A4 The original designation of the early German rocket that flew as the V-2 missile.

ablative heat shield see heat shield aerospaceplane A spaceplane designed to operate in the Earth's atmosphere using an alternative to rocket propulsion - usually a ramjet or scramjet.

Aerozine A rocket fuel consisting of a mixture of hydrazine and unsymmetrical dimethylhydrazine (UDMH).

Agena An upper rocket stage used on Thor, Atlas, and Titan launch vehicles and also as a docking target for several Gemini missions.

Almaz A Soviet military space-station design, flown as Salyuts 2, 3, and 5.

apogee The point in the orbit of a satellite or spacecraft where it is furthest from the Earth.

Ariane A series of European launch vehicles, operating since 1979 and widely used for commercial and scientific satellite launches.

Atlas A long-running US launch-vehicle series, originating from the first US Air Force Intercontinental Ballistic Missile.

attitude The orientation of a spacecraft or space station in space. Attitude adjustments can be made in roll, pitch, or yaw axes.

Baikonur Cosmodrome The main launch centre for the Soviet and Russian space programmes, located in Kazakhstan near the town of Tyuratam (originally named to deceive intelligence agencies into believing it was near the town of Baikonur itself).

ballistic A term used to describe a missile or spacecraft that makes its descent through the atmosphere under the influence of gravity and atmospheric drag alone, with no aerodynamic lift; the term also describes the behaviour of projectiles such as cannonballs.

boilerplate capsule A full-sized but not fully equipped replica of a finished spacecraft design, used in the early stages of testing for studying aerodynamic characteristics and other properties.

booster A small rocket attached to the side of a larger rocket stage to give extra thrust during launch.

Capcom An abbreviation for Capsule Communicator, normally the only person at NASA Mission Control who communicates with astronauts in space. Typically, the role is taken by a trained astronaut.

Centaur A type of upper rocket stage used to launch spaceprobes and satellites. The Centaur was the first rocket to successfully use high-energy cryogenic propellants.

Chang Zheng see Long March rocket

CM Abbreviation for the Command Module of the US Apollo spacecraft.

combustion chamber The part of a rocket engine where the fuel and the oxidant mix and combust, generating thrust against the forward-facing part of the chamber as the exhaust escapes from the nozzle at the rear.

comsat An abbreviation of communications satellite - a satellite used for receiving and re-transmitting signals to and from ground stations.

Cosmos A long-running series of Soviet and Russian satellites, comprising several different concealed programmes and often used to hide failed missions in other series.

cryogenic propellant A rocket propellant (fuel or oxidant) that must be stored at extremely low temperatures and which usually requires ignition in order to start a chemical reaction. Despite the problems in handling them, cryogenic propellants can be extremely powerful.

CSM Abbreviation for the combined Command and Service Module of the US Apollo spacecraft.

CZ see Long March rocket

Delta A long-running and highly successful series of US launch vehicles.

DOS A Russian acronym for Permanent Orbital Station, the Soviet space-station design developed in the late 1960s by the Korolev design bureau as an adaptation of the military Almaz station.

drogue parachute A small parachute used to slow a spacecraft down, usually directly after re-entry to the atmosphere and before the main parachute opens.

elliptical orbit An orbit with the shape of an ellipse (a "stretched circle"). As well as a centre, an ellipse has two foci, with the centre of mass being orbited at one focus. Because an orbiting object's speed is dependent on its distance from the mass that it orbits, it moves more slowly at one end of the ellipse than at the other.

Energia The Soviet/Russian space company formed from the former OKB-1 design bureau of Sergei Korolev. Also a heavy-lift rocket produced by the company for launching the Soviet Buran space shuttle.

equatorial orbit An orbit directly above the Earth's equator. Equatorial orbits are comparatively easy to reach because the Earth's rotation gives rockets an immediate boost if they are launched eastwards from on or close to the Earth's equator.

ESA The European Space Agency, formed from the merger of the European Launcher Development Organisation (ELDO) and the European Space Research Organisation (ESRO) in 1975.

escape velocity The speed at which a spacecraft must travel if it is to escape the Earth's gravitational field - 11.2km (7 miles) per second. It is not necessary to reach escape velocity in order to orbit the Earth.

