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9.4 Information systems 4. Geostationary satellites

Syllabus reference (October 2002 version)
4. Geostationary satellites relay and transmit information from the other side of the world	Students learn to: explain why the satellite must be at a height where its revolution period is the same as that of the Earth’s period of rotation explain why the Earth-based satellite dish must face a fixed direction if it remains in the same location with respect to the geostationary satellite	Students: gather, process and analyse information from secondary sources to identify the satellites used for ‘live’ telecast from other regions of the world to Australia and vice versa and to present reasons why communication satellites have different aerials and positional orbits

Syllabus reference (October 2002 version)

4. Geostationary satellites relay and transmit information from the other side of the world

Students learn to:

explain why the satellite must be at a height where its revolution period is the same as that of the Earth’s period of rotation

explain why the Earth-based satellite dish must face a fixed direction if it remains in the same location with respect to the geostationary satellite

Students:

gather, process and analyse information from secondary sources to identify the satellites used for ‘live’ telecast from other regions of the world to Australia and vice versa and to present reasons why communication satellites have different aerials and positional orbits

Extract from Senior Science Stage 6 Syllabus (Amended October 2002). Board of Studies, NSW.

[Edit: 28 May 09]

Prior learning: Science Stages 4–5 syllabus, Outcome 4.6 (content 4.6.10: gravitational force).

gather, process and analyse information from secondary sources to identify the satellites used for ‘live’ telecast from other regions of the world to Australia and vice versa and to present reasons why communication satellites have different aerials and positional orbits

Information can be gathered from various sources, such as the Internet, books and CD-ROMs dealing with space and communication technologies.
- Satellite orbits Entertainment: Television, Ezilon Infobase, Community News and Articles. This article isn't specifically about Australia but talks generally about satellite communication and orbits of the satellites
- A particularly relevant chapter on satellite communication is published in Space Australia, the story of Australia’s involvement in space by Kerrie Dougherty and Matthew James from the Powerhouse Museum, Sydney.
- Optus B, Australia's Second National Satellite System Boeing, Los Angeles, California, USA
  This site is more about Australia's telecommunications within Australia than with the rest of the world but it has some excellent information about it's launch, specifications and functions.
- Bringing You the Latest in Satellite Communication News Newsletter August 08, TC Communications, Auburn, NSW
- SatCom Group This is an international company based in the UK that has an office in Australia and is used in Australia. Choose a satellite system by clicking on one on the left, eg Iridium.
Process information by producing a list of satellites used by Australia for sending and receiving live broadcasts.
Analyse all the gathered information to identify the satellites used for communication and present information about their positional orbit (e.g. low earth orbit satellites) and the types of aerials used (including frequencies) by each satellite and why they differ.

explain why the Earth-based satellite dish must face a fixed direction if it remains in the same location with respect to the geostationary satellite

A geostationary satellite is one that orbits the Earth once every 24 hours, in an equatorial orbit, and therefore remains over the same point on the Earth at all times. The size and weight of the antennae (transmission and receiving) is too great to allow them to be easily or quickly moved to stay pointing at each other.
The signals are in the microwave region, so the satellite dish must face the same direction at all times to ensure that signals are received and retransmitted in the correct directions to intended receivers.

explain why the satellite must be at a height where its revolution period is the same as that of the Earth’s period of rotation

In order for a satellite to remain in orbit over the same point on the Earth’s surface at all times, it must be located 36 000 kilometres above the equator. In this orbit, the satellite travels at a speed that keeps it in the same position relative to the Earth’s surface and so the signal can be sent directly to and from the dish antenna on the Earth to the satellite.
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. Thus, if they are travelling with exactly the correct speed they never actually get any closer to the Earth’s surface. Tracking stations on Earth use radio signals to activate small rockets on the satellite to keep them in the correct orbit.

An activity: Why do satellites stay in orbit?
Gulf of Maine Aquarium, USA