Definitions list
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eccentricityAn orbit’s eccentricity, usually denoted by e, is the eccentricity of the conic section (circle, ellipse, parabola or hyperbola) described by a satellite or celestial body. It is the ratio of the distance between the foci to the length of the major axis. If the eccentricity is zero, the orbit is a circle; if less than one, an ellipse; if equal to one, a parabola; and if greater than one, a hyperbola.
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eclipticPlane of the Earth’s orbit around the Sun.
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El NiñoClimatic phenomenon observed in the Pacific Ocean. During an El Niño event, surface waters off the west coast of America warm abnormally by 4 to 6°C. Such conditions affect the ocean and atmosphere, and may last for a year or more. El Niño conditions return every 2 to 7 years and vary in intensity.
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electric propulsionMode of jet propulsion that uses electrical energy to accelerate the propulsive fluid. If the fluid is a gas, we use the term electrothermal propulsion; if a flow of ions, ionic propulsion; and if a plasma, plasma propulsion.
Electric propulsion is sometimes used to stabilize satellites or probes.
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electromagnetic waveWave characterized by varying electric and magnetic fields. Examples are radio waves and light waves. An electromagnetic wave propagates in a vacuum.
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elliptical orbit
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endurance testLong-duration test to determine an item of equipment’s ability to withstand particular stresses over a given period of time.
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engine-frameStructure supporting an engine.
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enveloppePart of a balloon filled with the gas that provides buoyancy. It is made of light, flexible and gastight material.
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environmental testTest performed under specified environmental conditions, comprising climatic, mechanical, electrical and electromagnetic tests, or combined tests. An environmental test may be sequential, in which case the equipment is subjected to different sets of environmental conditions in succession.
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equatorial orbit
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equipment bayPart of a launch vehicle housing the main electrical equipment used for guidance, positioning, measuring and control.
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evaluation testTest designed to evaluate the performance of an item of equipment.
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exobiologyScience that studies the possibility of extraterrestrial life forms existing in the Universe. Synonym: astrobiology.
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expandableTerm describing a traditional, non-reusable launch vehicle. It also describes any element of a satellite consumed over time, for example, propellants.
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extrasolar planetPlanet orbiting a star other than the Sun.
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extravehicularTerm used to describe activities conducted by an astronaut outside a spacecraft (extravehicular activity, synonym: spacewalk).
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Extravehicular activity (EVA)See extravehicular