ET Abbreviation for the large external fuel tank of the Space Shuttle.

flight deck In the Space Shuttle orbiter, the upper deck containing flight controls and seating for most of the crew during launch.

fuel One element of a spacecraft's propellant. The fuel mixes with an oxidant and combusts to create exhaust that pushes the spacecraft forward.

g force A measure of acceleration forces. 1 g is typical Earth gravity, but during launch and re-entry spacefarers experience accelerations of several g.

geostationary orbit Also known as geosynchronous orbit. An orbit in which a satellite above the Earth's equator moves around the planet in the same direction as the Earth's rotation and with the same period (roughly 23 hours, 56 minutes). This means that the satellite remains over the same point on the equator and occupies a fixed point in the sky as seen from Earth. Geostationary satellites are ideal for weather-observation and comsats.

GPS An abbreviation for Global Positioning System - a network of satellites that allows a computerized Earthbound receiver to work out its position by receiving signals from three or more satellites in orbit. The original GPS system uses US NAVSTAR military satellites, but rival systems, including the Russian GLONASS and the European Galileo, are also often known simply as GPS.

gravitational slingshot see gravity assist gravity An attractive force generated by a massive object, which pulls other objects towards it or holds them in orbit.

gravity assist A technique used to speed up and change the direction of a spaceprobe without burning fuel, by flying close to and "borrowing" a small amount of energy from a planet or moon.

ground station A radio receiving dish for communication with spacecraft, satellites, and spaceprobes.

Guiana Space Centre The launch site for the European Space Agency's Ariane rockets, at Kourou, French Guiana.

heat shield A protective layer that shields a spacecraft from the heat of re-entry. Most heat shields are ablative - they burn away during reentry, carrying the heat away from the spacecraft. Other systems, such as the Space Shuttle orbiter's ceramic tiles, must absorb heat without transmitting it to the hull.

H-series rocket Japan's most widely used launch vehicle.

hydrazine A toxic chemical, commonly used as a rocket fuel because of its violent and spontaneous chemical reaction with many oxidants. It is used in the Space Shuttle's Auxiliary Power Units.

hypergolic propellant A rocket fuel that reacts spontaneously with its oxidant (avoiding the need for an ignition system), and which can usually be stored at relatively normal temperatures.

inertia! guidance A guidance system that uses gyroscopes and accelerometers to calculate a vehicle's position and motion by dead reckoning (a method of navigation in which position is determined relative to a known point of departure using measurements of speed, heading, and time).

Inertial Upper Stage A large independent rocket stage used for putting satellites or other payloads into their final orbit or escape trajectory after they have been deployed to low Earth orbit by the Space Shuttle or another launch vehicle.

ion engine A propulsion system that uses the ionization of a chemical propellant in a strong electric field in order to generate thrust. Ion engines are very efficient but produce very small amounts of thrust for very long periods, contrasted with chemical rockets that produce large amounts of thrust for brief periods. They are usually powered by solar arrays.

JAXA The Japan Aerospace Exploration Agency, Japan's space agency, founded in 2003 from the merger of the Institute of Space and Astronautical Science (ISAS), the National Aerospace Laboratory of Japan (NAL), and the National Space Development Agency (NASDA).

Johnson Space Center (JSC) The site of NASA's main Mission Control and many other elements of its manned spaceflight programme, at Houston, Texas.

Juno An adapted version of the Jupiter-C used to launch some of the first US satellites.

Jupiter-C A modified Redstone missile used to carry the warhead of a Jupiter missile into space for reentry tests.

Kennedy Space Center (KSC) The main US launch complex at Cape Canaveral in Florida. The Cape itself was known as Cape Kennedy between 1963 and 1973 in memory of the assassinated US President.

kick motor A small rocket motor built into a satellite and used to move it from low Earth orbit to its final location.

Korabl Sputnik Any of the later Soviet Sputnik satellite launches (4 onwards) that were in fact unmanned tests of Vostok spacecraft.

launch vehicle A complete vehicle, usually consisting of several rocket stages, boosters, and perhaps other components, used to launch payloads into space (often simply referred to as a rocket).

