Space Station W3, also known as the Wheel, was a space station located in the Sol system in the 21st century. It was used for many functions, serving as a radio/visual relay for Earth, a stopping point for deep space ships, a research station, and an early warning monitor for stellar activity such as meteorite storms. It was armed with an x-ray laser and a force field.
Two Cybermen invaded the station, intending to use it as a beacon for their invasion fleet. The Doctor freed the crew from the Cybermen's hypnotic control and destroyed their fleet. (DW: The Wheel in Space)