Sub-Light Spacecraft

Spacecraft that traverse normal space are subject to all standard laws of physics, applying their engines for direct acceleration to adjust their orbit. These spacecraft vary in their configuration depending on a variety of circumstances, and have changed drastically as technology has developed.

Early Spacecraft

The earliest spacecraft used chemical engines, which have low efficiency for their fuel requirements. These engines had an upper bound of only several minutes worth of acceleration, enough to reach low orbit or adjust course for a months-long hohmann transfer. While leaving the atmosphere of Home and establishing orbital infrastructure was initially costly due to the planet’s gravity, once humanity achieved a foothold in space the costs of operation drastically lowered as ships could be operated and maintained entirely in orbit of Home and its moon. Chemical fuels nevertheless remained an inhibitor, with transit times between planets of months to years and only feasible for certain windows of time.

Torchships

Torchships are nuclear spacecraft powered by either fission or fusion, and are designed for lengthy sustained thrust. Their engines are configured to burn for hours, days, or even weeks at a time, providing a constant acceleration that allows a ship to traverse several AU in a matter of weeks and with little reliance on current orbital locations. Torchships provide directional simulated gravity during their acceleration, a feature that habitation modules are typically configured to take advantage of.

Nuclear-Thermal

Nuclear thermal rockets (NTRs) are the most common torchship design. They use fissile material to heat propellant for acceleration, with a number of potential configurations dependendent on available material and the intended route of the spacecraft. NTRs often do not require extensive radiators, as in many configurations the fuel is the propellant which carries heat away with it, although many outer-system spacecraft use their fuel internally to generate electricity. NTRs have been in use since before the first warp drives, but have had extensive development since then.

Fusion

Fusion drives are a newer and still relatively experimental engine type, only viable on spacecraft for the last few decades. These engines induce fusion reactions between sets of reactants by compressing the material through various means of induced confinement. Fusion drives are far more efficient than fissile ones, but there are a variety of associated challenges that currently inhibit widespread adoption. The technology to induce the reaction, maintain its confinement, and cool the entire system is very complex in a miniaturized configuration for the purposes of spaceflight.