Discovering Space - Satellite Technology

Satellite Technology

Satellite technology has become part of all our everyday lives. From telling us what the weather is going to be like, and how to get from one place to another, to offering us a far wider choice of programmes to watch on TV.

What is a satellite?

Satellite is a word that simply refers to one body orbiting another. There are natural satellites that orbit planets, such as our Moon, and artificial, man-made satellites that serve a variety of different purposes. The first man-made satellite, Sputnik 1, was sent into space on 4 October 1957 by the former Soviet Union. Today there are over 3,000 satellites in orbit, owned by more than 40 countries worldwide.

What are they used for?

Man-made satellites have six main uses:

- Scientific investigation
- Earth observation
- Weather
- Communications
- Navigation
- Military

What are the different types of orbit?

There are many different orbits a satellite can be put into, depending on what it's being used for. But the majority use one of the following orbits.

- Geosynchronous Earth Orbit (GEO) is where the satellite sits directly over the equator, about 35,775 km above Earth. It will rotate in the same direction and at the same speed as our planet, so always appears to be in the same place in the sky. Communications and some weather satellites are placed in this type of orbit.

- Low Earth Orbit (LEO) is commonly described as the region between 200 and 2,000 km. Most artificial Earth satellites are placed in LEO, where they travel at about 27,000 km/h (8 km/s), making one revolution in about 90 minutes. Different orbits are used for different applications, e.g. Earth observation satellites often use the Sun synchrous orbit, travelling over the Poles and thus seeing most of the Earth's surface over time, while LEO communications satellites travel in orbits centred on the equator. Some scientific missions such as Hubble look out into space from LEO.

- Medium Earth Orbit (MEO) has many definitions but is essentially the region above LEO (2,000 km) to 1,000 km below GEO (34,775 km). This region is used by the various Global Navigation Satellite Systems (GNSS). The European Galileo system will reside there as well as the existing US GPS and the Russian Glonass. Many other satellites pass through this region either operationally or during deployment.

Satellite technology and instruments

Every satellite launched into space will carry its own unique set of instruments or technology, relevant to the mission. So a satellite studying outer space will have a telescope that can see in different wavelengths of light, one monitoring the weather might have a camera to measure cloud movement, while one used for communications will carry a payload that allows it to redirect messages back to one part of the Earth that have been sent up from another part.

They will also have a group of devices called "subsystems" that will help power the satellite, co-ordinate the instruments and send data back to Earth. The subsystem that powers the satellite will usually include solar panels that gather energy from the Sun.

How are satellites launched?

Some satellites, such as Hubble, are launched via a space shuttle. But the majority will be sent into orbit on rockets, which then fall into the ocean when they've used up all their fuel.

How do they remain in orbit?

Two factors combine to keep a satellite in orbit:
- the speed of the satellite
- the gravitational pull between the Earth and the satellite

This is similar to attaching a ball to a string and swinging it around in a circle. If the string were to break, the ball would fly off in a straight line. But because it is tethered (like gravity tethers a satellite), it orbits you instead.

What happens they stop working?

A satellite will stay in orbit until it starts slowing down. Gravity will then pull it into a denser part of the atmosphere, the friction generated as the satellite moves at very high speed through this denser atmosphere generates a lot of heat which can be enough to cause the satellite to burn up before it reaches the Earth's surface. The ones that are too big to burn up are guided to come down in a remote part of the ocean away from people.

What is small satellite technology?

Small satellite technology, being pioneered in the UK, uses a range of new techniques that enable scientists to build and launch satellites faster and for much less money than previously possible.

Many of these new small or "micro" satellites are currently being tested to determine whether simple, economically-built spacecraft can achieve the same results as traditional satellites.

If successful, these new techniques could have a huge impact on the future of space missions and significantly reduce the cost of launching satellites.