CryoSat - A Satellite with an icy Mission
Berlin/Friedrichshafen, le 01 mai 2002
Astrium is building the new European environmental and climate satellite CryoSat . The ESA satellite is planned for an April 2004 launch into a polar orbit and will measure changes in the thickness of the ice sheets and the polar ocean sea-ice cover for at least three years with unprecedented accuracy. The satellite will provide climate researchers with data, which were previously not available from these uninhabited regions. The industrial contract amounts to some 70 million Euros.
The evidence of climate warming can be ignored no longer. As the Intergovernmental Panel on Climate Change (an international board of climate experts) in its most recent report of 2001 confirmed: the average global surface temperature rose by 0.6 degrees in the 20th century; the year 1998 was the warmest since 1861, the start of instrumental recording. Climate data estimate that the 20th century was the warmest in the last thousand years. At the same time, the concentration of greenhouse gases in the atmosphere, such as carbon dioxide and methane have grown by 30 and 150 percent respectively as a result of human activities.
Using the models available at the moment, it is only partially possible to predict how these developments affect the climate. The predictions waver between a global warming of between 1.4 to 5.8 degrees Centigrade in the next hundred years. As a consequence, experts expect some polar ice and glaciers to thaw. This could result in the water level of the oceans rising by up to a metre.
Polar ice as a climate factor
The presence of ice at the poles plays a central role for the global climate. Despite being thousands of kilometres away from the most inhabited areas, this ice has a profound effect on the climate in Europe, Asia and the Americas. Three aspects are most important:
* Snow and ice reflect sunlight extremely well
* A sea-ice coverinsulates the water underneath and
* Large amounts of thawing ice can affect the large-scale ocean currents
Polar ice reflects a large portion of the sunlight, and the amount of the absorbed and reflected light is balanced with the climate. If the polar ice begins to melt, less sunlight is reflected and therefore the polar region warms up. Consequently, more ice begins to melt and the reflective capabilities are thus further reduced. Due to this positive feedback effect, a self-accelerating warming ensues.
In the night, open water radiates a large heat output of about 90 Watts per square metre. A snow-covered sea-ice slab floating upon the ocean beneath has a negative effect on this. To a certain extent, it acts as a thermal blanket and therefore plays a significant part in regulating the heat balance of the Earth. This effect is reduced as soon as the ice thins or decreases in extent.
Ocean currents have a special influence on the climate. They act as heat pumps, as they disseminate the energy stored in the oceans around the entire globe. The most well-known example is the Gulf Stream. This transports warm water from the tropics diagonally over the Atlantic to North Europe and maintains the mild English climate and ice-free ports up to North Scandinavia. If the ice sheets and the outer sea ice cover melt, the relatively larger quantities of fresh water could disrupt or even change these ocean currents - with unforeseeable effects for the climate.
CryoSat - the first mission of ESA´s "Living Planet" Programme
A large part of the uncertainties in the climate models of today is due to the fact that there is a lack of precise measurements of the polar ice and its development. Experts conjecture, that the sea ice has receded by 10 to 15 percent since 1950. The thickness of the Arctic ice is reported to have reduced by 40 percent in the last few decades. These statements, however, are extremely uncertain, due to the lack of widespread information on sea-ice thickness.
CryoSat should fill in this gap in climate research. The satellite will start as the first Earth Explorer mission of ESA´s "Living Planet" programme, created in 1998. This science-driven programme, whose target is to provide critical observations to address pressing scientific questions, involves Core Missions, which comprise relatively complex and innovative Earth Observation satellites (costing about 350 million euros), and Opportunity Missions, which will use maturer technology currently available in industry, thus allowing speedier implementation.
CryoSat will be the first Earth Explorer Opportunity Mission. In July of 1998, ESA called upon all scientists from its member countries for mission proposals for this programme. Researchers from University College London and other collaborating institutes, were supported by employees of Astrium in proposing CryoSat. Astrium´s early engagement in this mission was unusual, which secured cost-effective realisability through simple and effective technical concepts as early as the first phase. In April of 1999 the ESA programme committee selected CryoSat from among 27 submitted projects.
It is not yet completely certain, which launcher will be used to transport the satellite into space.
Radar Altimeter measures ice thickness
CryoSat will circle the Earth in a polar orbit 720 km high. From there, its radar will measure the thickness and circumference of the polar ice sheets and sea-ice cover. Previous radar satellites, such as the European ERS 1 and 2 are only equipped with a single antenna. With this, they can deliver information about uniform ice surfaces with a large extent. CryoSat, on the other hand, has two antennae at its disposal. Similar to the way in which humans, with two eyes, can see spatially, CryoSat´s double radar will be able to scan the upper surface very precisely. This is known as "Radar-Interferometry" to experts. With this system, an average accuracy of one to three centimetres can be reached. Thus it can also collect data on inhomogeneous ice structures in the polar seas and glaciers or ice sheets with very steep walls.
In order for this extreme precision of measurement to be attained, the orbiting altitude of the satellite must be constantly known. To determine this to within a few centimetres, ground stations emit signals, which are received and processed by an instrument named DORIS. The information about altitude, which is thereby produced, is then conveyed via the normal data stream to the ground station.
CryoSat´s outer side also sports a Laser-Retroreflector. Similar to cats´ eyes in warning posts on the edge of a road, it reflects a ray of light. If one were to send a laser beam to CryoSat from a ground station and receive the reflected signal from the satellite, one would be able to determine the height of the satellite from the transit time.
CryoSat´s radar altimeter functions regardless of daylight and can also penetrate clouds. Therefore, it is particularly suited to the research of the large polar ice sheets, which rise up to 4000 metres above sea level and which are often covered by clouds. The data from the CryoSat mission should deliver information about the rate of change of these ice sheets.
Working with a tight budget
Astrium is the prime contractor for CryoSat and thus is responsible for a consortium of some 30 firms. Astrium itself supplied the satellite platform and will later take on the integration of all the instruments. Ultimately, Astrium is responsible for the reliability of the whole satellite to ESA.
Astrium´s engineers face a special challenge with the CryoSat project from the word go, insofar as they have to integrate high reliability, fast realisation and a low cost. In order to meet this challenge, Astrium developed a satellite model which is based on simplicity. For example, the development mechanisms and additional costly control systems have been left out. During CryoSat´s construction, Astrium and its contractors largely fall back upon established hardware components. Added to this, the close partnership between scientists, ESA and the industrial consortium facilitates a loose managemental structure and, related to this, faster reaction time during the development and construction phases.
Friedrichshafen, May 2002/02018
For further information:
ASTRIUM (FR)
Rémi ROLAND ++33 (0) 1 34 88 35 78
ASTRIUM (UK)
Alistair SCOTT ++44 (0) 1438 7736 98
ASTRIUM (GER)
Mathias PIKELJ ++49 (0) 7545 8 9123
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