Browsing by Author "Anderson, William"
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Item 3D Printed Thermal Management System for the Next Generation of Gallium Nitride-based Solid State Power Amplifiers(49th International Conference on Environmental Systems, 2019-07-07) Ababneh, Mohammed; Tarau, Calin; Anderson, WilliamCurrent Gallium Nitride (GaN)-based solid state power amplifiers (SSPAs) are limited in their operational capabilities due to the limitations of the overall thermal management system in dissipating the high heat fluxes. However, GaN based SSPAs are desirable for satellite communication due to their superior linearity, built-in redundancy, reliability, power density and energy efficiency as compared to current technologies such as traveling wave tube amplifiers (TWTAs). In order to enable higher power GaN amplifiers and next generation phased arrays, it is critical to reduce the heat flux on the thermal management system by spreading the heat efficiently across a larger area. Aluminum/ammonia constant conductance heat pipes have been a proven technology for spacecraft thermal control for more than 40 years with both high heat transport capability (76 to 254 Watt-m) and reasonably low mass. Unfortunately, ammonia only works up to about 80°C, while the use of high- temperature electronics such as GaN power amplifiers, allows operation up to 150 °C. This further allows significant reduction in radiator size and mass. Advanced Cooling Technologies, Inc. (ACT) is devloping a novel, low-cost and low-mass thermal management system (TMS) which is capable of handling power densities and temperatures of next generation GaN power amplifiers and phased arrays. The design is based on integration of 3D printed vapor chamber and freeze/thaw tolerant titanium-water heat pipes with several novel features designed to ensure cooling of GaN devices during start-up or operation in space (vacuum and zero gravity) as well as earth environments.Item Advanced Hot Reservoir Variable Conductance Heat Pipes for Planetary Lander(2020 International Conference on Environmental Systems, 2020-07-31) Lee, Kuan-Lin; Tarau, Calin; Lutz, Andrew; Anderson, William; Huang, Cho-Ning; Kharangate, Chirag; Kamotani, YasuhrioThe next generation of Lunar rovers and landers require variable thermal links to maintain payload temperatures nearly constant over wide sink temperature fluctuations. It has been demonstrated on earth that a hot reservoir variable conductance heat pipe (VCHP) can provide a much tighter passive thermal control capability compared to a conventional VCHP with cold-biased reservoir. However, previous ISS test results revealed that the fluid management of a hot reservoir VCHP needs to be improved to ensure its long-term reliability. Under an STTR Phase I program, Advanced Cooling Technologies, Inc. in collaboration with Case Western Reserve University performed fundamental research to understand the complex transport phenomena within a hot reservoir VCHP. A novel loop VCHP configuration was developed during the program. This loop design allows a net flow to be induced and circulate along the NCG tubing system, which will continuously remove the excessive working fluid from the reservoir (i.e. purging) in a much faster rate compared to diffusion alone. Two potential mechanisms to induce net transport flow were identified: 1. By momentum transfer from vapor to NCG through shearing in the condenser/front region. It was called “DC” mechanism. 2. By filtering the pulses (via a tesla/check valve) generated in the heat pipe section of VCHP loop. It was called “AC” mechanism. Although these two mechanisms are independent, the AC mechanism can be further added/superimposed on the top of the DC mechanism to achieve a higher flow rate. This paper presents the work performed in Phase I to proof the existence of momentum transfer flow (“DC flow) and its effectiveness on VCHP purging. The work includes theoretical analysis, numerical modeling, prototype development and experimental demonstration.Item Advanced Passive Thermal eXperiment (APTx) for Warm Reservior Hybrid Wick Variable Conductance Heat Pipes on the International Space Station(48th International Conference on Environmental Systems, 2018-07-08) Tarau, Calin; Ababneh, Mohammed; Anderson, William; Alvarez-Hernandez, Angel; Ortega, Stephania; Farmer, Jeff; Hawkins, RobertAs NASA prepares to further expand human and robotic presence in space, it is well known that spacecraft architectures will be impacted by unprecedented power requirements and thermal environments in deep space. In addition, there is a need to extend the duration of the missions in both cold and hot environments, including cis-lunar and planetary surface excursions. The heat rejection turn–down ratio of the increased thermal loads in the above-mentioned conditions is crucial for minimizing vehicle power needs. Therefore, future exploration activities will have the need of thermal management systems that can provide higher reliability and performance, and power and mass reduction. In an effort to start addressing the