Satellites Glossary

A-C|D-K |L-R|S-Z Akebono: A Japanese scientific studies satellite that became operational in 1989. It contained only one non-Japanese instrument: Canada's Suprathermal Ion Mass Spectrometer, sent to investigate the Earth's outer atmosphere.

Alouette: Canada's first satellite. Alouette, an atmospheric studies satellite, brought Canada into the space age. With its launch on September 29, 1962, Canada became the third country in the world to have a satellite in orbit, after the Soviet Union and the United States.

angle of inclination: The angle at which a satellite's orbit is tilted in relation to the Earth's equator. A 90 degree angle of inclination is a polar orbit. A zero degree angle of inclination is an equatorial orbit.

anechoic chamber: Also called an "echo free" chamber. A room at the David Florida Laboratory where satellites are tested to make sure they are sending and receiving clear signals. Anechoic chambers duplicate the silence of space, where there is no medium (like air or water) through which the sound waves can travel. The walls of the anechoic chambers are made of carbon compound pyramids which absorb any microwave and radio signals that hit them.

Anik A: A communications satellite launched by Telesat Canada in 1972. Anik A made Canada the first country in the world to have a satellite in geostationary orbit for domestic communications purposes. Anik A improved telephone and television communications, bringing Canadians closer together.

Anik B: A communications satellite launched by the firm Telesat Canada on Dec 16, 1978 to replace the Anik A satellites. The purpose of the Anik satellites was to improve communications across Canada, especially for those Canadians living in remote areas.

Anik E: A communications satellite launched by the firm Telesat Canada in 1991. Anik E was a series of two satellites - Anik E1 and Anik E2. They are the fifth generation of Anik satellites, and they are still a large part of Canadian communications.

antenna: A piece of equipment that allows transmission and reception of radio signals. Satellites need antennas to communicate with Earth. A satellite may need to receive instructions and transmit the information it collects, or it may relay the information sent to it to another site on Earth. Since the information is transmitted using radio waves, which move at the speed of light, this method allows for very fast communications (only a very small time lag).

aperture: A small hole. Usually with reference to a camera, the aperture is the hole in a camera that allows light to hit film. The amount of light that gets through the aperture determines what a picutre will look like.

astronomy satellite: A telescope orbiting the Earth. An astronomy satellite's vision is not clouded by the gases that make up the Earth's atmosphere, unlike that of telescopes on Earth. Astronomy satellites study stellar phenomenona like black holes, quasars, and distant galaxies. These are not to be confused with space exploration satellites, which also study these phenomena.

atmosphere: The many layers of gases that surround a planet. The Earth's atmosphere is composed of several layers of gases that separate our planet from space. The major gases in the Earth's atmosphere are nitrogen and oxygen. The air we breathe is part of the atmosphere.

atmospheric studies satellite: A type of scientific satellite that studies the Earth's atmosphere. They were some of the very first satellites launched into space, including Canada's first satellite Alouette.

attitude: The position in space of a spacecraft or aircraft. A satellite's attitude can be measured by the angle the satellite makes with the object it is orbiting, usually the Earth. Attitude determines the direction a satellite's instruments face. The attitude of a satellite must be constantly maintained; this is known as attitude control.

attitude control:

Stabilizing a satellite's attitude (direction) in its orbit. Attitude control can be done by spinning the satellite, or by having it remain stabilized in three axes using an internal gyroscope and thrusters.

aurora borealis: Also known as the northern lights. They are streams of coloured light that appear in the northern night sky, often in the winter. They are caused by disturbances in the ionosphere.

Auroral Imager: A Canadian Space Agency instrument aboard the Swedish scientific satellite Viking in 1986. It measures the direction, the energy, and the type of particles hitting the Earth.

black hole: A region of space where gravity is so strong that nothing, not even light, can escape. Black holes with over a million times the sun's mass are found in quasars.

body:

The non-technical term for a satellite's bus.

Brazilsat: Brazil contracted the Canadian firm Spar Aerospace Ltd. to build Brazilsat 1 and 2. This series of satellites was intended to give Brazil the ability to communicate within the entire country by satellite for the first time. Brazilsat 1 was launched on February 8, 1985 on a French Ariane 3 rocket.

bus:

The body of a satellite. The bus holds all of the scientific equipment and other necessary components of the satellite. The bus of a satellite is made of a variety of materials that are selected to protect the satellite from things like collisions, a buildup of electric charge, extreme temperatures, and radiation.

Canadarm: The nickname for Spar Aerospace's SRMS (Space shuttle Remote Manipulator System). The first Canadarm was a gift from Canada to NASA's space shuttle program; NASA subsequently bought Canadarms to equip the rest of the shuttle fleet. The Canadarm is used during shuttle flights to release satellites into orbit, retrieve them if they malfunction, and aid in their repair.

Canadian Space Agency (CSA): A central agency created in 1990 to bring together the existing space activities of the Canadian federal government. The CSA manages projects such as Radarsat, the Mobile Servicing System (MSS) (Canada's contribution to the International Space Station), the Astronaut Program, the David Florida Laboratory, the Space Science Program, and Canada's cooperation with international partners such as NASA and the European Space Agency (ESA). The CSA's mandate is to promote the peaceful use and development of space for the social and economic benefit of Canadians.

Chapman, John: The leader of the team from Canada's Defence Research Telecommunications Establishment that designed and constructed Canada's first satellite, Alouette.

charge coupled device (CCD): A highly sensitive camera, this counts individual photons of light to put together an image. It can take very detailed photographs of small areas.

charged particle: Also known as an ion.

cold plasma analyzer: An instrument on board the Swedish scientific satellite Freja. By sweeping its sensor through plasma, it obtains measurements of the charged particles in a layer of the atmosphere, the magnetosphere and upper ionosphere, and thus helps scientists understand Earth's atmosphere and how to protect it from pollutants.

communications satellite: A type of satellite used for communications on Earth by allowing radio, television, and telephone transmissions to be sent live anywhere in the world. Before satellites, transmissions were difficult or impossible at long distances. The signals, which travel in straight lines, could not bend around the round Earth to reach a destination far away. Because communications satellites are in orbit, the signals can be sent instantaneously into space and then redirected to another satellite or directly to their destination.

conductive:

Allows electricity to travel through it well. Conductors are conductive.

conductor: A material that carries an electrical charge. Conductors are conductive.

Cospas-Sarsat satellites: Search and rescue satellites in polar orbit. The Cospas-Sarsat system is a partnership between several countries including the United States, Canada, and Russia. The first satellite in the Cospas-Sarsat system was launched in 1982, and by 1984 the system was operational.

cryogenic: Frozen at extremely low temperatures. The field of cryogenics is attempting to produce temperatures as close to absolute zero as possible. Absolute zero is the temperature at which molecules stop moving altogether.

CSA: The Canadian Space Agency.

A-C|D-K |L-R|S-Z A-C|D-K| L-R|S-Z David Florida Laboratory: A Canadian laboratory in Ottawa where satellite equipment is tested before launch to make sure that it can withstand the shock of launch and the harsh conditions of space.

dawn-to-dusk orbit: A type of sun-synchronous orbit where the satellite is always in the sun. This allows the satellite to be powered almost entirely by its solar panels.

Deep Space Network: A worldwide effort, coordinated by NASA, that communicates with spacecraft in an Earth orbit at any time in that spacecraft's orbital period. There are three ground stations in the Deep Space Network, each at a different place on the globe so that they can each reach a spacecraft when it is over a different position on the Earth. The ground stations have very large dishes that act as antennas to receive and transmit signals to the spacecraft. There is also a control centre on Earth, run by NASA, that coordinates all the transmissions.

design criteria: Guidelines or specifications that an engineer must decide on before designing something. Design criteria are generally written as: "the ____, the better". For example, some satellite design criteria are "the lighter, the better" and "the more durable, the better".

