Original Date: 04/26/1999
Revision Date: 01/18/2007
Information : Long Term Vacuum Testing of Lubricants
Lubricants used for space applications must be able to operate in a vacuum environment. Parameters include low vapor pressure, wide temperature range, and minimal outgassing. To determine which ones are compatible for NASA missions, Marshall Space Flight Center (MSFC) performs long term vacuum testing of lubricants. In most cases, these lubricants are evaluated in a vacuum environment over a one-year period.
Lubricants in a vacuum environment tend to outgas at a much higher rate. This phenomena causes them to loose their beneficial properties and, in some cases, condense on nearby objects. Finding lubricants which possess superior space operational properties can best be accomplished in a vacuum test apparatus (bell jar). Each bell jar contains four samples of five different lubricants, which are tested in 20 small motors. During the test period, the motors are periodically examined for failure. At the end of one year, the bearings of each motor are removed and examined. MSFC then identifies the cause of failure (motor armature or lubricant); measures the lubricant’s mass loss to determine the outgassing effect; performs a visual inspection with an optical microscope; and calculates the bearing wear (depth of wear track on bearing races) via a Taly-Surf Profilometer. Due to the ban on ozone depleting cleaners, MSFC is currently investigating other ways of cleaning the bearings. Similar testing is performed on oils, but the setup typically uses one motor (sometimes two) per workstation.
MSFC’s long term vacuum testing of lubricants is a unique capability. The Center incorporates all test data into a central lubricant database, which engineers extensively use to select lubricants for space applications.
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