Satellites

1. Satellites Monitoring the Earth Communications Monitoring Space

2. Satellites • Satellites are objects that orbit other bodies • They are held in orbit by the force of gravity of the body they are orbiting • The Moon is an example of a natural satellite • Artificial satellites are made by man and have been put into orbit for a number of reasons

3. For astronomy… • The Hubble telescope is an example of a satellite used to study deep space • It has the advantage of not having to receive light rays that have passed through the Earth’s atmosphere • The atmosphere distorts light rays by refraction – this is why stars appear to twinkle when seen from Earth

4. Studying the Earth’s surface… • Satellites can examine the Earth’s geology, soil types and even crop growth • This can help farmers decide what fertilisers to apply • Observing geology could give clues as to when volcanoes or earthquakes occur

5. Communications • Satellites have revolutionized communication by making worldwide telephone links and live broadcasts common occurrences. • A satellite receives a microwave signal from a ground station on the earth (the uplink) • It then amplifies and retransmits the signal back to a receiving station or stations on earth at a different frequency (the downlink). • A communication satellite is in geostationary orbit, which means that it is orbiting at the same speed as the earth is revolving. The satellite stays in the same position relative to the surface of the earth, so that the broadcasting station will never lose contact with the receiver.

6. Monitoring the weather • A common occurrence on our weather forecasts is the inclusion of satellite images to show the position of cloud or rain! Navigation • Five satellites in orbit around the Earth provide the GPS system that allows the positioning of an object to within 10m anywhere on the Earth’s surface

7. Military uses… • There are many satellites in orbit designed to collect information about military matters • Governments often want to know about the position of armies and the equipment they might have • ‘Spy’ satellites are one way of collecting this information

8. Geostationary orbits • In a geostationary orbit, a satellite orbits at a distance of 35 800km from the Earth and completes an orbit every 24 hours • This means it appears to stay in the same position above the Earth’s surface • This is important for communications satellites (e.g. SkyTV) so that ground station dishes can point to the same region of the sky and not need constant alteration

9. Low Polar Orbits • These are much lower orbits and need the satellite to travel extremely fast • By flying from pole to pole, the satellite is able to monitor all the Earth’s surface • This is because as the satellite travels over the Earth, the Earth is spinning beneath it • This means that the satellite appears to follow a spiral track over the Earth’s surface

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36. Uses of polar orbits • Since they can observe (eventually) the entire surface area of the Earth, satellites in these orbits are useful in any role that involves studying the Earth