SATELLITE COMMUNICATIONS SMART EDGE 2025

Satellite Communications Overview

Definition

  • A satellite is a spacecraft placed in orbit around the Earth that carries microwave receiving and transmitting equipment (repeater), relaying signals from one location on Earth to others.

Key Milestones in Satellite Technology

Early Developments

  • 1945: Arthur C. Clarke proposed satellite message transmissions.

  • 1940s - 1950s: The moon was the first passive satellite.

Landmark Events

  • 1954: U.S. Navy's Earth Moon Earth experiment.

  • 1957: Launch of Sputnik 1 by Russia, the first active satellite.

  • 1958: The U.S. launched "SCORE", rebroadcasting President Eisenhower's Christmas message.

  • 1960: NASA and Bell Labs launched the "Echo", enabling the first transatlantic transmission.

  • 1962: Introduction of TELSTAR 1 by AT&T, showcasing first duplex satellite transmission.

  • 1963: Launch of TELSTAR 2 for various forms of transmission (phone, TV, fax).

  • 1965: COMSAT's EARLY BIRD, facilitating messages to five Earth stations with 66 telephone circuits.

  • 1966: Establishment of DOMSAT, advancing satellite technology in the Philippines.

  • 1970s: Various countries launched significant satellites, including China's first in 1970 and the USA's LANDSAT 1 in 1972 to support remote sensing missions.

Satellite System Components

  • System Structure: A satellite system includes:

    • Transponder

    • Ground station for operation control

    • User network of Earth stations for transmitting/receiving data.

Types of Satellite Links

  • Uplink: Transmission from ground station to satellite.

  • Downlink: Transmission from satellite to ground station.

Applications of Satellites

  • Remote Sensing: Collecting data for environmental monitoring.

  • Weather Forecasting: Monitoring climatic conditions.

  • Agriculture: Supporting crop production forecasting.

  • Intelligence/Security: Involvement in surveillance operations.

  • Navigation: Providing geospatial data for location services.

  • Telecommunications: Facilitating voice, data, and broadcasting.

  • Education: Offering interactive learning opportunities.

  • Scientific Exploration: Supporting research in outer space.

  • Search and Rescue: Enhancing efforts in locating and assisting individuals in need during emergencies.

Advantages of Satellite Communications

  1. Wideband Capability: Supports large bandwidth communication.

  2. Large Coverage Area: Can cover remote regions effectively.

  3. Reliability: High system reliability compared to terrestrial systems.

  4. Direct Access: Services can be directed to subscriber premises.

  5. Flexible Services: Point-to-point and point-to-multipoint services.

  6. Compatibility: Easily integrates with modern technologies.

  7. Uniform Access: Offers multiplayer access across varied locations.

  8. Mobility: Flexibility for movement of Earth stations.

  9. Lower Ground Facility Needs: Reduces need for extensive ground infrastructure.

Disadvantages of Satellite Communications

  • High Initial Costs: Requires significant investment to establish.

  • Limited Lifespan: Typically lasts between 7 to 10 years.

  • Maintenance Costs: Expensive to maintain operational status.

  • Reliability Risks: Dependent on launch vehicle stability.

  • High Investment for Stations: Earth station setup is costly.

  • Signal Vulnerability: Susceptible to interception and jamming.

  • Propagation Delay: Can experience latency and delays in response time.

  • Orbital Launch Risks: Potential for failures during orbit insertion.

Satellite Transmission Types

  • Payload Transmission: User information carried through the satellite system.

  • Bus Transmission: Involves mechanisms ensuring payload operational support.

Classification of Satellites by Function

  • Passive Satellite: Reflects signals without amplification.

  • Active Satellite: Receives, amplifies, converts, and retransmits signals.

Orbital Patterns

Satellite Orbital Pattern - Orientation of Satellite Orbit with respect to the earth.

Angle of Inclination - angle formed by the Equatorial and orbital planes.

  1. Equatorial Orbit: Geosynchronous satellites cover about 42.5% of the Earth's surface. θi = 0˚

  2. Polar Orbit: Used for global and non-communication observations, covering 100% of the Earth’s surface. θi = 90˚

  3. Inclined Orbit: Easier to launch with a broad coverage area but poses tracking difficulties; 0˚<θi<90˚; Coverage area: >42.5%(surface area)Classifications of Satellite.

Categories of Satellite (Based on Orbits)

  • Non-Synchronous or Orbital - satellites that do not maintain a fixed position relative to the Earth's surface, allowing for flexible coverage of specific regions as they orbit at lower altitudes. (circular pattern.)

  • Prograde Orbit - satellites that move in the same direction as the Earth's rotation, providing consistent coverage over specific areas and allowing for easier tracking and communication. (counterclockwise)

  • Retrograde Orbit - satellites that move in the opposite direction of the Earth's rotation, which can be beneficial for certain applications but may complicate tracking and increase fuel consumption. (clockwise)

  • Geostationary or Geosynchronous - orbit in a circular pattern with an angular velocity equivalent to that of earth with an orbital time of about 24 hours. (23 hours,56 mins, 4.091 sec) ; ωs = ωe; orbits eastward, ccw; orbital pattern: equatorial, θi= 0˚; coverage area: 42.5% earth surface.

According to Elevation:

Frequency Allocations

  • Common Frequency Bands:

    • C band: 4 to 8 GHz

    • Ku band: 12.5 to 18 GHz

    • Ka band: 26.5 to 40 GHz (high data rates)

    • L band: 1 to 2 GHz

    • X band: Military applications

Satellite Control & Tracking

  • Satellite Control: Involves positioning, tracking, and commanding of satellites.

  • Tracking Techniques: Include azimuth, elevation, and satellite look angles for effective communication link establishment.

Launching Satellites

  • Types of Rockets: Differentiations between solid and liquid propellant rockets, both required to lift communications satellites into orbit.

  • Post-Launch Adjustments: Minor orbit adjustments necessary once in space, facilitated by thrusters.

Recent Developments in Satellite Technology

  • Increased Number of Small Satellites: Dominating Low Earth Orbit (LEO) for better quality communication and IoT usability.

  • Multinational Collaborations: Countries sharing satellite technology resources to maximize operational capabilities.