Orbital Speed | Universe Today

Written by Tega Jessa

The orbital speed of an object measures its speed around another object's center of gravity. This can be its speed at a given instant and point in its path or its average speed. Depending on the eccentricity of its orbit this speed changes as a satellite or moon gets closer to its center of gravity or further away. The two points were these speeds change the most are the pericenter and the apicenter.

Orbital speed also means the speed required for a satellite to balance the gravity of its system's center of gravity against its own inertia. This speed is what makes it possible for artificial satellites to stay in orbit around the Earth.

The speed needed to stay in orbit varies according to the satellites mass and distance from the object it orbits. This means that different types of satellites only work best in certain types of orbits. In the case of artificial satellites they have to stay in a certain region over the Earth to operate. For geostationary satellites this just over the Earth's equator.

An orbital speed is also just a scalar or numerical measurement. The actual speed and direction needed to balance the pull of gravity with a satellite's inertia is actually orbital velocity. It pretty simple to explain. Any moving object tends to move in a straight unless influenced by an outside force. In space that means gravity.

The gravity of a massive object near the satellite at the right distance can exert a gravitational pull just strong enough to change the direction of the satellite curving it into a circular path or orbit. Its easy to explain using the example of a ball on string. If you were to swing the ball you would notice that when you let it go it flies of in a generally straight path. If hold the string while swinging the ball, you will notice that the tension of the string pulling the ball, but the speed of the ball keeps it from leaving its orbit.

Orbital speed is important to space flight. We know that exceeding orbital speed gives us the escape velocity needed to escape the Earth's gravity. By calculating the orbital velocity we are able to place objects in orbit such as satellites, space shuttles, and even the International Space Station. The understanding of this concept makes the majority of human space exploration possible.

If you liked this article there other related articles on Universe Today you might like. First there is an interesting article about space debris and their danger to orbiting satellites and astronauts. You also might this article about the LRO orbiter.

There are also some interesting links on the web. Check out NASA article about it Lunar Mission. Also check out this article on how satellites work.

You can also check out the podcast archive at Astronomy Cast. Episode 115 The moon part 3 the Return to the Moon.

Filed under: Astronomy

Tags: gravity, keplers laws, orbit velocity, orbital speed