NASA’s Vision for Space Exploration calls for a return of humans to the Moon by no later than 2020. Reducing risk to astronaut safety and mission success will require technology development in a wide variety of areas, including the protection of astronauts and their equipment from the lunar environment. The exploration community is beginning to come to consensus with Apollo 17 astronaut Harrison Schmitt who recently declared, "Dust is the number one environmental problem on the Moon" (ref. 1). The Apollo record shows that dust caused a wide variety of problems for those missions, including vision obscuration, false instrument readings, equipment clogging, radiator degradation, seal degradation, abrasion, and respiratory and eye irritation (ref. 2). Abrasion of the fabric of the extravehicular activity (EVA) suits was much more extensive than anticipated. The following electron micrograph shows abrasive damage of a portion of Alan Bean’s suit from Apollo 12. The Apollo 12 astronauts also reported, "The suit material just beneath the top of the lunar boots chafed sufficiently to wear through the outer suit layer in several spots" (ref. 3). This is of particular concern since the missions are being planned to last as long as 6 months, and the Apollo damage was incurred in less than 3 days.
Portion of the EVA suit worn by Alan Bean
during Apollo 12. Lunar dust particles are
embedded in the fabric, and abrasion can be
observed on several of the individual fibers.
Although the abrasive damage was much worse than anticipated, exactly why has not been determined. Certainly a major factor is the nature of the lunar regolith—the upper part of the lunar crust, which is composed of pulverized rock, dirt, and dust. The lunar surface is weathered primarily by the impacts of meteoroids, which vary in size from mountains to microns. Impacts melt and weld regolith together at the impact point, and impact shock waves break regolith apart. This results in very sharp particles, some of which have irregular and protruding shapes. These particles tend to hook into fabric fibers and become difficult to dislodge. They work their way into the fabric and abrade it. In addition, the lunar environment is filled with radiation from the Sun, so these fabrics also are subjected to thermal extremes, energetic x-rays, ultraviolet light, solar wind protons and electrons, and cosmic rays. In addition to possibly embrittling the suit fabric in long-term use, these conditions make the surface of the regolith chemically active, which may change the adhesive and abrasive characteristics of the dust and dirt.
In fiscal year 2007, a fixture was designed and fabricated at the NASA Glenn Research Center for studying abrasion in a lunar-like environment—the Lunar Dust Adhesion Belljar (LDAB, see the following photograph). The LDAB was designed to mimic the vacuum, thermal, illumination, and radiation environment of the lunar surface (ref. 4). The fixture was adapted from a standard abrasion test (ref. 5), but testing is being carried out under simulated lunar conditions. Preliminary tests were done with lunar simulants, such as JSC-1A, but later testing will be done with actual lunar regolith. Electron microscopy is being used to match the abrasive damage of samples with that experienced by the Apollo fabrics. This will enable ground test conditions to be developed that will result in realistic testing of fabric abrasion on the lunar surface.
Abrasion fixture with four fabric samples
installed in the LDAB at the conclusion of a test.
Long description of figure 2.
Last updated: October 31, 2008
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