Aaron Pollyea’s Science Academy: Impulse Edition

After writing about rockets, and how they can fit into your game, I decided the next logical step would be to write about something that is in everyone’s games already, impulse drives. What are they beyond what’s easy to read from Memory Alpha, and are there any areas where the show really doesn’t talk about them much? I wouldn’t be writing this if the answer was “Nope! Move on!”

First here are some basics courtesy of Trekmovie.com.


There is a big jump between rockets as spoken about previously and impulse drives seen in Enterprise. And in my mind there is a simple ‘missing link’ that fits into that area, NERVA. Nuclear Engine for Rocket Vehicle Application to spell it all out. And to make it even easier to understand it’s effectively a nuclear engine with a rocket nozzle at its end. This kind of engine, developed between the 50’s and 70’s, could provide immense amounts of Delta-V as long as the propellant would hold out. In addition, making a nuclear reactor produce power was already something most nuclear engineers were already trained to do, so a spacecraft wouldn’t require huge solar panels or fuel cell banks for onboard systems.

The Nuclear Engine for Rocket Vehicle Application (NERVA) was a nuclear thermal rocket engine development program that ran for roughly two decades. NERVA was a joint effort of the Atomic Energy Commission (AEC) and NASA.

Now, let me stray into my own head canon for a moment. The Star Trek universe seems to split away from our own soon after the airing of the Original Series. As this technology was already around and the space program seemingly was an even bigger part of the Star Trek universe, to me it seems likely these NERVA style rockets were used all the way into World War 3 and beyond, helping mankind push out into the Solar System and giving even Botany Bay the legs to be used to Khan and his Augment followers to fly into exile. These types of ‘impulse’ propulsion could easily have been onboard the Phoenix’s upper stage when Cochraine had to pilot his warp ship back to Earth.

An additional few decades of research and development of these systems could have generated some impressive propulsion systems capable of moving a crew from Earth to Mars in just a few days rather than the half a year minimum with conventional rockets.

Impulse power would truly come into its own once fusion power was made more effective for spacecraft. It’s not too clear when this occurred—before Cochrane’s flight or after—but after that point sub-light travel would have become far more effective and efficient.

parts of an engine
Fig. 001

The addition of Bussard ramscoops (See Fig. 001) on most human-produced vessels would also mean that fuel for your reactor, along with a small amount of propellant that would be generated from the reactor itself and the other trace elements floating around space, would give a far longer reach to humanities trek to the stars. The rest are things that we’ve seen in the series, the addition of subspace fields to better direct exhaust to allow a ship to slow down without having to flip and burn, multistage reactors, and using inertial dampening fields to reduce the acceleration forces felt to give a starship some truly nail-biting performance characteristics.

So, how would a Gamemaster put these types of systems into their game? Carefully, as with most high-tech wonders that we dream about. Older impulse drives that use the fission process would have all the problems of modern nuclear reactors including waste products that are fairly toxic to life. Additionally, you have these reactors operating in conditions that may not allow for easy access for repairs in more primitive craft due to the large amount of radiation shielding needed to ensure the crew may have children in the future. Though I may try to be light about this, radiation is no joking matter. Even more advanced fusion reactors may (and will) produce radiation when operating, but at least their waste product is most likely only going to be helium.

The Atomic Age!
Nuclear fission reactor

On a ship that is using fission reactors for sub-light travel, an engineer tasked with maintaining that reactor/propulsion system is most likely going to be the most highly trained person in the crew. They are also going to be the first person to die if anything even minor goes wrong, maybe by radiation poisoning or perhaps by rupturing coolant lines that will scald them to death.

On Starfleet vessels of the 22nd to 24th centuries, the only time an engineer would find themselves next to a fission reactor is when they encounter a race that hasn’t developed fusion power yet, an older vessel that hasn’t been retrofitted, or when they encounter an enthusiastic hobbyist who enjoys such devices. However, an engineer may find themselves in a situation where building a fission reactor may save lives when all they have available is radioactive material and an unpowered subspace transmitter they need to use to signal for help.

LCARSImpulsePropulsionFusion reactors for impulse drives are everywhere, and any engineer worth their salt will know how to repair and maintain them, but in the end, they would be very difficult to construct from scratch. On the other hand, it would be almost child’s play to produce a fission device capable of heating water to boiling and driving a turbine if the engineer had the means and the training.

As a Gamemaster, keep in mind the usefulness and complexities of such reactors and engines, have them in your game and make sure your players who have engineering characters know and respect the tech. Just keep in mind how they can fail, and how death won’t be painless like a warp core breach, but slow and painful like the firefighters at Chernobyl.

warp core happy
Not all warp core breaches are this jolly.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.