Researchers conducting space research, particularly those sending payloads to the ISS or during parabolic flights must have a tight temperature control for the optimal growth of all biological models and increase their viability, leveraging the efforts of long-duration spaceflights aboard prospective payloads, free flyers beyond low earth orbit, the Lunar Gateway, and beyond. This paper discusses the performance of an active thermal control system design and provides details on preliminary optimization methods performed to maintain a prescribed thermal environment for sensitive biological payloads (eg. Escherichia coli). The thermal pad application times, and desired temperature settings are varied, system responses are recorded and recommendations for hardware and software systems are identified to mature such technologies which can be scaled down for prospective biological systems with tight temperature-sensitive profiles on prospective suborbital and orbital payload missions. Our results indicate that our system can target temperatures ranging from about 22°C to 40°C with less than 1°C average error and maintain such thermal profiles when exposed under different environmental conditions. The estimation of bacterial cell count from optical density and the colony-forming units will be provided using our thermal management system and a different incubator with fixed temperature. The length of the experiments can last between 12 hours and 48 hours, but the thermal system can run for longer periods. Preliminary Escherichia coli optical density (630 nm) results for 12 hours tests at 30°C show an 8%-10% average error across all samples. About 80% of the samples suggest that the Escherichia coli optical density is higher for the samples in the thermal system than in the incubators. The goal is to obtain a more stable thermal profile while reducing the optical density error to less than 5% across all samples among the thermal system and incubators.
Llanos et al. (Sun,) studied this question.