Of course the philosopher Socrates would not have been thinking about satellites or spacecraft at this time, but his famous quote is quite apt! Artificial satellites have helped us to discover and learn more about our world and beyond from above Earth’s surface. But what exactly are satellites and what is their function?
A satellite can be defined as an artificial body which has been placed in orbit around the Earth or another planet in order to collect information or for communication purposes. It can also be described as a celestial body orbiting the Earth or another planet, for example our ownMoon. I will be looking at artificial satellites opposed to natural satellites.
The notion of sending an artificial object into orbit around the Earth has been around for centuries. As far back as 1729 in fact, when Isaac Newton published his famous cannonball hypothesis. Basically he asserted that if you were to place a cannon on top of a mountain and fire it horizontally it will travel parallel to the Earth’s surface before succumbing to gravity and falling to the ground Newton then began to think about adding more gunpowder which would make the cannonball travel further before landing back to Earth. He theorised if you were to add enough gunpowder to create the right velocity to the cannonball then it would travel around the planet in an orbit, never falling to the ground. So who was going to prove this hypothesis correct?
It was the Soviet Union in 1957 (228 years after Newton published his theory) that was the first nation to send an artificial satellite into orbit when they launched Sputnik 1. This was quickly followed by Sputnik 2 later that year in which the first living passenger was aboard and sentt into orbit; this was a dog called Laika. This kick-started the “Space Race” and resulted in several other nations launching their own satellites. The US launched Explorer 1 in January 1958 and calculated in 1961 that there were around 115 Earth-orbiting satellites! As of today there have been tens of thousands of satellites launched! Satellites vary in shape and size as well. One is as big as a football field, the the International Space Station, while some cubesats could be smaller than your laptop!
They may look very different but they have many similarities. For instance all of them have a metal or composite frame and body which holds everything together. They have a computer on board and a power source, and all have a radio and antenna system in place. They are not usually mass-produced but custom-made for a particular purpose, and satellites have wide range of purposes which we will look at:
We have weather/observational satellites that monitor the weather and climate on Earth. They can observe clouds and cloud systems, see city lights, fires, effects of pollution and even view aurorae. Other environmental information such as sand and dust storms, snow cover, ice mapping and ocean currents can also be monitored. This information can help meteorologist predict the weather and provide information on environmental issues such as the melting ice-caps. Weather geostationary satellites are operated by the USA (GOES), Japan (MTSAT), China (Fengyun-2), Russia (GOMS) and India (KALPANA). They orbit at the equator at a height of 38 500km. At this height, the speed of the satellite is the same as the Earth’s rotation thus it stays stationary over a certain point on the equator allowing the satellite to continually observe the same area. Polar orbiting weather satellites are operated by the US (NOAA, QuikSCAT), Russia (Meteor) and China (Fengyun-1). They provide global coverage from a single satellite.
Communication satellites allow us to relay telephone and data conversations. Their origins can actually be traced back to the Moon and a pre-Space Age project started by the US Navy called “Communication Moon Relay”. This was where the Moon was used as a natural communications satellite bouncing radio signals off our natuarl satellite and back to Earth. The first artificial communications satellite was launched by NASA in 1960, it was called Echo 1 and was simply a giant reflective balloon. If you are a user of services such as Sky TV you have Satcom 1 to thank which was launched in 1975. It was the first broadcast satellite used by American networks like ABC, CBS and NBC. These communication satellites are again in a geostationary orbit which means they have an orbit time the same as Earth’s rotation so they appear to remain in the same place in the sky. If you look at satellite dishes on homes across the country, you will notice that they all point up in the same direction and are fixed. If the transmitting satellite in space was not geostationary then the dish on your home would have to move to track the satellite in space to get the signal.