Satellite facts and information

- a potpourri of interesting and not so interesting facts and information about satellites

Facts about numbers of satellites in orbit
There are over 2500 satellites in orbit around the Earth
There are also over 10 000 man made objects orbiting around the Earth. These include a variety of pieces of satellite debris ranging from panels to disused equipment.

Facts about satellite firsts
The first satellite named Sputnik 1 was launched by the Soviet Union on 4th October 1957. It was a football sized globe that transmitted a "beep beep" sound as it orbited the Earth. The word Sputnik means satellite. It continued transmitting for about 21 days. It was followed four months later by the US satellite Explorer 1 which was launched on 31st January 1958.

Possibly one of the best known satellites was Telstar 1. Built by AT&T it was launched on July 10, 1962, and on the same day live television pictures originating in the United States were received in France.

Lift off of Telstar 1 in 1962
Image courtesy NASA

Facts about satellite orbits
Most communications satellites use what is termed a geostationary orbit. These are at an altitude of, around 22,000 miles and as a result of their speed and the circumference of the orbit they travel round the Earth above the equator in 24 hours. As they travel at the same rate that the Earth rotates, they stay above the same point on the Earth's surface all the time.

In contrast, Low Earth Orbits are just above the Earth's atmosphere and are typically between 100 and 800 miles in altitude. Orbiting at this altitude, an object may only take about 90 minutes to completely circle the Earth, travelling at around 17,000 miles per hour. Low Earth Orbit is used by manned vehicles such as the space shuttle and the International Space Station. It is also used for weather and remote sensing satellites. On a clear night it is usually possible to see with the naked eye several satellites in low earth orbit passing overhear.

Facts about the Global Positioning System (GPS)
The GPS system is run by the US Department of Defense. It consists of 24 operational satellites although there are some extra in orbit as spares in case of catastrophic failure even though each satellite is built to last for ten years. The satellites are named Navstar satellites and each one weighs around 1860 pounds. They are about 17 feet across with the solar panels extended, and they transmit about 50 watts, although the solar panels generate around 700 watts.

The satellites are in one of six orbits. These are in planes that are inclined at approximately 55 degrees to the equatorial plane and there are four satellites in each orbit. The orbits that are roughly 20200 km above the surface of the earth and the satellites travel at a speed of around 14000 km / hour (i.e. about 8500 mph) which means they complete each orbit in roughly 12 hours.