Discovery Science: Satellite Technology
Artificial satellites are spacecraft that orbit the Earth or other bodies in space. They carry out tasks that are difficult or impossible to undertake from the Earth’s surface.
Satellites are monitored and directed from ground stations. While in orbit, sensors determine their position with respect to the Earth or sun. They can then be guided or maneuvered as needed, using electrical gyroscopes and small course correction engines. A satellite’s electrical power is usually provided by solar cells mounted directly on the satellite or on wing like solar panels.
Battery power is used when the satellite travels through Earth’s shadow. Satellites are exposed to extreme temperature differences as they alternate between exposure to direct solar radiation and the shadow of the Earth. Accordingly, their instruments require protection with insulating or heat-reflecting shields.
Types of satellites
Telecommunications satellites serve as relay stations for data links and for radio, television, telephone, and fax signals. A satellite receives signals from a ground station, amplifies them, and sends them to another ground station. Earth observation and weather satellites monitor the sunlight and heat radiation reflected from the planet. Weather satellites also detect signals from the horizon, gathering data from various levels of the atmosphere.
De- tailed observations of the Earth’s surface can be produced using Synthetic Aperture Radar (SAR), which passes through the cloud layer. Satellite paths The paths followed by satellites in orbit can be circular or elliptical. An orbit of up to 620 miles (1,000 km) above ground level is considered a low Earth orbit. A satellite in low Earth orbit travels at approximately five miles per second (eight km/s). In a geostationary orbit, on the other hand, it travels at approximately two miles per second (three km/s).
Many observation and weather satellites are located at this level in order to be close to Earth’s surface. Orbits may be tilted with respect to the Equator and even cross the Poles. Since the Earth is always rotating under the satellites, large portions of the planet’s surface can be covered. Geostationary orbit is particularly useful for telecommunications and television satellites.
On this circular orbit, some 22,370 miles (36,000 km) above the Equator, the satellite’s orbit takes the same amount of time as the planet’s rotation. The device therefore stays over the same point on the Earth’s surface. Fixed antennas can be conveniently aimed at such a satellite without
needing to locate or track it.
SATELLITE NAVIGATION
Navigation satellites help individuals, airplanes, cars, and other satellites determine their location. Systems include the U.S. GPS and Russian GL0NASS, while the European Galileo system is under construction. Navigation satellites constantly transmit their positions in orbit over time.
A navigation device receives data from several satellites. It can calculate the signal’s travel time and thus its distance from the satellite. Using the positioning data from the satellites, it then triangulates its own precise location.