“Man must rise above Earth, to the top of the atmosphere and beyond, for only thus will he fully understand the world in which he lives” Socrates (circa 399BC).
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.
But for me probably the most significant and important use for a communication satellite was the development of long distance telephone networks. Satellite phone communication is also very important for remote places such as the Arctic and Antarctic . They are also used at sea, on oil rigs, and as back-ups for hospitals and the military.
A little aside is that the SF writer Arthur C. Clarke (Author of 2001: A Space Odyssey) was one of the early thinkers that an object could be placed into orbit at the same rate as the Earth’s rotation to aid communication. This was back in 1945 – proving science fiction theories can become reality.
Navigation satellites not only help ship and planes find their way, but they are regularly used by people today on roads through technology such as SATNAV. They are even built into the more modern cars as standard! A synopsis of how they work is by receiving signals from at least four navigational satellites to pinpoint your location. The receiver determines your distance from each of the satellites by measuring the time taken by the signal to travel from the satellite to your receiver antenna. When before, down through history, the stars and constellations were used as a means of navigation, technology and satellites have taken over and the benefit is you don’t need a clear sky for them to operate. However by using the stars correctly you can never go wrong, but I am sure we have all been in the situation when the satnav gets a little bit confused and you end up down a lonely county road instead of at your friend’s house in the town.
Rescue satellites respond to radio distress signals. A good example of this is the International Cospas-Sarsat programme. This is a satellite “search and rescue distress alert detection and information distribution system” according to its official website www.cospas-sarsat.int. Originally started by Canada, France, the US and the former Soviet Union in 1979 it now has 43 countries and organisations participating. It has been instrumental in the rescue of over 35,000 lives around the globe beginning with the rescue of three people from the crash of a light aircraft in Canada in September 1982. The “Latest News” section on their homepage makes some interesting reading and viewing with stories and video footage of rescues in which the activated emergency beacons have been relayed to rescue teams via satellite.
The most common use for satellites is for gaining intelligence, not to make us smarter, but for espionage and military communication. Military satellites are mainly used for reconnaissance and surveillance, navigation of military vehicles and the analysis of Earth’s surface. One of the first was Corona, a US military spy satellite system used for photographic surveillance of the People’s Republic of China, the Soviet Union, and other areas between June 1959 and May 1972. The Corona was operated by the CIA Directorate of Science and Technology, with assistance by the US Air Force. Between 1961 and 1994, the Zenit program was in operation. This was a successive launch of military spy satellites by the Soviet Union. However, the main reason for launching satellites was kept top secret.
Astronomical satellites are in an orbit but actually look away from the Earth. They are studying the Universe and our Solar System. The amazing Hubble Space Telescope, launched in 1990, and still functioning today, is a great example of this. Within the next five years it could have a companion called the James Webb Space Telescope (JWST) which will be able to look further into our Universe.
My favourite types of satellites are space stations. These are capable of housing a human crew orbiting around Earth and are normally positioned in low Earth orbits. As of June 2014 there are two space stations currently in orbit and these are the Chinese Tiangong 1 (unmanned most of the time) and the International Space Station (ISS) which has been constantly manned for over the past 10 years! You may have heard of other previous stations, there was the famous Mir station and Skylab to name but a few. Scientific studies are the main aim of astronauts travelling to space stations. The International Space Station has received a lot of attention of late with Astronauts such as Chris Hadfield tweeting and taking images of the Earth from it and Channel 4 broadcasting live from the station as well this year.
Did you know that you can see the ISS from your house? It will look like a tiny bright star coming across the sky. It lasts approximately four minutes and best of all you can see it with the naked eye. It’s quite bright because of its size (it is as big as a football field) and is an amazing sight to see. Websites such as www.heavens-above.com can aid you in getting times when the space station comes across the area you live. Give it a go and spot a satellite with astronauts on board!
As we have seen satellites can orbit at different heights. The three main categories are Low-Earth orbits used by many military satellites and by space stations. Medium-Earth orbits used by navigation satellites like GPS systems and Geosynchronous orbits which stay above the same position on Earth and are used for communications and television broadcasts.
When a satellite has reached the end of its function it can be de-orbited (like the Mir Space Station which disintegrated in Earth’s atmosphere). It can be moved into what is known as a “graveyard orbit” along with other “lifeless” satellites, or the most common thing to do is to just leave it in its current orbit. An example of this is the Vanguard 1 which was launched in 1958 and is still in orbit today, not functioning!
As you can see satellites have many uses and play an important role in everyday life for us today. When you next switch on your satnav system, tune into Sky Sports or look at a long-range weather forecast, remember the technology behind the information. It truly is wonderful what we can achieve, but we have to remember to keep space tidy at the same time and not clutter up our immediate surroundings with space junk. Perhaps we should be thinking about how to remove the “dead” satellites to create more room in space. But the future is bright, the possibilities are endless and our learning is only just beginning. I am looking forward to developments with the JWST and what other unique insights satellites can give us!
(Article by Sinead Mackle, Senior Education Support Officer)