Having finished writing about the space elevator, I am moving on to another spacelaunch method in this new article in the non-rocket spacelaunch series. Tether propulsion consists in using long, very strong cables (known as tethers) to change the velocity of spacecraft and payloads. The tethers may be used to initiate launch, complete launch, or alter the orbit of a spacecraft. This form of propulsion would be significantly less expensive than spaceflight using modern rocket engines. Artist’s conception of satellite with a tether. Image by NASA. How does it work? Tethers are kept straight by either rotating end for end, or by the difference in the strength of gravity over…