Definition and Launch
What Are They?: Man-made satellites are artificial objects created by people and launched into space. They are designed to orbit the Earth or other celestial bodies, like the Moon or Mars, for specific purposes such as communication, navigation, weather monitoring, or scientific research.
Compared to Natural Satellites: Natural satellites, like our Moon, are not made by humans. Man-made satellites are machines or devices built and placed in orbit by humans to serve planned functions.
How They’re Launched: These satellites are carried into space by powerful rockets. Once in space, the rocket releases the satellite at the correct speed and angle to allow it to enter and stay in orbit.
Why They Stay in Orbit: Earth’s gravity pulls the satellite toward it, while the satellite’s forward motion tries to move it away. These two effects balance out, so the satellite keeps circling the planet in a stable path called an orbit.
Types of Man-Made Satellites
Geostationary Satellites
Also Called GEO: These are known as Geostationary Earth Orbit satellites, often called GEO satellites. They are special because they stay directly above the same point on Earth’s surface all the time. This happens because their movement around Earth matches the planet’s rotation exactly.
Altitude and Position: These satellites orbit at a very high altitude, about 35,786 kilometers above Earth’s equator. This specific height allows the satellite to match Earth’s rotational speed.
24-Hour Orbit Time: GEO satellites take exactly 24 hours to complete one full orbit around Earth. Since Earth also rotates once every 24 hours, the satellite stays in the same position relative to the ground. This is why they appear to “hover” over one spot in the sky.
Orbital Direction: They move from west to east, which is the same direction Earth rotates. This movement is what keeps them aligned with the same spot on Earth.
Equatorial Orbit: GEO satellites orbit directly above the equator. This specific orbit allows them to cover a consistent area on Earth, providing continuous service to that region.
Main Uses: Because they remain in the same place relative to Earth’s surface, GEO satellites are very useful for communications (like internet and telephone), broadcasting television signals, and monitoring weather patterns. Their constant position allows uninterrupted coverage.
Example: One example is MEASAT, a Malaysian communication satellite that uses a geostationary orbit to provide services to the country and nearby areas.
Non-Geostationary Satellites
Variable Positioning: Not all satellites stay in one place. Non-geostationary satellites orbit Earth in paths that cause them to move across the sky. This means they pass over different parts of the Earth at different times.
Varying Altitudes and Speeds: The speed and altitude of these satellites change depending on their type of orbit. The higher the satellite, the slower it needs to move to stay in orbit.
LEO Range: Satellites in Low Earth Orbit (LEO) fly between 500 to 1000 kilometers above Earth’s surface. They travel very fast and can orbit the Earth in about 1.6 to 1.8 hours. This makes them great for short-term data collection or communication in specific regions.
MEO Range: Medium Earth Orbit (MEO) satellites are found between 8,000 and 12,000 kilometers above Earth. They take about 6 hours to orbit the planet. These orbits are commonly used for navigation systems like GPS.
HEO Range: High Earth Orbit (HEO) satellites go even farther, orbiting more than 36,000 kilometers above Earth. They are often used for special missions such as deep space monitoring.
Inclined Orbits Possible: Some non-geostationary satellites have inclined orbits, which means they don’t follow the equator but are tilted. These orbits help satellites cover parts of Earth that GEO satellites can’t see, such as the polar regions.
Main Functions: Non-geostationary satellites are used for many scientific and observational purposes. They take detailed pictures of Earth, monitor environmental changes, and conduct space research.
Examples: Weather satellites that track hurricanes, satellites that map forests, and those that collect climate data are examples of non-geostationary satellites.
Orbital Velocity of a Satellite
Formula for Velocity: The speed a satellite needs to stay in orbit is called its orbital velocity. It can be calculated with the formula v = √(GM/r), where:
- v is the orbital velocity,
- G is the gravitational constant (a fixed number representing the strength of gravity),
- M is the mass of Earth,
- r is the distance from the center of Earth to the satellite.
Radius Defined: To get the value of r, you need to add Earth’s radius (R) to the satellite’s altitude above Earth (h). So, r = R + h. This gives the total distance from Earth’s center to the satellite.
Altitude Affects Speed: When a satellite is closer to Earth, gravity pulls on it more strongly. So, it must move faster to stay in orbit and avoid falling back to Earth.
Velocity Decreases with Distance: If a satellite is farther from Earth, the gravitational pull is weaker. That means it doesn’t need to travel as fast to stay in orbit. So, the farther a satellite is, the slower it needs to go.
Relationship Between Orbital Velocity, Centripetal Force, and Gravity
Gravity Acts Centrally: Gravity is the natural force that pulls objects with mass toward one another. For satellites orbiting Earth, gravity is what keeps them from flying off into space. It acts directly toward Earth’s center and provides the necessary force to keep the satellite moving in a curved, circular path. This force is known as the centripetal force, and it always pulls the satellite inward, keeping it from drifting away.
