Satellite images with clouds moving across Europe are familiar to everybody
from the daily TV news. These images have been available since the launch of
the first European weather satellite of the Meteosat fleet in 1977. For more
than 24 years the Meteosat satellites have ensured a reliable and successful
supply of data for weather forecasts of unprecedented precision. But the
technical possibilities have changed enormously since the Meteosat premiere
and the technology of Europe’s first-generation weather satellites has aged.

Therefore, an international consortium of companies – in which Astrium is
also involved – is developing and building a new generation of European
weather satellites: Meteosat Second Generation (MSG). Meanwhile the first
satellite of this new Generation is finished and will be launched in the
beginning of 2002. MSG will further enhance the precision and reliability of
short-term weather forecasts, as the new satellite generation will offer the
meteorologists a considerably enlarged database for their forecast models.
In addition to Seviri (Spinning Enhanced Visible and Infrared Imager), the
most important measuring instrument aboard MSG, Astrium will deliver the
subsystems for power supply, attitude and orbit control and propulsion.
Precise Weather Forecasts are a Valuable Asset

Reliable weather forecasts not only mean a better quality of life to all of
us but also translate into hard cash since there are entire branches of
industry to which precise weather forecasts are of decisive importance. One
example is the construction industry. Bad weather not only has an adverse
effect on many types of work; some activities such as concreting simply must
have good weather for a guaranteed period of time.

Another branch of industry relying on precise weather forecasts is the
transport sector. Roads can be cleared of ice and snow if timely information
is available on bad weather, thus reducing the number of accidents and
casualties. On top of this, ecological damage caused by the use of salt and
de-icing chemicals is minimized. Furthermore, the amount of pesticides used
in the agricultural sector is reduced when the chemicals are not immediately
washed off the crops due to the onset of rain.

And not to be forgotten – the power industry. Weather forecasts play a
central role in establishing consumption estimates. Pressure in the gas
pipelines, for instance, has to be raised in good time before consumption
starts to rise. If the consumption does not rise, however, then the unused
gas must be liquefied – and this is expensive.

Furthermore, extreme weather phenomena, such as hurricanes or floods, seem
to be occurring more frequently than they used to. Man is possibly the cause
both of this and the long-term global climate changes Therefore, detailed
knowledge of the factors which have an influence on the weather and the
climate is more important than ever.

Meteosat – The Fleet of European Weather Satellites

The Meteosat fleet is operated by Eumetsat, the 17-member-state European
organization for satellite-based meteorology. The Meteosat satellites are
positioned 36,000 kilometers above the equator. Their position is
geostationary, i.e. it does not change in relation to a reference point on
the Earth.

A Meteosat spacecraft has a cylindrical body on which solar cells for power
supply and a telecommunications module are mounted. Inside the cylinder is
the satellite’s heart – the radiometer. Apart from imaging, the Meteosat
satellites fulfill two other functions. They receive environmental and
weather data from measuring stations located on ships, aircraft or buoys and
forward these data to a central station. In turn, the satellites transmit
the weather charts generated by the central station to user stations in over
130 countries. Eumetsat’s nerve center is located in Darmstadt, 25
kilometers south of Frankfurt. It controls the satellites and receives and
processes their raw data and subsequently returns them to the satellite
which acts as a relay station and sends the data on to the user stations
worldwide.

Meteosat Second Generation (MSG)

The Meteosat Second Generation (MSG) fleet consists of three satellites to
be launched into space in 18-month intervals, i.e. four years. The launch of
the first satellite is scheduled for January 2002. As for the first Meteosat
generation, only one satellite, the so-called primary satellite, is active.
This satellite is deployed in a geostationary orbit above the intersection
point between the zero meridian and the equator. The other satellite is in a
standby position to take over operations in the case of an emergency.
Once in space, MSG-1 will initially be in the standby position at ten
longitudinal degrees west of the seventh and last first-generation Meteosat
which will still serve as the primary satellite for the next six months.

Then, the two satellites will switch their positions and MSG-1 will start
operating as the primary satellite above the Gulf of Guinea, west of
Equatorial Africa. One and a half years after the launch of MSG-1, the
second MSG satellite will be launched into orbit so that both the primary
and the standby satellites are of the second generation. MSG-3 will follow
four years later or as required. The MSG satellite has an expected lifetime
of seven years. All together, the three satellites are to provide Europe
with weather data for at least twelve years. As with Meteosat, MSG also
forms part of the worldwide weather observation program of the World
Meteorological Organization. This program covers ten geostationary
spacecraft from Europe, the USA, Russia, China and Japan which monitor the
global weather events. When MSG-1 starts operating next year, it will be the
most advanced weather satellite worldwide with state-of-the-art technology
on-board.

