ERS-2 takes over where ERS-1 left off (1995)

ERS-2 in the clean room at ESA' s Technical Centre at Noordwijk in the Netherlands. The SAR antennas and the solar generator are folded up and packed against the satellite in the "launch configuration".
The second Ariane launch of 1995 will carry a very special payload into space: ERS-2, the European Space Agency's second environmental satellite. This will be the most complex satellite ever built in Europe to observe planet Earth and its environment.

ERS-2 will over the years 1995-98 carry on the work begun by its sister craft ERS-1, launched in 1991. The second ERS environmental satellite will however have to deal with an even more demanding range of tasks, equipped as it is with additional new instruments that will measure the ozone content of the atmosphere and monitor changes in vegetation cover more effectively. What is more, ESA has the option of operating the two craft "in tandem" for a period of time and this will open up completelynew perspectives for many research teams and high-tech firms.

In as little as three years ERS-1 has revolutionised many areas of theEarth sciences and their practical applications. The ERS user communityis now made up of thousands of scientists and hundreds of universities, research institutes and firms from all parts of the world. And that community is growing all the time; following an announcement of opportunity in Spring 1994, ESA selected, on very strict criteria, a further 250 research teams for preferential delivery of ERS data.

The second ERS satellite will combine more intensive use than its predecessor with a lower price tag. Extensive reuse of available technologies and existing facilities have made it possible to hold the cost of this programme to about 550 million ecu (650 million US$). This figure, some 60% of the cost of ERS-1, includes launch and operations and the difference would be greater still if account were taken of the general price increase over the last four years.

Built like ERS-1 by a consortium led by Deutsche Aerospace, ERS-2 willcarry the same active radar instruments. The largest of these will be the active microwave instrument, which in SAR imaging mode will generatethe familiar, detailed 100 x 100 km scenes of regions over which the satellite flies and determine, over the oceans, wind speed and direction together with wave height, length and direction. The second active instrument is the radar altimeter, which measures with extreme precision the distance between the satellite and sea or ice surfaces and mean wave height.

ERS-1 world map of the means sea level.
Unlike optical instruments, these radar systems function quite independently of light conditions and cloud cover which means they can operate around the clock.

ERS-2's passive instrument load includes an along-track (i.e. in the direction of flight) scanning radiometer equipped with six channels in the infrared and visible parts of the spectrum. The three channels in the visible spectrum are new and are used to observe vegetation, for example for crop forecasting or monitoring of deforestation.

The GOME, which stands for global ozone monitoring experiment, is an entirely new passive instrument which will monitor the ozone content of the atmosphere with an precision hitherto unobtainable from space. This highly sophisticated spectrometer was developed by ESA in the record time of five years.

Two further instruments on board ERS-2 will serve to enhance the accuracy of other instruments. These are PRARE (precise range and range rate equipment) units, which will have the task of measuring the satellite's orbit with outstanding precision, and a microwave sounder to determine atmospheric humidity.

ERS-1 has moreover already exceeded its planned operational life by 50% without a single essential system breaking down. ESA hopes to be able to keep the satellite in service until the end of 1995 and this offers the opportunity of operating ERS-1 and ERS-2 together for a period of time. And as two eyes see better than one, the 'ERS tandem mission' will double the number of measurement points for the radar altimeter and, more importantly still, will lay the basis for an accurate, three-dimensional digital map of the Earth's land surfaces, which would be a very expensive task using conventional maps and for some of the Earth's regions would be impossible.

Over the last three years ERS-1 has often been in the news, now keeping a watch on oil slicks following a tanker disaster, now determining the extent of catastrophic flooding or again measuring the tectonic movements resulting from the Landers earthquake in California in 1992. Of interest to a more specialised audience have been remarkable new research findings on climatic events, such as El Ničo and its global impact on climate, or the first ever topographical description of the ocean floor beneath the Arctic icecap. It is sometimes hard to believe that data from a single satellite can be put to such varied use in the hands of scientists and other users.

Offering his thoughts on the past and future of the ERS programme, Lanfranco Emiliani, in charge of Earth observation at ESA, had the following to say: "The uninterrupted supply of Earth observation data has always been a priority at ESA. Those who put their faith in ERS-1 three years ago have not been disappointed. Our aim now is to make sure that the data flow does not dry up in the years to come."

ERS-2 Technical Data (1995)

Satellite
Largely identical to ERS-1. The platform is based on the design developed for the French SPOT satellite.
Payload electronics accommodated in a box-shaped housing on the platform; antennas fitted to a bearing structure.

On-board systems
AMI - active microwave instrument consisting of a synthetic aperture radar (SAR) and a wind scatterometer (both in the C-band).
RA- radar altimeter: takes precise measurements of the distance from the ocean surface and of wave heights.
ATSR - along-track scanning radiometer (operating in the infrared and visible ranges): measures sea surface temperatures and the vegetation cover of land surfaces.
GOME - global ozone monitoring experiment, an absorption spectrometer which measures the presence of ozone, trace gases and aerosols in the stratosphere and troposphere.
MS - microwave sounder: supplies data on atmospheric humidity.
PRARE - precise range and range rate equipment: ERS orbit and trajectory determination.
LRR - laser reflector: determines satellite position using ground-based laser stations.
IDHT - instrument data handling and transmission: temporary on-board data storage by means of two 6.5 GBit tape recorders, equivalent to the data volume acquired in one orbit. Recording, formatting and transmission of data at 105 Mbit/s (transmission of SAR imaging data in real time), or 15 Mbit/s (transfer from tape recorder).

Dimensions
Overall height: 11.8 m
Solar generator: 11.7 x 2.4 m
SAR antenna: 10 x 1 m
Total mass: 2516 kg