LH2 An abbreviation for liquid hydrogen, a powerful cryogenic fuel.

lifting body An aircraft or spaceplane that has only small wings, if it has wings at all. Lifting bodies rely on the shape of the fuselage to generate aerodynamic lift - they are typically triangular, with convex upper or lower hulls.

liquid-fuelled rocket A rocket in which fuel and oxidant are mixed together and react explosively, creating an expanding mixture of exhaust gases that escape through an exhaust nozzle. The reaction against the escaping gases pushes the rocket forwards. Liquid-fuelled rockets are more complex than solid-fuelled ones, but they are also more versatile, since the flow of fuel can be throttled, stopped, and restarted.

LM An abbreviation for the Apollo spacecraft Lunar Excursion Module (also LEM) - the spiderlike lander that actually put astronauts on the Moon.

Long March rocket A series of Chinese launch vehicles, used in manned and unmanned space programmes.

low Earth orbit An orbit a few hundred kilometres above the Earth, often abbreviated to LEO. Low Earth orbits are typically used by manned spacecraft and space stations, Earth-observing satellites, and as a temporary orbit for satellites later launched into higher orbits by an Inertial Upper Stage, a Payload Assist Module, or a kick motor.

LOX An abbreviation for liquid oxygen, a powerful cryogenic oxidant.

Marshall Spaceflight Center (MSFC) The principle US centre for launch-vehicle development and testing, developed from the US Army's former Redstone Arsenal facility at Huntsville, Alabama.

mass A property of the amount of material present in an object. Mass is unaffected by a gravitational field, unlike weight.

microgravity The term for conditions experienced in orbit - although the effects of gravity are much reduced, they are almost never completely absent.

mid-deck The lower habitable deck of the Space Shuttle orbiter, where equipment and, sometimes, experiments are stored.

MKS A Russian abbreviation for Reusable Space System, the Soviet attempt to develop a reusable space shuttle, also known as Buran.

Molniya orbit A highly elliptical, inclined orbit typically used by communications satellites for countries at high latitudes and named after the Soviet Molniya comsat system. A Molniya orbit sees a satellite spend a large amount of time visible in the skies of a particular part of the Earth, so that it can be easily tracked by ground stations.

monopropellant A class of rocket propellants that can act as both fuel and oxidant in the right conditions - one example is hydrogen peroxide.

multispectral imaging A technique used by remote-sensing satellites and other spacecraft that involves photographing areas at different wavelengths of light (different colours) and analyzing the images to bring out hidden features and reveal surface composition.

N204 Dinitrogen tetroxide, a commonly used hypergolic propellant that functions as an oxidant.

NASA The National Aeronautics and Space Administration, the US space agency, established in 1958 as successor to NACA, the National Advisory Committee for Aeronautics.

nozzle The exhaust outlet from the combustion chamber of a rocket. Exhaust gases typically escape from the combustion chamber at high temperatures through a narrow opening - the bell-shape of the nozzle forces the gases to expand rapidly, cooling them but increasing their speed so that they leave the rocket at up to ten times the speed of sound.

from 1946 until his death in 1966. OKB-1 (sometimes known simply as Korolev) was responsible for much of the Soviet space effort. Since 1974 it has been known as Energia.

OMS The Orbital Maneuvering System, a pair of medium-sized rocket engines at the rear of the Space Shuttle orbiter that are used for adjusting the spaceplane's orbit and as retrorockets for re-entry.

orbit A path that one object follows around another, more massive one due to the force of gravity. An orbit traces a path through space along which the tendency of the object to fly off in a straight line is precisely balanced by the inward gravitational pull of the more massive object.

orbiter The proper name for the spaceplane element of the Space Shuttle system - the orbiter is the vehicle that reaches space, carries out its mission, and then returns to Earth.

oxidant A chemical, used as a rocket propellant, that undergoes a violent chemical reaction (combustion) with a fuel to generate exhaust gases and push a rocket forwards. In contrast to other types of engine, rockets require an oxidant as well as fuel because they must operate in a vacuum - other engines use oxygen from the atmosphere to burn their fuels.

payload The cargo that a launch vehicle delivers into orbit.

