Satellites, Science of

Many of our modern global communication systems depend on satellite technology. In the most general sense, a satellite is any object that orbits another object in space. Hence the Earth is a satellite of the sun, and the moon is a satellite of the Earth. However, when thinking about satellites today, most human-made satellites in orbit around the Earth come to mind. These are critical to any number of modern technological systems. They enable communication across continents but also monitor the Earth's weather, look for evidence of climate change, help us create accurate maps, and track everything from the movements of arms and armies to the delivery of packages.

Any object in orbit is actually a satellite, from a dropped wrench used by an astronaut to the [Page 672]International Space Station (ISS). There are more than 500 human-made operational satellites in orbit as of 2009, and over 8,000 separate human-made objects larger than 10 centimeters (baseball sized) tracked by the Space Surveillance Network (SSN), mostly items referred to as “space junk.” The SSN has tracked over 24,500 objects in space since 1957, the year that the Sputnik, created by the Union of Soviet Socialist Republics (USSR), became the first-ever human-made satellite.

Every human-made satellite goes through different stages in its life. First it must be designed, built, and tested. Then it must be launched into a specific orbit. It must be properly deployed and activated. Then it has a normal operational life span as it completes many orbits, doing whatever tasks it is meant to. When the satellite reaches the end of its useful life span, it is disposed of. At any point in this general timeline, there are many opportunities for things to go wrong.