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Sarsat:
See Cospas-Sarsat.




satellite:
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 9 giga - the number of Hertz at which satellites transmit signals
  • 10 6 mega - the distance around the Earth
  • 10 3 kilo - a person's weight
  • 10 -2 centi - the width of a computer monitor
  • 10 -3 milli - the head of a pin
  • 10 -6 micro - -the width of human tissue
  • 10 -9 nano - the wavelength of visible light
  • 10 -12 pico - the width of a virus




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. Sun-synchronous 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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