Step by Step

It makes sense to build technology prototypes and subscale space elevators before attempting to construct a real one. The LiftPort Group has published a roadmap that presents a stepwise approach, where the complexity of the technology and prototypes increases with time. This allows space elevator engineers to gradually build up experience and to solve the problems they encounter before moving on to the next major development (Fig. 6.7).

The LiftPort roadmap starts with two balloon-lofted tethers for testing tether materials, dynamics, and lifter technology (LiftPort calls its climbers "lifters"). A first tether is planned to reach up to an altitude of 3 km (2 miles) and a second to 10 km (6 miles). Both are to be ascended by experimental lifters powered by batteries rather than beamed energy, because the LiftPort roadmap initially focuses on development of the actual lifter rather than the power supply. According to the original plan that was published in 2006, this early development phase was to last until about 2010. LiftPort did put up a 1.6-km (1-mile) balloon tether in January 2006, but the battery-powered lifter managed to get only about 460 meters (1500 feet) above the ground. Even taking into account the achievements of the Space Elevator Games, the current development of the space elevator is thus somewhat behind LiftPort's schedule. On the other hand, the Games already incorporate climbers/lifters powered by laser energy beamed up from the ground, which is a more advanced stage of lifter power supply technology than that incorporated in the two high-altitude balloon experiments originally planned by LiftPort.

A next step in the plan is the development of a powerful laser system for

Detailed design, prototyping, etc.

Not lo Scale

Laboratory

Detailed design, prototyping, etc.

Academic research

Top of Stratosphere

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Power beam

Retired Satellite r

Balloon-lofted

Ribbon + Lifter

MatcriaJ Exposure Satellite

Year

Figure 6.7: The LiftPort Group's space elevator technology development plan. (Courtesy of the LiftPort Group.) ^

beaming energy to lifters at very high altitudes. A prototype could shine its laser light on the solar arrays of a (retired) satellite, to test target tracking, to test the focusing laser beams from the ground, and to verify how much energy actually reaches through the atmosphere to orbital altitudes. Continuing tether material development should make it possible by 2015 to deploy a stratospheric balloon, reaching 30 km (19 miles) or higher, with a suspended tether strong enough for small lifters to ascend. These lifters could then be powered by a powerful laser beam sent up from the ground.

In parallel to the laser system development, LiftPort suggests the launch of GEO tether-satellites with increasingly longer cables, for the testing of tether deployment and dynamics. Between 2020 and 2025, a satellite could be launched with a tether some 30,000 km (19,000 miles) long, incorporating a lifter powered by the latest ground laser beaming technology. In addition, a material exposure satellite launched around 2020 is intended to test how space elevator ribbon material holds up in low Earth orbit and the atomic oxygen present there. Around 2030 all required technologies should then be sufficiently mature for a full-scale space elevator to be constructed, although this heavily depends on the success of each development step and especially the improvements in carbon nanotube ribbon strength.

Edwards has much criticized the LiftPort plan in a document he posted on www.spaceelevator.com. According to him, tether material development is already well ahead of LiftPort's roadmap, and laser tracking and focusing has already been sufficiently demonstrated by the military. Data on material exposure to the space environment is available from NASA's Long Duration Exposure Facility (LDEF) mission since the early 1990s. Moreover, LiftPort's material exposure satellite would move much faster than a space elevator tether at the same altitude, and therefore not realistically test material degradation due to atomic oxygen. Edwards also states that some critical issues have not been addressed, such as "acquisition of financing, regulatory approvals for deployment and power beaming, ribbon design studies and testing, deployment spacecraft design, ribbon deployment studies, detailed laser and power beaming studies, system protection, system trade-off, system integration, etc.''

It is evident that a stepwise approach to the development of something as complicated as a space elevator is required, but exactly what the roadmap should look like is much less clear. Let us hope that whatever development logic will be implemented, it will be more successful than the construction of the mythical Tower of Babel.

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