Each satellite function answers a need that is hard to meet from the ground. To explain a function, state the need, name the function, and give the advantage of being in space.
This lesson is part of space technology within the SPM Science guide. The next lesson, comparing orbit and launch concepts, explains where satellites go.
What does each function do?
Use the table to link a need to a function and to the space advantage.
| Need | Function | Why from space |
|---|---|---|
| Send TV or data between distant places | Communication | Signals travel in straight lines, so a satellite relays them past the Earth’s curve |
| Forecast storms | Weather observation | Views whole cloud systems at once |
| Find a position or route | Navigation | Signals from several satellites can be compared |
| Map land or forest cover | Earth observation | Wide, repeated views of the same area |
Worked example: matching needs
The situations are original. A coastal village wants early warning of a storm. A ship wants to know its position in open sea. A remote island school wants to receive a broadcast.
Village. Weather observation: a satellite sees the cloud system forming over a wide area, well before it reaches the coast.
Ship. Navigation: signals from satellites let the ship work out its position where there are no landmarks.
School. Communication: the broadcast is sent up to a satellite and relayed down to the island, which a ground station cannot reach directly.
The mistake that costs marks
The common slip is to write only the function, such as “communication satellite”, for a three-mark question. That names the use but gives no need and no reason.
| Step | Wrong | Right |
|---|---|---|
| Function | Communication satellite | Communication satellite |
| Need | (missing) | The island is too far for a direct signal |
| Why from space | (missing) | A satellite high above relays the signal past the Earth’s curve |
| Marks | 1 of 3 | 3 of 3 |
The fix is to write one clause for each column of the table.
How long does a signal take?
Radio waves travel at about 3 × 10⁸ m/s. State this speed as your assumption, then use time = distance ÷ speed.
For a satellite 1 200 km above the ground, the distance is 1 200 000 m. The time is 1 200 000 ÷ 300 000 000 = 0.004 s for one way up. The round trip up and down is 0.008 s, assuming the signal goes straight up and straight down.
Check yourself
Explain why a farming town in a mountain valley might rely on a satellite for communication. Then find the time for a signal to travel 900 km to a satellite, using 3 × 10⁸ m/s.
Answer
Mountains block signals that travel in straight lines, so a direct link to a distant city may not work. A satellite above the valley can receive the signal and relay it past the mountains.
Time = 900 000 ÷ 300 000 000 = 0.003 s. Assumption: the signal travels in a straight line at the speed given.
What to study next
Continue with comparing orbit and launch concepts within scope, then test the cluster with the space technology practice set.
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