The joint LIP6 - INRIA Rocquencourt Virtual Virtual Machine project and the Observatory of Paris-Meudon associated themselves to propose a reconfigurable space-embedded software platform (PLERS). This is one of the first attempts to define a systematic and provable way to update software embedded in the very constrained space systems. Our approach relies on a reconfigurable execution environment on-board the satellite and a software lifecycle that incorporates software update and maintenance together with software design and development in a common framework. An Architecture Construction Language is defined. It recursively describes a software configuration by expressing the architecture changes to do on a previous version. Compact low level reconfiguration commands are automatically produced. They are uploaded and interpreted by the flight software execution environment.