Freeze-Tolerant Radiator for Spacecraft Thermal Control

Future space exploration missions require advanced thermal control systems to dissipate heat from spacecraft, rovers, or habitats to external environments. These systems must be lightweight, reliable, and able to effectively control cabin and equipment temperatures under widely varying heat loads and ambient temperatures. Current state-of-the-art thermal control systems face the challenge of freezing in the harsh space environment when heat loads are low, and the ambient temperature is extremely cold. The Microgravity Demonstration of Freeze-Tolerant Radiator for Spacecraft Thermal Control is a new radiator technology capable of three-phase operation. The radiator is placed within a vacuum-insulated tube, and a small flow of liquid nitrogen metered to the chamber provides a thermal shroud (panel) for radiative heat sink – a common thermal management system to transport heat energy. The vaporized liquid nitrogen is vented overboard. This technology has the potential for a wide variety of applications given that spacecraft, habitats, payloads, and rovers must adequately remove heat from the operating environment to the external environment. 

Problem Statement Thermal control systems will be required for future space missions. Typically, spacecraft radiators are engineered to reject the maximum anticipated heat load for the maximum temperature design environment. When the heat loads are minimal and the ambient temperature is cold, the radiator working fluid can fall below the freezing point. Thermal control systems must be designed to avoid ice formations when the head load is minimal. Deployable radiators are especially vulnerable given their large surface area and low thermal mass. This technology is designed to overcome mass and system complexity in current solutions, as well as the need for freeze-tolerant solutions. 

Technology Maturation Parabolic flight tests are expected to demonstrate the radiator’s thermal performance and freeze-tolerance at several heat loads at variable-gravity conditions and measure the motor power during deployment under microgravity. Researchers intend to use data collected during these flight tests for further model validation. The flight tests aim to advance this innovation’s technology readiness level (TRL) to TRL 6. This work is closely tied to and builds upon previous flight testing under T0337. (This work focuses on testing a freeze-tolerant radiator. T0337 tested all other primary components but does not include a radiator.) 

Summary of May 5, 2025 Flight Test
Creare has successfully tested its two-phase thermal flow loop which includes an innovative freeze-tolerant radiator, a microgravity two phase separator, and a microgravity accumulator. The team is steadily increasing the viability and reliability of two-phase heat rejection for a broad range of space applications. The heat rejection system achieves high specific power, high reliability, and good isothermality in the harshest conditions. The team is excited to deploy this technology on new space missions and infrastructure. Funding for the development and testing of this technology was provided by the NASA SBIR program and NASA Flight Opportunities.

- Enabling: Provides an innovative solution for a freeze-tolerant condensing radiator capable of three-phase flow in the harsh space environment 
- High efficiency: Reduced pumping power and high heat transfer coefficient; high turndown capacity 

Future Customers 
- Environmental control for surface habitats (advanced habitation systems) and spaceborne platforms 
- Potential fit for the Human Landing System (HLS) for NASA’s Artemis program 
- Extreme environment (lunar, solar system) exploration 
- Commercial low Earth orbit (LEO) satellites for telecommunications

This is early/mid-stage (TRL 4) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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