Space travel is a tremendously costly enterprise, largely because today's spacecraft use rockets to move around, and launching the significant amounts of fuel needed to propel those rockets is very expensive. For humankind to move beyond its current tentative foothold in low Earth orbit and begin frequent travel to the Moon, Mars, and other planets, the cost of traveling through space must be substantially reduced. To do this, it may be necessary to rely less on the pyrotechnics of rocket technologies and utilize simpler and less complex technologies. This could entail the use of long strings or wires to move payloads around in space without the need to burn large quantities of fuel.

A concept for a system in which an orbiting tether would pick a payload up from a hypersonic airplane flying at the top of the atmosphere and pull the payload into space.

A space tether...