January 25, 2011

ESA’s Space Laser Mission Being Reevaluated

European scientists are being asked whether they still want to go ahead with the European Space Agency's (ESA) space laser mission.

The EarthCARE satellite would study the role clouds and atmospheric particles play in a changing climate.

However, difficulties in developing the spacecraft's lidar instrument means the cost of the venture will rise from $614 to $805 million.

ESA is now reviewing the science value and technical risks of proceeding with the mission.

"European Space Agency (ESA) member states have asked us to bring together all the pros and cons in this formal review," Dr Volker Liebig, ESA's director of Earth observation, told BBC News.

"They want us to speak to the scientists, to look into whether there are any alternatives which lead to the same scientific results. We will then take the conclusions of this review to the member states so they can decide what to do," he said.

EarthCARE was chosen to be one of ESA's Earth Explorers, which is a series of spacecraft that will do innovative science in obtaining data on issues of pressing environmental concern.

Three missions have gone into orbit, returning remarkable new information on gravity, polar ice cover, soil moisture and ocean salinity.

EarthCARE would study how clouds and aerosols form, evolve and affect our climate, the weather and air quality.

Scientists say knowledge gaps in areas like this severely hamper their ability to forecast future change.

Different types of clouds have different effects.  However, developing the primary instrument on EarthCARE to gather the proper information has proved to be difficult.

The lidar would fire pulses of ultraviolet light down into the atmosphere.

Scientists would be able to build up a picture of where in the atmosphere different cloud types and aerosols reside, and work out their impact on the energy budget of the Earth.

However, the instrument's prime contractor, EADS Astrium SAS, has had a torrid time arriving at a design that would reliably work in the vacuum of space.

Engineers found during tests that the instrument would contaminate itself with molecular deposits released from the mechanism's own materials whenever they ran the laser conditions similar to those expected in orbit.

"It was only happening when we operated it in a vacuum," Dr Liebig told BBC.

"We've had to organize a lot of research but we now understand what happens. It led to the decision that we should go from a monostatic laser which means you have the transmitting and receiving parts in one, to a bi-static laser which divides the two. On top of that, we pressurize the laser. This is a big change."

The final preferred configuration has delayed EarthCARE's progress and added significantly to the project's cost.

It is now unlikely that EarthCARE will get off the ground before 2016.

Some of the extra cost is a result of the additional investment required to build the lidar in the new configuration, but part of the inflation is a consequence of having to use a more powerful rocket to launch what will now be a bigger and heavier satellite.

EarthCARE will require the more expensive Soyuz vehicle rather than the less expensive Vega rocket.

ESA's Earth observation program board has asked for a review of the EarthCARE project.

ESA's member states want to establish the technical risks of moving ahead with the mission.

They want to know that costs will not go on climbing, and they also want reassurance that the promised advances in scientific knowledge can still be delivered by the satellite.

Professor Anthony Illingworth from Reading University, U.K. is the European chair of the panel of scientists that advises EA on the EarthCARE mission.  He told BBC that there was still a huge amount of knowledge to be gained from flying a space lidar.

"When we look at climate models, the principal cause of uncertainty is the clouds," he said.

"There is a big, what we call, 'forcing effect' from high and low-levels clouds, and at the moment they almost cancel out - the effect of the clouds on the Earth is a slight cooling. But of course in a future climate, if the balance of high and low-level clouds changes - which is why EarthCARE is important because it would tell you where the clouds are - and you get more high-level clouds then that would warm the Earth up even more."

The scientific case has also been bolstered in the past year by the Eyjafjallajokull eruption in Iceland, which led to economic losses across the EU.  One of the most valuable datasets in determining the precise distribution of the volcanic plume came from the lidar on the U.S. Calipso satellite. 

EarthCARE could make similar contribution if such conditions were ever repeated.


Image Caption: Artist's impression of EarthCARE (Earth Clouds, Aerosols and Radiation Explorer) satellite. EarthCARE addresses the need for a better understanding of the interactions between cloud, radiative and aerosol processes that play a role in climate regulation. Credits: ESA


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