Glossary - E

Earth observation satellite
a spacecraft which images the Earth's surface generally using visible or infra-red light or radar imagery
(Earth observation)

Earth segment
the part of a satellite communications system consisting of the earth stations and the interfaces with the terrestrial telecommunications infrastructure
(satellite communications)

Eccentricity (e)
a measure of the shape of a conic section (e=0 circle, 0<e<1 ellipse, e=1 parabola, e>1 hyperbola); for an ellipse, a measure of how much the shape of an ellipse deviates from that of a circle
(orbits)

Ecliptic
the plane in which the Earth orbits the Sun
(orbital geometry)

Edge of coverage
limit of a satellite's defined service area
(satellite communications)

Electromagnetic radiation
waves of electric and magnetic fields which propagate through free space at the speed of light and which are quantised as photons; radio waves, microwaves, infrared (IR) light, visible light, ultraviolet (UV) light, X rays and gamma rays are all types of electromagnetic radiation
(physics)

Element set
a data file which defines a satellite's orbit
(orbital geometry)

Elevation
angular altitude of the satellite above the horizon at the earth station
(orbital geometry)

Encryption
the technique of modifying the form or structure of a transmission so that, without a decoder and the appropriate key, the signal is unintelligible
(communications)

Encryption algorithm
a mathematical process (such as DES and RSA) which can be used to scramble and descramble a data stream
(communications)

Enterprise network
large network connecting most major points in a company; differs from a WAN in that it is typically private and contained within a single organisation
(communications)

Equalisation
method of compensating for the distortion introduced during the transmission of a signal through a channel with different gain at different frequencies
(communications)

Equator
an imaginary line around a body which is equidistant from both poles
(orbits)

Equatorial Orbit
an orbit with inclination i=0°, ie and orbit in the same plane as a planet's equator
(orbits)

Equinox
the times when the centre of the Sun is directly above the Earth’s equator
(orbits)

Escape velocity
the minimum speed required to escape from a body’s gravitational field
(orbits)

Event TV
televising of one-off events to the business community
(broadcasting)

Exobiology
the scientific study of non-terrestrial life; also known as astrobiology
(biology)

Exoplanet
a planet which orbits a star other than the Sun
(planetary science)

Exosphere
the part of the atmosphere surrounding a planet, moon or asteroid in which the molecules are gravitationally bound to the body, but in which the density is so low the molecules do not collide with other molecules; in a planet with a thick atmosphere such as the Earth, the exosphere is the uppermost layer of the atmosphere extending to space; in bodies without a thick atmosphere the exosphere is the only layer in the atmosphere extending from the bodies surface to space (surface boundary exosphere)
(atmospheric physics)

Extended IF
the enlarged receiver IF tuning range (950 - 2050 MHz) to enable it to use the whole frequency range supported by triple band LNBs
(satellite communications)

Extrasolar planet
a planet which orbits a star other than the Sun
(planetary science)

Extremophile
an organism capable of living in conditions normally considered to be too extreme for life to survive
(biology)