Payload Assist Module An independent rocket engine (smaller than an Inertial Upper Stage) attached to the base of a satellite released from the Space Shuttle, which is used to put the satellite into its final orbit.

perigee The point in the orbit of a satellite or spacecraft at which it comes closest to the Earth.

pitch The rotation of a spacecraft about its lateral (side-side) axis - for example, the angle from nose to tail of a Space Shuttle.

nuclear propulsion A theoretical propulsion system that would use the explosions of countless small nuclear devices to push a large spacecraft forwards. Nuclear propulsion is one potential way of accelerating a future starship to very high speeds.

OKB-1 The design bureau run by Sergei Korolev, Soviet Chief Designer of Rocket and Space Systems,

Plesetsk Cosmodrome The northern launch site for Soviet and Russian rockets, located close to the Arctic Circle and ideal for launching rockets into polar and high-inclination orbits.

polar orbit An orbit around the Earth that passes over (or very close to) the planet's poles. Typically used by Earth-observing satellites, a polar orbit allows the satellite to fly over most of the Earth's surface as our planet rotates beneath it each day.

Proton rocket A Soviet heavy-lift rocket used for launching heavy unmanned payloads such as space-station components.

R-7 A Soviet ballistic missile developed by Sergei Korolev, which forms the basis of the Soviet launch vehicles such as the Sputnik, Vostok, and Soyuz rockets.

ramjet A jet engine with few moving parts and no turbine, in which the speed of the aircraft through the atmosphere forces air into the engine at high pressure. Fuel is then added, with the combustion producing forward thrust. Ramjets are a key element of many aerospaceplane concepts, but they only function efficiently at supersonic speeds.

RCS An abbreviation of Reaction Control System, a series of small rocket engines (thrusters) scattered over the surface of a spacecraft and used for adjusting its attitude in yaw, roll, and pitch axes.

Redstone An American ballistic missile, developed by Wernher von Braun at Redstone Arsenal, which formed the basis for many early US launch vehicles.

re-entry The return of a spacecraft or other object into the Earth's atmosphere, during which it may be heated to extreme temperatures by friction with air molecules.

remote sensing The scientific study of the Earth from space.

retropack A set of discardable retrorockets strapped over the heat shield of the Mercury space capsule in order to slow it for re-entry.

retrorocket A rocket system used for slowing a spacecraft down rather than accelerating it. Retrorockets are used to begin re-entry to the Earth's atmosphere, or to slow spaceprobes down when they arrive at their destination.

rocket A propulsion system that drives a vehicle forwards through the principle of action and reaction and is capable of working in a vacuum. The term is also used casually to refer to entire launch vehicles.

roll The rotation of a spacecraft about its longitudinal (front-back) axis - for example, the tilt of the Space Shuttle's wings.

RP-1 A form of kerosone used as fuel in US rockets.

RSA An abbreviation for the Russian Federal Space Agency, formed in the early 1990s to manage various aspects of the former Soviet Union space programme. It is also known as Roskosmos.

RTG An abbreviation for Radioisotope Thermoelectric (or Thermal) Generator. An RTG uses heat produced by a sample of radioactive material to generate electricity for spaceprobes travelling in distant parts of the Solar System.

Salyut A series of Soviet space stations, incorporating both DOS (Salyuts 1 and 4) and Almaz (Salyuts 2, 3, and 5) stations, along with more advanced designs (Salyuts 6 and 7).

satellite Any object that moves around a more massive one due to the effect of its gravitational attraction. Satellites may be either natural (moons of the various planets) or artificial.

