Silent Mountain decelerates into orbit around Saturn, its radiators glowing with waste heat from its mighty 1.5 terawatt fusion drive.
Unlike chemical rockets, a fusion reaction can't dump much of its waste heat into its own exhaust plume. It must radiate it through carefully engineered structures.

A scale comparison with recognizable buildings and spacecraft. The ship's diameter at the outer habitat is 1.4 kilometers to provide an artificial gravity of 0.8 gees when rotating once every minute. Thanks to SpinCalc for the centrifugal force calculations.

A map of the major blocks of one of the habitat arms. Each square in the grid is ten meters on a side. The curved lines on the right side of the illustration show the increasing effect of artificial gravity as one travels further from the center of the structure.

A diagram of the guts of the fusion drive. This is the most science-fictional part of the spacecraft, as fusion technology is currently very immature. One extra point of realism, however, is that the fusion drive does not actually create energy on its own—as with current fusion reactors, it eats more energy than it puts out. There is an external, feasible fission reactor much like the nuclear powerplants in use today. This provides enough energy to bridge the gap and powers the rest of the ship.

The purpose of the fusion drive is to accelerate the exhaust to extremely high velocities, not create power. Thus the nuclear hybrid design. The biggest problem with the concept is heat dissipation; if this were real, there's absolutely no way a reaction chamber this size could dissipate heat fast enough, and the ship would vaporize.

The Stefan-Boltzmann equation for heat energy radiated from an object in a vacuum via black body radiation. This is useful for designing the thermal management systems.

Tsiolkovsky's rocket equation. Determines the maximum change in velocity possible with the amount of propellant carried onboard the spacecraft.