doppler effect: An apparent shift in the frequency of a wave. For example, when someone is listening to the sound of an ambulance siren, and that person is staying still but the ambulance is driving by, the person will hear a change in pitch of the ambulance siren. That change in pitch is caused by the doppler effect. The frequency of a sound wave determines the pitch, and the distance of the source of the sound from the sound's observer determines the amount that the frequency seems to have shifted, known as the doppler shift.

downlinked: The process by which a satellite sends information from space back to Earth. The satellite translates its computer information into radio waves and sends those waves back to Earth via its antenna. On Earth, another antenna, usually in the form of a dish, picks up the radio waves and translates them back into a form that computers can understand.

eccentricity: Eccentricity is a measure of how circular a satellite’s orbit is. For a perfectly circular orbit the eccentricity is zero; elliptical orbits have eccentricities between zero and one. The higher the eccentricity, the more "squashed" the orbit is.

electromagnetic spectrum: Different kinds of electromagnetic waves can be classified by their wavelenghts. They are classified into sections called bands. The electromagnetic spectrum is the collection of these bands. The following types of waves make up the electromagnetic spectrum: gamma rays, x-rays, ultraviolet rays, visible light, infrared waves, and radio waves. The length of these waves ranges from 10-12 metres to 102 metres long; this is known as the wavelength. Click here for a picture of the electromagnetic spectrum.

electron: A small charged particle with a negative charge. Every atom has electrons. The number of electrons is different in every element. A transfer of electrons produces electricity.

elliptical orbit: An orbit where the satellite moves in a big ellipse (a shape like a flattened circle). A satellite in an elliptical orbit is sometimes close to the object it is orbiting and sometimes far away from it. A satellite in an elliptical orbit, especially a highly eccentric one, will move faster when it is close to the planet and slower when it is far away. An elliptical orbit can be useful to a communications satellite.

encryption device: An instrument often used in spy satellites. It encodes digital images or data before it is sent back to Earth.

equator: The imaginary circle drawn around the middle of the Earth. It runs east-west, marking latitude (side to side). It is found halfway between the north pole and the south pole.

equatorial orbit: The satellite flies along the line of the Earth's equator. Equatorial orbits can be useful for satellites observing tropical weather patterns, as they can monitor cloud conditions around the globe.

Faint Object Camera (FOC): An instrument built by the European Space Agency, which is currently in use on the Hubble Space Telescope.

focal length: The distance needed between a lens and an object to make the object visible and in focus. The human eye has different focal lengths depending on how much the muscles in the eye around the lens are contracted. That is how the human eye focuses.

footprint: The area with which a satellite in geostationary orbit can communicate. A footprint can be as large as an entire country; for example, many Canadian satellites have footprints almost the entire size of Canada, from coast to coast. Click here for a picture of a satellite's footprint.

frequency: The number of times a wave completes its cycle per unit of time. The frequency of a soundwave determines the pitch. Usually, frequency is measured in Hz which is the number of cycles (undulations) of the wave per second. Click here for a picture of a wave cycle.

frequency bands: The grouping together of electromagnetic waves of a similar frequency. In spectroscopic studies, one type of wave from the electromagnetic spectrum will show up as a band of colour that can be interpreted as a frequency band. This allows scientists to figure out what kind of energy is coming from a particular source For example, X-rays would make up a frequency band. Some bands are wider than others.

Galileo: A NASA space exploration satellite that was launched on October 18, 1989. Galileo was sent to Jupiter to study the planet's atmosphere , moons, and surrounding magnetosphere, for 2 years starting in December 1995. It was named for the Italian Renaissance scientist who discovered Jupiter's major moons in 1610 with the first astronomical telescope.

geomagnetic: Having to do with the magnetic properties of the Earth. Geomagnetic activity includes anything that changes the numbers of charged particles found in one area of the Earth.

geostationary (geosynchronous) orbit: An orbit in which a satellite appears to remain in the same spot in the sky all the time. When a satellite is in geostationary orbit, it travels at exactly the same speed as the Earth is rotating below it. A satellite in geostationary orbit is very high up, at 35 850 km above the Earth. Geostationary satellites are always located directly above the equator. The area with which a satellite in geostationary orbit can communicate is called its footprint.

