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.

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.

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.
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