Conclusion

Abstract

Humanity requires more efficient, more sustainable, and much less costly access to space, if it wants to dramatically expand its use of Earth orbit and make interplanetary space part of its economical sphere. We need ways to get into orbit and to reach other planets that do not leave large amounts of debris, require enormous amounts of propellant, or take incredibly long periods of time. The space tether systems described in this book offer various solutions. Space elevators could provide an easy and regular way to get into Earth orbit, and electrodynamic momentum exchange tethers could send space¬craft from low orbits up to higher ones and vice versa. Tethers could even de-orbit return capsules or send spacecraft on their way to other planets. Further out into space, momentum exchange tethers or aerobraking tethers could be used to capture spacecraft into orbits around the Moon, Mars, and Jupiter. Artificial gravity, provided by long spinning tethers, can ease the life of astronauts during their interplanetary travels and counter unwanted physiological changes. To ensure that people can live and work in orbits with too high levels of radiation, electrostatic tethers that sweep away dangerous charged particles around the Earth or even Jupiter may be deployed. Tethers may one day become as invaluable to space travel as chemical rockets today. The 22nd century may see a fleet of spinning tethers strategically placed around Earth, the Moon, and Mars, creating efficient interplanetary highways for spacecraft that require almost no propellant. The tether applications with potentially the most dramatic impacts are complex and will need large-scale, long, and expensive development. The space elevator requires revolutionary new materials, and all large-scale tethers will exhibit complex dynamics that need to be fully understood to ensure stability and control under all circumstances. Damage protection is an important issue, both in terms of tether materials and concepts and in terms of collision and impact avoidance. There are serious risks associated with having a cable tens of kilometers long rotating in orbit together with other satellites.