Launches and orbits

Our satellites are launched from two main launch sites on different types of launchers — Ariane and Soyuz. Both rockets are designed to launch the satellites into certain positions in the Earth's orbit.

The launch of a new weather satellite is one of the most important activities in the EUMETSAT calendar. The continuity of the weather 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. For Meteosat it is around 30 minutes, for Metop it is around three hours. 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.

Satellite launches

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 weather 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.

Guiana Space Centre, Kourou

The Guiana Space Centre has several major advantages for the launch of satellites. French Guiana is scarcely populated and 90% of the country is covered by equatorial forests.

There are also no risks of cyclones or earthquakes. With a clear trajectory over the oceans towards the north and east, the Kourou site is in an ideal place to launch polar-orbiting and geostationary satellites.

Geostationary satellites can be launched towards the east and, at only 5°N latitude, a launch from Kourou can place satellites directly into an equatorial orbit with a minimal use of the fuel.

To reach its final orbit, the satellite goes through the Launch and Early Orbit Phase (LEOP).

After separation from the launcher and injection into transfer orbit, the geostationary satellite is manoeuvred via several intermediate orbits into its final geosynchronous orbit at 36,000 km above the Earth, correctly aligned with the Earth axis. Its spin rate is stabilised to 100 revolutions per minute.

Baikonur Cosmodrome, Kazakhstan

Baikonur Cosmodrome is the world’s largest space launch facility. Baikonur covers 7360 square kilometres and extends 75 kilometres from north to south and 90 kilometres from east to west. The base contains dozens of launch pads, five tracking-control centres, nine tracking stations and a 1500-kilometre rocket test range.

Launchers

Launcher procurement is EUMETSAT's responsibility. Currently we use both Arianespace and Starstem launchers.

Meteosat launchers

All EUMETSAT Meteosat satellites (except Meteosat-1) have been launched on Ariane vehicles from the space centre in Kourou.

Ariane has strap-on boosters (liquid and solid) to augment the first stage and provide sufficient thrust to launch either a much larger satellite than Meteosat or two satellites at once.

Meteosat-10 was launched in 2012 together with the EchoStar XVII communications satellite. Total payload lift performance was approximately 9,640 kg, which included the combined mass of the two spacecraft, plus the launch vehicle’s dual-passenger dispenser system and satellite integration hardware. Being able to launch with a co-passenger is a more efficient and cheaper approach when using an expensive launch vehicle.

Metop launcher

A higher than 97% success rate makes it one of the most reliable launch vehicles in the world.

The current three-stage version of Soyuz is a direct evolution from the R7 rocket used to launch the first satellite, 'Sputnik', in 1957, as well as the Vostok launch vehicle that launched Yurij Gagarin as the first man in space in 1961.

Starsem provide the technical interface and integration facilities at Baikonur Cosmodrome in Kazakhstan.

The Soyuz rocket usually comprises three stages. Stage 1 is the lower portion, consisting of four conical boosters grouped around stage 2, which is the cylindrical central core. Stage 3 is an upper stage with the payload adapter and fairings.

The four side boosters and the central core ignite at the same time before lift-off. After the first stage has used all its fuel (after around 118 seconds) it separates and the central core continues to burn (for around 290 seconds).

Ignition of the third stage's main engine occurs around two seconds before shutdown of the central core. The third stage separates itself from the central core by the thrust of the engine, which burns for 240 around seconds. All three stages use liquid oxygen and kerosene fuel.

A fourth stage — known as Fregat — was used for the Metop launch. The Soyuz ST/Fregat version for Metop incorporated new digital avionics and a larger fairing which, flown for the first time with Metop. After engine cut-off and separation of the Fregat, the third stage performed an avoidance manoeuvre by opening an outgassing valve in the liquid oxygen tank. The main Fregat engine was ignited twice to raise the satellite orbit around the Earth to a nominal 820 km. The Fregat uses unsymmetrical dimethyl hydrazine (UDMH) and nitrogen tetroxide as fuel.

Orbits

EUMETSAT satellites operate in two orbits — Meteosat in a geostationary orbit and Metop in a Lower Earth Orbit (LEO).

The two types of weather satellite, polar and geostationary, are complementary. Each type has advantages and disadvantages, and an ideal observing system combines both.