Centripetal Force Formula: To move in a circle, a satellite needs a force pulling it toward the center of the circle. This required force is called centripetal force. It is calculated using the formula Fc = mv²/r. In this formula, “m” stands for the satellite’s mass, “v” is its velocity (speed in a specific direction), and “r” is the radius of its orbit, which means the distance from the center of Earth to the satellite. This formula shows that faster-moving satellites or those in tighter orbits need more centripetal force to stay on track.
Gravitational Force Formula: Gravity pulls two objects toward each other, and this force can be calculated with the formula F = GMm/r². Here, “G” is the gravitational constant (a number that never changes), “M” is the mass of Earth, “m” is the mass of the satellite, and “r” is the distance from Earth’s center to the satellite. This formula tells us that the gravitational force becomes weaker the farther away the satellite is from Earth.
Equating Forces: When a satellite is in a stable circular orbit, the inward force caused by gravity is exactly equal to the centripetal force needed to keep the satellite moving in a circle. This balance keeps the satellite in place. So, we can set the two force equations equal to each other: mv²/r = GMm/r². This helps scientists understand how fast a satellite needs to travel to stay in orbit without falling or flying away.
Velocity Derived: If you rearrange and simplify the equation mv²/r = GMm/r², you get a useful formula for orbital speed: v = √(GM/r). This formula shows that a satellite’s speed depends on the mass of Earth and the distance from Earth’s center. The farther away the satellite is, the slower it needs to move to stay in orbit.
Escape Velocity
What It Means: Escape velocity is the minimum speed that an object must reach to completely break free from Earth’s gravitational pull. Once it reaches this speed, it will not fall back to Earth, even if no additional force is applied. It’s like throwing a ball so hard that it never comes back down.
Escape Velocity Formula: The formula used to calculate escape velocity is v = √(2GM/r). In this formula, “G” is the gravitational constant, “M” is the mass of Earth (or any other planet or star), and “r” is the distance from the center of Earth to the object. This equation shows that escape velocity depends on how massive the planet is and how far you are from its center.
From Earth’s Surface: If a rocket or object starts at sea level on Earth, it would need to move at a speed of about 11.2 kilometers per second (or 40,320 kilometers per hour) to overcome Earth’s gravity. This is extremely fast and far beyond the speed of any plane.
Factors Affecting It: Escape velocity only depends on the mass of the planet and its radius. It does not depend on how much the object weighs. Whether it is a tiny metal bolt or a giant rocket, the escape velocity remains the same at a given location.
Calculating for Other Bodies: You can use the escape velocity formula for other planets, moons, or even stars by plugging in the correct values for mass and radius. For example, smaller planets like Mars have lower escape velocities, while massive bodies like the Sun require much higher speeds.
Moon and Sun Values: On the Moon, which has much less mass than Earth, the escape velocity is about 2.37 kilometers per second. On the other hand, the Sun is incredibly massive, so its escape velocity is about 617.59 kilometers per second.
Planes Can’t Escape: Regular airplanes can’t fly fast enough to reach escape velocity. That’s why they stay in the atmosphere and can’t go into space. They are not designed to move at such high speeds.
Rockets Need Fuel: Rockets are built to go very fast and use a large amount of fuel to reach escape velocity. The fuel provides the thrust needed to push the rocket out of Earth’s gravitational grip and carry its contents—like satellites or astronauts—into space.
Applications of Satellites
Communication Services: Satellites are used to send communication signals all around the world. They make it possible for people in different countries to make phone calls, watch live television, and use the internet. These signals are sent from Earth to the satellite, and then from the satellite to another place on Earth.
Weather Data Collection: Satellites orbiting Earth carry special tools to observe the weather from space. They can track clouds, rainfall, wind patterns, and temperature. This helps weather scientists predict storms, warn people about natural disasters, and study long-term climate patterns.
Medical Advancements: Scientists do experiments in space to learn more about how the human body works in low-gravity environments. For example, they study how bones, muscles, and organs respond when there is almost no gravity. This helps doctors improve treatments and understand aging, bone loss, and muscle weakening.
Navigation Aid: Global Positioning System (GPS) satellites help people figure out where they are on Earth. These satellites send signals to GPS devices in cars, phones, and airplanes. By receiving signals from several satellites at once, a GPS device can calculate its exact location.
Military Use: Military organizations use satellites for many tasks. They can spy on other countries, send secure messages, guide missiles, and track the movements of vehicles or people. Satellites give military forces a view of the whole Earth and allow them to act quickly and accurately.
Supporting Exploration: Satellites also help space agencies study other planets, stars, and galaxies. Some satellites orbit Earth to look into space, while others travel far away to gather information about distant worlds. They help scientists answer big questions about the universe and support future space missions.