Electrically Powered Space Rockets

Ion engines may be (technically) electrically powered, but I think what was meant by the question was more of "Can we make a Conventional Rocket Engine-to-Electric Engine like we used Electrical engines in CARS. The thing is something like that does not create enough force to achieve launch velocity. An electric engine can creat rotation, like a propeller or shaft but that ain't gonna take ya to space, nor is it going to work in space. You can use electricity as an accelerant or an aid, but a purely electric engine for a rocket just ain't gonna cut the mustard. You need a lot of power. And as it is, combustion is currently the way to go for straight off-the-ground shots. Now if we could establish a main launch area on the moon Ion Engines would become a big thing and would be aptly suited for such a job. But as it is a pure electric engine is just not feasible unless we can uncover some new, previously unknown use of electricity for propulsion.

Originally posted by Distortion
There is no set velocity for escape velocity because it depends on the mass of an object. The formula is 1/2 mv2 = GMm/R solving for V

Escape velocity from the surface of the earth is about 11.2 km/s. Your forgetting that within your equation is the mass of the earth which..hopefully does not compare anything in scale to the mass of the object your trying to send to space.

Also with your 1/2mv^2 side, you have to remember that kinetic energy has to equal your potential energy to keep conservation. So as you go higher and higher you have to create more and more kinetic energy, which is where the high velocity is required.

[edit on 13-9-2005 by Aether]

Originally posted by Frosty

Originally posted by Distortion
There is no set velocity for escape velocity because it depends on the mass of an object. The formula is 1/2 mv2 = GMm/R solving for V

But gravity is a constant here on earth so there should be no reason for any change in velocity, no?

Originally posted by stumason
With escape velocity, surely if you head upwards, under constant acceleration, you could get to the moon doing only 5mph...Obvously the fuel requirements for that would be enormous, but it would be possible. As long as your acceleration exceeded 1G

Isn't escape velocity only used when the object isnt under constant acceleration? I mean, you get it up too a certain speed using up your fuel. Once it is at that "escape velocity" it would require no more fuel in order to escape the Earths pull.

[edit on 12/9/05 by stumason]

Cool we both made the mistake of saying 5mph rather than the appropriate 5mps. Thankfuly only ourselves caught us.

Indeed you are correct. Escape velocity on earth is 11100 m/s no matter the mass of an object. I was thinking back to physics questions asking how much energy would be needed or acceleration given a certain amount of time.

Did some research on electric propulsion. There are many, and all having in common that they don't provide a massive amount of thrust and thus need another way to get into orbit before turning on the electric engine.

One that came up in my searches is MPD thrusters:

en.wikipedia.org...

Magneto-Plasmadynamic (MPD) thrusters are a form of electric Propulsion which use the Lorentz force (a force exerted on charged particles by magnetic and electrical fields in combination) to generate thrust. Generally, a gaseous fuel is ionized and fed into an acceleration chamber, where the magnetic and electrical fields are created using a power source. The particles are then propelled by the Lorentz force out through the exhaust chamber. Unlike chemical propulsion, there is no combustion of fuel. As with other electric propulsion variations, both specific impulse and thrust increase with power input.

Two main problems are that they STILL use up fuel (that's what you ionize then expel out the back to cause thrust in the other direction), and they have massive power requirements. Even if you solve the power problem (on-board fusion reactor or whatever), you'll still use up that precious fuel. But, the specific impulse would be much higher than chemical rockets and thus you'd eventually manage to accelerate to a speed much higher and can get there faster.

Understandably, you're probably hoping for an electric rocket that doesn't require the using up of fuel for the purposes of expelling it (except perhaps whatever fuel is being used to generate the electricity, such as that which is found in a fission reactor). i.e. as long as electricity is SOMEHOW put into the system, it thrusts in one direction. That'd be most awesome to have!

Unfortunately, I know of no way of doing this. All techniques except solar sail types require expelling mass out one side, so the expellant gets used up. With this approach, the best you can hope to do is to increase the amount of force (well, actually the "specifc impulse") you get from it. Expelling by burning chemicals, heating them up and going out one end is the most quick and dirty way to do it but not the most efficient.

Heating up the fuel by use of a fission reactor and then expelling the heated gasses works quite a bit better than chemicals; more force for the same volume of fuel. They still haven't done any missions like this even though the technology is readily available.

A much more complex engine would use the fission reaction's byproducts as the expellent, rather than just using its heat to expel hydrogen fuel. Possible, but not ready as far as I know.

When I was a teenager, I tried pondering how one might use electric motors to provide thrust (without having to push against the ground or the air -- no wheels or propellers). I wondered if you rotated multiple gyros in just the right way if it could produce more force in one direction than another. But no matter how you do the calculations, the forces always cancel each other out. Try sitting in a wheeled chair while holding a heavy object. Shove that object away from you, and you'll go careening the other way. But try to keep up that propulsion endlessly and it won't work... try tying a string to the object and pull it back to you, then throw again. The forces will cancel out from having to pull the object back so you can throw again. Grrr.... lousy laws of physics.... grumble grumble...