The NASA News item NASA’s New Shape-Shifting Radiator Inspired by Origami describes a technique for spacecraft temperature regulation combining both a shape-changing surface and an emissivity-changing material applied to it.
I don't understand what is really happening here. How can one shape be better for cooling (radiating into space) while another be better for warming (presumably from sunlight)? Wouldn't you just want the maximum area? It seems the deeper the folds, the smaller the total area exposed to the environment.
To reiterate, the deeper the folds, the smaller the cross-sectional area because the total amount of surface is fixed. Is it really true that a smaller cross-section with deeper folds is better than spread out and planar?
This novel radiator controls the rate of heat loss by performing shape-shifting maneuvers. The resulting topographical changes could be achieved with temperature-sensitive materials like muscle wire or shape-memory alloys. As temperature-sensitive materials experience a change in temperature — caused by spacecraft electronics or the absorption of heat from the Earth or sun — the radiator could automatically change its shape to either shed or conserve heat.
The deeper the folds or cavities, the greater the absorption, explained Mulford, adding that scientists have investigated the use of cavities to affect heat loss for nearly 100 years, but no one has approached the challenge in quite this way. “Origami allows you to change the depth of these cavities in real time, thereby changing the heat loss from a surface in real time,” he said.
below: "Brigham Young assistant professor Brian Iverson and doctoral student Rydge Mulford have teamed with NASA technologist Vivek Dwivedi to advance the design of a three-dimensional, foldable radiator, inspired by the art of paper folding. Still early in its development, Iverson and Mulford are experimenting with different shapes to determine which configuration would work best as a radiator." Credits: Brigham Young University