How spacecraft heat regulators wear
doi:10.1038/nindia.2012.174 Published online 27 November 2012
New research has come up with insights into how the thermal-control materials of a spacecraft degrade when exposed to solar radiation during long-term space missions.
Thermal-control materials have shown darkening, bleaching, and cracks in simulated space environments rich in solar ultraviolet (UV) radiation and charged particles. These new findings will be very useful in producing better thermal-control materials for future spacecraft.
During any space mission, spacecraft are constantly bombarded with solar radiation and other cosmic rays emanating from distant celestial bodies. All spacecraft are equipped with materials that absorb and dissipate radiation-induced heat, to ensure proper functioning of the spacecraft. However, such radiation exposure during a long-term space mission could degrade the thermal-control materials, which are not easy to repair. This could prematurely end the life of a spacecraft.
To throw new light on the degradation of such materials, the researchers carried out experiments in a simulated space environment at ONERA, a French aerospace research centre. They tested the degradation of various thermal-control materials, exposing them to solar UV rays and high-energy protons and electrons in a vacuum for 3 months, equivalent to a three-year exposure to solar radiation in space. For the experiments, thermal-control materials were bonded to aluminium plate.
The main degradations observed were colour change in test samples, darkening of low-absorbing materials, and bleaching of the black paint. Some cracks were found on the flexible optical solar reflectors (OSRs), along with many micro cracks on the varnish of varnish-coated aluminized polyimide used as an alternative to flexible OSRs and to radiate internally generated heat into outer space.
"The indium tin oxide-coated aluminized polymide film underwent moderate degradation mainly due to particle irradiations," says lead researcher A. K. Sharma. "Degradation was faster during the initial stage of irradiation and subsequently slowed," he adds.