Near Space
you’ll find that L-1 is more like a hill
than a bowl. A marble remains
stationary at the top of a hill, but give
it a little shove and it becomes unstable and rolls away. The same is true
of a satellite located at L-1. To remain
at L-1, a satellite, or tower, requires
active maintenance of its position.
There are four additional stationary points located within the Earth-Moon system and two of them, L- 4
and L- 5, are stable like a marble is at
the bottom of a bowl. L- 4 and L- 5 will
make great locations for space
colonies and industry.
Materials strong enough to form
a 36,000-mile-tall tower above the
lunar surface exist today. Spectra (a
kite string I use) and Kevlar are two of
the suitable materials with which
you’re probably familiar. Pearson
believes the best material is a fiber
manufactured by Magellan Systems
called M5. A 36,000-mile-long lunar
SE made of M5, and with the strength
to lift a climber and 400 pounds of
payload, weighs only 15,000 pounds.
That is small enough to be carried by
a single Space Shuttle launch.
The climb up a lunar SE is slow,
so it’s not suitable for transporting
people. However, the Moon contains
resources useful for space colonies
and exploration. A commodity like
ice trapped at the lunar poles is useful as fuel and water. The Moon’s raw
dirt (regolith) is valuable as a shielding material for space colonies. To
reduce the time required to haul lunar
ice from the lunar poles to the lunar
SE, a second lunar SE can be set up
from a lunar pole to the L-1 position.
So engineering models show that
the lunar SE is feasible today, but
what about a SE on Earth?
Back to the
Earth-based SE
Otis, the elevator company, has
developed the technology for
five-mile high elevators. Within 10
years, they believe they can develop
the technology for an elevator that
can climb to geostationary orbit on
an SE.
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Several SE papers were presented at the 55th Astronautical Congress
in 2004. Several of the papers
focused on an Earth SE constructed
as described below.
The SE of the future begins as a
15-centimeter-wide ribbon launched
into geostationary orbit. The ribbon
bootstraps itself until it’s a one-meter-wide ribbon. The base of the ribbon is
tethered to a floating ocean platform,
where it’s protected from acts of
terrorism and from the political
upheavals possible in countries with
unstable governments.
An additional benefit of tethering
the SE to a floating platform is that
there are equatorial regions where
peaceful weather is the norm. For
instance, hurricanes cannot form on
the equator because the Coriolis
Effect is nonexistent there. Orbital
predictions are used to schedule
movements of the floating platform in
order to avoid orbital collisions
between the ribbon and satellites.
Cargo is sent up the SE inside a
climber — a climbing robot. SE
climbers carry a photovoltaic array
for power. Electrical power is beamed
to climbers via lasers. Climbers use
the electricity to scale the SE
ribbon with a set of pinching rollers.
Solid-state continuous lasers with 1
kW output currently exist and have
efficiencies of 30%.
Combined laser modules form
the SE power station. The ribbon is
made from carbon nanotube (CNT)
fibers embedded within a matrix.
CNTs of the required strength exist
today. To support the weight of the
SE and its climbers, the SE ribbon
must have a strength of 100 GPa.
Current CNTs have a strength of
200 GPa, but only a length measured
in millimeters.
The climbers are multi-functional
robots. Not only do they climb the ribbon, but they also lay ribbon, identify
ribbon damage, repair ribbon damage, and rescue stranded climbers.
Transit time to geostationary orbit is
500 hours, so it’s not a convenient
system to carry people into orbit.
Climbers must be reliable, as they’ll
climb for 500 hours without stopping
to reach the top of the SE.
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