Understanding Orbital Altitude and Dynamics

Orbital altitude refers to the distance between a satellite or spacecraft and the surface of the celestial body it is orbiting. Unlike distance from the center of mass, altitude specifically measures the height above the mean sea level or mean planetary radius. This calculator helps researchers, students, and hobbyists determine the necessary physics parameters to maintain a stable circular orbit around Earth, the Moon, or Mars.

How to Calculate Orbital Velocity

To stay in orbit at a specific altitude, an object must travel at a precise speed. This is known as orbital velocity. If the object moves too slowly, gravity will pull it back toward the surface; if it moves too fast, it will escape into a higher orbit or deep space. The formula for orbital velocity (v) is v = sqrt(GM / r), where G is the gravitational constant, M is the mass of the planet, and r is the distance from the center of the planet (radius of the planet plus altitude).

The Relationship Between Altitude and Period

According to Kepler's Third Law, the square of the orbital period is proportional to the cube of the semi-major axis of its orbit. In simpler terms, the higher the altitude, the longer it takes to complete one full revolution. For example, the International Space Station (ISS) at roughly 400 km completes an orbit in about 90 minutes, whereas geostationary satellites at approximately 35,786 km take 24 hours to match the Earth's rotation.

Frequently Asked Questions

What is Low Earth Orbit (LEO)?
LEO typically refers to altitudes between 160 km and 2,000 km. It is used for most human spaceflight and imaging satellites.

How does gravity change with altitude?
While gravity weakens as you move further away, it is still very strong in LEO. At 400 km, Earth's gravity is roughly 90% as strong as it is on the surface. The "weightlessness" felt by astronauts is due to constant free-fall, not a lack of gravity.