Design of an Incubator Platform for Biological ISS Experiments

Abstract: The first European commercial research facility aboard the ISS, Space Applications Services' ICF, provides a platform for standardized plug-and-play experiments called ICE Cubes. The ICE Cubes Service provides engineering and operational support for ICE Cubes missions. In order to facilitate rapid and affordable access to space, a programmatic choice was made to mainly use COTS components in Cube design. As part of a company-internal project to develop a generic ICE Cubes platform for biological experiments, a scientific requirements document was drawn up in cooperation with interested scientists. A decision was made to aim for an experiment size of 2U (200x100x100mm). The main scientific requirements are to accommodate six reaction chambers (referred to as "wells") of standardized size; to control the temperature at well level to remain in the nominal interval of (37 +- 1)C; to accommodate a combined volume of 230ml of fluids; to provide capability to image each of the wells; and to allow for freezing of the biological payload to -80C for return to ground. The development of a prototype design for this platform, dubbed BioCube, is the topic of this thesis. Technical requirements were derived, and a functional breakdown was defined. From this, the system was partitioned into five subsystems: Thermal, Imaging/Avionics, Structure, Software, and the biological Payload. The development of the biological system is considered beyond the scope of this thesis, and the development of the software beyond that required for prototyping is left for a later stage in the design process, as significant heritage exists from previous experiments. Using a rapid prototyping approach, a prototype design for this experiment has been developed. The proposed solution utilizes a (205x104x101)mm outer structure, manufactured from aluminium and closed with two lids on the small faces. Inside, the system is split into a 3D printed avionics compartment and a payload compartment, surrounded by an air gap serving as thermal insulation. The payload compartment structure consists of aluminium, closed on one face with a transparent material through which the samples can be imaged, and provides a sealed interface connector for exchange of power and data. Both the outer structure and the payload compartment are sealed at the interfaces using O-ring seals, providing a combined two levels of biosafety containment to the payload. Manual latches on one of the lids of the outer structure allow it to be opened and the payload compartment to be extracted.The system avionics are based on a Raspberry Pi Zero with USB & Ethernet Hub and Motor Control expansion boards. A 5W silicon heating pad attached to the inside of the payload compartment provides heating, and is controlled using a PWM signal from the motor control board.Two cameras arranged in parallel are used to image wells arranged in two rows, reducing the required motion. One axis motion is implemented using a leadscrew mechanism actuated by a DC motor, driven by the motor control board. Prototyping has been performed on nearly every part of the proposed design. The leadscrew assembly has been successfully tested, and tests on a thermal model have successfully demonstrated binary thermal control achieving the nominal temperature range. Some points regarding the design remain to be defined, and more thorough verification and validation of the design remains to be performed.