Artificial Satellite
An artificial satellite is any human-made object intentionally placed into orbit around a celestial body — most commonly Earth — to perform specific functions such as telecommunications, Earth observation, weather monitoring, navigation (GPS), scientific research, or military surveillance. Satellites follow orbital paths determined by the balance between gravitational attraction and their tangential velocity; they are classified by orbital altitude into Low Earth Orbit (LEO: 160–2000 km), Medium Earth Orbit (MEO: 2000–35,786 km), and Geostationary Orbit (GEO: 35,786 km). Sputnik 1, launched by the Soviet Union on 4 October 1957, was the first artificial satellite, marking the beginning of the Space Age.
Key Formula
v = sqrt(G × M / r)
LaTeX: v = \sqrt{\frac{GM}{r}}
| Symbol | Meaning | Unit |
|---|---|---|
| v | Orbital velocity of the satellite | m/s |
| G | Universal gravitational constant (6.674 × 10⁻¹¹) | N·m²/kg² |
| M | Mass of the central body (Earth: 5.972 × 10²⁴ kg) | kg |
| r | Orbital radius from centre of Earth | meters (m) |
Worked Example
Problem
Calculate the orbital velocity of the International Space Station, which orbits at an altitude of 400 km above Earth's surface. (Earth's radius R_E = 6.371 × 10⁶ m, M_E = 5.972 × 10²⁴ kg, G = 6.674 × 10⁻¹¹ N·m²/kg²)
Solution
Step 1: Find orbital radius: r = R_E + altitude = 6.371 × 10⁶ + 4.00 × 10⁵ = 6.771 × 10⁶ m. Step 2: Apply the orbital velocity formula: v = sqrt(G × M / r). Step 3: Numerator: G × M = 6.674 × 10⁻¹¹ × 5.972 × 10²⁴ = 3.986 × 10¹⁴ m³/s². Step 4: v = sqrt(3.986 × 10¹⁴ / 6.771 × 10⁶) = sqrt(5.888 × 10⁷) = 7674 m/s.
Answer
Orbital velocity v ≈ 7,674 m/s ≈ 7.67 km/s (approximately 27,600 km/h)
Satellite Orbit Types and Their Applications
| Orbit Type | Altitude | Orbital Period | Applications |
|---|---|---|---|
| LEO | 160–2,000 km | 90–127 min | ISS, Earth observation, Starlink |
| MEO | 2,000–35,786 km | 2–24 hours | GPS, GLONASS, Galileo |
| GEO | 35,786 km | 24 hours | TV broadcast, weather, comms |
| HEO (Molniya) | Elliptical (500–40,000 km) | ~12 hours | High-latitude communications |
| SSO | 600–800 km | ~100 min | Earth imaging, reconnaissance |
Interactive Tools
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Related Terms
Escape Velocity
Escape velocity is the minimum speed an object must achieve to escape the gravitational field of a massive body without any further propulsion, assuming no atmospheric drag and a radial (straight-up) trajectory. It is derived by equating the kinetic energy of the object to the magnitude of its gravitational potential energy. Escape velocity is a critical concept in rocketry and planetary science: Earth's escape velocity is approximately 11.2 km/s, while the Sun's is about 617.5 km/s, and a black hole's escape velocity at the event horizon equals the speed of light.
Space Station
A space station is a large, crewed spacecraft in low Earth orbit (LEO) designed to support long-duration human habitation and scientific research in the microgravity environment of space. Unlike capsules or shuttles, space stations are not designed for interplanetary travel but serve as orbiting laboratories, assembly platforms, and staging posts for future deep-space missions. The International Space Station (ISS), a joint project of NASA, Roscosmos, ESA, JAXA, and CSA, has been continuously inhabited since November 2000 and represents the largest human-made structure in space, orbiting at approximately 400 km altitude with an orbital period of ~92 minutes.
Orbital Mechanics
Orbital mechanics (also called astrodynamics) is the branch of aerospace engineering and applied physics that studies the motion of spacecraft, satellites, and celestial bodies under the influence of gravitational forces. It is governed by Newton's law of universal gravitation and Kepler's three laws of planetary motion, and it underpins the planning of satellite launches, orbital transfers, interplanetary trajectories, and re-entry profiles. Mastery of orbital mechanics is essential for mission design, ground-track prediction, and spacecraft manoeuvring.
From Latin artificialis (made by human skill, from ars/artis meaning "skill") and satellitem (an attendant or bodyguard, from satellite). The term "satellite" for orbital bodies was introduced by Johannes Kepler in 1610 to describe the moons of Jupiter.