Global Positioning System (GPS): A satellite technology that uses mathematics to calculate the position in three dimensions (latitude, longitude, and altitude) of something on the Earth by measuring the time it takes for the satellite's radio transmissions, travelling at the speed of light, to reach the a receiver on the ground. It requires a fleet of satellites in space. Applications of this technology include determining a position on the Earth, measuring the Earth's movement after an earthquake, or locating drop points for airlifted relief supplies.

grapple fixture: A long metal pin affixed to satellites so that they can be grasped by the Canadarm for launch, retrieval, or repair.

Greenwich meridian: The central meridian line from which all time zones are set.

gyroscope: A spherical object that spins stably in all three planes. It takes a lot of energy to move a gyroscope because its spin is so stable. Satellites can either spin themselves, acting as large gyroscopes, or they can have small internal gyroscopes which act as sensors to tell the satellite when its direction is changing, so the satellite can correct the problem using its thrusters. Gyroscopes have long been used as a tool to keep ships and airplanes stable. They are also common as toys.

Hermes: The first satellite to experiment with small satellite dishes for television. This use of small dishes made live news reports from remote locations possible. The Canadian Hermes satellite was launched on January 17, 1976.

Hertz: an SI unit for measuring frequency. It is measured in cycles per second where a cycle is one full undulation of a wave. The symbol for a Hertz is Hz; one million Hz is known as MHz; one billion Hz is known as GHz.

Hubble Space Telescope: A satellite launched by NASA in April, 1990. It is the largest telescope ever built to go into space. It is known as an astronomical observatory - in both senses of the word! Hubble is extremely powerful, able to look deep into space to study distant galaxies and stars.

infrared: Light waves that are slightly longer than visible light waves. They are found to the right of visible light in the electromagnetic spectrum. Infrared rays create most of the heat from sunlight and incandescent light bulbs.

infrared camera: An instrument that measures heat. Infrared cameras are often used to detect weather patterns or volcanic erruptions.

internal computer: The satellite's method of storing and analyzing data collected by the satellite, and a way of controlling its various systems. The technical term for this satellite subsystem is TT&C (Telemetry, Tracking, and Control).

ion:

An atom or a molecule that has lost or gained an electron. An ion is also known as a charged particle. Ions are usually more reactive than neutral, uncharged particles. They cause all sorts of things from static electricity and chemical reactions like smog, to body processes like cellular respiration and digestion.

ionization: The process of becoming an ion.

ionosonde: an instrument used to measure the ionization of gases in the atmosphere of a planet or a moon.

ionosphere: a region of gases, very high up in the atmosphere, that contains ionized gases.

ISDN lines: ISDN stands for Integrated Services Digital Network. Normally, people are connected from their home to the phone company through a phone line. When using a modem to connect to the Internet, the signals would go through this phone line. People can, however, also use a digital connection for their phones and modems. When connecting to the Internet, where all the data is digital because it is stored on computers, the connection through the ISDN line is much faster with fewer errors.

ISIS:

An acronym for the International Satellites for Ionospheric Studies program. After the successful launch of Canada's first satellite, Alouette, Canada and NASA embarked on this international project for atmospheric studies. The ISIS program launched Alouette 2, ISIS 1, and ISIS 2.

Klein, George: A National Research Council engineer who solved an important engineering problem in the design of Alouette, Canada's first satellite. Klein invented STEM antennas, allowing Alouette to have the necessary long antennas while still being small in size.

A-C|D-K| L-R|S-Z A-C|D-K |L-R|S-Z Lacrosse: A spy satellite launched by NASA in December of 1988. Lacrosse's main instrument, like most spy satellites, was its image sensor. It also carried Synthetic Aperture Radar (SAR).

