind would take far more than the available solar power but it is doable with nuclear power. Fortunately in space you do not need to shield the entire reactor. The crew can live in the shadow of a small shield when the reactor is powered up or tow an unshielded reactor far behind the space craft on a tether.

 

Can electric ion propulsion engines be used for automobiles?

 

As for the nuclear reactor. Hydrogen-boron fusion beats any fission, without a doubt.

 

H-B fusion is clean.

[Sisyphus]

Can electric ion propulsion engines be used for automobiles?

 

No. It generates only very small amounts of thrust. It's advantage is that it uses so little fuel (compared to chemical rockets), and so can fire continuously (again in contrast to chemical rockets, which are used up very quickly). The thrust is small enough (the ion engines that have so far employed have about as much thrust as the weight of a piece of paper) that it's really only useful in space, with almost zero friction and weeks, months, or years to accelerate. It wouldn't even move a car on the ground. And there would be no point, since cars have the advantage of not needing to be propelled by flinging mass out the back - they can push off the ground, with their wheels.

 

As for the nuclear reactor. Hydrogen-boron fusion beats any fission, without a doubt.

 

H-B fusion is clean.

 

It doesn't exist yet, though.

[Moontanman]

Then there is He3 fusion, but we'd have to go to the moon for the fuel for that.....

[CDizzle]

Yes this can work.

 

If a little light/electricity touches a certain object it pushes it ever so slightly. It works, just need a lot of electricity.

 

Look up Robert Forward’s interstellar laser sails.

 

It can give you a little idea on how this ion engine can work.

[Mike187]

I'd like to just elaborate on how the ion engine works. A ion engine/electric rocket uses essentially a radio antenna to strip the fuel's atom's of their electrons. These newly formed cations are expelled out of the engine at high velocity (~290 000m/s, VASMIR engine) using a magnetic nozzle. Unfourtunately because the mass of the cations is so small it does not accelerate very fast. As everyone has said, it has very low thrust but very high specific impulse. It can go extremely fast but needs the time to get there.

 

There is one other problem with ion engines. The speed that they can travel at diminishes over time because all those stripped electrons have to go somewhere so they are stored on the space craft as there is no ground to ground the engine. It takes a lot of voltage to keep all those electrons in check. Seen as the power supply is limited in voltage on the space craft eventually the voltage used to accelerate the ions goes down and the speed of the exhaust is less. So if that happens before the maximum speed is achieved the engine travels stays stuck at that speed even though it still can have fuel. One of the first uses of an ion engine was for the Deep Space 1 mission (Google me!).

 

I hope that helps.

 

Mike

 

Oh btw, I'm new on this forum and I cannot find the introductions section. The only one I can see that I could post an introduction is in the general section.

[D H]

From the Wikipedia article on Mars colonization:

Another vibrant possibility would be constant-acceleration technologies such as solar sails or ion drives which would permit passage times at close approaches on the order of several weeks. Both of these are in our current stable of techniques and we could readily obtain a constant acceleration of 0.1g.

I changed Sisyphus' emphasis. Neither solar sails nor ion drives are anywhere close to being in our "current stable of technologies", particularly with respect to accelerating a massive vehicle at a constant acceleration of 0.1g for several weeks. The Wiki article on Mars colonization has undergone a lot of editing since Sisyphus' post. The article currently reads "Both of these are currently feasible" rather than "Both of these are in our current stable of techniques".

 

Solar sails remain purely in the realm of science fiction. Ion propulsion has been used on small vehicles. SMART-1, which massed all of 367 kg, used a Hall effect thruster to accelerate at just under 0.00002 g. SMART-1 was launched on September 27, 2003 and achieved lunar orbit on November 15, 2004. Not exactly speedy.