Download Geostationary Answers

The Physics of Communication.
Worksheet Three
Geostationary satellites
Name ___________________
Geostationary satellites relay and transmit all over the world
What is a satellite?
A satellite is a moon, planet or machine that orbits a planet or star. For example, Earth is
a satellite because it orbits the sun. Likewise, the moon is a satellite because it orbits
Earth. Usually, the word "satellite" refers to a machine that is launched into space and
moves around Earth or another body in space.
What Was the First Satellite in Space?
Sputnik 1 was the first satellite in space. The Soviet Union launched it in 1957.
What do satellites do?
Some take pictures of the planet that help meteorologists predict weather and track
storms. Some take pictures of other planets, the sun, black holes, dark matter or faraway
galaxies
Many satellites are used for communications, such as beaming TV signals and phone calls
around the world. A group of more than 20 satellites make up the Global Positioning
System, or GPS. If you have a GPS receiver, these satellites can help figure out your exact
location.
What is a geostationary satellite?
Geostationary satellites orbit the Earth's axis at the same speed as the Earth spins. They
hover over a single point above the Earth at an altitude of about 36,000 kilometres
(22,300 miles). To maintain constant height and momentum, a geostationary satellite
must be located over the equator.
Why are satellites important?
The bird's-eye view that satellites have allows them to see large areas of Earth at one
time. This ability means satellites can collect more data, more quickly, than instruments
on the ground.
Satellites also can see into space better than telescopes at Earth's surface. That's because
satellites fly above the clouds, dust and molecules in the atmosphere that can block the
view from ground level.
Before satellites, TV signals didn't go very far. TV signals only travel in straight lines. So
they would quickly trail off into space instead of following Earth's curve. Sometimes
mountains or tall buildings would block them. Phone calls to faraway places were also a
problem. Setting up telephone wires over long distances or underwater is difficult and
costs a lot.
With satellites, TV signals and phone calls are sent upward to a satellite. Then, almost
instantly, the satellite can send them back down to different locations on Earth
Why should the receiving dish on earth be large and always face the direction of the
satellite?
The receiving dish on earth must be large as the signal is relatively weak, due to the
satellite dish being quite far away at approximately 36,000 km. The satellite dish must
face the same direction at all times to ensure that signals are received and retransmitted
in the correct directions to the intended receivers.
How does the geostationary satellite stay in position?
The Earth’s gravitational pull keeps the satellite in orbit. Satellites don’t fall towards the
Earth because of their tremendous speed. Although they are pulled towards the Earth by
gravity, their speed enables them to keep falling over the horizon.
Why have communication satellites different aerials and positional orbits?
Communication satellites use microwaves. Microwaves travel in straight lines and are
therefore ‘very directional’. This means the aerials that send and detect microwaves must
be pointing in the correct direction. The Earth-based satellite dish is constantly receiving
signals from the communication satellite. Because the Geostationary satellite remains
above the same point of the earth, the Earth-based satellite dish must face a fixed
direction if it remains in the same location with respect to the geostationary satellite.