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Why Don’t Satellites Fall Out of the Sky?

 

 

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Wednesday, September 27, 2017

If you’ve ever wondered how satellites maintain their orbit and don’t just drop out of the sky you’re not alone. It turns out this is one of the most asked questions about how satellites work.

GOES-R satellite
Illustration of NOAA's GOES-16 Satellite.

So, How Do Satellites Stay in Orbit?

Satellites are able to orbit around the planet because they are locked into speeds that are fast enough to defeat the downward pull of gravity. Satellites are sent into space by a rocket launched from the ground with enough energy (at least 25,039 mph!) to get outside our atmosphere. Once the rocket reaches its determined location it drops the satellite into its orbit. The initial speed of the satellite maintained as it detaches from the launch vehicle is enough to keep a satellite on orbit for hundreds of years.

A satellite maintains its orbit by balancing two factors: its velocity (the speed it takes to travel in a straight line) and the gravitational pull that Earth has on it. A satellite orbiting closer to the Earth requires more velocity to resist the stronger gravitational pull.

Satellites do carry their own fuel supply, but unlike how a car uses gas, it is not needed to maintain speed for orbit. It is reserved for changing orbit or avoiding collision with debris.

Why Don't Satellites Crash Into Each Other?

Actually, they can. NOAA, NASA and other U.S. and international organizations keep track of satellites in space. Collisions are rare because when a satellite is launched, it is placed into an orbit designed to avoid other satellites. But orbits can change over time. And the chances of a crash increase as more and more satellites are launched into space.

In February 2009, two communications satellites - one American and one Russian - collided in space. This, however, is believed to be the first time two man-made satellites have collided accidentally.

Discovr Satellite
America’s first operational deep space satellite, NOAA's DSCOVR, orbits one million miles from Earth. Positioned between the sun and Earth, it is able to maintain a constant view of the sun and sun-lit side of Earth. This location is called Lagrange point 1. (Illustration is not to scale) 

How Long Can Satellites Stay in Orbit?

Satellites can sustain operations in their orbit for a long time. NOAA’s GOES-3 Satellite for example had an operational life spanning five different decades and six different U.S. presidents.

The GOES-3 satellite made history on June 16, 1978, when it became NOAA’s third Geostationary Operational Environmental Satellite (GOES) placed in orbit. In 2016, after 38 years and a second life as a communications satellite, GOES-3, one of the oldest continuously operating satellites in orbit, made history again when it reached the end of its life and completed the decommissioning process on June 29 when the satellite was carefully placed into a “graveyard” orbit.

This orbit requires little velocity to maintain its position because at this distance there is very little gravitational pull from the Earth. The closer satellites are to Earth the more likely it is that they will run into traces of Earth’s atmosphere which create drag.  The drag decays the satellite’s orbit and causes it to fall back towards Earth.

Learn more about NOAA Satellites: