Over the past 5 years ESTEC has funded work at the Rutherford Appleton Laboratory and BAe concerning the development of very low temperature (4K and 2.5K) cryocoolers with operational lifetimes in excess of 3 years. Therefore it was natural when taking into account the advantages of a closed cycle 3He refrigerator and the ESA 2.5K cryocooler that the idea of incorporating them into a 0.3K cryocooler should arise. In-house work at ESTEC started in 1992 with the goal of eventually obtaining a space qualified 3He refrigerator/2.5K cryocooler for long term operation, free of cryogen replenishment, which should weigh less than 40Kg and require less than 110W of power input. Two 3He refrigerators have been manufactured, which are still being tested. In this paper we will present the design of those 3He refrigerator. The experimental results on the thermal/mechanical behaviour of the refrigerator, using a liquid 4He bath cryostat as the pre-cooling stage, will be presented at the conference.