SATELLITES
The object we frequently hear when it comes to space missions is a satellite. In this module, we will understand, what satellites are, what keeps them in their orbits and why we inject satellites into a particular orbit for a specific purpose? Parts of satellites and how are satellites used in our day-to-day activities.
What is a Satellite
A Satellite is a body that orbits around a planet or any celestial body in space. Generally, we categorise satellites based on their formation as natural and artificial.
Natural Satellites:
As the name suggests, they are natural objects that revolve around a planet or a star. Natural satellites of a star are called ‘planets’, and the planet’s natural satellites are called ‘moon’. For example, the Earth is a planet in the Solar System as it revolves around the Sun (and so are the other seven planets). The Moon is Earth’s natural satellite, and moons of other planets have unique names. For example, Mars has two moons, named Phobos and Deimos.
Artificial Satellites:
Artificial satellites are designed and manufactured by people and put into orbit to revolve around planets and other bodies using rockets. While artificial satellite orbit, it does a specific task and send the response to ground station on Earth. They serve various purposes such as communication, remote sensing, navigation and scientific exploration. The term spacecraft is more general which includes satellites, interplanetary and lunar crafts, human space modules, space stations, etc.
A satellite consists of 8 major subsystems, each with specific functions:
1) Payload Subsystem
- Core component designed for the mission (e.g., imaging, communication, navigation).
- Types:
- Space science payloads
- Earth observation payloads
- Communication & navigation payloads
2) Propulsion Subsystem
- Changes satellite’s orbit or position.
- Uses propellants and thrusters (solid, liquid, electric, ion-based) for:
- Orbit transfer
- Station keeping
- Decommissioning
3) Structural & Mechanical Subsystem
- Provides physical framework.
- Ensures stability during launch vibrations and space conditions.
4) Thermal Subsystem
- Maintains temperature balance in harsh space environments.
- Uses thermal blankets and heat shields to protect electronics.
5) Attitude & Orbit Control System (AOCS)
- Controls orientation and positioning in orbit. Prevents collisions, assists in orbital maneuvers using actuators and sensors.
6) Electrical Power Subsystem
- Generates power using solar panels. Stores energy in rechargeable batteries for use when sunlight is absent.
7) Telemetry, Tracking & Command (TT&C) Subsystem
- Acts as the “brain” of the satellite. Collects system data and communicates with ground stations.
8) Application Payloads
- Instruments for mission tasks: e.g., cameras, radars, radiometers, transponders.
