Spacecraft designed for missions beyond low earth orbit (LEO) face a difficult thermal control challenge, particularly in the case of crewed vehicles where the thermal control system (TCS) must maintain a relatively constant internal environment temperature despite a vastly varying external thermal environment and despite heat rejection needs that are contrary to the potential of the environment. A thermal control system may be required to reject a higher heat load to warm environments and a lower heat load to cold environments, necessitating a relatively high turndown ratio. A modern thermal control system is capable of a turndown ratio of on the order of 12:1, but crew safety and environment compatibility have constrained these solutions to massive multi-loop fluid systems. This paper discusses the analysis of a unique radiator design that employs the behavior of shape memory alloys (SMAs) to vary the turndown of, and thus enable, a single-loop vehicle thermal control system for space exploration vehicles. This design, a morphing radiator, varies its shape in response to facesheet temperature to control view of space and primary surface emissivity. Because temperature dependence is inherent to SMA behavior, the design requires no accommodation for control, instrumentation, or power supply in order to operate. Thermal and radiation modeling of the morphing radiator predict a turndown ranging from 11.9:1 to 35:1 independent of TCS configuration. Coupled thermal-stress analyses predict that the desired morphing behavior of the concept is attainable. A system level mass analysis shows that by enabling a single loop architecture this design could reduce the TCS mass by between 139 kg and 225 kg. The concept has been demonstrated in proof-of-concept benchtop tests.

No abstract

The Fusible Heat Sink is a novel vehicle heat rejection technology which combines a flow through radiator with a phase change material. The combined technologies create a multi-function device able to shield crew members against Solar Particle Events (SPE), reduce radiator extent by permitting sizing to the average vehicle heat load rather than to the peak vehicle heat load, and to substantially absorb heat load excursions from the average while constantly maintaining thermal control system setpoints. This multi-function technology provides great flexibility for mission planning, making it possible to operate a vehicle in hot or cold environments and under high or low heat load conditions for extended periods of time. This paper describes the experimental investigation and model validation of the Fusible Heat Sink technology. This technology was developed to meet the radiation and heat rejection requirements of a nominal Multi-Mission Space Exploration Vehicle (MMSEV) mission. Development parameters and results, including sizing and model performance will be discussed. A scaled test-article was modeled, designed, and fabricated for experimental investigation of the technology at JohnsonSpace Center (JSC) thermal vacuum chamber facilities. Testing showed performance comparable to the model at nominal loads and the capability to maintain heat loads substantially greater than nominal for extended periods of time. Nomenclature CHx = Chiller location FTCx = Frame temperature measurement location HVx = Hand (ball) valve location IRIP = Integrated Radiator Ice PCM JSC = Lyndon B. Johnson Space Center LN2 = Liquid Nitrogen MMSEV = Multi-Mission Space Exploration Vehicle NVx = Needle valve location PCM = Phase Change Material Q x = X case of heat rejection from the radiator SPE = Solar Particle Event Txxx = Surface temperature measurement location

No abstract

Flow regimes and bubble growth are observed in a pin-fin micro-scale heat exchanger with R-11 as the working fluid. The heat exchanger is machined in silicon and derived from a DNA micro-array consisting of 150 µm-square fins separated by 50 µm-square passages. The fins are staggered and oriented 45 degrees to the flow direction such that approximately 750 channel intersections occur within the volume of the exchanger. The purpose of the study is to determine if this multiplyconnected geometry produces the flow blockage, reversal, and other instabilities observed in single and parallel microchannel configurations. The upper surface of the exchanger is a glass plate that provides optical access. High-speed digital photography and microscope optics are used to obtain real-time images of the flow at a framing rate of 5 kHz. The lower surface is electrically heated and instrumented with a heat flux gage. Inlet and outlet temperatures and pressures, heater and wall temperatures, and volumetric flow rate are monitored. Nucleation is observed near the entrance of the heat exchanger. In the central section, developed vapor regions are composed of broad slug-like vapor fronts immediately followed by a slowly growing bubbly flow. An annular regime dominates the downstream section of the exchanger with drop-like liquid structures appearing at the downstream edge of fins. The heat transfer coefficient decreases with exit quality as in other micro-scale exchangers; however, the flow instability present in parallel channel exchangers is not observed in this configuration.