Satellite: Artificial Object Orbiting Earth

Satellites—artificial objects engineered and launched by humans—have become critical infrastructure in the modern world. From enabling global communications and navigation to unlocking the mysteries of the universe, satellites underpin technologies that drive economic growth, national security, scientific discovery, and daily convenience.

1. Definition and Context

Artificial satellites are human-made objects intentionally placed into orbit around Earth or other celestial bodies. Unlike natural satellites (such as the Moon), artificial satellites are designed for specific tasks: broadcasting television signals, providing GPS navigation, monitoring weather patterns, conducting scientific experiments, and supporting military operations. Their construction and operation involve advanced materials and sophisticated subsystems for power, control, data processing, and communication.

International organizations like the International Telecommunication Union (ITU) and the International Civil Aviation Organization (ICAO) manage radio frequency allocations, orbital slots, and regulatory compliance to prevent interference and promote sustainable use of space.

Natural satellites are celestial objects formed by natural processes that orbit planets or other large bodies. Earth’s Moon is a prime example, as are the dozens of moons orbiting Jupiter and Saturn. The primary difference is origin: natural satellites are products of cosmic evolution, while artificial satellites are the result of human design, engineering, and mission planning.

2. Natural vs. Artificial Satellites

• Natural Satellite: A body formed through astrophysical processes, such as moons orbiting planets.
• Artificial Satellite: A human-engineered device, launched into orbit to fulfill a specific function.

The distinction is fundamental to international space law and operational protocols, as outlined in treaties like the Outer Space Treaty of 1967, which sets standards for liability, registration, and environmental responsibility.

3. Historical Overview

The era of artificial satellites began with the Soviet Union’s launch of Sputnik 1 on October 4, 1957. This 58-cm sphere, weighing 83.6 kg, transmitted radio signals that were detected worldwide, igniting the “space race.” The United States followed with Explorer 1 in 1958, which discovered the Van Allen radiation belts. The ensuing decades saw rapid advancement:

• 1960s/1970s: Weather satellites (TIROS-1), communications (Telstar, Intelsat), and navigation (precursors to GPS).
• 1970s/1980s: Geostationary satellites enabled real-time global communication and television.
• Late 20th/21st Century: Miniaturization, improved power systems, and the rise of CubeSats democratized access to space. As of 2024, over 7,500 artificial satellites are active, with mega-constellations (e.g., Starlink) reshaping the orbital landscape.

4. What Is an Orbit?

An orbit is the curved path an object follows around a planet, star, or other body due to gravity. For satellites, orbits are defined by:

• Altitude: Distance above Earth’s surface.
• Inclination: Angle relative to Earth’s equator.
• Eccentricity: Shape of the orbit (circular or elliptical).
• Orbital period: Time for one complete revolution.

Orbits are selected based on the satellite’s mission. For example, Earth observation satellites often use low Earth orbits (LEO) for high-resolution imaging, while communications satellites may use geostationary orbits (GEO) to maintain a fixed position relative to the ground.

5. How Satellites Stay in Orbit

A satellite “stays up” by balancing its forward (tangential) velocity with the pull of gravity. At the right speed and altitude, it is in continuous free fall around Earth—falling toward the planet but always missing it due to its horizontal motion. Orbital velocity varies with altitude:

• LEO (~300 km): ~7.8 km/s
• GEO (35,786 km): ~3.1 km/s

Propulsion systems on board enable periodic adjustments for station-keeping and collision avoidance, as required by international guidelines for orbital safety and debris mitigation.

6. Types of Artificial Satellites

By Orbit

By Function

7. Technical Structure and Components

Core Subsystems

1. Satellite Bus: The structural framework supporting all systems and payloads.
2. Power System: Solar panels (primary source), batteries (for eclipses or peak loads), and sometimes radioisotope thermoelectric generators (RTGs) for deep space.
3. Thermal Control: Radiators, insulation, heaters to protect from extreme temperatures.
4. Attitude and Orbit Control (AOCS): Reaction wheels, gyroscopes, thrusters, sensors for precise pointing and orbit maintenance.
5. Command/Data Handling: Onboard computers, memory, and data buses for payload and telemetry management.
6. Communications: Antennas, transponders, transmitters, and receivers for ground/satellite links.

