Connecting optical observations to chemical changes

Imagine that you could determine the structural health of spacecraft materials simply by observing their color. Researchers at the Georgia Institute of Technology will use the International Space Station (ISS) to evaluate changes in the optical properties of common spacecraft materials as they are exposed to the extreme conditions of space.

The research team will correlate this optical property data with material chemistry and expected lifetime data to produce a database that will be valuable both in remotely diagnosing the material health of spacecraft and in improving ground-based space environment simulation for materials testing.

This investigation was awarded through an ISS U.S. National Laboratory solicitation for flight experiments that use the MISSE Flight Facility, an in-orbit platform from Alpha Space Test and Research Alliance deployed externally onboard the ISS.

The Georgia Institute of Technology research team will prepare samples of conventional and novel spacecraft materials, including liquid crystal polymers (LCP), polyhedral oligomeric silsesquioxane (POSS), carbon fiber reinforced polymers, and polyethylene teraphthelate (PET) polyester films.

After launch to the ISS, the samples will be mounted outside the station on the MISSE Flight Facility for a six-month exposure. During this time, samples will be optically characterized periodically and cross-referenced with radiation and atomic oxygen exposure data. After returning to Earth, the samples will be optically, chemically, and mechanically characterized to develop correlations between color and chemical changes in the material.

Diagnosing Material Health at a Distance
The stress of launching to space coupled with the harsh, dynamic operating environment there imposes very stringent requirements on spacecraft materials. Atomic oxygen, unfiltered ultraviolet radiation, and high-energy electrons all combine to induce chemical and structural changes in the materials, particularly polymers and composites.

This extreme environment causes chemical damage that manifests as changes in optical properties such as reflectance and absorptance. It also leads to changes in physical properties such as mechanical strength, electrical conductivity, and chemical reactivity. Developing a correlation of the changes in these properties as function of radiation dosage will allow researchers to infer a host of material properties based on one experimentally convenient measurement: color change.

Using color as an indicator, earthbound observers could remotely diagnose the health of spacecraft and mission-critical components based on color shifts detected through remote observation. Aerospace engineers would significantly benefit from such insight into material behavior changes throughout a mission lifetime by remote and nondestructive examination.

Further, building a library of visual observations for correlation with material performance may one day result in a predictive database enabling artificial intelligence systems to constantly monitor materials for space-induced material color change indicating potential failure.

Improved Simulation-Based Materials Testing on Earth
With the constant development of new materials for spacecraft, accurate ground-based space environmental simulation is of primary importance to advancing spacecraft design. Ground-based simulation of the space environment is experimentally challenging because the space environment is very dynamic and varies wildly depending on many factors.

Therefore, ground testing of materials for spacecraft requires thorough validation in order to develop reliable models of material degradation. The results of this investigation will generate benchmark data from ground-based studies of materials degradation and weathering that aid in the validation of data from ground-based space weather simulation experiments.

"This potentially foundational work to correlate optical properties with chemical changes within spaceflight materials will improve situational awareness and reliability of satellites and space vehicles," said Dr. Ryan Reeves, program director of advanced materials at the Center for the Advancement of Science in Space, manager of the ISS National Lab. "This information will allow operators to access the material health of satellites and spacecraft from a distance to accurately pinpoint expected lifetimes."

Related Links
ISS National Lab
Space Technology News - Applications and Research

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