What is a TIE Fighter? It's a star fighter in the Star Wars universe usually piloted by the Imperial forces. Wookiepedia has more information that you could possibly imagine about the TIE fighter. I'm pretty sure that the TIE in TIE fighter stands for Twin Ion Engine. That's what makes it different.

The TIE fighter also looks like a bow tie. This must just be a coincidence. I have seen all of the Star Wars movies and extra cartoons but I don't recall seeing a character wearing a bow tie. But what the heck are those big side panels for? One theory is that they are solar panels used to power the star fighter.

Could this be a feasible technology? Before we get to the actual TIE fighter, let's look at some physics ideas.

ION Thrusters and Solar Panels ——————————

Star Wars is probably fiction (who knows for sure), but ion thrusters are real. The basic idea is to take some matter, maybe it is xenon gas. If you can add enough energy to one of these xenon atoms, an outer electron can be ejected. What you have then is a free electron and a positively charged xenon atom, an ion.

Now you can take that ion and put it in a region with an electric field. This accelerates the ion and eventually can propel it out of the spacecraft. Since the ion started at rest (or close to at rest) but it increased in momentum, there would have to be a force exerted on the ion (from the electric field). Since forces come in pairs, a force exerted on the ion means that an equal and opposite force must be exerted on the spacecraft. Boom. There you have a thrust.

Yes, this is not a very large thrust. Typically, an ion thruster would have a magnitude somewhere around 1 Newton. of course, there is no actual limit to the force from an ion thrusters you would just have to make it bigger.

What is the difference between a conventional thruster and an ion thruster? Really, the only difference is that a conventional thruster (chemical rocket) uses a chemical reaction to eject propellant from the rocket. The effect is the same, but the process is different. Typically, a chemical rocket will have a much greater thrust but not be able to run as long. An ion thruster can be on for very long periods of time so even a small thrust force can have a significant effect on the momentum of the spacecraft.

Image: NASA. The International Space Station

Solar panels are also real. They take light (usually from the Sun) and convert it into electrical energy. How much power can you get from a solar panel? Well, that depends on how bright the light is and how big of a solar panel you have. Oh, it also depends on the efficiency of your solar panels. Here on Earth, the most best solar panels have an efficiency of around 44%. In orbit around the Earth, the sunlight gives about 1,000 Watts per square meter. Move closer to the Sun and this increases (I guess that's obvious).

Acceleration of a TIE Fighter —————————–

I would like to start by pointing out that I'm not that crazy. People (well, internet people) often state that I'm a loser because I spend too much time calculating the physics involved in things like Angry Birds and the thermal properties of Gollum.

Now let me introduce to you another person like me (there are many of us out there): Ben Clewett. Ben also likes to calculate things. He has already crunched some numbers on the TIE fighter and put it together as a nice paper. You can read his first estimation on the TIE fighter propulsion system here.

Let's go over some of the key calculations. I am going to use the same idea that Ben uses but put in my own estimates. This will give slightly different results.

Maximum Solar Power. Suppose a TIE fighter was in a region similar to the location of the Earth. If it had one of it's solar panels perpendicular to the Sun's light, it would get it's highest power. Wookiepedia lists the length of of TIE fighter at 6.4 meters. It's mostly cubical in terms of dimensions so I will say that the solar panels are squares that are 6.4 m by 6.4 meters. This gives an area of one side at 40.96 m2 and a maximum solar power of about 4 x 104 Watts.

TIE Fighter mass. Really, we just have to guess here on the mass of the star fighter. An F-16 fighter has a mass around 12,000 kg. I would suspect the TIE fighter to have a lower mass since it is more advanced and used in space (where you can use thinner materials). Let's just go with 10,000 kg for the mass.

Thrust and Power. First, for thrust this is just like a normal rocket. The change in momentum of the ejected ions over time gives a thrust force. This can be approximated in terms of the fuel mass rate:

Here I am using v i for the velocity of the ejected ions. The NASA ion engine has xenon ions leaving with a speed of 4 x 104 m/s. Maybe the TIE fighter has a thrust speed twice that value. Oh, the mass of a xenon ion would be about 2.18 x 10-25 kg. I can use this thrust along with the mass of the tie fighter to calculate the maximum acceleration.

Now, what about power? Suppose I take one ion and speed it up to eject it as thrust. How much energy would that take? It would just be the kinetic energy of that ion. Now if I do it a whole bunch of times, I can use the time interval to calculate the power.

I really want the acceleration. Let me use this power expression to get the mass rate and then rewrite the acceleration in terms of the power. This is what I get:

Now I just need the power, the mass of the TIE fighter and the ion thrust speed. Putting in these values, I get a maximum acceleration of 0.001 m/s2. That's not too great for a star fighter. Oh, maybe they also have internal batteries? Well, if that's the case the solar panels probably won't help too much. But maybe the solar panels on the side just look cool? You can't have a star fighter that doesn't look cool, so that makes sense.

Ben comes to essentially the same conclusion in his paper. Well, he doesn't say anything about the cool-factor of having these solar panels on the side.

Other Considerations of TIE Fighter Design ——————————————

Ben has other ideas too. What about maneuverability? If a star fighter's thrust is near the center of the vehicle, it would take some torque to get the thing to turn left of right. By adding these large solar panels (even if they look cool) on the side far from the center of thrust you would increase the moment of inertia making it much more difficult to turn. In short, the TIE fighter would not be very good in a dog fight.

But maybe they aren't even solar panels on the side of the TIE Fighter. What if these side panels do something different? Perhaps the TIE fighter is designed to receive power from a nearby Star Destroyer - maybe through magnetic induction. In Ben's second paper title "TIE Fighter: Propulsion through Induction" he looks at this possibility. It turns out that this is a much more feasible energy and propulsion system for a TIE fighter.