Thousands of satellites orbit above us, yet we often know little about their composition or how they function. A satellite is an object that orbits a celestial body, such as a planet or a star. There are natural satellites, such as the Moon and some asteroids, and artificial satellites, which are human-made objects intentionally placed in orbit around celestial bodies (like Earth). In this article, we will focus on these artificial satellites.
There are various types of artificial satellites, each designed for specific missions: Earth observation, navigation, space exploration, scientific research, telecommunications, defense, and space logistics. Depending on their mission, these satellites are placed in different orbits: low Earth orbit (LEO) up to 2,000 km in altitude, medium Earth orbit (MEO) between 2,000 km and 20,000 km, geostationary orbit (GEO), and so on.
However, despite having specialized payloads, satellites share a common basic structure consisting of three main elements: the payload, the bus, and the subsystems that make up the bus. Let’s explore this common structure to better understand what a satellite is made of.
The Anatomy of a Satellite
Despite the diversity in satellite missions—from Earth observation to deep space exploration—most satellites share a common structural framework comprising two primary sections:
- The Bus: This is the satellite’s structural frame, housing all the essential subsystems required for operation.
- The Payload: Contains the mission-specific instruments and equipment.
1. Structural Frame (Bus)
The structural frame provides the necessary support for all satellite components. The platform is designed to withstand the mechanical stresses experienced during powered flight, including liftoff and acceleration (up to 4-5G), noise (decibels), and temperature differences. This requires materials with low thermal expansion, such as carbon composites. It needs to be strong and stiff to survive the launch but also as light as possible to reduce launch costs. The housing is constructed from robust materials capable of withstanding the harsh space environment. These materials should have good stiffness and strength properties relative to their weight, such as aluminum or carbon-fiber-reinforced polymers.
Materials Used:
- Aluminum Alloys: Lightweight and strong, offering an excellent strength-to-weight ratio.
- Titanium: Known for its high strength and corrosion resistance.
- Carbon-Fiber-Reinforced Polymers: Provide exceptional strength and low thermal expansion.
Key Considerations:
- Durability Under Extreme Conditions: Materials must withstand temperature fluctuations, space radiation, and the immense forces experienced during launch.
- Low Thermal Expansion: Ensures structural integrity despite temperature changes.
- Weight Reduction: Minimizing weight is crucial for reducing launch costs and increasing payload capacity.
2. Subsystems
2.1 Power System
A satellite’s power system is its lifeline, supplying energy to all onboard systems and the payload. Satellites primarily generate energy using solar panels oriented towards the sun. During eclipse periods, when they are in Earth’s shadow, they rely on rechargeable batteries that have been previously charged by the solar panels. The power control system monitors and regulates the battery charge and voltage.
Components:
- Solar Panels: Convert sunlight into electricity using photovoltaic cells.
- Batteries: Store energy for use during periods when the satellite is in Earth’s shadow.
- Power Control System: Manages the distribution and regulation of electricity.
Materials Used:
- Gallium Arsenide or Silicon Solar Cells: Chosen for high efficiency in energy conversion.
- Lithium-Ion Batteries: Preferred for their high energy density and rechargeability.
Key Considerations:
- Energy Conversion Efficiency: Higher efficiency reduces the size and weight of solar panels.
- Resistance to Space Degradation: Materials must endure radiation and micrometeoroid impacts.
- Compactness: Space constraints require power systems to be as small and lightweight as possible.
2.2 Propulsion System
The propulsion system is responsible for adjusting the satellite’s orbit and orientation using various propulsion technologies. Different methods include cold gas propulsion, chemical propulsion, and electric propulsion. All work on the same principle: thrust is generated by accelerating mass through a nozzle.
Types of Propulsion:
- Cold gas propulsion: works by expelling a pressurized gas, producing relatively low thrust, which limits its use to applications requiring minimal thrust.
- Chemical Propulsion: relies on the combustion of liquid or solid fuels, provides substantial thrust and is primarily used for initial orbital launches or rapid changes in speed or direction.
