Space ship propulsion drives: the power source.

A starship matter-antimatter reactor.

propulsion drive sharpenedPictured above is a schematic that I scribbled which represented a propulsion drive system. Yes, I know it isn’t on CAD but it gives you a feel for the device. In effect, this is the power supply behind the drive and not the drive itself, which i’ll describe later.

The drawing is complete with all of my usual harebrained notations and corrections. Somehow, I like drawings like this. When I worked as a mechanical design engineer, all of my stuff started like this. It’s simply the way I am most comfortable with getting all of my thoughts out onto paper.

So what is the drive all about. Well, not all of my starship travel is done superluminally (faster than light). In fact, a great deal of it is carried out in real space at speeds much slower than 3×10^8 m/s. The ships are heavy, even with the most advanced materials of construction I was prepared to imagine. I had also produced ideas for how the superluminal travel would work and needed my vessels to be able to cross into deeper space to engage their star drives. All of this meant that I had to move very large masses very rapidly around solar systems. I wanted my warships to be able to accelerate like the proverbial s**t off a shovel. That’s where the drive above stemmed from.

Firstly, to cross even the distances involved in a solar system is no mean feat. To do it in a short time is staggering. I have not attempted to ignore the currently accepted rules of physics. Newtonian physics and Relativity are not going to be violated by me, even as a sci-fi writer. That means covering 2 x 10^12 meters in a matter of days at worst. The formula s=ut + 0.5at^2 can be used to estimate the acceleration needed, so long as the final velocity does not get too close to light speed. initial velocity u can be assumed to be zero. Let’s say we want to cover the distance in a day. This means accelerating at over 50G (5oo+ m/s^2). That’s rapid. The power required by the drive is just too great to come from rockets or even nuclear fusion. My power source had to be antimatter.

If you’re dubious about the need for such a drastic fuel, let’s consider a simple bit of maths.

Force is mass times acceleration, or F=ma. Once again this works well even at the speed of 40,000 km/s that our ship is doing as it leaves the solar system. There’s no need to bother about relativity corrections just yet.

Work done is force times distance, or W=mas. Power is work done every second. Since distance per second is velocity, P=mav. Let’s say our ship is fairly small and weighs only forty tonnes.

Now lets plug in the figures. Since power is at it’s highest at highest velocity, Pmax=40,000 kg x 535 m/s^2 x 40,000,000 m/s. Thats 856 million megawatts, or 856 terawatts. The fusion reactor to produce and sustain these levels of power would be vast. The ship could not be built.

On the other hand, when antimatter collides with normal matter, it liberates energy to the tune of Einstein’s ding-dong equation, E=mC^2. Now we’re talking proper engines! Never mind burning rubber outside the shopping centre, just think how you could wreck your tyres with n antimatter engine! Burning 1 gramme per second of antimatter with the same amount of matter liberates 180 terawatts of power. That means we only need to hold a few kilogrammes of fuel in our space ships…sweet!

.In the sketch are two containers. One labelled MCO2, the other PAM CO2. This is carbon dioxide and ‘passive antimatter’ carbon dioxide.

Now we’ve entered the realms of science fiction! I had to invent ‘Passive antimatter’ because let’s face it the fuel will react to blow its own container and the entire ship to atoms, just as well as it would react in the engine. Passive antimatter does not exist, so far as I know. I invented it for the Biform Solution trilogy. In the book, the stuff is mentioned. The scientist who discovers it (one researcher is killed in the process) hated the term for the new state of matter. It is not antimatter at all, passive or otherwise. It is a state of matter that can be converted to antimatter by bombardment with a specific combination of radiation. You will see in the schematic that there are staged PAM/AM converters. These are the devices that render the PAM into a plasma of antimatter particles that are then guided by magnetic fields into the main reactor.

Follow this into the reactor, where it meets a second flow of ionised ordinary carbon-dioxide, admitted to the reactor. Shutting the reactor down involves stopping PAM flow and continuing to admit ordinary CO2 until the temperature cools and pressure builds, after which the safe gas is vented.

More about the reactor itself before we finish with it. The technology for controlling the ionised matter and antimatter by magnets already exists, though it has yet to be perfected to my unending frustration. Ying-yang magnets have already been used similarly in fusion reactors, so this bit is not fantasy. When I stated the power, I blithely ignored the fact that in a matter-antimatter reaction, around half of the energy is liberated in the form of quantum particles called neutrinos. These are particles that possess neither charge nor mass. Indeed, about the only property that they possess is spin. Trillions of these things are emitted from the sun every second and pass harmlessly through all matter. They are whizzing through your own body as you read this. I have at some stages of my writing referred to neutrino recuperation. Such devices would absorb and reclaim the power that would otherwise be lost as neutrinos fled the reactor. To do this would be unrealistic at the moment but I am writing sci-fi!

Why did I choose CO2 as the fuel? Well, it was a bit of green thinking at first, rather than something born of engineering practicality. To fuel the ships from something that is abundant and detrimental to a planet’s climate stability seemed like a good idea. Afterwards, for safety reasons and the practicality of control systems, I thought that water would be better because it would not need to be stored under pressure and would be controlled by boiling at low temperature under controlled vacuum, which would be generated by the reactor itself. I have used both ‘fuels’ in my writing.

At the bottom of the schematic is an arrow pointing to some un-drawn GAG drive. What the hell is this, when it’s at home? Ah, that’s the next lovely little bit of fusion between science fact and science fiction. More on this in the next section.


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