Researchers Explore Materials Degradation in Space

  • Published
  • By Molly Lachance, AFRL/AFOSR
  • Air Force Office of Scientific Research
ARLINGTON, Va. --  When Space Shuttle Endeavor launched in March 2008, it carried aboard more than 1,000 new materials for testing as part of the sixth Materials International Space Station Experiment, or MISSE-6. AFRL initiated MISSE-6 to gain a theoretical understanding of the mechanisms involved in materials degradation as it occurs in space. MISSE-6 results will help scientists better understand the durability of various materials in the harsh space environment. In turn, recognizing which materials are truly suitable for space use will have important implications to the design of future spacecraft.

In low earth orbit--the zone beginning roughly 50 miles above the earth's surface and extending to a distant 1,240 miles--materials erode more quickly than in other environments. This accelerated degradation stems from the material's exposure to ultraviolet rays and atomic oxygen, an elemental form of oxygen not found in earth's atmosphere. MISSE-6 consists of two passive-experiment containers, resembling suitcases, attached to the outside of the International Space Station (ISS). Each container houses small samples of the hundreds of materials being tested for space exposure effects.

Some of the materials selected for MISSE-6 include an extremely hard, ceramic-like material (developed at the University of North Dakota); silica-encapsulated enzymes and cells (prepared by UES, Inc.); and spider silk thread (from Oxford University). AFRL and industry partner Boeing assembled and installed the material samples before sending the MISSE-6 containers to the National Aeronautics and Space Administration's (NASA) Langley Research Center for testing. Boeing is the prime contractor used by NASA to design, develop, integrate, test, and deliver US-built components of the ISS.

An astronaut carried both MISSE-6 containers outside the shuttle and mounted them at designated locations on the ISS. Following 1 year of exposure, another team of astronauts will retrieve the containers and return the material samples to earth. Researchers will then evaluate the materials based on their respective reactions to atomic oxygen erosion, direct sunlight, radiation, and extremes of heat and cold. This assessment will aid the determination of which materials can withstand the harsh space environment.

MISSE-6 is the first of the MISSE efforts to test biomaterials. In addition to its passive experiments, this sixth-running mission also includes several active experiments, such as shutters, biases placed on samples, and real-time data recording. Further, MISSE-6 is the first experiment of its kind to employ space station power, a benefit enabling astronauts to respond more quickly should any experiment encounter problems. The groundwork required for connecting to space station power has, in turn, paved the way for a MISSE-7 data link capability.