Descriptionary

Giotto a space probe launched to collect data on Halley's Comet in 1986.

gravity assist the use of a planet's gravity to deflect or slingshot a space probe deeper into space.

heavy space plane an experimental shuttle craft capable of "flying" into orbit by using ejector ramjet engines combined with rocket engines.

HESSI High Energy Solar Spectroscopic Imager; a probe to be launched early in the 21st century to study solar flares.

horizon sensor on a satellite, an onboard sensor that perceives Earth's horizon as an aid to maintain proper attitude.

Hubble Space Telescope a large, orbiting observa­tory, launched in 1990 from the space shuttle.

hydrazine space probe's onboard fuel used for atti­tude-adjusting rockets.

hydrogen peroxide a fuel sometimes used to power a satellite's maneuvering rockets.

International Space Station an orbiting space station composed of 100 separate elements, which will stretch more than 100 meters long when com­pleted and built cooperatively by 16 nations. The first two component modules, the Unity and Zarya, were linked by shuttle astronauts in 1998. Construction was slowed and in question after the loss of the space shuttle Columbia in 2003.

ion engine an experimental engine employing solar panels to accelerate charged atoms of xenon to create propulsion in space probes.

JPL Jet Propulsion Laboratory; the scientific facility and body of scientists in Pasadena, California, that oversees and maintains a space probe's mission.

Kepler launched in 2009, a spacecraft that trails Earth's orbit and searches a group of 100,000 stars in our galaxy for evidence of Earthlike or habitable planets.

lander any vessel designed to land on a planet or moon.

launch corridor a flight path.

launch window a span of time within which a sat­ellite or probe must be launched in order to meet eco­nomic, trajectory, or orbital location requirements.

lightcraft an experimental spacecraft powered by high-intensity laser light or microwave energy beamed from the ground to the bottom of the vessel to con­centrate heat and create thrust.

Lunar Prospector a space probe launched in 1998 to survey and collect data from the moon.

Magellan a probe launched in 1989 to map by radar the surface of Venus and to take measurements of the planet's gravity.

Mariner any one of various planetary probes, launched from 1962 to 1973.

Mars Direct Plan an inexpensive, speculative plan for sending humans to mars sometime around 2020.

Mars Express an orbiter and lander mission to Mars conducted by the European Space Agency. The mission failed when its landing craft, Beagle, attempted to touch down on Mars on December 25, 2003; it did not return radio signals and was presumed "lost."

Mars Global Surveyor a space probe launched in 1996 to map the planet Mars.

Mars Odyssey an orbiter that reached Mars in October of 2001 and circled the planet to collect data on radiation and surface minerals. It also served as a communications relay for the rovers Opportunity and Spirit.

Mars Pathfinder a planetary probe that landed on Mars in 1997 and radioed back photographs of a rock-strewn Martian desert.

Mars Surveyor a planetary probe launched in 1998 and 1999 in two parts to explore the south pole of Mars.

Mercury a NASA program featuring the first manned, suborbital and orbital missions, from 1961 to 1963.

microprobe a small probe launched from a larger, main probe.

Mir a Russian orbital space station, launched in 1986 and retired in 2001 when it reentered Earth's atmosphere.

modules independent subsystems on a satellite or probe.

NASA National Aeronautics and Space Admin­istration.

NEAR Near Earth Asteroid Rendezvous; a space probe launched in 1996 to collect data on Eros, a 40-kilometer-long asteroid in the solar system's main asteroid belt.

Opportunity and Spirit two planetary rovers that landed on opposite sides of Mars in January 2004 and gathered data on climate and geology and searched for evidence of past life forms.

orbit a path followed by a spacecraft or satellite around a planet or moon, and held in place by gravi­tational forces.

Orion shaped like the Apollo spacecraft but three times larger, a space capsule designed to carry four astronauts to the International Space Station in 2015 and to the Moon by 2020. In an expandable form, it may carry as many as six astronauts to Mars.

Pathfinder Rover an all-terrain vehicle launched from the Mars Pathfinder to explore the surface of Mars.

payload collective term for cargo, gear, and passen­gers taken into space by a spacecraft.

photovoltaics see solar cells.