LDEF: NASA's Long Duration Exposure Facility (LDEF) was launched in 1984 to study the effect of spending a long time exposed to the harsh conditions of space on different materials. In orbit for over five years, LDEF carried 57 experiments belonging to more than 200 investigators from universities, private companies, and NASA centres.

light year: The distance that light travels in one year. Since light travels at 3.0 x 108 metres per second, then light travelling for one year would travel a total distance of 946.08 x 1013 metres in total. Since that's a really big number, it's easier to call that number one light year.

low Earth orbit: An orbit within the Earth's atmosphere, but at its highest layer. Any satellite in a low Earth orbit can make observations of the Earth from fairly low down.

Magellan: A NASA space exploration satellite that was launched from the Atlantis space shuttle in May 1989. Magellan produced photograph-like images of Venus' surface using a radar system that could see through Venus' many clouds.

magnetosphere: The space around the Earth in which ions (charged particles) are controlled by the Earth's own magnetic field.

Mariner 2: A NASA space exploration satellite that measured the temperatures of the clouds and surface of Venus. It was launched on August 27, 1962.

Mars Observer: A NASA space probe launched September 1992 to study Mars.

Measurements of Pollution in the Troposphere (MOPITT): An instrument, designed and built by Canada, to measure the global distribution of carbon monoxide and methane in the troposphere. In 1998, Canada's MOPITT will be on board the first of NASA's Earth Observing System.

meridian lines: The imaginary lines that were drawn on the globe for navigational purposes. Meridian lines mark longitude and run through both the north and the south poles. They separate the Earth into time zones and they are used to indicate a coordinate on the Earth. The Greenwich meridian is the central meridian line from which all time zones are set.

meteorologist: Someone who studies the weather. Often, the person on the evening news who talks about the weather forecast is a meteorologist.

Meteosat: A geostationary weather satellite launched by the European Space Agency (ESA) and now operated by the company Eumetsat. The most recent version of Meteosat was launched in June 1988. It provides weather imaging of the Earth at both visible light and infrared wavelengths.

metre:

The basic unit for measuring length in the International System of Units (SI). This system is Canada's official system of measurement.

microwave: A form of electromagnetic radiation that is beyond the range of the visible light spectrum. Microwaves have very high frequencies and wavelengths of 1 mm to 50

cm.

MMU:

MSat:

Stands for Manned Maneuvering Unit. Astronauts on board a NASA space shuttle can strap on this large rocket backpack and maneuver during a spacewalk (officially known as an Extra Vehicular Activity) instead of remaining tethered to the shuttle or to the Canadarm.

A powerful communications satellite launched by the Canadian firm TMI Communications on April 20, 1996. MSat was Canada's first satellite designed to serve mobile users, especially those in remote areas out of the reach of conventional communication systems.

Mylar: The trade name of DuPont for their product used as thermal blanketing. It is a very thin material that has a shiny appearance. It is often used as an insulator in satellites, as well as for things on Earth like juice box packaging and emergency firstaid blankets.

NASA: An acronym for the United States National Aeronautics and Space Administration. NASA was created by Congress in 1958 to do three things: conduct aeronautical and space activities, create a science program using aeronautical and space vehicles, and inform the public as widely as possible about agency activities and their benefits.

navigation satellite: A type of satellite that gives ships and aircraft their coordinate positions on the Earth. Navigation satellites were developed in the 1950's, and they rely on the doppler effect to calculate the position of vessels emitting a radio signal. Navigation satellites are also widely used by the military.

Navstar: A series of American navigation satellites. The first satellite in the Navstar system was launched in 1978. Currently, there are 24 orbiting Navstar satellites. The threedimensional satellite navigational system of Navstar enables a traveller to find out his or her position anywhere on or above the planet.

Near Infrared Camera and Multi-Object Spectrometer (NICMOS):

An example of an infrared camera that is currently in use aboard the Hubble Space Telescope.

nebula: Cloud of glowing gas in space, lit up by hot young stars within it.

