Home > Senior Science > Core > Information Systems > Information Systems: 4. Geostationary satellites
9.4 Information systems 4. Geostationary satellites
Extract from Senior Science Stage 6 Syllabus (Amended October 2002). Board of Studies, NSW.
[Edit: 1 June 10]
Prior learning: Science Stages 45 syllabus, Outcome
4.6 (content 4.6.10: gravitational force).
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.
- 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.
why an Earth-based satellite dish must always face the geostationary satellite communicating with it
- A geostationary satellite is one that orbits the Earth at the same period as the period of rotation of the Earth,( that is approximately every 24 hours) so that its position in the sky relative to any position on Earth is always the same. It must be in an equatorial orbit.
- The receiving dish on earth must be large as the signal is relatively weak, due to the satellite dish being quite distant 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.
why the satellite must be at a height where its revolution period is the same as that of
the Earths period of rotation
- In order for a satellite to remain in orbit over the same point on
the Earths 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 Earths surface and so the signal can be sent directly to
and from the dish antenna on the Earth to the satellite.
- The Earths gravitational pull keeps the satellite in orbit.
Satellites dont 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 Earths 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