Slurry Carbon: The Perpetual Propellant of the Solar System

I first proposed the use of carbon nanoparticles suspended in liquid oxygen (LOX) as a monopropellant over a year ago. While its environmental footprint makes it less ideal for Earth-to-orbit launches, it is the perfect solution for my orbitally assembled deep-space rockets.

My previously proposed deep-space designs utilize cascaded "Cassette" rocket stages, which allow for precise micro-staging during long-duration missions. While liquid methane (Methalox) is a standard alternative, the Slurry Carbon monopropellant offers distinct advantages in the microgravity of orbit:

Mass Ratio Optimization: Because the engine doesn’t require a Thrust-to-Weight (T/W) ratio greater than 1 in orbit, the design can be radically simplified. Almost the entire volume of a Cassette can be allocated to propellant, yielding an exceptional fuel-to-total-mass ratio.

External Combustion: The "engine" is reduced to a simple nozzle that ejects the slurry. Since the primary combustion occurs outside the vehicle, only the bottom section of the rocket requires reinforcement.

Minimalist Plumbing: There is no need for complex piping, regenerative cooling, or turbopumps. Solar radiation and the heat from external combustion provide sufficient energy to slightly boil the LOX, maintaining the pressure needed to feed the nozzle.

Assembly in orbit and long-transit planetary missions pose a major risk: propellant boil-off and the freezing of mechanical parts. A descent engine that remains dormant for months in a cold vacuum is a single point of failure. The Slurry Carbon system is designed for these "delayed starts." It remains ready to operate regardless of the duration of the coasting phase. This setup is particularly effective for inner-solar system missions; as we approach the Sun, solar rays can be harnessed directly to facilitate tank pressurization and ignition.

The most compelling argument for Slurry Carbon is its universal availability. The propellant consists solely of carbon and oxygen—the primary constituents of the Mars and Venus atmospheres (CO₂). By harvesting these materials in-situ, missions become independent of Earth-shipped supplies. Whether you are landing on a carbon-rich body or operating within a CO₂ atmosphere, the raw materials for your propellant are everywhere. This makes Slurry Carbon not just a fuel, but the perpetual propellant of our solar system.