current technical gaps in thermal management systems, novel new passive thermal technologies have been selected and tested on the board of the International Space Station (ISS). This testing was performed under the Advanced Passive Thermal eXperiment (APTx) project that is a collaboration between the Johnson Space Center (JSC), Marshall Space Flight Center (MSFC), University of Texas, and Advanced Cooling Technologies, Inc. (ACT) with funding from ISS Technology Demonstration Office at JSC as well as NASA’s Small Business Innovative Research Program. A hybrid-wick copper-Monel-water Variable Conductance Heat Pipe (VCHP) with warm reservoir design that consists of a copper evaporator (with sintered wick), a monel adiabatic section and a condenser both with grooved wick inside was developed and tested successfully on ground. The VCHP worked on the board of the ISS, but at higher temperatures than expected. Hence, a new flight VCHP design is currently under development to mitigate the shortcomings encountered in microgravity. The final paper will include some results and conclusions from the original flight testing and the ground test results for the improved VCHP.Item Demonstration of Copper-Water Heat Pipes Embedded in High Conductivity (HiK™) Plates in the Advanced Passive Thermal eXperiment (APTx) on the International Space Station(48th International Conference on Environmental Systems, 2018-07-08) Ababneh, Mohammed; Tarau, Calin; Anderson, William; Alvarez-Hernandez, Angel; Ortega, Stephania; Farmer, Jeffrey; Hawkins, RobertCopper-water heat pipes are commonly used for thermal management of electronics systems on earth and aircraft, but have not been used in spacecraft thermal control applications to date, due to the satellite industry’s requirement that any device or system be successfully tested in a microgravity environment prior to adoption. Recently, Advanced Cooling Technologies Inc., (ACT), in coordination with engineers from NASA’s Marshall Space Flight Center (MSFC) and Johnson Space Center (JSC) demonstrated successful flight operation of these heat pipes in low-Earth orbit. The testing was conducted aboard the International Space Station (ISS) under the Advanced Passive Thermal eXperiment (APTx) project, a project to test a suite of passive thermal control devices funded by the ISS Technology Demonstration Office at NASA JSC. The heat pipes were embedded in a high conductivity (HiK™) aluminum base plate and subject to a variety of thermal tests over a temperature range of -10 to 38 ºC for a ten-day period. Results showed excellent agreement with both predictions and ground tests. The HiK™ plate underwent 15 freeze-thaw cycles between -30 and 70 ºC during ground testing, and an additional 14 freeze-thaw cycles during the ISS testing. The following was demonstrated during 10 days of testing on the ISS: 1. Successful operation of the copper-water heat pipes and HiK™ plate 2. Ability of the copper-water heat pipes and HiK™ plate to survive multiple freeze/thaw cycles 3. As-designed heat transport via Copper-water heat pipes. 4. Reliable, repeatable start up of Copper-water heat pipes and HiK™ plate from a frozen state. This paper describes the test hardware, ground and flight test campaign, and discusses the results and conclusions of the testing.Item Design Analysis and Performance testing of a Novel Passive Thermal Management System for Future Exploration Missions(48th International Conference on Environmental Systems, 2018-07-08) Alvarez, Angel; Ortega, Stephania; Farmer, Jeff; Breeding, Shawn; Tarau, Calin; Ababneh, Mohammed; Anderson, WilliamIn response to an announcement of opportunity from the NASA’s Science Mission Directorate (SMD) Discovery Program, the Southwest Research Institute in collaboration with the Aerospace Corporation and the NASA Johnson Space Center (JSC) proposed a lunar lander science mission. The Moon Age and Regolith Explorer (MARE) would use a lunar lander to reach a young, nearside lunar lava flow for the collection and analysis of the lunar soil. This would be used for the determination of the impact history of the inner solar system and the evolution and differentiation of the interiors of one-plate planets. The lunar lander proposed was based on the NASA JSC Morpheus lander vehicle. The thermal environments for the proposed mission were both challenging and unprecedented, since survival of multiple lunar day/night cycles at the south-west region of the Aristarchus plateau were required. Other thermal design challenges included the need of a low mass, simple, robust and reliable thermal management system that would assure the success of the proposed mission. As part of the proposal effort, and leveraging on existing NASA Small Business Innovative Research (SBIR), a completely passive thermal control system concept was used to meet mission requirements. The thermal management system proposed uses a novel type of hybrid grooved and sintered wick variable conductance heat pipe and a high conductivity heat spreader; the thermal management systems tested wer developed by Advanced Cooling