Glossary of Space Exploration Terminology

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
E
Earth
Third planet from the Sun, a terrestrial planet.
Earth radius
The average radius of the Earth, a convenient unit of distance in describing phenomena and orbits in the Earth's neighborhood in space. 1 RE = 6371.2 km approximately.
Earth-sensor
A light-sensitive diode which seeks the direction of Earth and then informs the attitude control system of a spacecraft.
Eccentric
Noncircular; elliptical (applied to an orbit).
Eccentricity
The amount of separation between the two foci of an ellipse and, hence, the degree to which an elliptical orbit deviates from a circular shape.
Eclipse
The obscuring of one celestial body by the passage of another in front of it.
Ecliptic
The great circle on the celestial sphere which traces the path of the Sun during the year.
ECM
Electromagnetic Countermeasures.
EDT
Eastern Daylight Time.
EELV
Evolved Expendable Launch Vehicle.
Ejection seat
A seat fitted with an explosive charge and designed to eject the occupant clear of an aircraft during an in-flight emergency.
ELDO
European Launcher Development Organization.
Electric propulsion
A form of rocket propulsion which depends on some form of electric acceleration of propellant to achieve low thrust over long periods of time. E.g. an ion or magnetohydrodynamic engine.
Electromagnetic
Relating to the interplay between electric and magnetic fields.
Electromagnetic waves
A wave propagated through space by simultaneous periodic variation in the electric and magnetic field intensity at right angles to each other and to the direction of propagation. The electromagnetic spectrum includes radio waves, microwaves, infrared, visible and ultraviolet radiation, X-rays, gamma rays and cosmic rays.
Elevation
The angular measure of the height of an object above the horizon; with azimuth, one of the coordinates defining celestial location and sometimes used in tracking spacecraft.
ELV
Expendable Launch Vehicle.
EMU
Extravehicular Mobility Unit.
Energetic particle
Particles that can penetrate outer surfaces of spacecraft. For electrons, this is typically above 100 keV, while for protons and other ions this is above 1 Mev. Neutrons, gamma-rays and X-rays are also considered energetic particles in this context.
Engine
In spacecraft, a rocket or thruster that burns liquid propellants and can be throttled to adjust thrust.
EOL
End Of Life.
Ephemeris
Table of predicted positions of bodies in the solar system.
Ephemeris time
A measurement of time defined by orbital motions. Equates to Mean Solar Time corrected for irregularities in Earth's motions.
Epoch
An instant in time that is arbitrarily selected as a point of reference, e.g. for a set of orbital elements.
Equator
An imaginary circle around a body which is everywhere equidistant from the poles, defining the boundary between the northern and southern hemispheres.
Equatorial orbit
An orbit in the plane of the equator.
ESA
European Space Agency.
Escape tower
A rocket-powered framework designed to separate spacecraft modules from their booster rockets in case of accident. Escape towers are mounted atop the spacecraft and jettisoned after launch.
Escape velocity
The precise velocity necessary to escape from a given point in a gravitational field. A body in a parabolic orbit has escape velocity at any point in that orbit. The velocity necessary to escape from the Earth's surface is 6.95 miles/sec. (11.2 km/sec.).
ESMC
Eastern Space and Missile Center.
EST
Eastern Standard Time.
Eurospace
Non-profit-making industrial association with headquarters in Paris (founded September 1961).
EVA
Extravehicular Activity.
Exhaust velocity
The velocity of the exhaust leaving the nozzle of a rocket.
Exosphere
The part of the Earth atmosphere above the thermosphere which extends into space. H and He atoms can attain escape velocities at the outer rim of the exosphere.
Extravehicular activity
Action performed by an astronaut or cosmonaut outside a vehicle in space; a spacewalk.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Rocketry & Space Technology

Glossary courtesy of Robert Braeunig's
Rocketry & Space Technology website.