From: Eugen Leitl (eugen@leitl.org)
Date: Sat Aug 24 2002 - 01:57:56 MDT
On Fri, 23 Aug 2002, spike66 wrote:
> The original calcs were on based on the required mass, assuming
> we completely master the C-C bond so that we can make diamond
> in any shape. We would need a mass driver on Mars for the source
> of most of the carbon (way too much to lift all the way out of Earth's
> relatively large gravity well, not enough total carbon available on
> Luna.)
Excuse me? The cable is but a ribbon, albeit 1 m x 0.1 Gm sized (I can't
parse what the thickness is supposed to be, 2 mm?). I personally think 10
G$ (most likely, it will be a lot more) would be better invested into next
generation one/two-stage liquid hydrogen-powered scramjet/rocket hybrids.
It would be really nice to be able to take from every airport to go
ballistic arc, touching LEO. If linear motors can accelerate the vehicle
to almost ignition regime, you could certainly go one-stage, and with a
really shrunk vehicle footprint.
http://www.eurekasci.com/SPACE_ELEVATOR/intro.html
[...]
For the last two years a detailed design study of the space elevator
concept has been funded under NASA's Institute for Advanced Concepts
(NIAC). The NIAC work laid out a detailed description of a possible space
elevator program. A small, carbon-nanotube-composite ribbon (5 to 11.5 cm
wide and microns thick) capable of supporting 495 kg payloads would be
deployed from geosynchronous orbit (picture) using eight shuttles and
liquid- or solid-fuel-based upper stages. Climbers (picture) (289) are
sent up the initial ribbon (one every 3 to 4 days) adding small ribbons
alongside the first to increase its strength. After 2.5 years a ribbon
capable of supporting 20,000 kg climbers would be complete. The power for
the climbers (50kW 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 set of rollers to pull
the climbers up the cable at speeds up to 200 km/hr. The spent initial
spacecraft and climbers would become counterweights at the space end of
the 100,000 km long cable. An ocean-going platform (picture) 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 cable 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 cable, being 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 well within what has
already constructed such as trans-oceanic cables and simple thread in
textile mills. The design of the cable 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 micron diameter laying side-by-side. The fibers will be
interconnected by tape sandwiches spaced every 10 cm along the length of
the cable. This design will allow the cable to survive small meteor
impacts and be easily used with a roller traction drive climbers. The
material required for construction of the cable is a carbon nanotube
composite. Carbon nanotubes will be under commercial production in the
near future and have the quality required for the space elevator.
Composites utilizing carbon nanotubes are also under development and may
be ready in the next 1 to 5 years. 2 In the NIAC work several possible
feasibility tests are being examined to demonstrate the validity of the
designs. Laboratory tests include placing carbon nanotube composite
segments in atomic oxygen and high-velocity impact chambers to understand
the degradation mechanisms are funded. The primary feasibility test under
consideration entails utilizing a tethered balloon (1000 m altitude),
prototype climber, 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 cable and power beaming of geosynchronous
satellites.
[...]
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