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.
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.
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.
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:
- climbers,
- power beaming system operation,
- low-Earth object tracking system operation, and
- 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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