Clusters outskirts at X-ray wavelengths: current status and future   prospects
  A solid observational characterization of cluster regions around the virial radius would allow us to improve considerably our understanding of the physics of galaxy clusters as a whole: sadly current and planned experiments will not allow us to study these regions. Unbeknownst to most but not all, the development of an experiment sensitive to cluster outer regions could be achieved with currently available technology, with no need for breakthroughs. Amongst the major factors that will decide whether and when such an experiment will be flown are the awareness of the cluster community of the importance of such a mission and its determination in supporting it. 
Silvano Molendi