Olympus: At its launch on July 12,1989, the largest civilian telecommunications satellite in the world. Olympus was an experimental satellite built for the European Space Agency (ESA) by British Aerospace.

orbit: The path of a satellite, planet, or heavenly body around another, larger, body in space. For example, the Earth is in orbit around the Sun. The Moon is in orbit around the Earth. Orbits differ in their eccentricities.

particle: A very small piece of matter that moves and has energy. Particles are the fundamental things that make up the universe.

payload: The equipment carried into space by a space vehicle. The payload of a satellite includes all of the instruments and science experiments - anything that is not essential to basic functioning of the satellite, but used for science, data collection, or tools.

Payload Bay: The storage compartment of NASA's space shuttle. The Payload Bay, found on the top of the space shuttle, has large doors that open into space. When satellites are sent into space aboard the space shuttle, they are held in the Payload Bay.

plasma: Gas that has very high numbers of ions (charged particles). In a plasma, the number of free electrons is almost the same as the number of positive ions.

Polar:

Satellite launched on February 24, 1996 by NASA in the Global Geospace Science project. Polar is an atmospheric studies satellite in polar orbit. One purpose of Polar is to gather information that will help scientists protect future satellites from radiation and other atmospheric dangers.

polar orbit: Usually has an angle of inclination of 90 degrees to the equator. On every pass around the Earth, it passes over both the north and south poles. Therefore, as the Earth rotates to the east underneath the satellite which is travelling north and south, it can cover the entire Earth's surface. A polar orbiting satellite covers the entire globe every 14 days.

polarization: The result of light being passed through a filter that makes the light travel in all different directions, therefore making different rays of the light behave differently from one another. The filter is called a polarizing filter.

quasar: Puts out tremendous amounts of energy from a very small source. Known as the most intense concentrations of energy in the entire universe, quasars shine with the light of a hundred galaxies, but they are no larger than our solar system.

radar:

By emitting high frequency radio waves and measuring where and how fast they were reflected, a radar instrument can measure things like distance, direction, speed, etc. A radar instrument can "see" objects in the dark as well as penetrate cloud cover.

Radarsat: A revolutionary new satellite launched by the Canadian Space Agency on November 4, 1995. This remote sensing satellite uses radar to take images useful for agriculture, oceanography, forestry, hydrology, geology, cartography, and meteorology.

radiation: The harmful combination of waves and particles, known as high energy rays, emitted from a source.

radio telescope:

An instrument to pick up radio waves for analysis. Radio telescopes "see" things that are too far away to see in normal light by usimg radio waves. Satellites often use parabolic dishes with radio telescopes.

radiometer: An instrument to measure the changing levels of radiation as well as visible and infrared light. They can produce cloud images even at night.

reconnaisance satellite: Also called a spy satellite because it is used to spy on other countries. It can provide intelligence information on military activities, detect missile launches or nuclear explosions, and pick up and record radio and radar transmissions while passing over a country. It can also be used as an orbital weapon by placing warheads on a low orbit satellite to be launched at a ground target, but this is not a recommended or frequent use of satellites.

remote sensing: The process of collecting data about something from a point far away. A satellite making observations of the Earth, therefore, is using its equipment for remote sensing.

remote sensing satellite: A type of satellite that performs remote sensing from space. Remote sensing satellites generally monitor important resources for humans. For example, they might be used to track animal migration, locate mineral deposits, watch agricultural crops for weather damage, or see how fast the forests are being cut down. Because they are in space, remote sensing satellites are ideal for monitoring areas with harsh climates or difficult terrains.

repeater: An instrument that receives and retransmits signals anytime the satellite is close enough to be in contact with a ground station.

