Avoiding Cluster Safe Modes

Cluster is a multi-spacecraft ESA mission launched in 2000 to study the Earth's magnetic environment. After more than 11 years in space, the performance of the batteries and the solar arrays has decreased dramatically limiting the available power on-board. This is becoming a serious problem for contingency situations because hard-coded sequences executed during safe modes require much more power than what it is provided by the solar arrays. As a consequence safe modes are no longer safe and they can trigger main bus under-voltages, multiple reboots or even an uncontrolled switch off of the on-board computer. Several techniques have been studied to avoid or minimize the impact of safe modes and have been successfully implemented and validated during 2011 eclipse season. An analysis of Cluster safe modes with limited power and the alternatives to deal with them is the subject of this paper.