Space elevator. Computer artwork of a future space elevator for space transportation. A counterweight places the elevator's centre of mass at a 35,900 kilometre altitude, a geostationary orbit. Here, the elevator rotates with the Earth, remaining connected to its distant anchor point on the equator. Electromagnetic propulsion systems could be used for the low-cost transport of people and materials into space. Objects descending from orbit would power ascending loads. Immensely strong materials are needed to build this cross between a tower and a rope. Carbon nanotube materials are thought to be suitable for the space section of an elevator.