Potential cooling chains for the NFI instruments of XEUS Original Research Article

The X-ray observatory (XRO), also known as XEUS (X-ray evolving-universe spectroscopy), is one of the potential future missions identified in the framework of the European Space Agency Cosmic Vision Programme. The core instruments have been selected and include at least one Narrow Field Imager working either in the 300 mK range (NFI-1) or in the 50 mK range (NFI-2). In this article, we describe potential cooling chains compatible with the requirements of these instruments as presently defined. We also give elements on alternative solutions.