At the time “2001” was made, spacecraft designers were convinced of the need to supply artificial gravity for space travelers. In principle, this is very easy to do. An object on the rim of a wheel rotating at a uniform speed is subjected to a constant force pushing it away from the center, and by adjusting the size of the wheel and the speed of its rotation, this centrifugal force can be made to resemble the force of gravity. Having accepted this notion, Kubrick commissioned the Vickers Engineering Group to make a centrifuge large enough for the astronauts to live in full-time. It took six months to build and cost $300,000.