Like the Meteosat first generation satellites, the MSG spacecraft will
stabilize their position in orbit using their own spin movement. They spin
100 times per minute in a counterclockwise direction around their own
longitudinal axis which is aligned to the Earth’s axis. Each MSG satellite
has a mass of 2,010 kg and a 2.40-in-high cylindrical housing with a
diameter of 3.20 m. The satellite’s power is supplied by eight curved solar
cell segments surrounding the housing. One of the segments is provided with
a recess for the instruments. The total capacity of the solar cells amounts
to 720 watts. The satellites can be launched by the European boosters Ariane
4 and 5.

The Eye of the MSG Satellites: Seviri

The most important measuring instrument on board Meteosat Second Generation
is Seviri (Spinning Enhanced Visible and Infrared Imager), a radiometer
developed and built by Astrium. This radiometer is a “telescope” which
measures the radiation from the Earth in various ranges of the
electromagnetic spectrum. Seviri is more powerful than the predecessor model
aboard the first Meteosat generation which was also developed by Astrium.
The old radiometers recorded three spectral channels, i.e. visible light,
infrared and water vapor. Seviri records the radiation in twelve different
channels of the electromagnetic spectrum. Thus, MSG offers the
meteorologists a considerably more differentiated database for numeric
weather forecast models.

However, the Seviri telescope not only provides more precise data but also
provides the data more frequently. Compared to the telescopes of the first
Meteosat generation which produced a satellite image every 30 minutes,
Seviri supplies an image every 15 minutes. This supports the meteorologists
in evaluating short-term weather developments. Thus, more precise and faster
forecasting of the build-up of dangerous weather phenomena, such as storms,
thunderstorms or heavy rainfall is possible. In the event of fog, airports
can be warned one to two hours in advance. The resolution of the Seviri
telescope is considerably higher than that of its predecessors (1 kilometer
compared to 2.5 kilometers in the first generation), thus allowing a more
precise location of storm fronts or fogbanks.

Technically, Seviri is a lightweight and compact telescope and scan
assembly. The telescope is equipped with three mirrors made of Zerodur, an
extremely light glass ceramic material. The scan assembly itself consists of
an additional movable Zerodur mirror which is positioned in front of the
telescope; it performs a linear scan of the Earth’s surface from north to
south. The telescope sends the collected radiation to the focal plane where
it is divided into twelve different channels of the electromagnetic spectrum
and transferred to 42 sensors. The sensors transmit the recorded data to the
Functional Control Unit (FCO), the interface to the data transmission system
of the MSG satellites. Thus, a new multispectral satellite image will be
produced every 15 minutes.

The compact structure of the telescope and the scan assembly enables the use
of a large passive cooler which improves the performance of the infrared
measuring systems by lowering their operating temperature to approx. -190 *
Celsius. The total weight of the Seviri telescope will not exceed 270
kilograms and its power consumption amounts to approx. 123 watts, i.e. equal
to that of two medium-power light bulbs.

MSG Supplies Data for Climate Research and Serves as a Relay Station
Seviri is the most important but not the only measurement instrument aboard
MSG. The GERB (Geostationary Earth Radiation Budget) instrument of the
second Meteosat generation provides important data for climate research.
GERB is a radiometer with two broadband channels, i.e. one covering the
solar radiation spectrum and the other one the entire electromagnetic
spectrum. These instruments will be used for measuring the solar radiation
reflected by the atmosphere and the heat radiation emitted by Earth.
Furthermore, the weather satellite is used as a relay station – but not only
for sending its own data which have been processed in the Control Center in
Darmstadt, to the end user. MSG also receives weather data from measuring
stations located on land, ships, buoys and aircraft and transmits them back
to Earth.

In addition, a so-called Search-and-Rescue Transponder aboard MSG is in a
position to receive emergency signals from ships and aircraft and to
transfer them to a central receiving station in Europe. Rescue organizations
all over the world can therefore be alerted quickly.

Paris/Le Bourget, June 2001/01012

For further information:

Astrium

Earth observation & Science

Mathias Pikelj

Telephone: ++49 7545 8 9123

Telefax: ++49 7545 8 5589