Satellites are placed in orbit around the Earth instead of on its surface for several reasons:
Escape velocity: The Earth has a gravitational field that pulls objects toward its center. In order to overcome this gravitational pull and remain in space, objects need to reach a certain velocity called escape velocity. The escape velocity on Earth is approximately 11.2 kilometers per second (6.95 miles per second). Placing a satellite on the surface would require launching it at this high velocity, which is currently not feasible or practical with our current technology.
Orbit stability: By placing satellites in orbit, they can achieve a stable trajectory around the Earth. Satellites are launched into specific orbits depending on their intended purposes, such as communication, weather monitoring, scientific research, or navigation. These orbits are carefully designed to provide the desired coverage and minimize interference or collisions with other satellites. In contrast, placing satellites on the surface would not allow them to remain in a stable position or follow a controlled path.
Line of sight: Satellites in orbit have a clear line of sight to different parts of the Earth's surface. This is particularly important for communication satellites that relay signals between different locations on Earth. Placing satellites on the surface would obstruct the line of sight, leading to significant limitations in their functionality.
Earth's rotation: Satellites take advantage of the Earth's rotation to achieve certain benefits. By placing a satellite in an orbit that matches the rotation of the Earth, called a geostationary orbit, the satellite appears stationary relative to a specific point on Earth's surface. This allows for continuous coverage of a specific region, such as for television broadcasting or weather monitoring. Placing a satellite on the surface would not provide this geostationary effect.
Overall, placing satellites in orbit around the Earth offers advantages such as stable trajectories, global coverage, line-of-sight communication, and leveraging the Earth's rotation. These factors make orbital placement the preferred choice for most satellite missions.