To enter into space in a substantial manner, we need to be able to carry large volumes of people and cargo at a fraction of the cost of present technology; tethered rings provide a potentially realistic means to achieve so using just existing technology.
Space tethers are long cables that could be used for a variety of purposes, including propulsion, momentum exchange, stabilization and attitude control, or maintaining the relative positions of the components of a large dispersed satellite/spacecraft sensor system. These tethers have the potential to significantly reduce the cost of spaceflight, making it more accessible and affordable for a wider range of missions.
But the uses of space tethers don’t stop there. A Tethered Ring, a giant cable loop suspended in the stratosphere, could potentially be used to achieve world-wide carbon neutrality by 2050 and to set up and maintain supply-lines to new space stations and colonies on the moon and Mars. How exactly would this work?
The Tethered Ring would support an electrically powered mass driver, a 1000km long evacuated tube containing a magnetic levitation (maglev) track. A space vehicle would enter the tube through an airlock, be accelerated down the track, and exit into the rarified atmosphere through a fast airlock at the other end. Because it only needs to generate a small amount of additional delta-V to reach a stable orbit, a space vehicle launched by a mass-driver can be much smaller in proportion to its payload than a traditional rocket launched from the surface of the Earth, which needs a lot more delta-V and thus must be much larger in proportion to its payload.
In addition to launching space vehicles, the Tethered Ring could also be used to decarbonize high-speed international travel by supporting a suspended electrically powered evacuated tube transport system. This system would quickly ferry people and freight vast distances between cities and over land and ocean, allowing us to retire many of the large kerosene-burning airliners currently used for long-haul routes. The tube transit system would be 4x faster, have 4x lower operating costs, be 10x more energy efficient, 20dBA quieter, and provide 30x more frequent departures than long-haul airliners.