Technologies, Inc. (ACT) in Landcaster, Pennsylvania. This publication will present the design, analysis and prototype component and system level performance testing done at NASA JSC.Item Development of a 3D Printed Loop Heat Pipe(49th International Conference on Environmental Systems, 2019-07-07) Richard, Bradley; Anderson, William; Crawmer, Joel; Augustine, Merryl; Chen, Chien-HuaAs the capabilities of CubeSats and SmallSats increase so do the heat rejection requirements. While loop heat pipes (LHPs) are capable of transporting heat across deployable radiators they are currently too expensive for most applications. The largest cost comes from the fabrication of the primary wick which requires multiple machining steps as well as a knife-edge seal. The focus of this work is the development of a 3D printed LHP evaporator using a direct metal laser sintering (DMLS) process to fabricate the primary wick. 3D printing LHP wicks offers several advantages. The overall cost can be significantly reduced by eliminating multiple machining steps, and the risk of failure can be reduced by eliminating the knife-edge seal. The challenge with 3D printing of LHPs us achieving a porous wick structure. A pore radius and permeability study was conducted for optimization of DMLS methods and parameters for fabricating both the primary and secondary wick. The primary wick and secondary wick were also fabricated as a single part to test the ability to connect areas of varying pore size. Experimental testing was completed on a complete LHP prototype with 3D printed primary wick fabricated using the optimized DMLS parameters. Life testing has been completed to demonstrate compatibility of the 3D printed stainless steel wicks with ammonia.Item Development of a Passive Thermal Control Valve for 3D-Printed Loop Heat Pipes(50th International Conference on Environmental Systems, 7/12/2021) Hoenig, Sean; Van Velson, Nathan; Ellis, Michael; Anderson, WilliamAs the capabilities of extended-duration science payloads on the Lunar surface increase, so do the thermal control requirements. The primary power source for near-term Lunar surface science missions is a combination of solar photovoltaic arrays and batteries. A thermal control system that rejects daytime heat efficiently and conserves energy through the night is essential to keep the payloads, batteries, and other critical components at suitable temperatures. Conventional loop heat pipes (LHPs) provide very efficient heat transfer between electronics and spacecraft radiators when necessary but require 2-3 W of power continuously to shut down and minimize heat transfer through the night. This can increase battery mass substantially if applied for the entire Lunar night. The focus of this work is the development of a passive thermal control valve (TCV) integrated with the design of a 3D-Printed LHP evaporator. In this study, it was demonstrated that an on/off TCV is sufficient to shut down an LHP quickly and is much less expensive than currently used proportional valves. Three different designs are demonstrated for the TCV: �open when cold�, �closed when cold�, and a 3D-printed integral (also �open when cold�). Benchtop testing demonstrated the functionality and feasibility of using an on/off TCV in an LHP system. Results for the two subtractive manufactured TCV designs, tested with an additively manufactured capillary pump, show that it is feasible to maintain a tight seal and passively shut down the LHP at a cold temperature setpoint. Additional progress is required to refine the additively manufactured TCV design to create a sufficiently tight seal.Item Experiments on a Loop Heat Pipe with a 3D Printed Evaporator(51st International Conference on Environmental Systems, 7/10/2022) Gupta, Rohit; Chen, Chien-Hua; Anderson, WilliamThe construction and testing of a loop heat pipe with a 3D printed evaporator is described in this paper. The system was developed as part of a larger engineering demonstration unit for thermal management on NASA's Volatiles Investigating Polar Exploration Rover. A state-of-the-art 3D printed evaporator, developed in a previous effort, was used in the current system. This evaporator had a cylindrical geometry with a length of 0.1 m and a diameter of 0.025 m and featured a primary wick with a bubble point pore radius of under 8 µm. The vapor, condenser, and liquid lines were constructed from 0.003 m diameter tubing and routed to conform to the geometry of the rover. A thermal control valve was also incorporated in the loop heat pipe to force the vapor to bypass the condenser at a lower-than-threshold temperature. The loop heat pipe was tested successfully under a range of thermal loads of up to 70 W against a mission-expected load of 50 W. Due to startup difficulties observed at the low condenser temperatures, a series of dedicated startup tests were conducted to identify the underlying causes and to study the effects of major variables, such as the heat location and charge quantity. Based on this analysis, a number of changes were identified to help improve the startup performance of