10-01-2012, 05:02 PM
The NIAC Space Elevator Program
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Introduction
The space elevator first appeared in 1960 (Artsutanov) in a Russian technical journal.
In the following years the concept appeared several times in technical journals
(Isaacs, 1966; Pearson, 1975; Clarke, 1979) and then began to appear in science
fiction (Clarke, 1978; Stanley Robinson, 1993). The simplest explanation of the
space elevator concept is that it is a cable 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 centrifugal acceleration at
the farther end keep the cable under tension and stationary over a single position on
Earth. This cable, once deployed, can be ascended by mechanical means to Earth
orbit. To place a spacecraft in geosynchronous orbit the climber simply ascends to
that altitude and releases its payload. To place a spacecraft in any other Earth orbit
the payload would require a small engine to achieve the proper orbital velocity. If a
climber proceeds to the far end of the cable it would have sufficient energy to escape
1 Eureka Scientific, brad_edwards[at]excite.com
2
from Earth’s gravity well simply by separating from the cable. The space elevator
thus has the capability in theory to provide easy access to Earth orbit and most of the
planets in our solar system (Pearson, 1975).
In comparison to many fields of active research there has been little
quantitative work done on the space elevator. Pearson and a few others did some
quantitative work in the 60’s and 70’s but in recent years the space elevator has been
largely ignored in the technical journals. An alternative area of research in sky hooks
(a cable between two orbits for orbital transfer) has emerged and produced some
interesting work (Proceedings of the Tether Technology Interchange Meeting,
Huntsville AL, Sept. 1997). Even though the basic ideas are similar, the
construction, utility, problems and operations are dramatically different between
space elevators and sky hooks. Because of these extensive differences we will not
discuss the sky hook here.
Our NIAC Phase I work laid out a detailed description of a possible space
elevator program (Edwards, 2000b) filling in the gaps found in Edwards, 2000a. A
small, carbon-nanotube-composite cable capable of supporting 495 kg payloads
would be deployed from geosynchronous orbit using seven shuttles and liquid- or
solid-fuel-based upper stages. Climbers (288) are sent up the initial cable (one every
4 days) adding cables to the first to increase its strength. After 2.3 years a cable
capable of supporting 20,000 kg payloads would be complete. The power for the
climbers is beamed up using a free-electron laser identical to the one being
constructed by Compower and received by photocells. The spent initial spacecraft
and climbers would become counterweights at the space end of the 100,000 km long
cable. An ocean-going platform based on the current Sea Launch program is used for
the Earth anchor. This anchor is mobile and able to move the cable out of the way of
low-Earth orbit satellites. The anchor location is in the Pacific Ocean, roughly 1500
km west of the Galapagos Islands to avoid lightning, hurricanes, strong winds, and
clouds. The specific cable design would be a curved and tapered ribbon with a width
increasing from Earth to geosynchronous and back down to the far end. Deviations
in the cable’s cross-sectional dimensions would be implemented to reduce the risk of
damage from meteors and wind. All of the raw technologies required to construct the
space elevator may be ready in 10 years. Carbon nanotubes require the most
development but they are now produced in the lab with characteristics close to that
needed for construction of a space elevator (see figure 1; Li, 2000; Cheng, 1998; Yu,
2000a; Yu, 2000b). Major risk of damage to the cable comes from meteor impacts
and atomic oxygen erosion, both can be mitigated through several methods.
The objective of our NIAC Phase I study was to examine all aspects of the
space elevator from the basic design and challenges to the overall system cost. There
were a large number of areas to investigate, calculations to be done and problems to
solve. The specific results of our Phase I study included:
· Finding a power beaming system using available laser and adaptive optics
technologies
· Examining the trade-off between laser-based and millimeter-based power
beaming systems
· Designing cables on scales of
microns to kilometers to survive
the environment and minimize
the overall mass.
· Calculating and dealing with
wind loading on the cable
· Examining and solving the
problem of low-Earth objects
impacting on the cable.
· Finding two suppliers of carbon
nanotubes and quantifying the
current state of technology
· Examining and solving the
atomic oxygen erosion problem
· Finding the optimal anchor
location west of the Galapagos
islands
· Discussing scenarios where the
cable might come down and
how to mitigate them
· Quantifying aspects of induced
oscillations, radiation damage,
and induced electrical currents
· Working out a deployment
scenario using current launch
systems and technologies that
requires only seven shuttles and
available upper stages
· Working out the orbital
mechanics involved in
deploying the initial cable.
· Finding a mobile anchor design based on oil drilling platform technology
· Working out the meteor fluxes and damage rate for our proposed cable
· Working out a cable design that will survive the expected meteor flux
· Examining the current state of spooling technology
· Determining the solar system destinations accessible for different elevator lengths
· Laying out a scenario for deploying a Martian elevator.
· Developing a detailed deployment schedule
· Working out a design for the climbers that fits the mass and power budget
· Laying out various program design options
· Refining the budget estimates for the entire system
