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 spacecraft from low orbits up to higher ones and vice versa. Tethers could even deorbit 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.

M. van Pelt, Space Tethers and Space Elevators, DOI: 10.1007/978-0-387-76556-3_8, © Praxis Publishing, Ltd. 2009

The development of large-scale space tether systems will be funded only if the benefits are clear. That means tethers will have to do the job better, more efficiently, and cheaper than competing alternatives such as advanced rocket systems. Projects requiring only modest development durations that promise fast and substantial economic return may be funded by private industries. However, high-cost and high-risk projects with long schedules will need considerable financial support from governments. Political sustainability may be a big issue in that case, because like the Apollo project of the 1960s, the development and construction of an orbital tether infrastructure or space elevator will have to be supported by several successive government administrations.

Space tether development will also require government organizations to set up the right legal frameworks. The current international space treaties that govern rocket launches and orbiting spacecraft are not suited for dealing with space elevators that continually send up cargo or long spinning tethers intersecting many orbits at the same time. As with the construction of the transcontinental railroad in the United States or the current developments in space tourism, government rules and regulations that support innovation will be an essential element of success.

The key to keeping the development of space tethers going appears to be credibility; space tether advocates need to show that their ideas are within the realm of reality and not just science fiction, and that the advantages are real enough to warrant further support from the government and industry. Space tethers will not be developed for their own sake, but to support the ongoing exploration and exploitation of space. Unfortunately, they do not play any role in the current plans that NASA, ESA, and other space agencies have for the near future of space exploration. It will require considerable advocating, publicizing, convincing, and lobbying to keep development going, and that may turn out to be even harder than meeting the technical challenges.

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