MODELING AND EXPERIMENTAL VALIDATION OF A RESILIENT  EXTRATERRESTRIAL HABITAT INTERIOR ENVIRONMENT .pdf

 The NASA-funded Resilient Extra-Terrestrial Habitat Institute (RETHi) aims at developing the necessary fundamental knowledge to enable the design of future resilient deep space habitats.  To achieve this, RETHi has developed a Modular Coupled Virtual Testbed (MCVT) consisting of various subsystems (such as power, structural, ECLSS, etc.) to simulate a range of deep space  hazardous scenarios and assess the ability of the systems to recover from expected and  unexpected fault scenarios under both crewed and uncrewed situations. The physics-based  Simulink models within MCVT allow for direct interconnections among components, including  damage cascading effects, repairability features, and various failures. Besides the MCVT  platform, a Cyber Physical Testbed (CPT) has also been conceptualized to perform real-time experiments with physical portions of the MCVT models (e.g., structural, thermal and pressure  management systems). The overarching goal of CPT is to implement and validate decision?making algorithms under various scenarios (e.g., leaks, thermal bridges, etc.), introduce  controllable and realistic uncertainties (e.g., communication delays, sensing faults, etc.), and  assess resilience, control effectiveness and autonomy. The CPT design consists of three main  physical systems: the inflatable bladder, the aluminum dome structure, and the thermal transfer  panels connected to a low-temperature chiller. Pressure and temperature controls inside the  bladder are achieved by means of a pressure regulator and a mini-split heat pump system,  respectively. 

One of the core aspects of both MCVT and CPT is the habitat interior environment which  includes the coupled temperature and pressure effects due to interior and exterior loads as well as  the necessary conditions to ensure the crew survival. 

As part of this work, a dynamic Habitat Interior Environment Model (HIEM) has been  developed to simulate the behavior of a two-zone habitat in real-time. The model can directly  interact with other subsystems such as the ECLSS and structural protective layer (SPL) and  features various disturbances including pressure leaks due to meteorite impacts or airlock failures.  The HIEM has been further extended to also include various fire intensity scenarios and also to  enable the isolation of the zones by means of a door in case of an emergency or simply due to the  architecture of the future habitat. 

The CPT system is utilized to test the capability of HIEM in predicting the behavior of the  interior environment in various scenarios. To impose the necessary thermal loads to the habitat  structure (i.e., aluminum skeleton and inflatable bladder) in the laboratory environment, thermal  transfer panels with coiled copper piping and aluminum heat spreaders have been designed to  provide uniform temperature distributions. A cryogenic chiller with Syltherm as the working  fluid is used to maintain and provide the necessary operating range between -40 °C and 60 °C.  The HIEM was modified to describe the physical sizing of the bladder as well as to capture  the heat transfer characteristics between the bladder, the aluminum structure, and thermal  transfer panels. In addition, the models also included the effects of air infiltrations within the  bladder, various sources of heat losses by conduction and convection, and thermal resistances  associated with non-perfect contacts between bladder and transfer panels. Experimental data was  used to validate the model predictions and different operating conditions as well as to improve  the model accuracy by identifying key thermal resistances and capacitances. 

The HIEM was able to predict the temperature variations inside the bladder with a relative  error of <3%. The accuracy of the HIEM temperature and pressure variations is affected by the  heat pump model and the dynamics of the bladder. To minimize the errors, a detailed thermal  resistance/capacitance network was developed. However, the equivalent thermal resistance  network built to predict the heat transfer characteristics of the aluminum plate of the thermal  transfer panel showed discrepancies up to 24% due to air gaps existing between the bladder and  the panels as well as additional heat losses. Further testing and appropriate insulation can  mitigate the thermal losses of the existing design. 

Finally, the HIEM has been updated to assess the ability of CPT to experimentally recreate  scenarios investigated within MCVT. Parametric studies have been conducted to predict  temperature variations within the bladder due to changes in boundary conditions imposed by the  transfer panels.  

Based on the numerical and experimental analyses resulted in meaningful recommendations  were identified to improve the design and operation of CPT.