Hey all, we have a guest post from writer and scientist M.T. Reiten about the technology behind the railguns in The Expanse universe. He talked through this with me years ago, long before we were producing the show, but it’s taken this long to get his guest post written and up because he’s an actual scientist who works on government projects and we had to be sure he wasn’t violating any non-disclosure kind of stuff. But we finally have permission, so here it is!
So I was at a party with Ty Franck and talking about science fiction. Specifically ship-to-ship combat and I shared an idea that I had been playing with. Because that’s what you do at parties.
A few months previously, I had gone in to talk with my old postdoc mentor and he asked me what I thought about railguns. I thought they were cool and admitted to wanting to build a miniature-scale railgun using semiconductor industry techniques in grad school. (Not because it was useful, but because it would be fun to have a one-shot millimeter-sized launcher that would require an ultrafast laser to trigger.) Then we talked about putting a railgun as a micro-satellite launch system. This would require putting it on an airplane. We thought we had a research proposal in the making. However, nothing came of it and we moved on to other things, but the idea had stuck in my writer’s brain.
A real railgun, as you can read about on Wikipedia or see in numerous Youtube videos, uses electromagnetic forces (Lorenz Force to be precise) to accelerate a projectile. It’s somewhat related to the Jacob’s Ladders that are sometimes seen in old movies featuring a mad scientist of some flavor. Except that bit of electrical discharge passes through a conductor which moves and can be used to fling a projectile. The nice thing is that it doesn’t use chemical explosives to accelerate a kinetic projectile to very respectable velocities. And we can do it right now. (Laser weapon technology still has limitations, but that’s a whole different discussion.)
The longer the accelerating force can be applied to a projectile, the higher the muzzle velocity will be when it exits the launcher. This is why longer barreled rifles typically have a much greater range than short barreled handguns using the exact same cartridge. But space on aircraft is at a premium. So how would one extend the barrel without adding more weight?
Digging back to my original interest in railguns, I thought of ultrashort high power laser pulses in the atmosphere. The cool thing about short laser pulses is that they compress a lot of energy into a very tight package. So you end up having these photon pancakes whizzing about at (nearly) the speed of light. All very good, but what does this have to do with railguns? This many photons corresponds to a very intense electric field. This intense electric field tears apart the gas molecules in the atmosphere creating an ionized plasma. Since the laser pulse is traveling in a straight line, the plasma stretches behind the pulse resulting in a plasma channel. This plasma channel can conduct electricity. If connected to the active elements of the railgun, the plasma can become a virtual barrel, imparting extra kick to a payload. A longer barrel for an aircraft-based micro-satellite launching railgun. Problem solved, except for all the hard work that will keep a dozen engineers employed for a decade.
But I write science fiction and how would this work on a spaceship? No readily available atmosphere in space! Simple. High velocity shock of gas spurts out the railgun port. The gas expands rapidly. Pump the volume with a short pulse laser to create the virtual barrel. Carefully shape the electromagnetic pulse to keep the plasma contained. FIRE!
So the awesome visual effects, with swirling ionized gases, is based in plausibility.
M. T. Reiten (www.mtreiten.com)