SENIOR SCIENCE INFORMATION SYSTEMS Part 4: Satellites

1 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

Geostationary Satellites Geostationary satellites are held in a fixed position in orbit above the Earth. Geostationary satellites orbit around 36 000 km above the Earth’s surface. Video

Geostationary Satellites For satellites to be held in a fixed position above the Earth, they must be: close enough to the Earth to be held in orbit by the Earth’s gravitational pull far enough away from the Earth to prevent it from being pulled from orbit to the Earth by the Earth’s gravitational pull.

Geostationary Satellites A geostationary satellite must orbit the Earth at the same rate as the Earth rotates–one revolution in a 24 hour period. This critical height above the Earth is called the high Earth orbit (HEO). All geostationary satellites orbit the Earth in the HEO. Video

Geostationary satellites 1 Geostationary satellites orbit the Earth. T 2 Geostationary satellites orbit 2000 km above the Earth. F 3 HEO stands for high Earth orbit. T 4 Geostationary satellites must orbit the Earth in the HEO. T 5 Satellites in HEO are pulled to Earth by gravity. F 6 Satellites in HEO may float off into space. F 7 A satellite is a man made object in orbit around a planet. F 8 A geostationary satellite orbits the Earth once in 24 hours. T 9 Geostationary satellites pass quickly across the sky at night. F 10 In your experiment, the toothpick represents 36 000 km. T 11 The large round piece of fruit represents a satellite. F 12 The small object on the toothpick represents a satellite. T

Geostationary Satellites A geostationary satellites is in a fixed position above the Earth’s equator. A geostationary satellite has a constant line of sight access to a specific area of the Earth. The area of the Earth a geostationary satellite can send and receive messages from is called a footprint.

Geostationary Satellites The information transmitted to and from geostationary satellites includes: live or commercial television programs telecommunications telephone conversations digital information transfer broadband internet access video conferencing.

Uplink and Downlink A ground level transmitting station transmits information such as a television broadcast from America to a geostationary satellite at a particular wave frequency. This is called the uplink. The satellite is capable of receiving, amplifying and retransmitting the electromagnetic wave to a target such as Sydney. Alternatively the satellite can receive the wave, amplify it then change its frequency before sending back to Earth. Either method can be used as a downlink from satellite to Earth.

Uplink and Downlink

2 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

Satellite Dish Alignment The Earth–based satellite dish needs to directly face the satellite to receive clear reception. A clear reception is dependant on the intensity of the waves hitting the dish. A dish must be calibrated at a right angle (90°) to the waves entering the atmosphere for optimum reception. If the dish is at another angle to the satellite, the intensity of the waves reaching the dish would be reduced, therefore reducing the quality of reception.

Satellite Dish Alignment Is the Earth–based satellite dish directly facing the satellite (which is sending the waves)? How do you know this? The satellite dish is directly facing the satellite, which is sending the waves because all the waves hitting the dish are being reflected to the receiver and the dish is at right angles to the waves. Is the Earth–based satellite dish receiving a strong or weak signal? Explain your answer. The satellite dish is receiving a strong signal because waves from the satellite are being reflected from the entire dish to the receiver and the dish is at right angles to the waves.

Satellite Dish Alignment Is the satellite dish facing the satellite, which is sending the waves? How do you know this? The satellite dish is not directly facing the satellite because the dish is not at right angles to the waves and waves are not hitting the entire dish. Is the satellite dish receiving a strong or weak signal? Explain your answer. The satellite dish is receiving a weak signal because waves are not hitting the entire dish for reflection to the receiver, cutting down on the energy received.

Radio Satellites Radio telescopes collect radio waves from space the same way satellite dishes do. Radio telescopes are much larger as they need to collect waves over a larger area to receive a signal from space. Radio telescopes are moveable to receive waves from specific co–ordinates in space. Satellite dishes differ from radio telescopes in that they are much smaller and are designed to remain stationary for uninterrupted contact with a specific geostationary satellite. Satellite dishes generally receive telecommunications and television transmissions.

Review Question Spotlight pg. 219 To Think About Questions Set 1 & 2