the system.Item High Heat Flux (>50 W/cm^2) Hybrid Constant Conductance Heat Pipes(48th International Conference on Environmental Systems, 2018-07-08) Ababneh, Mohammed; Tarau, Calin; Anderson, William; Fisher, JesseNovel hybrid wick aluminum-ammonia constant conductance heat pipes (CCHPs) are developed to handle heat flux requirements for spacecraft thermal control applications. The 5-10 W/cm^2 heat density limitation of aluminum-ammonia grooved heat pipes has been a fundamental limitation in the current design for space applications. The recently demonstrated >50W/cm^2 capability of the hybrid high heat flux heat pipes provides a realistic means of managing the high heat density anticipated for the next generation space designs. The hybrid wick high heat flux aluminum-ammonia CCHP transported a heat load of 275 Watts with heat flux input of > 50 W/cm^2 and with a thermal resistance of 0.015 ºC/W at 0.1 inch adverse elevation. This demonstrates an improvement in heat flux capability of more than 5 times over the standard axial groove aluminum-ammonia CCHP design.Item Hot Reservoir Variable Conductance Heat Pipe with Advanced Fluid Management(50th International Conference on Environmental Systems, 7/12/2021) Lee, Kuan-Lin; Tarau, Calin; Adhikari, Sanjay; Anderson, William; Kharangate, Chirag; Huang, Cho-Ning; Kamotani, YasuhiroA hot reservoir variable conductance heat pipe (VCHP) can offer a significantly tighter passive thermal control than a regular VCHP with a cold-biased reservoir. This attribute makes the hot reservoir VCHP an ideal thermal management device for future planetary landers and rovers and especially for the moon where surviving of the lunar night is energetically challenging. Since the hot reservoir cannot be wicked, it becomes a challenge to properly manage the presence of working fluid within the reservoir. To ensure a long-duration operation of the hot reservoir VCHPs in reduced gravity and in microgravity, advanced fluid management strategies and features must to be developed. Advanced Cooling Technologies, Inc (ACT) in collaboration with Case Western Reserve University (CWRU) is developing a reliable VCHP configuration under the NASA STTR program. The novel VCHP consists of a loop with well-engineered tubing configuration, that would generate a momentum induced continuous flow within the device. This induced flow would provide continuous maintenance of the NCG humidity in the reservoir as well as enable a much faster purging process (i.e. removal of moisture from the hot reservoir) if needed, significantly enhancing device�s reliability. The development of hot reservoir VCHP with advanced fluid management features will be presented in this paper, including both numerical and experimental efforts.Item Hybrid Heat Pipes for Lunar and Martian Surface and High Heat Flux Space Applications(46th International Conference on Environmental Systems, 2016-07-10) Ababneh, Mohammed; Tarau, Calin; Anderson, William; Farmer, Jeffery; Alvarez-Hernandez, AngelNext generation of polar rovers and equatorial landers is among the immediate NASA planetary applications. These landers and rovers have a Warm Electronics Box (WEB) and a battery, both of which must be maintained in a fairly narrow temperature range. So, a variable thermal link between the WEB and radiator is required. During the day, the thermal link must transfer heat from the WEB to the radiator as efficiently as possible, to minimize the radiator size. On the other hand, the thermal link must be as ineffective as possible during the Lunar night. This will preserve the electronics and battery warm with minimal power, even with the very low heat sink temperature. This variable thermal link can be a variable conductance heat pipe (VCHP) would require hybrid wick to allow liquid return during operation under unfavorable orientation of the evaporator. Also, future spacecraft and instruments developed for NASA's Science Mission Directorate will involve highly integrated electronics, such as for CubeSat/SmallSat. This high density electronics packaging leads to substantial improvement in performance per unit, mass, volume and power. However, it also results in requirement of sophisticated thermal control technology to dissipate the high heat flux generated by these electronics systems. For example, the current incident heat flux for laser diode applications is on the order of 5-10 W/cm2, although this is expected to increase towards 50 W/cm2. This is a severe limitation for the commonly employed axial groove aluminum/ammonia constant conductance heat pipes (CCHPs). Hence, high flux heat acquisition and transport devices are required. The paper reports on the development of VCHPs and CCHPs with a hybrid grooved and sintered wick.Item Integrated Hot Reservoir Variable Conductance Heat Pipe with Improved Reliability(51st International Conference on Environmental Systems, 7/10/2022) Lee, Kuan-Lin; Tarau, Calin; Anderson, William; Huang, Cho-Ning; Kharangate, Chirag; Kamotani, YasuhiroA hot reservoir variable conductance heat pipe (VCHP) that can offer tight and passive