In order to control system and component temperatures, many spacecraft thermal control systems use a radiator coupled with a pumped fluid loop to reject waste heat from the vehicle. Since heat loads and radiation environments can vary considerably according to mission phase, the thermal control system must be able to vary the heat rejection. The ability to "turn down" the heat rejected from the thermal control system is critically important when designing the system. Electrochromic technology as a radiator coating is being investigated to vary the amount of heat rejected by a radiator. Coupon level tests were performed to test the feasibility of this technology. Furthermore, thermal math models were developed to better understand the turndown ratios required by full scale radiator architectures to handle the various operation scenarios encountered during a mission profile for the Altair Lunar Lander. This paper summarizes results from coupon level tests as well as the thermal math models developed to investigate how electrochromics can be used to increase turn down ratios for a radiator. Data from the various design concepts of radiators and their architectures are outlined. Recommendations are made on which electrochromic radiator concept should be carried further for future thermal vacuum testing.

This paper describes a map-based, high-level control algorithm for autonomous thermal soaring. The algorithm combines ideas from occupancy grid maps and value iteration algorithms used in the robotics and machine learning communities. Estimates of the specific energy rate throughout the flight domain are built from three sub-function components. The first component is used to drive exploration when no favorable energy regions are known. A short-term memory component synthesizes recent sensor measurements to map the energy available in the neighborhood of the UAV and enables the detection of and centering in moving thermals. The final component uses a history of previous atmospheric energy measurements to identify patterns in the flight domain and allow the vehicle to return to locations that consistently form thermals.Seven variations on the high-level control algorithm are tested using a six degree of freedom simulation and compared to bounding cases where the controller either has perfect knowledge of the thermal field or has no thermal sensing ability and flies a large diameter circle. The objective of interest is to maximize the aircraft's average energy state over a one hour simulation. Due to the stochastic nature of the thermal model, 100 trials are run for each variation of control algorithm. Simulations indicate that on average the best performing autonomous thermal soaring controller achieves 62% of the possible improvement in the objective. For each algorithm there are large variations in the performance achieved due to the stochastic nature of the thermal fields.

Dynamic soaring is a technique for extracting energy from atmospheric wind gradients and is proposed as a strategy for significantly extending the range of small UAVs on specific missions. Enabling sensing technologies that make dynamic soaring feasible are reviewed. The combination of solar power and dynamic soaring is explored as a means primarily for storing energy in a battery that can be used to power onboard systems and provide a secondary means of propulsion if necessary. Conceptual vehicle design trade studies are presented as guides to preliminary sizing of a dynamic soaring UAV.

Abstract:This paper details the validation of modeling methods for the three core components of a Metabolic heat regenerated Temperature Swing Adsorption (MTSA) subassembly, developed for use in a Portable Life Support System (PLSS). The first core component in the subassembly is a sorbent bed, used to capture and reject metabolically produced carbon dioxide (CO 2 ). The sorbent bed performance can be augmented with a temperature swing driven by a liquid CO 2 (LCO 2 ) sublimation heat exchanger (SHX) for cooling the sorbent bed, and a condensing, icing heat exchanger (CIHX) for warming the sorbent bed. As part of the overall MTSA effort, scaled design validation test articles for each of these three components have been independently tested in laboratory conditions. Previously described modeling methodologies developed for implementation in Thermal Desktop® and SINDA/FLUINT are reviewed and updated, their application in test article models outlined, and the results of those model correlations relayed. Assessment of the applicability of each modeling methodology to the challenge of simulating the response of the test articles and their extensibility to a full scale integrated subassembly model is given. The independent verified and validated modeling methods are applied to the development of a MTSA subassembly prototype model and predictions of the subassembly performance are given.These models and modeling methodologies capture simulation of several challenging and novel physical phenomena in the Thermal Desktop and SINDA/FLUINT software suite. Novel methodologies include CO 2 adsorption front tracking and associated thermal response in the sorbent bed, heat transfer associated with sublimation of entrained solid CO 2 in the SHX, and water mass transfer in the form of ice as low as 210 K in the CIHX.https://ntrs.nasa.gov/search.jsp?R=20100040658 2018-05-11T09:23:15+00:00Z

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