SIEMENS

With winter sunlight flashing through the leaves of the olive grove, the Monte Cavo volcano’s crater towers in the distance beyond the grapevines. On the outskirts of the town of Frascati, Italy, south of Rome, the grass is a deep green even in the middle of winter and stray cats are often seen roaming. The felines have found a new home here, between the olive trees and a gigantic antenna. The installation, the heart of the Centre for Earth Observation of Molecular Detectives | Environmental Sensing the European Space Agency (ESA) may look like something from space itself, but it is where most of ESA’s satellite signals are received.

ESA’s data transmissions must always function reliably. That’s why Siemens engineers are developing special equipment for thorough testing of the satellites before they are launched into space. “In satellite images trees look like little holes. We can see they are trees only because they are in straight rows,” says Dieter Isakeit of Earth Observation center. The satellite images he is referring to have a resolution of one meter per pixel.

Isakeit likes the olive trees, which thrive here at the foot of Monte Cavo. The eruption of the volcano thousands of years ago replaced the soil with tuff and basalt, superb materials for containing water. “Although the volcano hasn’t been active since then, we shouldn’t let ourselves be lulled into a sense of false security,” he says. That’s because the planet’s interior is in constant movement. When the continental plates, which float on a malleable mantle, grind against each other, earthquakes can result. At the plates’ edges, the high-temperature rock forces its way to the surface and serves as fuel for volcanoes. “This is how the planet shows us it’s alive, and always changing,” says Isakeit.

Such changes are exactly what researchers at ESA want to capture. In the early 1990s they established the Living Planet program, a largescale science project designed to provide data to help us better understand the planet Earth. The first satellite, ERS-1 - short for European Remote- Sensing Satellite - was launched into a polar orbit in 1991. Until 2000 it was busy gathering measurements related to the earth’s surface, ocean temperatures, waves, air currents, and other information of importance for climate researchers. Additional satellites have joined it since then, including the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE), which was launched in early 2009. Since then the GOCE has been monitoring the earth’s gravitational field with unprecedented precision. Its results are of interest to climate researchers because gravity causes bodies of water with a higher salt content to settle to lower levels - a phenomenon that drives heat-bearing ocean currents, and thus affects the climate.

The Gulf Stream, for example, warms northern Europe every year with the equivalent of the energy of 100,000 large power plants. Measuring the gravity is necessary because it is far from constant on the earth’s surface. High mountain ranges increase it, and deep troughs in the sea weaken it. Yet another factor is the density of the rock in the ground. A higher density results in a higher local gravitational field. The Indian Ocean provides a clear example of how gravity changes. “If you cross by ship, you pass through a depression 100 meters deep - without being aware of it,” explains Prof. Volker Liebig, Director of ESA’s Institute for Earth Observation. The rea son for this is that the ocean surface always adjusts itself to the earth’s vertical gravitational field.

To ensure that all the information collected by GOCE reaches the earth, the satellite’s data transmissions to the ground station must function reliably. Anything less than this could compromise the value of the satellites, associated scientific studies, and the hundreds of millions of euros invested in ESA’s facilities.

Engineers from Siemens Aerospace Solutions have developed solutions for GOCE, including radio frequency testing equipment. This system puts the satellites’ communication technology through its paces during the test phase. First of all the satellite is subjected to all kinds of stress that could occur during its mission. In a vacuum chamber, for example, a setting like that of outer space is created and the satellite is violently shaken on platforms that simulate the forces from the launch rockets at liftoff. The Siemens system simultaneously monitors the satellite’s telecommunication functions to ensure they work reliably even under such extreme conditions.