Mass Drivers: Queens of Space
The paddle-wheeled steamboats that plyed the mighty Mississippi River during America's frontier days had an important edge: if they ran out of firewood they could simply pull over to the bank and collect dead wood to use as fuel for their boilers. The mass driver ships of the high frontier operate on a similar principle: they can use pulverized debris, lunar soil, crushed asteroids, frozen oxygen or anything else available as reaction mass.
As shown in the schematic diagram (right) taken from page 140 of The High Frontier by Gerard K. O'Neill, the mass driver consists of a long, solar-powered electromagnetic conveyor belt. By the action of magnetic impulses driven by electrical energy, it can accelerate a small bucket containing reaction mass to very high velocities. The ejected mass produces thrust just like a conventional rocket only much more efficiently. Exhaust velocities for a mass driver engine can be twice as high as the best chemical rocket engine. However, their performance is far surpassed by fusion drives.
Above is a photo of my scratchbuilt model of a typical mass driver transport. The model was based on the ship featured in the hard-SF short story, Miranda and the Space Pirates by Mike Combs. Visible in the photo are a portion of the thousand meter-long electromagnetic conveyor boom with multiple solar cell arrays mounted along its length; and the habitat spheres mounted on counter-rotating booms to produce artificial gravity. The sphere at the forward end of the long conveyor boom houses the ship's "spacevan" garage and repair bay. The ship's payload is mounted at regular intervals along the length of the conveyor boom. The photograph of the model featured on this page was taken by Free Trader using a Polaroid "Spectra SE" camera.