The Space Elevator

(copied from Research at ISR: The Space Elevator)

The NASA Institute for Advanced Concepts (NIAC) Phase I study examined the entire system in detail and found a space elevator design that will work with current or near-future technology, a method to deploy the elevator, and specific scenario for safe operation.

Current research on the space elevator is continuing to refine the design and bring the required technology to completion as quickly as possible.

In simple terms, the space elevator is a ribbon with one end attached to the Earth's surface and the other end in space beyond geosynchronous orbit (35,800 km altitude). The competing forces of gravity at the lower end, and outward centripetal acceleration at the farther end, keep the ribbon under tension and stationary over a single position on Earth. This ribbon, once deployed, can be ascended by mechanical means to Earth orbit. If a climber proceeds to the far end of the ribbon and releases, it would have sufficient energy to escape from Earth's gravity and travel to the Moon, Mars, Venus and the asteroids.

Climber A detailed design study of the space elevator concept has been funded under NASA's Institute for Advanced Concepts (NIAC). The NIAC work produced a detailed description of a possible space elevator program. Initially, a small, carbon-nanotube-composite ribbon (10 to 20 cm wide and microns thick) capable of supporting 990 kg payloads would be deployed from geosynchronous orbit using four rockets and a magnetoplasmadynamic upper stage. Climbers (230) are sent up the initial ribbon (one every 3 to 4 days) adding small ribbons alongside the first to increase its strength. After 2.3 years a ribbon capable of supporting 20,000 kg cargo climbers would be complete. The power for the construction and cargo climbers (100 kW to 2.4 MW) is beamed up using a free-electron laser (840 nm) and 13 m diameter segmented dish with adaptive optics, identical to the one being constructed by Compower Inc. and received by GaAs photocells (80% overall efficiency at this wavelength) on the climber's underside. This power, converted to electricity, would be used by conventional, niobium-magnet DC electric motors and a set of rollers to pull the climbers up the ribbon at speeds up to 200 km/hr. The spent initial spacecraft and construction climbers would become counterweights at the space end of the 100,000 km long ribbon. An ocean-going platform, based on the current Sea Launch program, would be used for the Earth anchor and located in the equatorial Pacific. Major risk of damage to the ribbon comes from meteor impacts and atomic oxygen erosion; both can be mitigated through several methods (curved ribbon design, metal coating) and are discussed in detail in the NIAC Phase I final report. Modifications to this baseline scenario are expected to greatly improve the deployment and reduce the risk and construction costs.

Climber The ribbon, the only component of the space elevator not commercially available, is the major hurdle in the construction of the space elevator. The sheer length, 100,000 km, is considerable, but is comparable to what has already been constructed such as trans-oceanic ribbons and simple thread in textile mills. The design of the ribbon is very specific and requires high-performance materials. The ribbon of our proposed 20,000 kg capacity elevator will have a 2 square millimeter cross-sectional area, be 1 meter wide and microns thick, on average. It will be composed of individual fibers 10 microns in diameter lying side-by-side. The fibers will be interconnected by tape sandwiches spaced every 10 cm along the length of the ribbon. This design will allow the ribbon to survive small meteor impacts and be easily used with a roller traction drive climbers. The material required for construction of the ribbon is a carbon nanotube composite. Carbon nanotubes will be under commercial production in the near future. Composites utilizing carbon nanotubes are also under development and may be ready in the next one to five years.

In the NIAC work, several possible feasibility tests are being examined to demonstrate the validity of the designs. Funded laboratory tests include placing carbon nanotube composite segments in atomic oxygen and high-velocity impact chambers to understand the degradation mechanisms. The primary feasibility test under consideration entails utilizing a tethered balloon (1000 m altitude), a prototype climber, a free-electron laser (20 kW) and focusing optics to illustrate how the components operate together, splicing techniques, and wear and tear on the system. Additional tests will include geosynchronous deployment of a ribbon and power beaming of geosynchronous satellites.

Climber In addition, the NIAC analysis examined the development, construction and deployment schedule and costs. With a concerted and well-funded effort the raw technologies could be ready in two years, further engineering would take three more years. Once construction begins it will take six years to complete construction and launch the initial spacecraft. Two and a half additional years will be required to build up the ribbon to a 20,000 kg capacity. The operational space elevator will launch 5 ton payloads every day within 15  years. Recent analysis also finds that the first space elevator could be built for $7 to $10 billion total, including launch costs, and a second elevator would cost a small fraction of the first. The first elevators could be financially self-supporting (including recovering the initial construction costs and the cost of borrowing this money) within the first 10 years of operation on the commercial satellite market. The recurring costs are:

  1. climbers,
  2. power beaming system operation,
  3. low-Earth object tracking system operation, and
  4. anchor operations.

For the initial space elevator, these recurring costs combined with repaying the initial capital investment would equal total launch costs of $100/kg ($45/lb or 1/10 to 1/100 of conventional systems).

The space elevator would allow for the lifting of large fragile structures, such as solar energy satellites which would provide clean renewable energy to Earth, inflated stations for manned activities, factories for pharmaceuticals, and payloads for exploration of space. Climbers can be tested easily to insure reliability and brought back if there is a problem. The reliability and safety of the space elevator is calculated to be much better than any rocket-based launch system. A second generation, larger space elevator (100,000 kg capacity) would allow for extensive human activities in space including a large geosynchronous station (hundreds of permanent residents) and settlements on Mars within the first few years of operation. The space elevator qualifies as a revolutionary system in cost, capabilities, risk reduction, and transported cargo. The NIAC work has illustrated that a space elevator be built.

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