Each year, in autumn, the Cluster fleet must pass several times through the Earth's shadow with respect to the Sun. During these eclipses, which last about three hours, sunlight is blocked by the Earth and the spacecraft solar panels cannot generate electricity.
Batteries then generate electrical power, which is used to run heaters - keeping the spacecraft warm - and to operate on-board computers and maintain spacecraft control.
However, the Cluster fleet, launched in mid-2000, has been in orbit for over six years and batteries, in particular, are beginning to age. This year, spacecraft No. 1, Rumba, had the most severe battery problems; three out of five have already been declared non-operational for nominal use and one has a high leakage current.As a result, mission engineers forecast that only about half of the battery power required by Rumba would be available during eclipse season.
The team created a computer model of the spacecraft's thermal behaviour to identify how, exactly, it could survive eclipses with reduced, or even with no, active heaters. There were also issues with the on-board computer, designed to restart itself automatically in the event that power is ever lost.
"The most difficult aspect was to find a safe method to switch off the onboard computer, deactivating its auto-recovery function and then to be able to wake it up again from its 'artificial coma' after the eclipse," said Juergen Volpp, Spacecraft Operations Manager at ESOC, in Darmstadt, Germany.
When the predicted eclipse passage ended at 22:13 UTC (00:13 CEST), engineers sent commands to wake the on-board computer. They had to wait one minute for the computer to restart itself, plus four seconds of telemetry processing and signal travel time. "We never thought that sixty-four seconds could seem so long," said Volpp.
But the meticulous preparations and months of planning paid off handsomely as Rumba emerged from the shadow, grabbed the wake-up signal and powered up its computer just as expected; controllers quickly verified that nothing onboard had cooled below acceptance temperatures, and all systems were back in operation a few hours later.
The strategy was again proven two days later during the next - and longest - eclipse, early on 18 September. The last eclipse was successfully negotiated on 20 September and the Cluster fleet is now back in nominal operation, continuing one of ESA's most successful astrophysics missions.
Juergen Volpp | EurekAlert!
Pulses of electrons manipulate nanomagnets and store information
21.07.2017 | American Institute of Physics
Vortex photons from electrons in circular motion
21.07.2017 | National Institutes of Natural Sciences
Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.
For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...
What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.
To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...
The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....
A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...
Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision
Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...
21.07.2017 | Event News
19.07.2017 | Event News
12.07.2017 | Event News
21.07.2017 | Earth Sciences
21.07.2017 | Power and Electrical Engineering
21.07.2017 | Physics and Astronomy