- Electric Propulsion: uses electricity to ionize a gas like xenon, accelerating these ions through an electric field to generate thrust. Although the thrust is lower compared to chemical systems, electric propulsion is far more fuel-efficient, making it ideal for placing satellites into geostationary orbit and for long-term orbital adjustments.
Materials Used:
- High-Temperature Alloys and Ceramics: Withstand extreme temperatures and corrosive propellants.
- Propellants: Chemicals like hydrazine (chemical propulsion) or noble gases like xenon (electric propulsion).
Key Considerations:
- Fuel Efficiency: Critical for long-duration missions.
- Maneuverability: Precise control is essential for orbit adjustments.
- Longevity: Components must function reliably over the satellite’s operational life.
2.3 Thermal Control System
Satellites are exposed to extreme temperatures. Parts of the payload must be kept within narrow temperature ranges to function properly, and batteries or electrical components that experience temperatures beyond their limits are at risk of failure. Thermostat-controlled electric heaters activate at low temperatures to prevent certain components from getting too cold. Additionally, the attitude control system can aid thermal control by adjusting the orientation of radiators and other surfaces.
Components:
- Heat Pipes: Transfer excess heat away from sensitive areas.
- Radiators: Dissipate heat into space.
- Insulation Blankets (Multi-Layer Insulation or MLI): Minimize heat loss and protect against temperature extremes.
Materials Used:
- Aluminized Plastic or Mylar: Used in MLI for reflecting thermal radiation.
- Ammonia or Water in Heat Pipes: Due to their high thermal conductivity.
Key Considerations:
- Temperature Regulation: Maintains components within operational temperature ranges.
- Material Durability: Must withstand thermal cycling without degradation.
- Stable Thermal Environment: Essential for the optimal performance of sensitive instruments and electronics.
2.4 Electronics and Avionics
Onboard Computers and Control Systems
These systems manage satellite operations, including navigation, communication, and data processing. They centralize command processing through the Command and Data Handling (C&DH) system, executing instructions received from ground control and distributing them to the appropriate subsystems. These systems continuously monitor the health and status of all onboard components—such as power levels, temperatures, and functionality—ensuring optimal performance.
They also handle data processing by collecting, processing, and storing information from the payload before transmitting it back to Earth.
Additionally, they are responsible for fault detection and correction, identifying anomalies in system operations and initiating corrective actions or switching to redundant systems when necessary.
Components:
- Microprocessors and Microcontrollers: Execute commands and process data.
- Data Storage Units: Store mission data and software.
- Control Software: Manages hardware operations and system health.
Materials Used:
- Radiation-Hardened Semiconductors (e.g., Silicon Carbide): Resist space radiation.
- Shielding Materials: Provide additional protection for electronics.
Key Considerations:
- Radiation Tolerance: Prevents data corruption and hardware failures.
- Redundancy: Ensures functionality in case of component failure.
- Power Efficiency: Conserves energy to extend the satellite’s operational life.
Guidance, Navigation, and Control (GNC) System
The Guidance, Navigation, and Control (GNC) system is critical for the satellite’s ability to position and orient itself accurately in space. The Attitude and Orbit Control System (AOCS) adjusts the satellite’s orientation using sensors (star trackers, sun sensors, inertial measurement units) and actuators (reaction wheels, magnetorquers). Gyroscopes in the inertial measurement unit continuously measure changes in orientation. Reaction wheels control the satellite’s orientation around its three axes by generating rotations opposite to the center of mass.
- Guidance: Determines the desired path for the satellite to follow.
- Navigation: Calculates the satellite’s current position and velocity.
- Control: Executes maneuvers to adjust the satellite’s trajectory and orientation.
Components:
- Attitude and Orbit Control System (AOCS): Adjusts the satellite’s orientation using sensors and actuators.
- Sensors: Star trackers, sun sensors, and inertial measurement units (IMUs) provide data on the satellite’s position and movement.
- Actuators: Reaction wheels, control moment gyroscopes, and magnetorquers apply forces to change orientation.