Saturn rockets A series of US heavy-lift launchers developed by Wernher von Braun in the early 1960s. Saturn I was based on a cluster of Redstone-type rockets, while the Saturn V used massive new engines and high-energy cryogenic propellants. Saturn IB was a hybrid, based on Saturn I but with an upper stage borrowed from the Saturn V.

scramjet A modified ramjet design in which combustion happens while the fuel and air are moving at supersonic speed.

shaft and trunnion NASA's term for the two axes in which the telescope and sextant of the Apollo guidance computer could be moved for targeting the Sun, stars, and other astronomical objects.

solar array A panel-like or wing-like arrangement of solar cells that converts sunlight into electricity for use by spacecraft.

solar sail An experimental propulsion method that uses the pressure of radiation from the Sun to push a spacecraft forwards. Solar sails are only capable of low acceleration but can reach very high speeds.

solid-fuelled rocket A rocket in which fuel and oxidant are mixed (usually with other chemicals) and stored in a solid state. When ignited, the rocket burns like a firework and gases escape through an exhaust nozzle, pushing it forwards. A solid-fuelled rocket can only be ignited once.

Soyuz A long-running Soviet spacecraft series, first launched in 1967 and later upgraded to Soyuz-T (1980), Soyuz-TM (1987), and Soyuz-TMA (2002).

Soyuz rocket A reliable Soviet/Russian rocket, derived from the R-7 missile and used to launch Soyuz spacecraft.

spaceplane A spacecraft with aerodynamic properties that allow it fly like an aircraft or glider for at least part of its time in the atmosphere.

spaceprobe An automatic vehicle sent to explore the Solar System away from Earth. Spaceprobes can include flyby missions, orbiters, and landers.

Sputnik rocket A Soviet rocket developed by Sergei Korolev from the R-7 missile and used to launch the first satellites.

SRB An abbreviation of Solid Rocket Booster, the rockets that assist the Space Shuttle during launch.

SSME An abbreviation of Space Shuttle Main Engine, the engines on the back of the Shuttle orbiter that burn fuel from the External Tank during launch.

stage A section of a launch vehicle that burns its fuel and then separates and falls away from the rest of the vehicle.

steering vane A movable deflector that can affect the path of exhaust from a rocket engine, controlling the direction in which the vehicle moves.

STS An abbreviation for Space Transportation System, the official name of the US Space Shuttle. Each Shuttle mission is given an STS designation followed by a number (though the numbers do not necessarily indicate launch order).

Sun-synchronous orbit A polar orbit that also circles the Earth's equator once a year, keeping pace with the angle of the Sun so that the ground below is illuminated at a constant angle.

telemetry A stream of data sent automatically from a spacecraft to Earth, containing information about the status of its onboard systems.

thrust The forward force generated by a rocket engine, often measured in kilograms-force (kgf). One kilogram-force is the force exerted by a weight of one kilogram in Earth gravity, equivalent to 9.81 newtons (the official SI unit of force).

thruster A small rocket engine used, for example, in attitude adjustments, such as in an RCS.

thrust structure A structure above a rocket engine that takes the brunt of the engine's forward thrust, thereby preventing it from pushing into its own fuel tanks.

Titan A long-running series of US launch vehicles, originating in the US ballistic missile programme.

TKS A Soviet ferry spacecraft that was developed for use with the Almaz space stations but was eventually used as the basis for several of the modules on the Mir station.

translunar Literally "moon-crossing" - the path taken by a spacecraft from the Earth to the Moon.

turbopump A high-speed pump that supplies fuel and propellant from the tanks of a liquid-fuelled rocket to the combustion chamber.

UDMH Unsymmetrical dimethylhydrazine, a widely used hypergolic rocket fuel.

V-2 The first large liquid-fuelled rocket, designed by Wernher von Braun and used as a missile by Germany during the Second World War.

Vernier engine A small rocket engine on a movable gimbal, mounted away from the main engines and used to steer a launch vehicle.

VfR An abbreviation of Verein fur Raumschiffahrt, the German rocketry society of the 1930s.

Vostok rocket A Soviet launch vehicle, derived from the R-7 missile, used to launch the first manned spacecraft.

weight The force that acts on an object with mass in a gravitational field - while an object's mass remains constant, its weight may vary depending on the strength of local gravity.

weightlessness The condition of "free fall" experienced by people and objects when the effects of gravity are cancelled out in orbit.

yaw The rotation of a spacecraft around its vertical axis, the "crossways" orientation of a vehicle such as the Space Shuttle.

zero gravity see microgravity


Page numbers in italic refer to illustrations.

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