Important degradations of white silicone paints were observed in low Earth orbit (LEO) on CNES' THERME experiments. These degradations were in the order of 0.2 to 0.3 in terms of solar absorptance (αS) increase in as little as a few years whereas other materials such as Kapton films or Teflon secondary surface mirrors (SSM) did not age nearly as much. Previous experiments have tried explaining such over-degradation of white paints in LEO in ONERA's SEMIRAMIS aging facility but the simulated LEO environment (especially ultraviolets, UVs) almost did not cause any degradation on such paints. Combined UV irradiation with atomic oxygen (ATOX) did not cause excessive degradation either.

Here, we present the results of experiments carried out in order to study hypotheses were contamination processes are involved. Indeed, contamination seems to be able to explain what happens to Kapton films or Teflon SSM on LEO satellites, with healing happening during solar maxima (induced by the erosion of the contamination layer by ATOX). Nonetheless, considering only contamination and assuming it be the same for every material, the degradation of white silicone paints still happens much faster than that of other mentioned substrates. For this reason, the contamination hypothesis was not further explored.

Recently, efforts were put towards explaining the THERME flight data and a plausible explanation involving synergetic effects between UVs and contamination, modifying the morphology of the contamination deposits was proposed. These results show that contrary to what was thought, the aging of white paints was nominal but the other substrates' ones were in fact weaker, due to the morphology of the contamination deposits. These results are backed up with a model reproducing satisfactorily the observed thermo-optical properties changes during UV aging.