Basics and Definitions
- Adaptive Optics
- A technique for reducing the blurring effects of
light travelling through the atmosphere. The problem is that when you want to
use a large mirror for astronomy or, in our case, to beam power to space the
light in different parts of the large beam are distorted differently by the
atmosphere. To eliminate this problem adaptive optics has been developed.
Adaptive optics is a technique to rapidly distort the mirror to correct for
these atmospheric distortion and reconstruct the blurred beam.
- Atomic oxygen
- Single oxygen atoms as compared to oxygen molecules
(two oxygen atoms) found in air. Atomic oxygen is found in the upper atmosphere
where it has been created by solar radiation. It is extremely reactive and
corrodes must materials radidly.
- Carbon nanotube
- A carbon nanotube is an ordered molecule of pure
carbon as illustrated at right. The diameter of a carbon nanotube is on the
order of 10 nanometers (1x10-8 meters, 4x10-7 inches). Per
kilogram of mass, a carbon nanotube theoretically will be over 30 times as
strong as Kevlar and 250 times as strong as steel.
- Centrifugal acceleration
Centrifugl acceleration is the outward acceleration experienced by an
object travelling in a circle. For example, on a rapidly spinning merry-go-round
you will have to hold on to keep from getting thrown off. The outward 'force'
you experience in this case is due to centrifugal acceleration. In our case the
cable experiences an acceleration away from the Earth because of its orbital
velocity. This translates into an upward force on the cable from the perspective
of someone standing on Earth.- EMF or Electromagnetic Fields
- When there is a electrical potential
difference between two points or a magnetic field then in general it can be
referred to as and electromagnetic field. In our discussions here we use
electromagnet fields to refer to the magnetic fields near Earth which the space
elevator can pass through and the electrical potential fields that can build up
in a storm and produce lightning. Geosynchronous orbit is where the downward
gravitational acceleration and the upward centrifugal acceleration are equal for
an object stationary above a point on Earth.
- Geosynchronous orbit (GEO)
- Geosynchronous orbit is at an altitude of 35,800 km.
- GPa
- Gigapascals is a unit of pressure which can be used to express
the strength of a material. It is 109N/m2 or
1.5x105psi. This means that a 1 inch square cable of a material with
a tensile strength of 1 GPa could lift a 150,000 pound load.
- Gravity Gradient
- In the context of our discussions, gravity gradient
is used in reference to the orientation of our cable. For a structure as large
as our space elevator different parts of it will feel different amounts of
gravity. The end nearest the Earth will feel considerably more pull from Earth
than the furthest end. What this tends to do is to orient objects in orbit such
that their longest dimension points toward the center of the Earth.
- Kilogram (kg)
- A kilogram is a metric unit off mass equivalent to 2.2
pounds (in a standard Earth gravity environment).
- Kilometer (km)
- is a standard metric unit of length equivalent to 0.62
miles.
- Low-Earth Orbit
- These are generally circular orbits with several
hundred kilometer altitudes as compared to geosynchronous orbit for example
which has an altitude of 35,000 km. The shuttle and most other satellites
operate in low-Earth orbit.
- Power beaming
- The act of sending power over large distances using
energy beams (lasers, microwaves, etc.) as compared to more conventional methods
that use wires and electricity.
- Shuttle-C
- The shuttle-C is an unmanned version of the standard U.S.
Space Shuttle. The "C" in this case refers to "Cargo". This is an option that
has been discussed and studied but not implemented. The payload of the Shuttle-C
would be roughly three times that of the standard Space Shuttle.
- Space Debris
- Space debris refers to the remnants of rockets,
satellites and other objects left in space by man's activities. Most of this
debris is located in orbits with altitudes between 500 and 1700 km.
- Taper ratio
- The taper ratio as we use it in this manuscript refers to
the ratio of the cross-sectional area of the space elevator cable at
geosynchronous to the cross-sectional area of the cable at the Earth
end.