i'm in the early stages of designing a scifi game and want to use as little handwavium as possible (without ruining the fun). The first part of the game takes place in the asteroid belt and includes handwavium in the form of being able to break down just about anything into individual atoms and using a 3d printers make everything from an ingot to a fighter craft.
The intended reaction mass is blocks made of ~11.75% Invar (FeNi 64/36% 8,100kg/m³ specific heat capacity peaks at 545j/kg K at 200C Curie temp of 230C) ~88.25% silica harvested from asteroids. Depending on the ship the blocks may be as small as 0.01m³ ~30kg or as large as 1m³ ~3,000kg.
I had the thought of hitting the pellets with high powered lasers and feeding the resulting plasma through a VASIMR thruster.
Or lunching the pellets with a coilgun and hitting them with lasers in something akin to a rocket nozzle to direct the expanding gas while avoiding the whole chunks of very high speed material flying around the solar system. Would the expanding gas cause more thrust than just the momentum from the magnetic acceleration?
The smallest drone has a single 5m long coil, followed by quad 20m, quad 40m, and eight 60m for the largest thrusters.
Backstory Edit: Your ship was sent in advance to build the infrastructure for our first colony at Proxima b. The follow on ship with the colonists was scheduled to arrive 1 year after you but after 2 years the captain decided to head back and find out what was going on. FTL comms don't exist and the experimental FTL drives that we were testing maxes out at 2c and only works in interstellar space so the crew was all in cryo sleep for the trip. When you wake up you find the ship is badly damaged and floating in the asteroid belt.
Edit 2: FeNi 64/36% means the alloy is 64% iron 36% nickel. 8,100kg/m³ means a cube that is 1 meter on each side has a mass of 8,100 kg. Specific heat capacity is how much energy you can pump into the material to heat it 1C (or K). The higher it is the more you can heat it can absorb without losing necessary properties like... Curie temp is the temperature that a magnetic metal rapidly loses it's magnetism.