thermal control is an ideal thermal link for future planetary landers and rovers. This is especially useful for the moon operation as surviving during the lunar night is energetically challenging. Under a Small Business Technology Transfer (STTR) program, Advanced Cooling Technologies (ACT) and Case Western Reserve University (CWRU) developed an advanced integrated hot reservoir VCHP with improved reliability. This novel design enables a momentum-induced flow to circulate through a non-condensable gas (NCG) loop, which can continuously and effectively remove the excessive working fluid vapor from the reservoir (i.e. purging) without using an electric heater. Based on the purging test results, the bulk induced flow velocity is in a cm per second range. Without the flow, purging is dominated by diffusion and it will take hours to complete. With momentum-induced flow, the purging rate is much faster and the heat pipe can get back to normal operation within 20 minutes. This paper summarizes prototype development and experimental study of hot reservoir VCHP loop, including a detailed analysis of the VCHP purging process, purging, and startup testing of VCHP loop. A compact hot reservoir VCHP loop prototype with both reservoir and NCG tube integrated was developed and tested.Item Loop Heat Pipe Wick Fabrication via Additive Manufacturing(48th International Conference on Environmental Systems, 2018-07-08) Richard, Bradley; Anderson, William; Pellicone, DevinAs the capabilities of CubeSats and SmallSats increase so do the heat rejection requirements. While loop heat pipes (LHPs) are capable of transporting heat across deployable radiators they are currently too expensive for most applications. The largest cost comes from the fabrication of the primary wick which requires multiple machining steps as well as a knife-edge seal. The focus of this work is the development of a 3D printed LHP evaporator using a direct metal laser sintering (DMLS) process to fabricate the primary wick. 3D printing LHP wicks offers several advantages. The overall cost can be significantly reduced by eliminating multiple machining steps, and the risk of failure can be reduced by eliminating the knife-edge seal. The challenge with 3D printing of LHP primary wicks is that a very small pore radius is required to supply sufficient capillary pumping power. A pore radius and permeability study was conducted for optimization of DMLS methods and parameters for fabricating primary wicks. The result of this study is DMLS parameters for wicks with pore radii less than 10 µm. In addition, a DMLS parameter optimization study was performed for fabrication of the coarser secondary wick. Experimental testing is being completed on a complete LHP prototype with 3D printed primary wick fabricated using the optimized DMLS parameters. Modeling is being completed to optimize the design of the primary wick using geometries that are compatible with DMLS. Life testing has begun to demonstrate compatibility of the 3D printed stainless steel wick with ammonia.Item Loop Heat Pipe Wick Fabrication via Additive Manufacturing(47th International Conference on Environmental Systems, 2017-07-16) Richard, Bradley; Pellicone, Devin; Anderson, WilliamAs the capabilities of CubeSats and SmallSats increase so do the heat rejection requirements. While loop heat pipes (LHPs) are capable of transporting heat across deployable radiators they are currently too expensive for most applications. The largest cost comes from the fabrication of the primary wick which requires multiple machining steps as well as a knife-edge seal. In this work the feasibility of fabricating a loop heat pipe (LHP) primary wick using a direct metal laser sintering (DMLS) process was investigated. 3D printing a LHP wick offers several advantages. The overall cost can be significantly reduced by eliminating multiple machining steps and the risk of failure can be reduced by eliminating the knife-edge seal. The challenge with 3D printing of a LHP primary wick is that a very small pore radius is required to supply sufficient capillary pumping power. Most primary wicks have a pore radius of 1-2µm. A pore radius and permeability study was conducted using a range of DMLS methods and parameters to optimize for LHP primary wicks. The results of this study was a minimum pore radius of 6µm which provides a capillary pumping power of 11kPa. Based on this information CubeSats and SmallSats which have smaller heat loads and heat transport distances than traditional satellites can benefit from wicks made using a DMLS process. A 3D printed primary wick was designed and fabricated with a fully dense outer shell for direct welding to the compensation chamber and vapor line. A complete LHP prototype was built and tested to demonstrate the performance of the 3D printed wick. Life testing has begun to demonstrate compatibility of the 3D printed stainless steel wick with ammonia, and the long term structural integrity of the wick.Item Progress on 3D Printed Loop Heat Pipes(50th International Conference on Environmental Systems, 