Space isn't empty. Space is considered an environment — an extreme environment, filled with entities that can be harmful to spacecraft.
In space, there are several environmental threats that can harm materials used to create spacecraft. These threats include ultraviolet rays and x-rays from the sun; solar wind particle radiation; thermal cycling (hot and cold cycles); space particles (micrometeoroids and debris); and atomic oxygen.
It is essential for NASA to research and understand how materials are affected by the environmental threats that exist in space. Since 2001, NASA and its partners have operated a series of flight experiments called Materials International Space Station Experiment, or MISSE. The objective of MISSE is to test the stability and durability of materials and devices in the space environment.
Testing on the International Space Station
MISSE experiments have been flown in space on five different occasions, and will be flown once more. During each mission, either one or two Passive Experiment Containers (PECs) are flown. PECs, which are attached to the exterior of the International Space Station, are about 2-feet by 2-feet and hold a variety of materials samples and devices whose reactions in space are of interest.
"Each PEC has two trays that are hinged like a suitcase. Samples are loaded onto the top surface of the trays, and then the PEC is closed to protect the samples during launch on the space shuttle," says Kim de Groh, the principal investigator for the MISSE Science program at Glenn. "The PECs are taken up to the space station, where an astronaut does a spacewalk and installs each PEC at its designated location on the outside of the space station. The PEC is opened by the astronaut and the trays are placed back-to-back and secured, exposing the samples to the space environment."