How does an impulse engine work?

Question

And what are the possible implications of having an engine like this available for use in space exploration?

JPL has been developing these ion/impulse engines for years, but I've yet to hear and explanation that an average joe like myself can understand. I don't have a phd in astrophysics.

Answer 1

DAG is close, but I will try to simplify all this for you.

Also, FYI, Astrophysics is the study of the physics of planets, stars, and all other extra terrestrial objects in space. The only thing astrophysicists would care about as far as space craft go is how they would orbit a body... but I digress.

What you are talking about are really two different things as well. There are many types of EP (Electric Propulsion):

The three main types are:
Electro-thermal, Electro-static, and Electro-magnetic.

I won't go into to the meaning of each, but I will say that each has specific traits and processes in creating thrust.

Now, electro-static and electro-magnetic are the only EP engines that use ions to create the thrust. electro-thermal actually just electrically heats up a propellant gas to give it energy and lets it expand through a nozzle (much like a hair dryer without the fan, and obviously a little more advanced).

Anyway, back to your question:

An impulse engine is just one type of EP thruster. One specific version of this is a Pulsed Plasma Thruster, or PPT. The most used version of this thruster uses Teflon (yes the non-stick stuff) as a fuel. A spark is used to "ionize" a sheet of the Teflon (this sheet is nanometers thick and weighs nothing). This "sheet" of ionized teflon is then between 2 charged flat plates. One is being charged by some type of electric power (nuclear or otherwise). When the sheet bridges the gap the charge flows through the sheet of Teflon and plasmizes it. (That is, that so much energy is placed into it that it becomes plasma, the 4th state of matter). Without getting too technical, essentially what happens is in a circuit a current creates a magnetic field, which in turn exerts a force on charged particles. The ions in the plasma sheet feel this force and are pushed out of the nozzle of the thruster.

All of that happens in thousandths of a second. And it happens over and over again very quickly in "pulses". Providing the impulse and thurst for the engine.

I'm sorry if that got a bit technical, but I hope you get the idea.

There are many other types of EP thrusters and all work off of the same principles. Either using electro-static, electro-magnetic, or electro-thermal energies and forces to give energy to the fuel and force it out the nozzle creating the thrust.

To answer your other question:
The fact of the matter is, EP thrusters are already in use widely in satellites. The Russians have used EP since the early 70's on satellites.

The pros of EP are the extremely, EXTREMELY high efficiency of the thrusters. Isp (specific impulse, measured in seconds) is a measure of the efficiency of a rocket/EP motor. Most conventional (chemical) rockets that we know and love today have Isp's in the range of 250-450 seconds. Some EP thrusters can reach Isp's of 1,000-2,000 seconds... theoretically even up to 10,000 seconds! They also have relatively high thrust efficiencies. These types of efficiencies are very desirable on rocket motors as they reduce the weight of the overall rocket and thereby the cost.

However, the cons are the reason we don't use them widely quite yet.

One big con is thrust. Many conventional rockets reach thrusts of 1-2 million lb-force of thrust. Even more for some rockets. EP engines can reach a max (at there current development state) of maybe 1-2 lb-force of thrust... or even less.

As you can see this is a huge difference. EP is simply not powerful enough yet to be widely used on manned missions. However, it is very promising on unmanned missions. The high Isp coupled with low thrust means very little fuel is required to go reallly far. However, it takes much more time to get up to speed. And missions require greater planning and a much longer timeline with that little thrust.

The implications of such efficient engines using alternative fuels such as inert gases like Argon and Xenon, or Teflon as the case may be is huge. The issue if developing them to the point that they have comparable Thrusts to conventional rockets.

Our next step for manned rocket boosters will most likely not be EP, but nuclear thermal or nuclear pulsed engines. That a whole other story, and I'm not gonna bore you with that. Look them up on Google for more info.

Answer 2

A conventional rocket engine reaches maximum speed quickly even if the engine is left burning. The Ion engine is initially slower but continues to accelerate while the engine is engaged. Over time, the Ion engine will deliver greater velocity. Therefore the Ion engine is suited to interplanetary travel. The Ion engine was deployed in a NASA autonomous space craft Deep Space 1 (DS1). This capability enables space craft to cover greater distance in the same time and provides enhanced information gathering.

Answer 3

As far as I know, if I'm correct as to what you're asking about (I'm going on the JPL comment), the basic idea is to take some atoms, bump an electron or two off to give the atoms charge (a positive charge, to be exact), and then put the charged atoms in an electric field to accelerate them out the rear of the spacecraft, providing thrust. This works because of Newton's 3rd Law of Motion ("Every action has an equal and opposite reaction."), which means that by sending lots of atoms out the rear of the spacecraft at very high speeds, the spacecraft will be pushed in the opposite direction in order to have an "equal and opposite reaction". As to electric fields, the electric field (or the electric force) is the same one that lets you rub a baloon on your shirt and then make it stick to your hair.

Answer 4

This would not be an optimal design for an electric motor. If it was people would be selling electric motors in this configuration. The main drawback here would be friction losses from the pistons to the piston cylinders. It would wipe out most of the energy that you get from the magnetic repulsion you are talking about. Conventional electric motors are 80-95% efficient, and petrol motors are much much less efficient than that. So the moral of the story is that yea you could probably do it, but who would want to when there are so much more efficient ways of doing the same thing.

Answer 5

I think an impulse engine is a fusion plant combined with a linear accelerator. It splits atoms into ions, fuses the nuclei, and accelerates the fused nuclei and electrons in a chosen direction in order to provide rocket thrust in the opposite direction.

Answer 6

By impulse. Beats me I'm an astronaut, I don't build 'em, I just fly em.

Answer 7

It was an invention of a sci-fi TV show. There are none.