Shields Up!

Steven Den Beste has a fascinating post about the critical characteristics of space warships. He approaches the question from a realistic angle, mostly relying on current technology, only extrapolating reasonable advances. He rules out the sci-fi stuff ("hyperspace," "subspace," "leap cannon," etc...) right from the start, and a few things struck me while reading it.

This post will deal with one of the things that he has (reasonably) decided not to include in his discussion: energy shields. I'm doing this mostly as a thought exercise. I've found that writing about a subject helps me learn about it, and this is something I'd like to know more about. That said, I don't know how conclusive this post will be. As it stands now, the post will raise more questions than it answers. Another post will deal with a subject I've been thinking about a lot lately, which is how unglamorous technological advance can be, and how space battles might be a good example. It sounds like a battle using the weapons and defenses described would be punctuated by long periods of waiting followed by a short burst of activity in which one side was completely disabled. There is a reason why science fiction films flaunt the rules of physics. But that is another topic for another post.

Once he discards the useless physics-defying science fiction inventions, Den Beste goes on to list a number of possible weapons, occasionally mentioning defense systems. Given that I'll be focusing on defense systems, it's worth noting the types of attacks that will need to be repelled. Here is a basic list of weapons for use in a space battle:
  • Lasers
  • Masers (Similar to lasers, but operating at microwave frequencies)
  • Particle Beams
  • Missiles (with a variety of warheads)
  • "Dumb" Projectiles
Strangely enough, I recently came across the concept of cold plasma, which may be able to shed some light on how to defend against the weapons Den Beste laid out. Cold plasma in the quantities and density required to repell attacks is not yet technologically feasible, and articles like this aren't always reliable (sometimes exaggerating the effects of new technology).

Plasma is basically a collection of molecules, atoms, electrons and positively charged ions, and it makes up 99% of the known universe. Hot plasma is present in the sun - at high temperatures hydrogen nuclei can fuse into heavier nuclei despite a mutual electric repulsion. When these particles collide in the sun, they aquire enough energy to fuse, and release a tremendous amount of energy. Unfortunately, hot plasmas are not of much use for defensive purposes, as the temperatures are too high, and would be destructive.

Colder plasmas, however, would do the trick. A plasma's charged particles interact constantly, creating localized attractions or repulsions. An external energy attack, from weapons such as lasers, high powered microwave bursts, or particle beams, would theoretically be caught up in the plasma's complex electromagnetic fields and dissapated or deflected. If the plasma could be made sufficiently dense, it could even deflect missiles and other projectiles. The process of absorbing and dissapating energy could also go a long way into defeating radar... but as Den Beste noted, IR detectors would be the primary sensor used in space, so this sort of "cloaking" ability would be of limited use.

Interestingly, such a cold plasma shield could also be applied to projectiles such as missiles, shielding them from the defensive measures Den Beste thinks would be used against them.

Unfortunately, cold plasma requires a lot of energy to produce. And since I can't seem to find an adequate explanation of what cold plasma really is or, rather, how it is produced, the use of cold plasma brings up a number of questions. My primary concern has to do with the energy needed to produce cold plasma, and how the excess heat would be dissapated. Den Beste notes:
Warships will be hot and will have to shed a lot of heat in order to avoid destroying themselves.

There are lot of ways of getting rid of waste heat, and convection is by far the easiest and most convenient. It's what cars use, and what nuclear power plants use, and what our bodies use. A fan moves air past the radiator of a car, and since the radiator is warmer than the air, it is cooled and the air is warmed. The cooling tower of a nuclear reactor sheds heat into cold water, boiling it and turning it into water vapor which is dispersed into the atmosphere. Our bodies shed heat in expelled breath, and through our skins into the air, sometimes aided by sweat.

Unfortunately, in space there's no atmosphere to convect heat into, and you have to rely on radiation.
Now, you've created a cold plasma force field around your spacecraft that could theoretically deflect electromagnetic attacks from weapons like lasers, masers, and particle beams, but what about the heat produced on your own ship? How would heat interact with the cold plasma? Would the plasma absorb the heat? If it did, wouldn't you saturate the plasma shield (after all, you'd be producing an awful lot of heat even without the massive amount of energy needed to set up the plasma field, and when you add that, couldn't you overload it)? If you surrounded your ship, how would the heat escape? Exposing the radiator would defeat the purpose of having a shield in the first place, as the radiator would be one of the primary targets.

Well, perhaps I've figured out why Den Beste ruled out energy shields in the first place. Sorry if this seemed like a waste of time, but I found it at least somewhat interesting, even if it wasn't conclusive. And I've also found a new respect for the type of theoretical discussions Den Beste is so good at... Stay tuned for a more general (and hopefully more interesting) discussion on the unglamorous march of technology.

Update: Buckethead has an excellent series of 4 posts on War in Space (one, two, three, four). I am clearly outclassed. One of these days I'll crank out that post about the unglamorous side of technology advancement, but for now, I'll leave the technical aspects in the capable hands of Den Beste and Buckethead...