Satellite Types and Design Challenges

Orbit Choice

  • Orbit choice depends on mission requirements.
  • Types of orbits:
    • Low Earth Orbits (LEO)
    • Medium Earth Orbits (MEO)
    • Geostationary Orbits (GEO)

Space Environment

  • Space is mostly a vacuum, lacking air.
  • Vacuum affects heat transfer, radiation, and material behavior.
  • Satellites face various forms of radiation:
    • Solar radiation
    • Cosmic rays
  • Radiation can damage electronic components and materials.
  • Microgravity (weightlessness) affects:
    • Fluid flow
    • Object movement
    • Biological systems (including humans)
  • Satellites experience extreme temperature variations.
  • Risk of collision with micrometeoroids or space debris.

Satellite Design Challenges

  • Components must withstand radiation.
  • Need effective thermal control systems:
    • Insulation
    • Radiators
    • Heat pipes
  • High reliability and redundant systems are crucial.
  • Robust communication systems for data transmission to and from Earth.
    • Consideration of delay due to distance.

Types of Satellites

Communication Satellites

  • Designed for information transmission:
    • Television signals
    • Internet data
    • Telephone calls
  • Critical for global telecommunications.
  • Relay information over long distances.
  • Often placed in geostationary orbits (GEO).
    • Orbit at the same rate as Earth's rotation.
    • Remain stationary relative to a specific point on Earth.
  • Purposes:
    • Telecommunications: Backbone of long-distance telephone and Internet communication.
    • Television Broadcasting: Relay television signals for distribution.
    • Internet Connectivity: Provide Internet access to remote areas.
    • Navigation: Used in global positioning systems (GPS) for location and time determination.
  • Frequency Bands:
    • Operate in various frequency bands like C band, Ku band, and Ka band.
    • Higher frequency bands (e.g., Ka band) offer greater bandwidth but are more susceptible to atmospheric signal degradation.

Earth Observation Satellites

  • Also called EO satellites or remote sensing satellites.
  • Capture data and images of Earth's surface, atmosphere, and oceans.
  • Applications:
    • Environmental Monitoring: Climate change, deforestation, land use.
    • Resource Management: Monitoring and managing natural resources.
    • Disaster Management: Real-time monitoring of natural disasters.
    • Weather Forecasting: Climate and weather prediction.
    • Scientific Research: Geology, ecology, metrology, oceanography (ocean currents, surface temperatures, marine life).
  • Orbits:
    • Low Earth Orbits (LEO): High-resolution images, limited coverage area.
    • Sun-Synchronous Orbits (SSO): Consistent angle relative to the sun for consistent lighting.
    • Geostationary Orbits: Continuous coverage over a fixed area, limited spatial resolution.

Earth Observation Satellites Data Transfer

  • Satellite communication experiences time delay due to distance.
  • Delay depends on distance and data transmission method.
  • Faster data transfer can be achieved at the speed of light.
  • Caltech Space Solar Project one:
    • Launched in January 2023.
    • Harvests energy from the sun in space.
    • Transmits energy to Earth or other satellites using lasers, one of the most efficient methods.
    • Accuracy of transmission depends on the way energy is transmitted.

Factors Affecting Data Transmission

  • Distance between satellite and Earth.
  • Method of transmitting energy.
  • Electromagnetic (EM) waves are currently the fastest.
  • EM waves are susceptible to atmospheric factors.

Sensors Used in Earth Observation Satellites

  • Optical Cameras: Capture high-resolution images in visible and infrared light.
  • Synthetic Aperture Radars (SARs): Penetrate clouds and darkness, used for terrain mapping and disaster monitoring.
  • Thermal Infrared Sensors: Detect temperature variations on Earth's surface.
  • Multispectral and Hyperspectral Sensors: Capture data across multiple spectral bands for detailed analysis of vegetation and land cover, including UV, visible, and infrared.
  • LiDAR (Light Detection and Ranging): Measures elevation changes and creates 3D models of Earth's surface and ocean surface; also used for mapping underground structures.

