  Passive radiative cooling is currently the frontier technology in
renewable-energy research. In terms of extraterrestrial applications, radiative
cooling is a critical component to the thermal management system of a
spacecraft, where the extreme environment of space can cause large temperature
variations that can break and damage equipment. For terrestrial applications,
nocturnal or daytime radiative cooling is expected to lead to cost-effective
passive heat management without the need of inefficient and costly artificial
refrigeration technologies. However, most currently available radiative cooling
systems cannot be changed dynamically and radiate a constant static amount of
thermal power. Dynamically tunable adaptive radiative cooling systems will be a
critical development to prolong the lifetime of spacecraft or improve the
efficiency of terrestrial cooling systems. Here we propose stretchable
radiative cooling designs that can be substantially tuned by using the simple
physical mechanism of mechanical strain. When their structure is stretched, the
radiated power is significantly reduced. We develop a modeling method that can
simulate mechanical stretching combined with electromagnetic response to
compute the tunable thermal emission of these new adaptive radiative cooling
systems. The presented photonically engineered structures can be used as
coatings to achieve efficient adaptive thermal control of various objects in a
cost-effective and environmentally friendly way. The proposed designs are much
simpler to be realized than others found in the literature and the best design
achieves a high thermal emission power with a tunable range on the order of 132
W/m2.
