Abstract. The A3M project aimed to define basic building blocks of a middleware meeting both dependability and real-time requirements for a wide range of space systems and applications. The developed middleware includes Uniform Consensus (UCS) and Uniform Coordination (UCN) protocols and two services implemented to solve two recurring problems of space applications: “distributed consistent processing under active redundancy” and “distributed replicated data consistency, program serialization and program atomicity”. The protocols have been verified through extensive and accurate testing under the Real Time OS simulator RTSim supporting fault injections. The performances measured on a representative platform based on three LEON SPARC microprocessors interconnected with point-to-point SpaceWire links show that A3M solution may be applied to very different fields, from high performance distributed computing to satellite formation flying coordination.