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TRIBOLOGY OF HIGH-SPEED MOVING MECHANICAL SYSTEMS FOR SPACECRAFTS: LUBRICATION SYSTEMS
OF BALL BEARINGS
K. Sathyan
(typically 5 seconds each) and the oil discharge at the delivery tip is
collected and weighed. It can be seen from the figure that the total
discharge in 50 cycles is about 750 mg, which is only half of the swept
volume, i.e. oil available for lubrication. It is estimated that the average
loss of lubricant from the bearing of a momentum wheel is about 10
mg/year (Sathyan et al., 2010). This shows that if a quantity slightly in
excess of this amount is supplied every year, the bearing failure can be
eliminated. Therefore, if one drop (8 mg) oil is supplied every six
months or a maximum of three drops per year, the failure due to
lubricant starvation can be completely eliminated. From the calibration
data of the CLS, which shows that one operation of duration 5 seconds
deliver approximately 15 mg, even if two operations of 5 seconds each
are planned every year, this system would provide lubrication up to 25
years. The amount oil discharge from the CLS can be varied by varying
the duration of operation time. The oil discharge can be properly
controlled by selecting suitable actuator motor, fine pitch ball screws
and suitable size bellows.
Fig.11. Measured oil discharge from CLS (Sathyan et al., 2010)
Jansen, M. J., Jones, Jr. W. R., Pepper, S. V. Evaluation of an in-situ,
liquid lubrication system for space mechanisms using a vacuum spiral
orbit tribometer. In: NASA-TM-2002-2111683; June 2002.
Jones, W. R. Jr., Shogrin, B. A., Kingsbury, E. P. “Long –Term
Performance of a Retainerless Baring Cartridge with an Oozing Flow
Lubricator for Space Application”. NASA Technical Memorandum
107492, August 1997.
Kingsbury, E.P., Hanson, R. A., Jones, W. R., Mohr T. W. Cartridge
bearing system for space applications. In: Proceedings of the 33rd
aerospace mechanisms symposium. NASA conference publication, vol.
209259, 1999, 137–43.
Loewenthal, S. H., Scibbe, H. W., Parker, R. J., Zaretsky, E. V.
“Operating Characteristics of a 0.87 kW-hr Flywheel Energy Storage
Module”. NASA Technical Memorandum 87038, August 1985.
Marchetti, M., Jones, W. R. Jr., Pepper, S. V., Jansen, M. J., Predmore,
R. E. “In-Situ, On-Demand Lubrication System for Space
Mechanisms”. Tribology Transactions, Vol. 46, Issue 3, 2003, 452-459.
Marchetti, M., Meurisse, M. H., Vergne, P., Sicreb, J., Durand, M.
“Analysis of oil supply phenomena by sintered porous reservoirs”.
Tribology Letters Vol. 10, No. 3, 2001, 163-170.
Sathyan, K, Hsu, H.Y., Lee, S.H, Gopinath. K. Long-term lubrication
of momentum wheels used in spacecrafts—An overview. Tribology
International, 43, 2010, 259–267.
CONCLUSION
Tribological failures of spacecraft mechanical systems are often single
point failures affecting entire mission. In many high speed moving
mechanical systems failures occur mainly due to insufficient supply of
lubricant. Currently, missions are planned to last for decades as
opposed to the short missions of the past. Therefore, providing
uninterrupted lubrication of these systems is a challenging task before
the tribologists. To help tribologists in their design, an account of
different types of lubrication system currently used in the space
industry is presented. The centrifugal lubricator-a passive type
lubricator, and the command lubrication system – an active type
lubricator, presented here are two promising candidates for lubrication
systems of the future long-term spacecrafts.
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