- Propulsion Subsystems: Small thrusters used for fine-tuning orbit and attitude adjustments.
- Onboard Algorithms: Software that processes sensor data and determines control actions.
Materials Used:
- MEMS Technology: Used in sensors for high precision and reliability.
- High-Strength Alloys: In actuators and mechanical components to withstand operational stresses.
- Radiation-Hardened Electronics: Ensure the GNC system functions correctly despite radiation exposure.
Key Considerations:
- Precision Control: Accurate positioning is essential for mission success, especially for tasks like Earth observation or communication signal alignment.
- Reliability: The GNC system must operate flawlessly over the satellite’s lifespan.
- Redundancy: Critical components are often duplicated to prevent mission failure due to a single-point malfunction.
- Autonomy: The system may need to operate independently of ground control due to communication delays or interruptions.
3.5 Communication System
The communication system on a satellite is a comprehensive suite that enables all forms of data exchange between the satellite and ground stations. It encompasses both the reception (uplink) and transmission (downlink) of mission-specific data and the critical functions of Telemetry, Tracking, and Command (TT&C).
- Downlink (Payload Data Transmission): This is the primary mission data sent from the satellite to ground stations. It requires high bandwidth and reliable transmission to ensure data integrity.
- Uplink (Command Reception): Allows ground controllers to send instructions to the satellite, such as adjusting its orbit, changing the orientation, or managing the payload operations.
- TT&C Telemetry, Tracking, and Command (TT&C) System: Manages the health monitoring, tracking, and command functions essential for satellite operation.
- Telemetry Transmitters: Send health and status data of the satellite’s systems back to Earth.
- Tracking Beacons: Emit signals that help ground stations determine the satellite’s position and velocity.
- Command Processors: Interpret and execute commands received from the ground.
Components:
- Antennas: Transmit and receive signals.
- Transponders, Transmitters, and Receivers: Process communication signals.
Key Considerations:
- Signal Strength and Bandwidth: Essential for high data rate transmission.
- Reliability: Must maintain communication despite interference and distance.
- Resilience to Signal Degradation: Ensures consistent data transmission quality.
3. The Payload
The payload is the heart of the satellite, containing all mission-specific instruments and equipment.
In a nutshell, it’s everything used to carry out the satellite’s mission. Each payload is specific to the satellite’s mission. For example, the Sentinel-1A satellite launched by the ESA carries a radar payload to monitor the planet, including observing changes in the Arctic ice sheet.
Examples of Payload Components:
- Cameras and Spectrometers: For Earth observation satellites.
- Communication Arrays: For telecommunication satellites.
- Scientific Instruments: For research and exploration missions.
Key Considerations:
- Mission-Specific Design: Payloads are custom-built for each mission’s requirements.
- Weight and Power Constraints: Must be optimized to maximize efficiency.
- Data Transmission Needs: High-resolution instruments generate large amounts of data requiring efficient transmission.
Conclusion
The composition of satellites is a complex integration of various systems and materials that come together to perform specific missions in the harsh environment of space. Despite the diversity in their functions, satellites share a common basic structure consisting of the payload, the bus, and the subsystems that make up the bus. As applications evolve and satellite sizes shrink, especially with the rise of miniaturized satellites like CubeSats, their design and materials continually adapt. Each advancement must meet the stringent demands of the space environment, including extreme temperatures, vacuum conditions, and radiation.
Understanding the fundamental structure of satellites—the bus, the payload, and the various subsystems—provides valuable insight into how these technological marvels function. By dissecting each component, from the structural frame to the communication systems, we gain a clearer picture of what a satellite is made of and the considerations involved in its design and operation.
In a forthcoming article, we will delve deeper into space-grade materials and manufacturing techniques such as 3D printing, which are transforming satellite construction. We will also explore the challenges and innovations in satellite design, including miniaturization and space debris management, that are critical for the future of space exploration and utilization.
In the meantime, if you’re looking for a reliable partner to supply the communication system for your satellite, Anywaves is ready to help craft the best antenna solution tailored to your mission needs.
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