Glossary of Terms

Altitude - The distance of a spacecraft above the surface of the Earth.

Ammonia - A liquid coolant (with a freezing point lower than water) used in the cooling loops of the External Thermal Cooling System.

Attitude - The three-dimensional position of a spacecraft in relation to another point. Also called orientation.

Bandwidth (or stream bandwidth) - A rate of data transfer, measured as a bit rate or throughput per unit time.

Beta Gimbal Assembly - Motors used to rotate the solar arrays so that they face the Sun to provide maximum power.

Conduction - Transfer of thermal energy from a substance from a high temperature to lower temperature.

Control Moment Gyroscopes - Four gyroscopes which maintain the attitude of the ISS.

Convection - Transfer of thermal energy by circulation or movement of the heated parts of liquid or gas.

Corrosion - Degradation of material due to a reaction with its environment.

Data - A set of numbers which shows the value for measurements such as temperature and status: open or closed, on or off.

Debris - The remains of something broken down or destroyed.

Demultiplexer - A computer that has a single-input and multiple-output switches.

Dew point - Temperature at which a vapor must be cooled at constant pressure to condense to liquid.

Electrocardiograph  - Instrument used to detect abnormal heart action by recording changes in the electrical potential during heartbeat.

Ephemeris - The collection of state vectors over a certain period of time.

External Thermal Control System - An ammonia system which collects heat from the ITCS and other "loads" (warm equipment) and radiates that heat to space.

Force - Causes an object at rest to move, or an object already in motion to move faster or slower. A force that is purely perpendicular to the direction of motion only changes the direction of motion.

Frequency - Number of wavelengths passing a fixed point per second.

GHz - A frequency of one billion cycles or wavelengths per second.

Gimbal - A device with two mutually perpendicular and intersecting axes of rotation, thus giving free angular movement in two directions.

Global Positioning System - A navigation system made up of satellites and receivers that can determine the latitude and longitude of a receiver by computing the time difference for signals from different satellites to reach the receiver.

Grappling vehicle - Maneuvers spacecraft in place.

Greenwich Mean Time (GMT) - The time the crew uses onboard the ISS and the ground team's use.

Gyroscope - A mechanical device made up of a spinning wheel able to rotate about one or more gimbals.

Internal Thermal Control System - Uses water to transfer heat from inside the ISS to the ETCS.

J2000 - The inertial reference frame used by the ISS for navigation. The origin is at center of Earth. The +X axis points toward the mean vernal equinox on January 1, 2000. The +Z axis points toward the north pole along the Earth's mean axis of rotation. The +Y axis completes the right-handed coordinate system.

Jettison - To intentionally throw away; to discard by spacecraft.

Kilowatt - Unit of measurement to express output power and is equal to 1000 watts.

Mass spectrometry - The measurement of the levels of gases in the atmosphere.

Microgravity - Near-weightlessness experienced in orbit as a result of the spacecraft "free falling" around the Earth.

Multiplexer - A computer that has multiple-input signals and a single-output switch.

Orientation - See attitude.

Particulates - Very small particles.

Photovoltaic Thermal Control System - The system used to cool the nickel-hydrogen batteries of the ISS.

Position - How high and where the ISS is located above the Earth.

Radiator - Transfers thermal energy from one substance to another for the purpose of cooling.

Reboost - Engines are fired to boost a spacecraft to a higher altitude.

Satellite - A man-made object that orbits around the Earth.

Solar Alpha Rotary Joint - A joint which allows for rotation of either entire arm of solar arrays.

Solar array - A panel comprised of solar cells which collect energy from the Sun and convert the energy into electricity.

Spacecraft - A manned or unmanned device designed to be placed in orbit around the Earth or sent to another celestial body such as a moon or distant planet.

State determination - Determining the position and velocity of a spacecraft.

State vector - The position and velocity of an object at a specific time.

Teleconferencing - The holding of a conference among people remote from one another by means of telecommunication device.

Thermal Radiator Rotary Joint - A joint used to rotate three large ISS radiator panels. See radiator.

Three-dimensional - Having three dimensions of length, width and depth.

Translation - Movement in a straight line without rotation.

U.S. Strategic Command - The part of the Air Force which detects, identifies and tracks all man-made objects in Earth's orbit.

United States On-orbit Segment - The United States portion of the ISS.

Vacuum - A region or volume where the internal pressure is [nearly] zero.

Velocity - A quantity equal to the speed an object is moving in a given direction.

Visiting vehicle - Any spacecraft carrying cargo or crew which docks with the International Space Station.

Vital Signs - Signs of life, such as pulse rate, respiratory rate, body temperature, and blood pressure.

Volt - The difference in electric potential between two points.