Future manned space missions will require thermal control systems that can adapt to larger fluctuations in temperature and heat flux exceeding the capabilities of current state-of-the-art technologies. Specifically, these missions will demand novel space radiators that can vary the system heat rejection rate to maintain the crew cabin at habitable temperatures throughout the entire mission. While current systems can provide a turndown ratio (defined as the ratio of maximum to minimum heat rejection rates) of 3:1 under adverse conditions, future missions are projected to demand thermal control systems that can provide a turndown ratio of more than 6:1. A novel morphing radiator concept autonomously varies the system heat rejection rate by altering the shape of the panel exposed to space, where composite materials can provide an ideal compromise between thermal conductivity, restorative stiffness and deformation capability. Shape change is accomplished through the use of shape memory alloys, a class of active materials that exhibit thermomechanically driven phase transformations and can be used as simultaneous sensors and actuators in thermal control applications. This work details progress towards testing and modeling a spaceflight-quality, high turndown ratio morphing radiator prototype in a relevant thermal environment. A prototype composite morphing radiator with shape memory alloy strip actuators and high performance thermal coatings achieved a turndown ratio of 7.2:1, while an associated multi-physical model thereof has been shown to capture all major effects and will enable future design improvements.