Dancing for Science
from Gerhard Holtkamp, 01. September 2010, 22:34
What do South American dances have to do with space science? For the past ten years a quartet of satellites named Rumba, Salsa, Samba and Tango have been orbiting the Earth in kind of a formation dance yielding valuable insights into the plasma processes in the Earth's magnetosphere...
Cluster is one of the Cornerstone missions of the European Space Agency ESA. The idea behind it is to have a set of satellites fly around the Earth in a highly elliptical orbit to investigate the interaction between the solar wind and the Earth's magnetosphere in 3-D and time. At least four spacecraft are needed for this task. Depending on the scientific objectives their mutual distance has been as low as 16 km and as large as 10000 km.
Each Cluster spacecraft carries an identical set of 11 instruments to investigate charged particles, electrical and magnetic fields. The Cluster scientific community includes more than 200 Co-Investigators from many parts of the world. To date 1266 papers have been published with results from the Cluster mission in refereed journals.
Although fundamental science its findings are important for satellite operators as the complex phenomena inside the magnetosphere especially at times of high solar activity have let to disturbances and even total loss of some satellites as well as disruptions of power grids on Earth. The knowledge gained has also implications for many other fields of astronomy and even fusion research where strong magnetic fields and plasma processes are dominant.
The mission started with a bang - literally. Four Cluster satellites were perched on top of the very first Ariane 5 on 4 June 1996 to get a free ride on its inaugural flight. Unfortunately, the launch ended one minute after liftoff with the explosion of the Ariane rocket.
A few pieces which were picked up in the marshes of Kourou are now on display in a showcase next to the Cluster control room (see picture).
Space scientists deemed Cluster to be too important to let it die. Four new satellites were quickly assembled with little change from the original design and in the summer of 2000 Cluster was relaunched using two Soyuz rockets with two satellite each to spread the risk.
To celebrate a highly successful decade in orbit a media briefing was held today (1-SEP-2010) at the European Space Operation Centre ESOC which I was able to attend.
Philippe Escoubet, Cluster Mission Manager, outlined some of the important scientific results achieved so far.
When magnetic fields collide the field lines can connect differently and allow previously separated plasmas to mix. This "magnetic reconnection" frees a lot of energy and this can accelerate particles and heat the plasma. Cluster data were able to shed light on one key issue of this process - the "magnetic null" point which is right at the heart of such a reconnection. Magnetic reconnection is thought to play a major role in generating solar flares but also for the creation of relativistic jets in astrophysics.
Electrically charged particles emanating from the Sun form what has been termed the solar wind. Just like wind blowing over the surface of an ocean can produce waves the solar wind sliding past Earth's magnetic field produces waves in the magnetosphere. Sometimes giant whirlpools of plasma can form. Cluster found the size of these vortices to be around 40000 km across which is nearly six times the Earth's radius. This in turn leads to complex processes during which plasma can cross the usually impenetrable bounary of the magnetosphere topping it up with electrified gas.
Such plasma processes can be very fast. Cluster's high temporal and spacial resolution has been instrumental for many investigations.
Göran Marklund from the Royal Institute of Technology, Stockholm, reported on something called "Black Auroras". These are dark empty regions within the visible northern and southern lights. Cluster has shown that this is due to what might be termed holes in the ionosphere. These are caused by electrons moving upwards into space rather than downwards which causes the usual auroras. So this is kind of an anti-aurora. Cluster also showed that after a few tens of minutes these holes will be filled in again by a normal aurora.
Cluster led to the first cooperation between ESA and the Chinese National Space Administration. ESA contributed eight scientific instruments identical to Cluster's instruments for two Chinese Double Star satellites which were operated between 2004 and 2009. These satellites were on lower orbits than Cluster and could complement the measurements. This enabled interesting investigations into fluctuations of the magnetotail.
These and other scientific results did not come easy. In the words of David Southwood, ESA Director of Science and Robotic Exploration, there is no such thing as routine operations with science satellites. Jürgen Volpp, Spacecraft Operations Manager for Cluster could vouch for that.
Designed in the early 1990s the Cluster satellites were equipped with silver cadmium batteries rather than nickel cadmium batteries which were the standard at the time. The reason for this was that nickel being magnetic would have affected Cluster's sensitive measurements. But silver cadmium batteries typically last for no more than 3 or 4 years. In fact hydrogen and oxygen builds up inside of them and this can lead to explosions.
This had not been a problem as long as Cluster was designed for a mere four years of operations. But being so valuable and successful the mission has been extended twice and is now far beyond the original design lifetime. Although for much of its elliptical orbit (which extends almost 1/3 the distance to the Moon) Cluster is in sunlight and can rely on solar cells there are times when the satellites move through Earth shadow. (The solar cells have also degraded from the original 280 Watt to 200 Watt. This is typical for satellites exposed to the harsh environment of space.)
Special procedures had to be adopted to have the Cluster satellites survive this eclipse period. Just think of what happenes when you pull the plug from your computer and an hour or so later put it in again! Yet the operations team has been so efficient dealing with this that about 90% of the Cluster orbit can still be used for science.
At present the Cluster mission is extended until 2012 and there is some thought about extending it even until 2014. This would be valuable in following the onset of the new solar cycle.
The large amount of high-resolution space plasma physics data are made available at the Cluster Active Archive. Already there are more than 1000 users of this archive.