Sarsat: See Cospas-Sarsat.

satellite:

A-C|D-K |L-R|S-Z

Something that is in orbit around something else. The Moon is a satellite of the Earth, for example. An artificial satellite is a satellite that was constructed and placed in orbit by humans.

scientific notation: The system used when talking about very small or very large quantities. In scientific notation there is always a base unit, for example metre, Hertz, gram. Instead of using lots of zeros, scientific notation uses prefixes to indicate multiples of ten. Below is a chart of these prefixes, what they mean, and what they might measure:        

10 10 10 10 10 10 10 10

9

giga - the number of Hertz at which satellites transmit signals mega - the distance around the Earth 3 kilo - a person's weight -2 centi - the width of a computer monitor -3 milli - the head of a pin -6 micro - -the width of human tissue -9 nano - the wavelength of visible light -12 pico - the width of a virus 6

search and rescue satellite: A type of satellite used to help locate a ship, airplane, or individual lost or in distress in a remote area. Search and rescue satellites use devices like radio signals coming from beacons, the doppler effect, and radar to calculate where a distress signal is coming from. Usually, search and rescue satellites operate in fleets of several satellites. That way, the satellites can cover a large area, and they can communicate with one another.

SI (International System of Units): This system is Canada's official system of measurement. The metre and the Hertz are among the units used in this system.

slingshot: The process by which many space exploration satellites and probes get into deep space. A space exploration satellite can enter the gravitational field of a large planetary body like the Earth or Mars, and use the force of that planet's gravity to give the satellite momentum. Basically, the satellite swings around a planet and uses the energy from the planet's gravitational pull to send it into space. This uses the planet's gravitational pull like a slingshot.

Solar Max: A NASA space exploration satellite that studied the sun. In 1984, when the satellite's instruments failed, astronauts on board the shuttle repaired it after first grabbing it with the Canadarm.

solar panel: a source of power for satellites, made up of many individual solar cells, which are devices for transforming the energy of sunlight into electricity.

Solid-State Imaging instrument (SSI): A camera currently in use on the space exploration satellite Galileo.

sounder: A special kind of radiometer which measures changes of atmospheric temperature and changes in water vapor content of the air at various heights in the atmosphere.

space exploration satellite: Technically a space probe because it is sent deep into space and does not necessarily orbit anything. These are not satellites because the definition of a satellite is something that is in orbit around something else. However, space exploration satellites are similar to orbiting satellites in design and function. Like astronomy satellites, they study faraway planets and other stellar phenomena.

space probe: A space exploration satellite.

Space Telescope Imaging Spectrograph (STIS): A special spectrograph found on the Hubble Space Telescope.

spectrograph: An instrument that spreads out the light gathered by a telescope so that it can be analyzed to determine many different properties of celestial objects. These properties

include the chemical composition and abundance of different elements, temperature, radial velocity, rotational velocity, and magnetic fields.

spectrometer: An instrument used to study the electromagnetic spectrum.

spectroscopy: The study of the electromagnetic spectrum.

spin-stabilized: Attitude control is done by having the entire satellite spin. It becomes very stable because the satellite as a whole is acting as a gyroscope.

STEM antennas: An acronym for Storable Tubular Extendible Member. STEM antennas are stored in the body of a satellite to save space at launch and unrolled when the satellite reaches orbit. Canada's first satellite, Alouette, used four STEM antennas.

sun-synchronous orbit: A special case of the polar orbit. In a sun-synchronous orbit, the satellite passes over the same part of the Earth at roughly the same local time each day. Sunsynchronous orbits are usually meduim or low orbits.

Swedish Viking: A scientific satellite launched in February 1986. Viking carried the Canadian Space Agency's Ultraviolet Auroral Imager which provided important new information about the aurora borealis.

Synthetic Aperture Radar (SAR): An instrument that uses radar to see through dark, clouds and fog. This type of equipment is on board only three satellites in the world, including Radarsat and Lacrosse.

telescope: A device used in astronomy to see distant objects. Most telescopes use lenses and mirrors to magnify light coming from phenomena deep in space. This makes the objects look bigger and closer. Newer telescopes, however, are using radio waves, infrared light, laser, and radar technologies.

thermal blanketing: Like insulation in a house, the covering on a satellite that regulates temperature. A material commonly used for thermal blanketing on a satellite is Mylar.

