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Nanofluids have been recently investigated as new working media for two-phase thermal control systems. However, conflicting reports have emerged, in which contradictory effects of the nanoparticles on the working performance of heat pipes have been described. Some studies have shown that gold or silver nanoparticles significantly improve heat transfer performances of heat pipes. Other studies have provided evidence that metal nanoparticles have no particular effect. This study is aimed at determining whether nanofluids are good candidates as heat carriers in a Loop Heat Pipe (LHP) system. Here, a nanofluid consisting of well-characterized citrate-stabilized gold nanoparticles in water is examined. The metallic nanoparticles are functionalized with citrate ligands in order to be soluble and stable in water at room temperature. An LHP hardware set-up was developed for this investigation.

Heat pipes, loop heat pipes and capillary pumped loops are heat transfer devices driven by capillary forces with high-effectiveness & performance, offering high-reliability & flexibility in varying g-environments. They are suitable for spacecraft thermal control where the mass, volume, and power budgets are very limited. The Canadian Space Agency is developing loop heat pipe hardware aimed at understanding the thermal performance of two-phase heat transfer devices and in developing numerical simulation techniques using thermo-hydraulic mathematical models, to enable development of novel thermal control technologies. This loop heat pipe consists of a cylindrical evaporator, compensation chamber, condenser along with vapor and liquid lines, which can be easily assembled/disassembled for test purposes. This laboratory setup is especially designed to enable the visualization of fluid flow and phase change phenomena.

Spacecraft attitude control provides the basic stability so that sensors, solar panels, antennas and other hardware are properly oriented to perform their functions. A Horizon scanner can automatically seek the earth horizon by detecting the sharp discontinuity in InfraRed intensity at the outer edge of the Earth's mesopause for purposes of a spacecraft's orientation and control. As a satellite in a Low Earth Orbit (LEO) and three-axis stabilized, the Canadian satellite RADARSAT-1 is equipped with two horizon scanners (HS) in order to scan dynamically across the Earth's disc and to establish the attitude relative to the Earth. This paper discusses the thermal design and analyzes the on-orbit thermal performance of the HS.

The paper addresses the thermal control of a lunar lander/rover by use of heat pumps enabling payload heat to be rejected at a higher temperature to the lunar day environment. The heat pump technologies considered include absorption, vapor compression, adsorption, hybrid and chemical heat pumps technologies. A trade-off of the various heat pump technologies for a 2kW payload cooling capability is presented based on the needs of space-based hardware in terms of low mass and power, high performance, reliability and compactness of the systems. Finally the selection of a novel variant of the chemical heat pump concept is presented as a promising technology to be further investigated through breadboard development.

The thermal control of lunar landers/rovers necessitates the use of a system to allow heat rejection to the high temperature lunar environment. In this context a vapour compression heat pump which is a proven technology in terrestrial and aeronautical applications has been studied; its suitability in providing 2 kW cooling capability with adequate temperature lift for final heat rejection by space radiators is assessed. The stringent requirements of space-based hardware in terms of temperature lift, compactness, mass, performance and reliability necessitates optimization studies. Mass optimization of the heat pump components has been carried out, as well as selection of refrigerants and thermodynamic cycles most suited for the application.