INVESTIGATIONS OF TRIBOLOGICAL CHARACTERISTICS OF SOLID LUBRICANTS EXPOSED TO ATOMIC OXYGEN

At low earth orbit (LEO) altitudes of 100-1000 km, pressures are relatively high (10(-5) Pa) and the residual atmosphere consists primarily of atomic oxygen (AO). Spacecraft orbital velocities, approximately 8 km/sec, at LEO altitudes result in a reactive chemical environment with 5eV AO. Long-term (10-30 years) operation of spacecraft at LEO altitudes requires lubricants that in an unshielded condition can withstand the harsh chemical environment. However, little is known about LEO environment interactions with solid lubricants. Using an AO generation facility, four kinds of solid lubricants, sputtered MoS2 film, inorganic binder-type spray-bonded MoS2 film, organic binder-type spray-bonded MoS2 film and ion-plated Pb film, were exposed to an AO beam. The effects of exposure on their lubricating performance were examined in a pin-on-disk sliding test under vacuum conditions (5 x 10(-5) Pa). Changes in the degree of oxidation of these films were analyzed by Auger electron spectroscopy. Exposure to the AO beam resulted in significant changes in lubricating performance and surface oxidation. Of the solid lubricant films tested, sputtered MoS2 film showed the most resistance to oxidation.