8.1 Spacecraft Types and Subsystems

Spacecraft come in various types, each designed for specific missions. From Earth-orbiting satellites to deep space probes, these marvels of engineering serve diverse purposes like communication, navigation, and scientific exploration. Understanding their applications is crucial for grasping the scope of space technology.

Spacecraft design is a complex process involving multiple subsystems working together. From propulsion to thermal control, each component plays a vital role in ensuring mission success. Designers must also consider redundancy, reliability, and the unique challenges posed by the space environment.

Spacecraft Types and Applications

Types of spacecraft and applications

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• Satellites
  • Earth observation satellites monitor Earth's surface, weather, and climate (Landsat, GOES)
  • Communication satellites provide global telecommunications and broadcasting (Intelsat, Iridium)
  • Navigation satellites enable global positioning and timing services (GPS, GLONASS)
  • Scientific satellites study the Earth, solar system, and universe (Hubble Space Telescope, Kepler)
• Space stations
  • Crewed orbiting laboratories for scientific research and technology development
  • International Space Station (ISS) and Tiangong space station are examples
• Space probes
  • Unmanned spacecraft designed to explore the solar system and beyond
  • Voyager 1 and 2, New Horizons, and Cassini-Huygens are notable examples
• Landers and rovers
  • Spacecraft designed to land on and explore the surface of planets, moons, or asteroids
  • Mars rovers (Curiosity, Perseverance) and Philae comet lander are examples

Spacecraft Subsystems and Design Considerations

Primary spacecraft subsystems

• Propulsion subsystem
  • Provides thrust for orbital maneuvers and attitude control
  • Chemical rockets, electric propulsion, and cold gas thrusters are common examples
• Attitude Determination and Control System (ADCS)
  • Determines and controls the spacecraft's orientation in space
  • Uses sensors (star trackers, sun sensors) and actuators (reaction wheels, magnetorquers)
• Power subsystem
  • Generates, stores, and distributes electrical power to the spacecraft
  • Solar panels and batteries are typically used
• Thermal control subsystem
  • Maintains the spacecraft's temperature within acceptable limits
  • Employs insulation, heaters, radiators, and heat pipes
• Communication subsystem
  • Enables the spacecraft to communicate with ground stations and other spacecraft
  • Utilizes antennas, transmitters, and receivers
• Command and Data Handling (C&DH) subsystem
  • Manages the spacecraft's onboard computer, data storage, and software
  • Controls and coordinates the other subsystems
• Payload
  • Equipment carried by the spacecraft to perform its specific mission
  • Scientific instruments, cameras, and transponders are examples

Redundancy in spacecraft design

• Redundancy involves having multiple components or systems that can perform the same function
• Ensures the spacecraft can continue to operate if one component fails
• Examples include multiple computers, communication paths, or power sources
• Reliability is the probability that a spacecraft will perform its intended function for a specified period under given conditions
• Achieved through rigorous testing, quality control, and fault-tolerant design
• Spacecraft operate in harsh, inaccessible environments, making repairs or replacements difficult or impossible
• High cost of spacecraft development and launch necessitates long operational lifetimes
• Mission success often depends on the continuous functioning of critical subsystems

Challenges of mission-specific design

• Launch vehicle constraints
  • Spacecraft must be designed to withstand launch loads and vibrations
  • Mass and volume limitations imposed by the launch vehicle
• Space environment challenges
  1. Vacuum causes outgassing, cold welding, and material selection issues
  2. Radiation damages electronics and materials, necessitating shielding and hardening
  3. Thermal extremes require robust thermal control systems
  4. Micrometeoroids and orbital debris pose potential for damage, requiring shielding or collision avoidance
• Distance and communication delays
  • For deep space missions, significant signal propagation delays complicate spacecraft control and data transmission
  • Requires autonomous operation and fault management capabilities
• Power limitations
  • Solar power becomes less effective at greater distances from the Sun
  • Alternative power sources (radioisotope thermoelectric generators) may be needed
• Propulsion requirements
  • Missions with high $\Delta v$ requirements (interplanetary travel) need efficient, high-performance propulsion systems
  • Electric propulsion or advanced chemical propulsion may be necessary