7/12/2021) Gupta, Rohit; Chen, Chien-Hua; Anderson, WilliamThe rapid growth of the miniaturized satellite industry has led to increased demand for low-cost and robust thermal management systems. Advanced Cooling Technologies, Inc. has been developing Loop Heat Pipes with 3D printed evaporators in an effort to reduce manufacturing costs and lead times by eliminating labor-intensive processes that are otherwise involved in the fabrication of standard evaporators. These processes include, but are not limited to, the primary wick fabrication, wick insertion, and knife-edge seal. The reported work describes the latest progress in this technology in the areas of primary wick advancement and thermal performance improvement. Following iterative optimization in this work, the pore size of the 3D printed wick was reduced to a sub-5-micron level, with a maximum radius of 4.9 ?m. A new evaporator was 3D printed, featuring a refined primary wick and a fully-dense front wall, in order to prevent vapors from the vapor plenum being forced back into the evaporator under strong adverse pressure gradients. The overall thermal conductance of the system was improved by over 15% by incorporating a new saddle design with a single, connected structure and featuring a horizontal clamping mechanism. The new 3D printed evaporator assembly was also shown to operate successfully at a steady state power level of 350 W using line tubing with diameter of 0.003 m and ammonia as the working fluid.Item Thermal Concept for Planetary Ice Melting Probe(2020 International Conference on Environmental Systems, 2020-07-31) Tarau, Calin; Lee, Kuan-Lin; Anderson, William; Morrison, Christopher; Hendrick, TerryTo support NASA future Ocean Worlds Exploration missions, Advanced Cooling Technologies, Inc (ACT) is developing an innovative thermal management concept for a nuclear-powered ice melting probe. The concept consists of multiple advanced thermal features that can offer the most efficient and reliable ice penetration process by maximizing the power fraction used for forward melting and mitigating a series of foreseen challenges related to icy-planetary missions. These thermal features include: 1) pumped two-phase loop for waste heat collection from the cold end of the thermoelectric convertors, transport and focus the heat at the front end of the vehicle for ice melting with minimal thermal resistance 2) front vapor chamber for forward heat focusing and melting 3) variable conductance side walls to enable lateral melting capability only when the probe gets stuck because of refreezing or meets obstacles 4) side high-pressure liquid water displacement for probe maneuverability and steering Under an SBIR Phase I program, ACT developed a preliminary full-scale probe design and assessed the technical feasibility of features (1) through (4). A lab-scale ice melting probe prototype with selected features was developed. Ice penetration and thermal behavior of the prototype were experimentally demonstrated in an ice environment system. Functionailties of variable conductance wall and vapor chamber were successfully proven.Item Two-Phase Thermal Switch for Lunar Lander and Rover Thermal Management(2023 International Conference on Environmental Systems, 2023-07-16) Van Velson, Nathan; Diebold, Jeffrey; Schulze, David-Paul; Tarau, Calin; Anderson, WilliamThe 14-earth day long lunar night poses a significant challenge to the thermal management of future lunar landers and rovers. For these vehicles to operate for long durations on the lunar surface, the on-board electronics must be maintained above their survival temperatures during the lunar night. Thermal switches are among the passive thermal management technologies that may be utilized for helping lunar vehicles survive the lunar night while minimizing the use of electric power for survival heating. Thermal switches are designed to minimize heat transfer in the OFF condition, and to maximize it when in the ON condition. In this work, a passive thermal switch design with high turndown is developed for lunar landers and rovers. This thermal switch design utilizes a sealed flexible bellows containing a two-phase working fluid. The switching mechanism is passively actuated by the temperature of the heat source. At low temperatures, the vapor pressure within the bellows is low, and the bellows is not in contact with the heat sink, restricting heat transfer through the switch. At higher temperatures, the increased vapor pressure causes the bellows to expand and come in contact with the heat sink, allowing more effective heat transfer through the switch. The actuation temperature is determined by the balance of forces on the bellows. A coupled thermal-mechanical model has been developed to illustrate the dynamic performance of the two-phase thermal switch. Several thermal switch prototypes were fabricated and tested for concept demonstration and model validation, and trade studies for enhancing the ON/OFF conductance ratio were performed. Finally, a prototype thermal switch with high ON/OFF ratio was developed and tested for a small lunar rover application.