Satellite Subsystems

Overview

Every satellite, regardless of size, is composed of distinct subsystems that work together to accomplish the mission. In this module, you'll learn what each subsystem does, how they interact, and how to make design decisions for your CubeSat project.

Structure Subsystem

The structure is the physical skeleton of the satellite. It provides mounting points for all other subsystems, protects components during launch, and interfaces with the deployer mechanism (P-POD, ISIPOD, etc.).

Key Design Considerations

• Material — Aluminum 6061-T6 or 7075-T6 are the most common choices, offering good strength-to-weight ratio and machinability.
• Mass Budget — The structure typically accounts for 20–30% of the total satellite mass.
• Deployer Compatibility — Rail dimensions, surface finish, and deployment switch placement must comply with the CDS (CubeSat Design Specification).
• Thermal Path — The structure also serves as a thermal conductor, dissipating heat from internal components to radiating surfaces.

Electrical Power System (EPS)

The EPS generates, stores, and distributes electrical power to all satellite subsystems. It is often considered the most critical subsystem — without power, nothing works.

Components

• Solar Panels — Photovoltaic cells (typically triple-junction GaAs or silicon) mounted on external faces. Body-mounted panels are simplest; deployable panels provide more area.
• Battery — Lithium-ion or lithium-polymer packs store energy for eclipse periods. Typical capacity for a 1U is 10–20 Wh.
• Power Distribution Unit (PDU) — Regulates voltage rails (3.3V, 5V, 12V), manages charging, and provides over-current protection and switchable power buses.

Command & Data Handling (C&DH)

The C&DH subsystem is the brain of the satellite. It runs the flight software, processes commands from the ground, collects and stores telemetry, manages the mission timeline, and handles fault detection and recovery.

Key Functions

• Command Processing — Receives uplinked commands, validates them, and executes or queues them.
• Telemetry Collection — Periodically samples sensor data (temperatures, voltages, attitude) and stores it for downlink.
• Data Storage — On-board flash or SD card storage for payload data and housekeeping logs.
• Fault Management — Watchdog timers, safe mode triggers, and autonomous recovery routines.

Communications Subsystem

The communications subsystem provides the radio link between the satellite and ground station. It handles both command uplink (ground to satellite) and telemetry/data downlink (satellite to ground).

Common Bands

Attitude Determination & Control (ADCS)

ADCS controls the satellite's orientation in space. Proper attitude control is essential for pointing antennas at ground stations, orienting solar panels toward the sun, and aiming payload instruments at targets.

Sensors

• Sun Sensors — Determine the direction to the sun. Simple and reliable.
• Magnetometer — Measures Earth's magnetic field for coarse attitude estimation.
• IMU (Gyroscope) — Measures angular rates for rotational state estimation.
• Star Tracker — High-accuracy sensor that identifies star patterns for precise pointing (advanced missions).

Actuators

• Magnetorquers — Electromagnetic coils that interact with Earth's magnetic field to generate torque. Simple, no moving parts, ideal for detumbling and coarse control.
• Reaction Wheels — Spinning flywheels that provide fine pointing control by exchanging angular momentum.

Knowledge Check

Test your understanding of satellite subsystems.