Key Vocabulary

An astronaut (American term) is a person who travels into space. In the United States, people who travel above an altitude of 50 miles (80 km) are called astronauts.

Atrophy is the partial or complete wasting away of a part of the body, caused by disuse, disease, poor nourishment or loss of nerve supply. Space travelers experience atrophy while in space for long periods of time; this is countered by extensive pre-flight conditioning, diet, exercise while in space and post-flight therapy.

"Big Whack" model
The Moon is thought to have formed as a result of a collision between the young Earth and a Mars-sized body.

Command Module
The Command/Service Module (CSM) consisted of two segments, the command module that housed the Apollo crew and their equipment needed for re-entry and splashdown and a service module that provided propulsion, electrical power and storage for various consumables required during a mission. The service module would be cast off and allowed to burn up in the atmosphere before the command module re-entered and brought the crew home.

A cosmonaut (Russian term) is a person who travels into space, or who makes a career of doing so.

European Space Agency
The ESA, established in 1975, is an inter-governmental organization dedicated to the exploration of space. It is headquartered in Paris, France.

Extravehicular Activity (EVA)
EVA is work done by an astronaut away from the Earth and outside of his or her spacecraft. The term most commonly applies to an EVA made outside a craft orbiting Earth (a spacewalk) but also applies to an EVA made on the surface of the Moon (a Moonwalk). EVAs may be either tethered (the astronaut is connected to the spacecraft, oxygen can be supplied through a tube, no propulsion is needed to return to the spacecraft) or untethered.

Gravity is the tendency of objects with mass to attract and accelerate toward each other.

Guidance System
A guidance system is a device or group of devices used to navigate a rocket, satellite or other craft, typically without direct or continuous human control.

Hubble Space Telescope
The Hubble Space Telescope (HST) is in orbit around Earth at an average height of 350 miles. Launched in 1990, its position outside the Earth's atmosphere allows it to take sharp optical images of very faint objects. It is named for Edwin Hubble, an American astronomer who proved the existence of galaxies outside our own.

International Space Station
The International Space Station (ISS) is a joint project of space agencies from many countries. The space station is located in low Earth orbit with an orbital period of 92 minutes. Due to the ISS, there is a permanent human presence in space, as there have always been at least two people on board ISS since the first permanent crew entered the ISS on Nov. 2, 2000.

Jet Propulsion Lab (JPL)
JPL builds and operates unmanned spacecraft for the National Aeronautics and Space Administration (NASA). JPL is a federally funded research and development center managed and operated by Caltech under a contract with NASA. JPL has sent unmanned missions to every planet in our solar system and has done extensive mapping missions of the Earth.

Lunar Module
The Apollo Lunar Module was the lander portion of the Apollo spacecraft built for the U.S. Apollo program. It was built to help achieve the transit from Moon orbit to the surface and back, carrying two crew members. It consisted of two stages—the descent stage module and the ascent stage.

Lunar Rover
The Lunar Roving Vehicle or LRV is a land vehicle for use on the Moon. LRVs allow the astronauts to explore further than traveling on foot.

The National Aeronautics and Space Administration (NASA), established on July 29, 1958, is the agency responsible for the public space program of the United States and for long-term civilian and military aerospace research.

Orbital Speeds
The orbital speed of a body (planet, satellite or star) is the speed at which it orbits, usually around a more massive body.

Planetary Society
The Planetary Society is a publicly supported, not-for-profit organization that does research projects related to astronomy. Based in Pasadena, California, with an international membership, the Society is dedicated to the exploration of Mars and the rest of the Solar System and the search for Near Earth Objects and extraterrestrial life. Its mission is "To inspire the people of Earth through education, research and public participation to explore other worlds and seek other life."

Radio Telescope
A radio telescope "sees" radio waves emitted by radio sources, typically by means of a large parabolic ("dish") antenna rather than the visible light waves seen by “ordinary” telescopes.

Rendezvous is when two space craft come together, with or without docking. The first space rendezvous took place on Dec. 15, 1965 when Gemini 6 came within 30 cm of Gemini 7 without physical contact. The first space rendezvous and docking took place on March 16, 1966.

Robotic Probe
A probe uses onboard instruments to gather and relay information from remote, hazardous or difficult to reach locations. Probes may return their data by radio links or collect and return physical samples. Robotic probes operating in space are known as space probes.

Rocket Propulsion
Rocket propulsion changes the velocity of spacecraft, usually by heating the reaction mass and allowing it to flow out the back of the vehicle.

A satellite is any object that orbits another object. Natural satellites include moons and planets. Artificial satellites are launched into orbit and may be moved from one orbital height to another from time to time, requiring propulsion.

Solar Flare
A solar flare is a violent explosion in the Sun's atmosphere with an energy equivalent to tens of millions of hydrogen bombs that produces electromagnetic radiation. Most flares occur around sunspots where intense magnetic fields emerge from the Sun's surface into the corona.

Space Race
The Space Race was an informal competition between the United States and the Soviet Union that lasted roughly from 1957 to 1975. It involved the parallel efforts by each of those countries to explore outer space with artificial satellites, to send humans into space and to land people on the Moon.

Space Transportation System (STS)
The STS is NASA’s current manned launch vehicle, known as the “Space Shuttle.” The shuttle orbiter is launched vertically carrying five to seven astronauts and lands as an unpowered glider.

The Sputnik program was a series of unmanned space missions launched by the Soviet Union in the late 1950s to demonstrate the viability of artificial satellites. The name "Sputnik" comes from Russian, meaning "fellow traveler," and also "satellite" (literally co-pather). The first launch on Oct. 4, 1957 began the “Space Race” between the United States and the Soviet Union.

The velocity of an object is its speed in a particular direction, defined as D/t or distance divided by time.