Each subsystem is built for redundancy and reliability, following strict international standards (ISO, ITU, ICAO).

Satellites are powered primarily by solar panels. Image credit: Pixabay/Pexels

Power: Solar Panels and Batteries

• Solar Panels: Arrays of photovoltaic cells (often gallium arsenide or silicon) generate electricity from sunlight. Mounted on deployable arms, they may track the Sun for optimal energy capture.
• Batteries: Rechargeable (lithium-ion, nickel-hydrogen) batteries provide power during eclipses and peak loads.
• RTGs: Used for missions far from the Sun, converting radioactive decay heat into electricity.

Attitude and Orbit Control

• Reaction Wheels: Precisely adjust orientation using conservation of angular momentum.
• Gyroscopes: Measure changes in orientation.
• Thrusters: Enable station-keeping, maneuvering, and de-orbit.
• Magnetorquers: Use Earth’s magnetic field for attitude adjustments (mainly in LEO).
• Sensors: Star trackers, sun sensors, magnetometers guide orientation.

Communications

Satellites communicate via radio waves, using antennas and onboard transceivers. Frequencies and protocols are regulated by the ITU to avoid interference. Sophisticated encryption and error correction ensure secure, reliable data transmission.

8. Major Applications

• Telecommunications: TV, radio, internet, mobile services.
• Navigation: GPS, Galileo, BeiDou, GLONASS enable global positioning, timing, and navigation for transportation and logistics.
• Earth Observation: High-resolution imaging for agriculture, disaster relief, climate monitoring, and urban planning.
• Weather Forecasting: Satellites provide real-time meteorological data and storm tracking.
• Military: Intelligence, surveillance, secure communications, and early warning systems.
• Science and Exploration: Space telescopes (e.g., Hubble, JWST), planetary probes, and technology demonstrators.

9. Challenges and Sustainability

Orbital Debris

With the proliferation of satellites, orbital debris—defunct satellites, spent rocket stages, and fragments—has become a major concern. Collisions can generate clouds of debris, threatening operational satellites and crewed missions. International guidelines (e.g., UN COPUOS, ITU, ICAO) urge satellite operators to deorbit or relocate satellites at end-of-life, minimize debris creation, and adopt active collision avoidance measures.

Frequency and Orbital Slot Management

The limited nature of usable radio frequencies and orbital slots (especially in GEO) requires meticulous international coordination. The ITU allocates frequencies and orbital positions to prevent interference and ensure equitable access for all nations.

Emerging Trends

• Mega-constellations: Thousands of small satellites (e.g., Starlink, OneWeb) for global broadband.
• Miniaturization: CubeSats and nanosatellites enable affordable, rapid deployment for diverse missions.
• Advanced Propulsion: Electric thrusters and autonomous navigation for efficient station-keeping and debris avoidance.
• AI and Autonomy: Machine learning for onboard data processing, anomaly detection, and mission planning.
• In-orbit Servicing: Refueling, repairs, and upgrades to extend satellite lifespans.

10. The Future of Satellites

Artificial satellites will play an even greater role in global connectivity, environmental sustainability, disaster response, and scientific discovery. Innovations in propulsion, materials, and AI are expanding mission possibilities. Ongoing international cooperation is essential to address orbital congestion, debris, and equitable access, ensuring the sustainable development of the space environment.

References & Further Reading

• NASA - How Do Satellites Work?
• International Telecommunication Union (ITU) Space Services
• European Space Agency – Satellite Basics
• Union of Concerned Scientists – Satellite Database
• United Nations Committee on the Peaceful Uses of Outer Space (COPUOS)

Artificial satellites, as technological marvels, have transformed human society—connecting continents, saving lives, and expanding the horizons of knowledge. Their continued evolution will shape the future of science, commerce, and our understanding of the universe.