Nursing 4 Cluster Spacecraft with aging Batteries through Eclipses

The Cluster mission was launched in 2000 to investigate for 3 years the interaction between the solar wind and the Earth magnetosphere. The mission has been extended until end 2009. The batteries of the four spacecraft are well beyond their design life and have started to fail. The power situation first became critical during the long eclipses in September 2006. The available battery power on one spacecraft could not support the heaters and the On-Board Computer. New operational strategies were developed to prevent a dangerous cool down of the spacecraft and to regain control after each eclipse after a power down. This paper describes the preparation and gradual implementation of new operational procedures and tools enabling a small team to perform routinely and simultaneously several spacecraft recoveries from survival mode.