The Materials International Space Station Experiment (MISSE) is a series of experiments mounted externally on the International Space Station (ISS) that investigates the effects of long-term exposure of materials to the harsh space environment. The MISSE project evaluates the performance, stability, and long-term survivability of materials and components planned for use by NASA, commercial companies and the Department of Defense (DOD) on future low Earth orbit (LEO), synchronous orbit and interplanetary space missions. The Long Duration Exposure Facility (LDEF), which was retrieved in 1990 after spending 68 months in LEO, revealed that space environments are very hostile to many spacecraft materials and components. Atomic oxygen, which is the most prevalent atomic species encountered in low earth orbit, is highly reactive with plastics and some metals, causing severe erosion. There is also extreme ultraviolet radiation due to the lack of an atmospheric filter. This radiation deteriorates and darkens many plastics and coatings. The vacuum in space also alters the physical properties of many materials. Impacts of meteoroids and orbiting man-made debris can damage all materials exposed in space. The combined effects of all of these environments on spacecraft can only be investigated in space. MISSE evaluates materials currently being used and those planned for use in future space missions. The MISSE program is a direct successor to the Mir Environmental Effects Payloads (MEEPs) that were attached for over a year to the Mir Docking Module of the space station Mir between shuttle flights STS-76 and STS-86; and is a descendant of the Long Duration Exposure Facility. Also MEEPS can trace their inception to the Passive Optical Sample Array (POSA) sample trays flown on STS-1 and STS-2, and their successor Effects of Oxygen Interaction with Materials (EOIM) on STS-3 and STS-5.
Materials tested About 1,508 samples are being tested on the MISSE project. Samples range from components such as switches, sensors and mirrors to materials like polymers, coatings, and composites. There are also biological materials such as seeds, spores and various types of bacteria being evaluated. Each material on the mission had to be individually tested in the laboratory prior to being selected. The ultimate test for the materials is when they are exposed to the space environment. In the laboratory, each material can only be exposed to one particular simulated environment at a time. In space, they are exposed to all of the environments at once. Besides testing new materials, MISSE will also be addressing questions concerning current materials, such as those being used in communication satellites which are being plagued with premature failures of the solar cell power arrays. New generations of solar cells with longer expected lifetimes will also be tested. MISSE will also be testing coatings used to control heat absorption and emission temperatures of satellites. The hostile environment of space limits the useful life of coatings. New coatings, which are expected to be much more stable in space and therefore have longer useful lives, will be tested. MISSE will also address a major problem for a crewed exploration of Mars: shielding the crew from the very energetic cosmic rays found in interplanetary space. New concepts for lightweight shields will be tested on MISSE. Ultra-light membrane structures are planned for solar sails, large inflatable mirrors and lenses. The effects of micrometeoroid impacts on these materials will also be investigated. MISSE data (MISSE 1 - 7) is now open to the public through a registered account at http://materialsinspace.nasa.gov/. Where possible NASA has tried to collect past MISSE experiments and make the data available to the public. Data is still being collected from researchers and added to the MISSE database.
Deploying MISSE The materials selected for the mission are placed into briefcase-like Passive Experiment Containers (PECs). The PECs are used for transporting experiments to and from ISS. During an EVA they are placed on handrails or at an exposed experiment facility of the ISS. The containers are opened fully (360°) so the two surfaces with experiments are facing in opposite directions. The experiments are photographed several times during their stay outside if possible, usually whenever an opportunity arises due to a scheduled EVA. After exposure in space, MISSE is retrieved in the same manner as it was deployed, the material samples are tested to see if they still have the unique properties needed to complete space missions. MISSEs have active and passive detectors to give a time-history reading, or a reading of what happened to the materials at certain points in time. Back on the ground, tests will be conducted to determine the effects of its exposure. These tests will determine which materials are strong enough to survive in space. Originally it was planned to have MISSE-1 and 2 deployed for about a year and MISSE-3 and 4 for up to three years. Due to the grounding of the shuttle fleet after the Space Shuttle Columbia disaster required that changes be made to these plans. MISSEs 1 and 2 provided the three-year data and MISSEs 3 and 4 have provided the one-year data.
MISSE-1 and MISSE-2 The first and second set of experiments was launched by Space Shuttle Discovery, during mission STS-105, on 10 August 2001 and contained 910 specimens of various materials. It was installed in two separate airlock handrails located on the Quest Joint Airlock and high-pressure gas tanks. On 30 July 2005, during the first EVA of mission STS-114, both experiments were retrieved.
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