Scientific Satellites

  • Also known as space science satellites.
  • Conduct scientific research and experiments in space: microgravity, beyond Earth's atmosphere.
  • Contribute to understanding the universe, Earth, and scientific phenomena.
  • Orbit depends on research objectives:
    • Low Earth orbits for Earth observation.
    • Higher orbits (geostationary) to study celestial bodies and interplanetary space.
    • Missions to explore solar system and beyond (e.g., Cassini, Voyager).
  • Purposes:
    • Observe Celestial Bodies: Stars, galaxies, black holes, cosmic radiation.
    • Space Exploration: Explore planets, moons, asteroids.
    • Monitor Earth's Atmosphere: Study climate changes, ocean currents, geology.
    • Microgravity Experiments: Advance knowledge of physics, biology, material science, such as plant growth experiments on the International Space Station.
    • Study High-Energy Particles and Cosmic Rays.
    • Investigate Earth's Magnetic Field: Interactions with solar wind.
    • Study Behavior of the Sun.
  • Famous Satellites:
    • Hubble Space Telescope
    • Voyager probes
    • Mars rovers
    • Earth observation satellites (Landsat, ESA Sentinel series)
  • Mission Lifespan:
    • Some are one-time missions, others are ongoing.
    • Satellites may be deorbited (details discussed later), left in orbit as space debris, or repositioned.

Search and Rescue Satellites

  • Assist individuals in distress in remote or emergency situations.
  • Detect distress signals, transmit information, and coordinate rescue operations.
  • Locate people, aircraft, or vessels in distress.
  • Detect emergency distress signals from beacons:
    • Emergency Locator Transmitters (ELTs)
    • Personal Locator Beacons (PLBs)
    • Emergency Position Indicating Radio Beacons (EPIRBs)
  • Provide location information to search and rescue authorities.
  • Equipped with specialized sensors to detect and process distress signals on dedicated frequencies.
  • Orbits:
    • Polar orbits: global coverage.
    • Geostationary orbits: remain fixed relative to a specific region of earth.
  • Data Relay and Ground Stations:
    • Data relayed to ground stations for coordinating rescue operations.
    • Ground stations operated by government agencies.
  • International Cooperation:
    • International COSPAS-SARSAT program: international effort that standardizes beacon technology and established the framework for detecting and responding to these distress signals.

Commercial Satellites

  • Owned and operated by private companies for profit.
  • Applications:
    • Telecommunications: Voice calls, Internet access, data transmission.
    • Television Broadcasting: Distribute television programs globally.
    • Earth Observation: High-resolution images and data for agriculture, environmental monitoring, urban planning.
    • Space Tourism: Companies like SpaceX and Blue Origin offer suborbital and orbital experiences.
    • Resource Exploration: Mining, oil and gas exploration.
  • Responsibilities: satellite construction, launch, operation, maintenance.
  • Return on investment: services, sales, data.
  • Competitive Market: compete with multiple companies like SpaceX, Boeing, Lockheed Martin, Intelsat, Amazon's Project Kuiper.
  • Regulatory Oversight: adhere to regulations regarding spectrum allocation, orbital slots, and avoiding space debris.
  • Satellite Internet Constellations: like SpaceX, high speed Internet access to remote areas globally.

Managing Orbits and Collisions

  • Mission planning prevents collisions, orbital mechanics come into play.
  • Collisions do happen and detailed study of satellite trajectories are required in orbit to minimize debris pollution.
  • Avoid collisions by detailed study of where satellite is going to orbit and are there other satellites that might come in the way?
  • Mission planning: ensure a path such that no lower orbit satellites collide with it when it is trying to deorbit.
  • Deorbiting:
    • Use solar sails instead of fuel.
    • Ocean landing.

Collision Examples

  • Anti-satellite missile test (China): destroyed a satellite in orbit creating space debris.
    • f one c satellite was destroyed by missile.
    • Creates shards and small components and small parts that basically create two space debris.
    • It created a dislike in the space community.
  • Iridium 33 and Cosmos 2251 satellite collision in 02/2009 (accidental).

Deorbiting Process

  • Cassini spacecraft was deorbited into Saturn.
  • Satellites can use LiDAR to prevent risk of collision with one another.
  • Orbital mechanics will be discussed in detail next week, including software used in the industry to deorbit satellites.