Satellites must operate around the clock in a harsh and extreme environment. While they seem to glide gracefully through space, reaction wheels inside are constantly spinning at high speed to provide small but precise adjustments for the position and altitude.
Essentially, the reaction wheel is a flywheel, where torque is applied to a single axis of the satellite causing it to react by rotating. Keeping the bearings in the reaction wheel spinning—and a billion dollar satellite in operation—is a thin layer of lubricant.
Once launched, there is no way to change the oil in a satellite after a million miles, so all mechanisms must be “Lube for Life.” This extreme lubrication challenge can be solved by using a multiply-alkylated cyclopentane (MAC) base oil. This unique oil, developed specifically for outer space, offers low volatility, good lubricity and long life.
The MAC oil is only the start of a long process that Nye Lubricants of Fairhaven, Mass. goes through to produce an aerospace lubricant. First, additives for the oil must be tested. Then, the lubricant is formulated in an ISO rated clean room by specially gowned technicians, followed by a multi-step ultrafiltration process. Next, the aerospace lubricant must pass a gauntlet of application related tests. For example, wear protection is confirmed by using a SRV test rig. This test, which incorporates oscillation, friction and wear, determines if the lubricant will provide the proper film strength over the life of the mission by testing the grease between two oscillating metal surfaces. Data obtained in this test includes wear scar diameters and coefficient of friction.
Under Vacuum is another application test performed at Nye. Samples are tested to measure for any volatile contamination that might escape from the lubricant. This test is critical to ensure that the optics for reconnaissance satellites will not fog by condensables from the lubricant. In addition to volatile contamination, the company also controls the solid particle contamination in the lubricant. To ensure the cleanliness, a sample is inspected under a 200x microscope to confirm that no large hard particles are present. Particles in the lubricant would cause vibration in the bearing, followed by wear and premature failure. Other tests the aerospace lubricants must pass include apparent viscosity, oil separation, wettability, FTIR and density.
Having passed all the specifications, the lubricant is ready for the ride of its life aboard a communication satellite the size of a school bus, or on a new-generation, toaster sized CubeSat satellite.
Filed Under: Aerospace + defense, ALL INDUSTRIES, Design World articles, Materials • advanced