thermal vacuum chamber: The closest thing to space on Earth. At the David Florida Laboratory, satellites are tested in this chamber which can simulate the temperature and vacuum of space to measure the cool-down and warm-up characteristics of a piece of hardware. This allows engineers to predict how the satellite's hardware might perform under the harsh conditions of space.

three-axis stabilized: Done with an internal gyroscope and thrusters. A gyroscope's stable spin can be used as a sensor to tell the satellite when its attitude is changing. The satellite can then correct the problem using thrusters. This is one form of attitude control.

thruster: A way of controlling a satellite's attitude. Thrusters usually contain compressed gas that when sent out of the end of the thruster will move the satellite in space. The force of the compressed gas (the action) causes the satellite to move in the opposite direction (the reaction). This is Newton's third law of motion - for every action there is an equal and opposite reaction.

transponder: An instrument used on communications satellites that receives a signal from a station on Earth at one frequency, amplifies it, and shifts it to a new frequency.

travelling wave tube: A hollow tube that is designed to fit a wave of a particular frequency. The width of the tube depends on the frequency of the signal. This results in a travelling wave.

trigonometry: An area of mathematics involving triangles. Trigonometric calculations use the relationships between the sides and the angles of triangles to calculate position, distance, speed, and many other things.

troposphere: The lowest layer of the atmosphere. The troposphere has distinctive winds and cloud formations, and it has a very marked drop in temperature with altitude. It is 10 - 16 km from the surface of the Earth.

TT&C:

An acronym for the satellite subsystem Telemetry, Tracking, and Control. TT&C refers to the brain of a satellite and its operating system. TT&C is the satellite's method for storing and analyzing the data it collects, and controlling its various systems. It also logs every activity of the satellite, receives information from the ground station, and takes care of any general upkeep, or "housekeeping", the satellite needs to do.

Ulysses: A NASA space probe that is studying the sun. In its passes over the polar regions of the sun in 1994 and 1995, Ulysses revealed the existence of fast solar winds coming from the poles. Ulysses will return to the sun in the year 2000 after making a slingshot around Jupiter.

uplinked: The process by which a ground station sends information and instructions up to a satellite. Often, scientists on Earth will have to send instructions to a satellite's on board computer. The ground station translates its computer information into radio waves and sends those waves up to the satellite via an antenna, usually in the form of a dish. Another antenna, on the satellite, picks up the radio waves sent from the Earth, and translates them back into a form that the satellite's on board computers can understand.

velocity: The measure of how fast an object is moving in a particular direction.

Viking:

A NASA space probe that gave us the first close look at Mars. Viking was made up of an Orbiter and a Lander, which was sent down to Mars to study the Martian soil and atmosphere.

visible spectrum: Visible light makes up only a small part of the electromagnetic spectrum. The visible light spectrum can be divided into different wavelenghts of light. The wavelength of the light determines the color of that light. The light spectrum goes from violet to red where red is the longest wavelength.

Voyager: Launched in 1977, NASA's twin Voyager space probes studied the outer planets before continuing on into deep space. The Voyager probes carried into space a record called "Sounds of Earth," bearing messages and pictures from our planet.

wave filter: An instrument that clarifies a signal by filtering out all other noise. A wave filter is useful for receiving communications in deep space where there are other stellar phenomena that emit frequencies too. These extra frequencies become part of the white noise always present in space. A wave filter will keep a satellite from being confused by this extra "noise" from space.

wave guide: An instrument that allows satellites to manipulate radio waves and redirect them within the satellite for processing. Wave guides are essential for any satellite performing a function concerning communications.

Wind Imaging Interferometer (WINDII): In 1991, the Canadian WINDII was launched on NASA's Upper Atmosphere Research Satellite and has been providing global information on temperatures, wind patterns, and concentrations of important gases in the upper atmosphere.

weather satellite: A type of satellite used to give meteorologists information about the weather. Weather satellites can do things like take pictures of cloud cover, monitor threatening weather systems like hurricanes, measure temperatures of the air and the sea, and generally give meteorologists the information that they need to make weather predictions.

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