Aerospace.
A physical region made up of Earth's atmosphere and the space beyond.
Aerospace plane.
A single spacecraft able to operate effectively in both the atmosphere and space. Also known as a "trans-atmospheric vehicle ."
Apogee.
The point of greatest distance from Earth (or the moon, a planet, etc.) achieved by a body in elliptical orbit. Usually expressed as distance from Earth's surface.
Atmosphere.
Earth's enveloping sphere of air.
Boost phase.
Powered flight of a ballistic missile - i.e., before the rocket burns out.
Burn.
The process in which rocket engines consume fuel or other propellant.
Circumterrestrial space.
The "inner space" or the atmospheric region that extends from sixty miles to about 50,000 miles from Earth's surface.
Constellation.
A formation of spacecraft orbiting for a specific combined purpose.
Deep space.
All space beyond the Earth / moon system, or from about 480,000 miles altitude outward.
Eccentric orbit.
An extremely elongated elliptical orbit.
Ecilptic plane.
The plane defined by the circle on the celestial sphere traced by the path of the sun.
Elliptical orbit.
Any non circular, closed space flight path.
Exosphere.
The upper limits of Earth's atmosphere, ranging from about 300 miles altitude to about 2,000 miles altitude.
Expendable Launch Vehicle (ELV).
A launch vehicle that cannot be reused after one flight.
Ferret.
A satellite whose primary function is to gather electronic intelligence, such as microwave, radar, radio, and voice emissions.
Earth orbit.
A geosynchronous orbit with 0 degrees inclination in which the spacecraft circles Earth 22,300 miles above the equator and appears from Earth to be standing still.
Geosynchronous Earth orbit (GEO).
An orbit at 22,300 miles that is synchronized with Earth's rotation. If a satellite in geosynchronous orbit is not at 0 degrees inclination, its ground path describes a figure eight as it travels around Earth.
Geosynchronous transfer orbit (GTO).
An orbit that originates with the parking orbit and then reaches apogee at the GEO.
Global Positioning System (GPS)
Constellation of twenty four satellites used by many organizations to determine a precise location on Earth. A small receiver takes signals from three or more GPS satellites within view and calculates a position. First widespread wartime use in the Persian Gulf War, creating increased demand for receivers, which military suppliers had trouble meeting Since then, the United States Department of Defense (DoD) has deployed GPS terminals to many more users. GPS is used by a large number of civilian organizations worldwide, and the DoD can broadcast both a highly accurate signal for use by specially equipped military receivers and a degraded signal for public use. Highly precise signal gives location within sixteen meters; the degraded signal is accurate to within 100 meters. GPS is finding wide applications throughout military, commercial, and civilian use.
Ground track.
An imaginary line on Earth's surface that traces the course of another imaginary line between Earth's center and an orbiting satellite.
High Earth orbit (HEO).
Flight path above geosynchronous altitude (22,300 to 60,000 miles from Earth's surface).
High resolution imagery.
Detailed representations of actual objects that satellites produce electronically or optically on displays, film, or other visual devices.
Inertial upper stage.
A two stage solid rocket motor used to propel heavy satellites into mission orbit.
Ionosphere.
A region of electrically charged thin air layers that begins about thirty miles above Earth's atmosphere .
Low Earth orbit (LEO).
Flight path between Earth's atmosphere and the bottom of the Van Allen belts, i.e., from about 100 to 1,000 miles altitude.
Magnetosphere.
A region dominated by Earth's magnetic field, which traps charged particles, including those in the Van Allen belts. It begins in the upper atmosphere, where it overlaps the ionosphere, and extends several thousand miles farther into space.
Medium Earth orbit (MEO).
Flight path between low Earth orbit (about 300 miles in altitude) and geosynchronous orbit at an average altitude of 22,300 miles.
Mesosphere.
A region of the atmosphere about thirty to fifty miles above Earth's surface.
Orbital decay.
A condition in which spacecraft lose orbital altitude and orbital energy because of aerodynamic drag and other physical forces.
Orbital Inclination.
Angle of flight path in space relative to the equator of a planetary body. Equatorial paths are 0 degrees for flights headed east, 180 degrees for those headed west.
Outer space.
Space that extends from about 50,000 miles above Earth's surface to a distance of about 480,000 miles.
Parking orbit.
Flight path in which spacecraft go into LEO, circle the globe in a waiting posture, and then transfer payload to a final, higher orbit.
Payload.
Any spacecraft's crew and/or cargo; the mission element supported by the
spacecraft.
Perigee.
The point of minimum altitude above Earth (or the moon, a planet, etc.) maintained by a body in elliptical orbit.
Period.
The amount of time a spacecraft requires to go through one complete orbit.
Polar orbit.
Earth orbit with a 90 degree inclination. Spacecraft on this path could pass over every spot on Earth as Earth rotates under the satellite's orbit (see "Orbital Inclination").
Remote Imaging.
Images of Earth generated from spacecraft that provide data for mapping, construction, agriculture, oil and gas exploration, news media services, and the like.
Rocket.
An aerospace vehicle that carries its own fuel and oxidizer and can operate outside Earth's atmosphere.
Semi-synchronous orbit.
An orbit set at an altitude of 12,834 miles. Satellites in this orbit revolve around Earth in exactly twelve hours.
Single stage to orbit (SSTO) system.
A radically new, reusable single - stage rocket that can take off and land repeatedly and is able to boost payloads into orbit.
Stratosphere.
That section of atmosphere about ten to thirty miles above Earth's surface.
Sun synchronous orbit.
A low Earth orbit inclined at about 98 degrees to the equator. At this inclination and altitude, a satellite's orbital plane will always maintain the same relative orientation to the position of the sun.
Thermosphere.
The thin atmosphere about fifty to 300 miles above Earth's surface. It experiences dramatically increased levels of heat compared to the lower layers.
Transfer.
Any maneuver that changes a spacecraft orbit.
Transponder.
A radar or radio set that, upon receiving a designated signal, emits a radio signal of its own.
Troposphere.
The region of the atmosphere from Earth's surface to about ten miles above the equator and five miles above the poles. This is where most clouds, wind, rain, and other weather occurs.
Van Allen belts.
Zones of intense radiation trapped in Earth's magnetosphere that could damage unshielded spacecraft.