A −180°C Cryogenic Freezer for the International Space Station

In the course of CRYOSYSTEM phase B (development phase) financed by the European Space Agency, EADS ST (Germany) has developed an optimized design of a −180°C freezer to be used on board the International Space Station for the freezing and storage of biological samples.

The CRYOSYSTEM facility consists of the following main elements:

• - the CRYORACK, an outfitted standard payload rack (ISPR) accommodating up to three identical Vial Freezers
• - the Vial Freezer, a dewar vessel capable of fast and ultra-rapid freezing, and storing up to approximately 750 vials below −180°C; the dewar is cooled by a Stirling machine producing > 6 W at 90 K. The Vial Freezer is operational while accommodated in the CRYORACK or attached to the Life Science Glovebox (LSG).

The CRYORACK will be able to remain permanently on-orbit for up to 8 years with 2 vial freezers operating as the same time for a maximum of 2 years cumulated of cold time. Vial freezers will be launched from KSC (Florida) inside the CRYORACK in hot conditions and cooled down on orbit when installed on board ISS. Cryogenic samples will be downloaded from vial freezer into passive dewar for return on earth. This paper presents an overview of the CRYOSYSTEM architecture and mission profile; the cryogenic design, which merges the cooling and cold storage functions in one freezer unit; and results of breadboards of critical components, such as the cooler and dewar.