2.1.2Space
Uses of Satellites — SQA National 5 Physics Revision Notes & Topical Questions
5 min read 6 parts Lesson 2 of 12
Curriculum Equation Key Circular Motion & Gravitation LawsFast Exam Solution
a_c = v² / r | F_c = (m × v²) / r | F_g = G × (m₁ × m₂) / r² | v_orbit = √(G×M / r)
Part 1 of 6Main Uses
Artificial satellites orbit the Earth at many different heights, and each type of orbit is chosen for its job.
Communications
- Satellites relay television, telephone and internet signals over long distances by receiving and re-transmitting microwaves.
Navigation
- Navigation satellite systems like GPS let receivers calculate position from signals sent by several satellites.
Weather
- Weather satellites take images of clouds and measure temperatures, helping forecasts and storm warnings.
Monitoring
- Earth-observation satellites survey crops, forests, ice, oceans and pollution, or carry out military surveillance.
Part 2 of 6Choosing an Orbit
Choosing an Orbit
Geostationary
- Orbits above the equator once every 24 hours, so it stays above the same point;
- ideal for television and communications.
Low polar
- Passes over the poles at a lower height and shorter period, scanning the whole Earth as it rotates beneath.
Navigation
- Systems use several satellites at once so that signals are always available from different places.
Telescopes
- Space telescopes avoid the atmosphere's distortion and absorption, giving clearer images of space.
| Type | Orbit | Typical use |
|---|---|---|
| Geostationary | 24 h, above equator | Television, communications |
| Polar | Shorter, over poles | Mapping, weather |
| Low orbit | Short period | Observation, space station |
Part 3 of 6Signal Travel Time
1
A ground station sends a microwave signal up to the satellite, travelling at the speed of light.
2
The satellite amplifies it and sends it back down to another ground station.
3
The distance to a geostationary satellite is about 36 000 km, so the one-way time is distance ÷ speed.
4
This delay of about a quarter of a second is noticeable on live links between continents.
Part 4 of 6Advantages and Limitations
Advantages and Limitations
Global coverage
- Satellites reach remote areas, ships and aircraft where cables or masts cannot go.
Delay
- The long signal path causes a short time delay in conversations.
Lifetime
- Satellites need fuel to adjust their position and eventually become space debris when they run out.
Cost
- Building and launching satellites is expensive but the services they provide are shared by millions of users.
Part 5 of 6Worked Example
Question
- A geostationary satellite is 3.6 × 10⁷ m above a ground station.
- Radio waves travel at 3.0 × 10⁸ m/s.
- Calculate the time for a signal to travel up, and for a signal to go up and back down.
- t = d ÷ v = 3.6 × 10⁷ ÷ 3.0 × 10⁸ = 0.12 s.
- Up and down = 2 × 0.12 s = 0.24 s.
- This is why speakers on live links may seem to pause before answering.
Answer 0.12 s up; 0.24 s up and down.
Part 6 of 6Exam Checklist & Tips
2.1.2 – Key Points for the Exam
- Geostationary satellite A satellite with a 24-hour orbit staying above the same point on the equator.
- Polar orbit An orbit that passes over the Earth's poles.
- GPS A satellite navigation system that gives position.
- Microwaves Electromagnetic waves used to send signals to and from satellites.
Common Mistakes
- Saying a geostationary satellite is not moving; it is orbiting at the same rate as the Earth rotates.
- Thinking satellites use sound waves to send signals.
- Forgetting that signals travel at the speed of light, not instantly.
- Placing a geostationary satellite over the poles instead of the equator.
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