Launching Satellites

The launch of a new satellite is one of the most important activities in any satellite operator’s calendar. The continuity of the satellite system depends on a series of successful launches and each launch represents a major financial investment. Launching satellites is a very complex business which involves teams from across the space industry, working together for months and years at a time.

For every launch there is a launch window — a precise period of time, in hours and minutes, within which a launch must take place if the spacecraft on board is to be placed into the correct orbit. Once the launcher, or rocket, is on the launch pad the countdown begins and all systems are fully tested, to ensure a successful lift-off. If the rocket is not launched within the launch window, it has to wait for the next window.

How does it work?

After completion, a newly manufactured satellite is transferred to the launch site for final testing and fuelling, before being mated to the launch vehicle. The launch is a complex operation conducted in several stages, which differ according to the system used.

One common method of placing satellites into geostationary orbit is based on the Hohmann transfer principle. Using this system the satellite is placed into a low earth orbit with an altitude of around 300 kilometers. Once in the correct position in this orbit rockets are fired to put the satellite into an elliptical orbit with the perigee at the low earth orbit and the apogee at the geostationary orbit. When the satellite reaches the final altitude the rocket or booster is again fired to retain it in the geostationary orbit with the correct velocity.

Alternatively the satellite is launched directly into the elliptical transfer orbit, typically between 200km and several thousand kilometres from the Earth. Again when the satellite is at the required altitude the rockets are fired to transfer it into the required orbit with the correct velocity.

Launch sites

Selecting the ideal launch site is crucial. Several factors influence the choice of launch site. For safety reasons, most launch sites are placed close to the sea — Guiana Space Centre in Kourou, French Guiana — or in an unpopulated desert, such as Baikonur Cosmodrome in Kazakhstan.

When launching geostationary satellites, it is important that the satellites can be launched towards the east, where the launch impulse is aided by the spin of the Earth. This ‘slingshot’ effect increases the speed of a launcher by 460 m/s. These factors save fuel and money, and prolong the active life of satellites. The launch site should be as close as possible to the equator, so that the assistance is as large as possible. For polar orbiting satellites it is better to have open water towards either the south or the north.

Did you know?

European built Ariane launcher is one of the world's most reliable launch vehicles. The main boosters in the Ariane 5 satellite launcher uses Liquid Hydrogen and Liquid Oxygen as the propellant.

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