How Satellites Work: CubeSats, Bus Systems, and Spacecraft Engineering

Introduction

Satellites are essential for global communications, scientific data collection, and space exploration. They can be understood as two linked systems: the payload, which carries out the mission, and the bus, which includes the structure and all systems that operate the satellite and support the payload. Satellite sizes span from Pico to large, with CubeSats representing a nanosatellite standard that emphasizes modularity and low cost.

Seven Fundamental Subsystems

Across sizes, satellites share seven core subsystems: mechanical structure, onboard computer, electrical power system, attitude determination and control system, propulsion system, communication system, and thermal control system. The video delves into how these subsystems interact to ensure mission success, from launch through onboard operation and data return.

Mechanical Structure and Materials

The structure must be strong yet light, using materials like aluminum alloys and carbon fiber. Outgassing in vacuum is a critical consideration, so bake-out procedures are used to release trapped gases before launch. Deployable mechanisms for solar panels and antennas help fit within launcher envelopes, while introducing potential failure points that engineers must mitigate.

Onboard Computer and Radiation

The onboard computer acts as the satellite’s brain, coordinating data processing and health monitoring. Space radiation poses a major challenge, especially in higher orbits and in the Van Allen belts. Designers mitigate this with radiation-hardened components and shielding, sometimes enveloping the device in aluminum or using robust shielding strategies.

Electrical Power System

Solar arrays are the primary power source, with multi-junction solar cells improving efficiency by capturing a wider wavelength range. In Earth orbit, spacecraft experience eclipses, so batteries store energy for these periods. A power control unit manages charging, discharging, and voltage regulation to keep all systems within safe limits.

Attitude Determination and Control

Attitude refers to satellite orientation, which must be continually assessed and adjusted. Attitude sensors include inertial measurement units with gyroscopes and accelerometers, star trackers for precise attitude references, sun sensors, and magnetometers. Star trackers are highly accurate but can be challenged by proximity to the Sun or rapid rotation. Attitude control uses reaction wheels, magnet torqueers, or thrusters to achieve three-axis stabilization, countering wheel saturation with magnetic or propulsion-based desaturation methods.

Propulsion and Orbit Management

Propulsion enables orbit changes and station keeping. Common methods include cold gas thrusters for attitude support, chemical propulsion (monopropellant and bipropellant) for higher thrust, and electric propulsion for high efficiency. The choice depends on mission requirements and satellite mass.

Communication Systems and RF

Communications involve downlink for payload data and telemetry, tracking and command links. Data is transmitted over RF bands between 1 and 40 GHz, with higher bands supporting higher data rates but greater atmospheric attenuation. Modulation schemes, transceivers, and antenna designs (including high-gain directional antennas and low-gain broad-coverage options) are chosen based on mission needs and robustness to tumbling. Ground stations receive and demodulate, extracting payload data and health information.

Thermal Control

Space is a harsh thermal environment with direct solar heating and deep shadow cool-downs. Since there is no convection in vacuum, satellites rely on radiation to shed heat. Thermal control employs radiators, heat pipes, heaters, multi-layer insulation, coatings, phase-change materials, and even attitude adjustments to regulate temperatures within safe ranges.

Design, Testing, and Applications

Engineers use extensive analyses and testing to ensure reliability. Deployable mechanisms for solar panels and antennas expand envelope constraints but introduce new risk factors. CubeSats illustrate how modular, low-cost designs can perform a range of missions from educational demonstrations to state-of-the-art scientific experiments. The video also highlights how today’s satellites blend sophisticated hardware with robust software to achieve resilient operations in the space environment.

Conclusion

Whether for research, communication, or exploration, satellite design integrates mechanical, electrical, and software disciplines to deliver reliable, high-performance space missions. The principles discussed apply from tiny 1U CubeSats to much larger platforms, guiding the future of space technology.