Cooling detectors down to 0.1K will be of great importance for future far infra red and submillimeter space telescopes during the next few years. This objective can be reached using a Stirling Cryocooler and a Joule Thomson (JT) expansion stage to precool to 4K. The low temperatures are then obtained by an open cycle dilution refrigerator circulating 3He and 4He. This system does not need any cryogenic reservoir and can be launched at room temperature. In this paper, we present the characteristics and performances of the two parts of the refrigerator measured separately, showing the feasibility of such a system. Expected performances of the complete system are a base temperature of 100mK with 100nW heat load and a life time of 5 years with a reasonable gas storage weight (20-50 kg).