Orbital Speed

Orbital speed is the velocity an object needs to remain in orbit around a larger body such as Earth or the Sun. Gravity continually pulls the object inward, while its forward motion carries it sideways, producing a curved path through space.

In the near-vacuum of space, an object can remain in orbit for long periods without continuously firing its engines. Spacecraft may still require occasional adjustments to counter effects such as atmospheric drag, gravitational influences from other bodies, or changes to their mission trajectory.

The required orbital speed depends mainly on the mass of the central body and the object's distance from it. In a circular orbit, objects closer to the central body must travel faster, while objects farther away can move more slowly.

Speed at Different Altitudes

In low Earth orbit, at an altitude of roughly 250 miles (400 kilometers), spacecraft travel at about 17,500 miles per hour (28,000 kilometers per hour) and complete an orbit in approximately 90 minutes. The International Space Station operates in this region.

Circular orbital speeds decrease at greater altitudes. GPS satellites in medium Earth orbit travel at roughly 8,700 miles per hour (14,000 kilometers per hour) and take about 12 hours to complete one orbit.

Geostationary satellites orbit much farther from Earth at approximately 6,900 miles per hour (11,100 kilometers per hour). Their orbital period matches Earth's rotation, allowing them to remain above nearly the same point on the equator.

On a much larger scale, Earth travels around the Sun at an average speed of about 67,000 miles per hour (108,000 kilometers per hour), completing one revolution each year.

• Low Earth Orbit: About 17,500 mph, with a period of roughly 90 minutes
• Medium Earth Orbit (GPS): About 8,700 mph, with a period of about 12 hours
• Geostationary Orbit: About 6,900 mph, with a period of one sidereal day
• Earth Around the Sun: About 67,000 mph, with a period of one year

Speed in Elliptical Orbits

In a circular orbit, speed remains nearly constant. In an elliptical orbit, it changes throughout the journey. An object moves faster when it is closer to the body it orbits and slower when it is farther away, as described by Kepler's Second Law.

Comets demonstrate this effect dramatically. They may crawl through the distant outer Solar System, then accelerate rapidly as they approach the Sun before slowing again during their journey outward.

Practical Applications of Orbital Speed

Accurate speed calculations are essential for space missions. A spacecraft traveling too slowly for its intended orbit may enter a lower path, while one traveling faster may move into a higher orbit or, if it reaches escape velocity, break free of the central body's gravitational influence.

Mission planners use carefully timed engine burns and gravity assists to change a spacecraft's speed and direction while conserving fuel. Missions such as Parker Solar Probe use repeated flybys of Venus to reshape their trajectories and reach extraordinary speeds as they approach the Sun.