As for now: Happy Anniversary, Cluster. Well done!
For more information on the Cluster mission see http://www.esa.int/science
Cluster is one of the Cornerstone missions of the European Space Agency ESA. The idea behind it is to have a set of satellites fly around the Earth in a highly elliptical orbit to investigate the interaction between the solar wind and the Earth's magnetosphere in 3-D and time. At least four spacecraft are needed for this task. Depending on the scientific objectives their mutual distance has been as low as 16 km and as large as 10000 km.
Each Cluster spacecraft carries an identical set of 11 instruments to investigate charged particles, electrical and magnetic fields. The Cluster scientific community includes more than 200 Co-Investigators from many parts of the world. To date 1266 papers have been published with results from the Cluster mission in refereed journals.
Although fundamental science its findings are important for satellite operators as the complex phenomena inside the magnetosphere especially at times of high solar activity have let to disturbances and even total loss of some satellites as well as disruptions of power grids on Earth. The knowledge gained has also implications for many other fields of astronomy and even fusion research where strong magnetic fields and plasma processes are dominant.
The mission started with a bang - literally. Four Cluster satellites were perched on top of the very first Ariane 5 on 4 June 1996 to get a free ride on its inaugural flight. Unfortunately, the launch ended one minute after liftoff with the explosion of the Ariane rocket.
A few pieces which were picked up in the marshes of Kourou are now on display in a showcase next to the Cluster control room (see picture).Space scientists deemed Cluster to be too important to let it die. Four new satellites were quickly assembled with little change from the original design and in the summer of 2000 Cluster was relaunched using two Soyuz rockets with two satellite each to spread the risk.
To celebrate a highly successful decade in orbit a media briefing was held today (1-SEP-2010) at the European Space Operation Centre ESOC which I was able to attend.
Philippe Escoubet, Cluster Mission Manager, outlined some of the important scientific results achieved so far.
When magnetic fields collide the field lines can connect differently and allow previously separated plasmas to mix. This "magnetic reconnection" frees a lot of energy and this can accelerate particles and heat the plasma. Cluster data were able to shed light on one key issue of this process - the "magnetic null" point which is right at the heart of such a reconnection. Magnetic reconnection is thought to play a major role in generating solar flares but also for the creation of relativistic jets in astrophysics.
Electrically charged particles emanating from the Sun form what has been termed the solar wind. Just like wind blowing over the surface of an ocean can produce waves the solar wind sliding past Earth's magnetic field produces waves in the magnetosphere. Sometimes giant whirlpools of plasma can form. Cluster found the size of these vortices to be around 40000 km across which is nearly six times the Earth's radius. This in turn leads to complex processes during which plasma can cross the usually impenetrable bounary of the magnetosphere topping it up with electrified gas.
Such plasma processes can be very fast. Cluster's high temporal and spacial resolution has been instrumental for many investigations.Göran Marklund from the Royal Institute of Technology, Stockholm, reported on something called "Black Auroras". These are dark empty regions within the visible northern and southern lights. Cluster has shown that this is due to what might be termed holes in the ionosphere. These are caused by electrons moving upwards into space rather than downwards which causes the usual auroras. So this is kind of an anti-aurora. Cluster also showed that after a few tens of minutes these holes will be filled in again by a normal aurora.
Cluster led to the first cooperation between ESA and the Chinese National Space Administration. ESA contributed eight scientific instruments identical to Cluster's instruments for two Chinese Double Star satellites which were operated between 2004 and 2009. These satellites were on lower orbits than Cluster and could complement the measurements. This enabled interesting investigations into fluctuations of the magnetotail.
These and other scientific results did not come easy. In the words of David Southwood, ESA Director of Science and Robotic Exploration, there is no such thing as routine operations with science satellites. Jürgen Volpp, Spacecraft Operations Manager for Cluster could vouch for that.
Designed in the early 1990s the Cluster satellites were equipped with silver cadmium batteries rather than nickel cadmium batteries which were the standard at the time. The reason for this was that nickel being magnetic would have affected Cluster's sensitive measurements. But silver cadmium batteries typically last for no more than 3 or 4 years. In fact hydrogen and oxygen builds up inside of them and this can lead to explosions.
This had not been a problem as long as Cluster was designed for a mere four years of operations. But being so valuable and successful the mission has been extended twice and is now far beyond the original design lifetime. Although for much of its elliptical orbit (which extends almost 1/3 the distance to the Moon) Cluster is in sunlight and can rely on solar cells there are times when the satellites move through Earth shadow. (The solar cells have also degraded from the original 280 Watt to 200 Watt. This is typical for satellites exposed to the harsh environment of space.)
Special procedures had to be adopted to have the Cluster satellites survive this eclipse period. Just think of what happenes when you pull the plug from your computer and an hour or so later put it in again! Yet the operations team has been so efficient dealing with this that about 90% of the Cluster orbit can still be used for science.
At present the Cluster mission is extended until 2012 and there is some thought about extending it even until 2014. This would be valuable in following the onset of the new solar cycle.
The large amount of high-resolution space plasma physics data are made available at the Cluster Active Archive. Already there are more than 1000 users of this archive.
As for now: Happy Anniversary, Cluster. Well done!
For more information on the Cluster mission see http://www.esa.int/science
