Artemis

When you phone your friends or send them an email, do you ever stop to think about how people communicated before telecommunications were invented?

Messages sent by word of mouth often changed so much in the telling that they lost their original meaning. Letters could take weeks or even months to arrive as messengers travelled by foot, horse or boat. If the messenger had an accident they might not arrive at all!

Communications started to improve in the mid-19^th century with the invention of the first mechanical telecommunications systems: the semaphore and the heliograph. The semaphore uses visual signals such as flags and the heliograph uses mirrors to reflect the sun's rays and send messages by Morse code. New inventions soon followed such as the electric telegraph, the telephone and the 'wireless' telegraph.

The most important breakthrough came with the invention of telecommunications satellites, a system first thought of in 1945 by a science fiction writer called Arthur C. Clarke. It took another 18 years before his idea could be put into practice, but in 1963 the first telecommunications satellite was successfully launched.

Just think, the latest satellites can carry 100 000 simultaneous conversations as well as several television channels at the same time, a far cry from laboriously sending messages via Morse code.

Artemis

ESA's new satellite Artemis marks another important advance in telecommunications. Artemis was launched on 12 July 2001 when it is was sent into orbit by an Ariane-5 rocket from Europe's spaceport in Kourou, French Guiana.

What will it do?

Artemis, developed by ESA, is a new breakthrough in telecommunication satellites. For the first time laser beams are being used, as well as radio, to communicate with other spacecraft. This, together with other new technology on board Artemis, will improve telecommunication systems in Europe.

Artemis can:

• Help you to find your way
  If you are lost in the Sahara desert or in the back streets of Paris, a satellite navigation system built into your mobile phone will soon have you back on track.
• Improve communications for people travelling by train, boat, car or lorry
  Contacts with moving vehicles, either by voice or by sending data, will be better and faster.
• Help to protect our environment
  The low-Earth-orbit satellites that are used to gather information on the environment will be able to transmit data to Artemis which Artemis will then forward to the local ground station waiting to receive it. All this will take place in a few seconds!

What does Artemis look like?

Look at the photo on the right, this will give you some idea of what Artemis looks like in space. The first things you probably noticed are the huge 'wings' which are 25 metres wide from tip to tip once they unfold, and the two satellite receiver dishes. The wings are made of solar panels that provide energy, while the two satellite dishes transmit information between satellites and to the Earth.

How did Artemis get into orbit?

A 51-metre tall Ariane-5 launcher carried Artemis into space. To do this the Ariane-5 had to reach a speed of around 9 km per second and a height of more than 1,600 km above the Earth, that is the same as the distance between London and Barcelona. At this point Artemis was injected into geostationary orbit at an altitude of 36,000 km. As this orbit takes 24 hours to complete, the same time as the Earth takes to rotate, the satellite remains 'stationary' over the same point on the Earth.
Artemis is now ready to fulfil its promise of improving telecommunications throughout Europe.