damage was created by oxygen plasma etching exposure control experiments on Earth.
Unexpectedly, laboratory analysis revealed that more than 80% of the silk and collagen protein
chains were chemically cross-linked by penetrating space radiation, which caused changes to
the proteins. Silk-silica composites or triple-helix structures in native Type I collagens were
more resistant to the impact of radiation in space than silk. It was also shown that resistance to
high heat decreased after space travel for the protein samples. Results suggested that protein
materials could be bioengineered to help protect them in the extreme space environments.
Black Kapton® XC polyimide films on MISSE-6A and 6B exhibited a higher erosion rate when the
films were stretched during the exposure period. Although a slight stress dependence was also
observed in the ground-based samples, both in appearance and in the erosion yield, it was not
to the extent seen in the space-exposed samples. Differences such as atomic oxygen, levels of
UV radiation, temperature, and charged particles between the ground based and space
environments could have caused this difference. Coatings of silicon dioxide and silicon showed
evidence of cracking while under stress. This type of cracking can lead to failure of the
underlying polymer material if cracks are exposed to high levels of atomic oxygen. This
appeared to be the cause of failure for the silicon oxide (SiOx) coated Kapton flown on the ram
side of MISSE-6A and 6B. Microscopic photos of the Kapton XC samples showed very little
erosion on the unstressed samples but noticeable surface texturing under slight stress, and
almost complete erosion under stresses greater than the tensile yield stress.
The failure of vapor deposited aluminum (VDA) polymer films appeared to be dependent on the
level of environment exposure. VDA samples under stress exposed on the ram side of MISSE-6A
and 6B failed while the sample exposed under stress on the wake side did not. MISSE-6A and 6B
hosted samples with titanium and aluminum oxide cermet coating having the optical properties
of high-solar absorptance and low infrared emittance. Spectral reflectance data obtained
before and after flight revealed essentially no change in the optical properties of solar
absorptance and infrared emittance upon low-Earth orbit exposure, consistent with ground
laboratory evaluation of similar cermet coatings.
An atomic oxygen fluence monitor, flown as part of the MISSE-6B, was designed to measure the
accumulation of atomic oxygen fluence with time as it impinged upon the ram (front) surface of
MISSE-6B. This was an active experiment for which data was to be stored on a battery-powered
data logger for post-flight retrieval and analysis. An atomic oxygen fluence of 1.37 ± 0.16×1021
atoms/cm^2 was measured. The fluence was approximately 30% lower than fluences measured
using Kapton® H samples from an adjoining MISSE-6A passive experiment container.
Further testing is needed to isolate the factors that resulted in increased erosion under
stress. These findings are critical for designing next-generation biocompatible materials and
measurement systems for the space environments, where the effects of heavy ionizing particles
and other cosmic radiation need to be considered. Further testing is needed to isolate the
factors that result in increased erosion under stress.