🧑‍🚀 Space Systems

Spacecraft Subsystems

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Spacecraft Subsystems

What is a Spacecraft Bus?

The “spacecraft bus” refers to the core framework or “platform” of any satellite or spacecraft. It houses and supports all the critical subsystems (e.g., power, propulsion, thermal control) that keep the spacecraft operational and enable the mission payload to do its job.

Related: Spacecraft Design Overview

graph TD
    Spacecraft["Spacecraft"]
    
    Spacecraft --> ADC["ADC<br>(Attitude Determination & Control)"]
    Spacecraft --> Propulsion["Propulsion<br>(Thrusters, Fuel)"]
    Spacecraft --> C&DH["C&DH<br>(Command & Data Handling)"]
    Spacecraft --> TT&C["TT&C<br>(Telemetry, Tracking & Command)"]
    Spacecraft --> Power["Power<br>(Solar/Battery)"]
    Spacecraft --> Structures["Structures<br>(Mechanical Support)"]
    Spacecraft --> Thermal["Thermal Control<br>(Heaters, Radiators, MLI)"]

Subsystems

1. ADC

Tagline: Ensures precise pointing using sensors and actuators.

  • Main Role: Maintains correct spacecraft orientation (pointing instruments, antennas, solar arrays).
  • Techniques:
    • Spin-stabilized: Simple but limited pointing accuracy.
    • Three-axis stabilized: Precision pointing with reaction wheels or Control Moment Gyros (CMGs).
    • Momentum dumping via thrusters or magnetotorquers if wheels saturate.
  • Sensors: Star trackers, sun sensors, horizon sensors.

2. Propulsion

Tagline: Provides the ability to alter orbit or momentum for maneuvers.

  • Main Role: Offers ΔV for orbit insertion, station-keeping, maneuvers.
  • Types:
    • Cold gas or mono-propellant (low ΔV).
    • Bi-propellant or electric/ion propulsion (high ΔV, more efficient but complex).
  • Key Point: Fuel storage and thruster placement strongly influence spacecraft layout.

3. C&DH

Tagline: Executes commands and processes payload data.

  • Main Role: Heart of onboard computing—receives, interprets, and executes ground commands; handles data processing and storage.
  • Reliability: Typically rad-hard, robust architecture, sometimes redundant for fault tolerance.
  • Data Storage: Buffers scientific and housekeeping data when downlink isn’t possible.

4. TT&C

Tagline: Handles all communication between spacecraft and ground stations.

  • Main Role: Communicates spacecraft health/status (telemetry) and receives instructions (uplink).
  • Tracking: Tracks spacecraft location and velocity for orbit determination.
  • Antenna & Power: Antenna size and transmitter power depend on distance and data rate needs.

5. Power

Tagline: Generates, stores, and distributes electricity to all subsystems.

  • Generation: Typically solar arrays (sometimes RTGs for deep-space).
  • Storage: Batteries for eclipse or night side operations.
  • Distribution: Regulated bus ensures each subsystem receives stable power.

6. Structures

Tagline: Provides the mechanical backbone to support and protect hardware.

  • Main Role: Must withstand launch loads, vibrations, temperature extremes.
  • Materials: Often uses lightweight composites (e.g., CFRP, aluminum honeycomb).

7. Thermal Control

Tagline: Maintains temperatures within operational limits.

  • Methods:
    • Passive: MLI (multi-layer insulation), radiators, surface coatings.
    • Active: Heaters, cryocoolers, fluid loops.
  • Drivers: Orbit (sun exposure), internal heat generation, required instrument temperature stability.

Design Flexibility

These seven subsystems are typical, but some missions may combine or split them differently. For instance, a small CubeSat might merge C&DH and TT&C into a single board.”

Graph View

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