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  • 1
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    Cartridge Bearing System for Space Applications (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Conventional spin axis ball bearings have been unreliable in spacecraft, often failing by two heretofore uncontrolled processes: ball retainer instability and lubricant breakdown. The Space Cartridge Bearing System (SCBS) addresses each of these mechanisms directly, leading to a bearing system with absolute freedom from retainer instability and negligible lubricant degradation rate. The result is a reliable plug-in bearing cartridge with a definite design life.
    Keywords: Mechanical Engineering
    Type: 33rd Aerospace Mechanisms Symposium; 137-143; NASA/CP-1998-209259
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Spiral Orbit Tribometry I: Description of the Tribometer (2002)
    In:  CASI
    Details
    Publication Date: 2014-05-10
    Description: A new rolling contact tribometer based on a planar thrust bearing geometry is described. The bearing 'races' are flat plates that drive a ball into a near-circular, spiral path. The spiraling ball is returned to its initial radius each revolution around the race by a 'guide plate' backed by a force transducer. The motions of the ball are analyzed and the force exerted by the ball on the guide plate is related to the friction coefficient of the system. The experimental characteristics of the system are presented and the system is shown to exhibit the behavior expected for a tribometer.
    Keywords: Instrumentation and Photography
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Touchdown Ball-Bearing System for Magnetic Bearings (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: The torque-limited touchdown bearing system (TLTBS) is a backup mechanical-bearing system for a high-speed rotary machine in which the rotor shaft is supported by magnetic bearings in steady-state normal operation. The TLTBS provides ball-bearing support to augment or supplant the magnetic bearings during startup, shutdown, or failure of the magnetic bearings. The TLTBS also provides support in the presence of conditions (in particular, rotational acceleration) that make it difficult or impossible to control the magnetic bearings or in which the magnetic bearings are not strong enough (e.g., when the side load against the rotor exceeds the available lateral magnetic force).
    Keywords: Man/System Technology and Life Support
    Type: LEW-17282 , NASA Tech Briefs, April 2003; 21-22
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Spiral Orbit Tribometry (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: The coefficients of friction and relative degradation rates of three lubricants run in the boundary regime in vacuum are evaluated in a Spiral Orbit Tribometer. This tribometer subjected the lubricants to rolling contact conditions similar to those found in angular contact ball bearings. A multiply alkylated cyclopentane (MAC) hydrocarbon lubricant suffered degradation at a rate almost two orders of magnitude less than the degradation rate of two perfluoropolyalkylether (PFPE) lubricants.
    Keywords: Nonmetallic Materials
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    A New Apparatus to Evaluate Lubricants for Space Applications: The Spiral Orbit Tribometer (SOT) (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Lubricants used in space mechanisms must be thoroughly tested prior to their selection for critical applications. Traditionally, two types of tests have been used: accelerated and full-scale. Accelerated tests are rapid, economical, and provide useful information for gross screening of candidate lubricants. Although full-scale tests are more believable, because they mimic actual spacecraft conditions, they are expensive and time consuming. The spiral orbit tribometer compromises between the two extremes. It rapidly determines the rate of tribochemically induced lubricant consumption, which leads to finite test times, under realistic rolling/pivoting conditions that occur in angular contact bearings.
    Keywords: Nonmetallic Materials
    Type: NASA/TM-2000-209935 , NAS 1.15:209935 , E-12180 , 2000 Spring Fuels and Lubricants Meeting and Exposition; Jun 19, 2000 - Jun 22, 2000; Paris; France
    Format: application/pdf
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  • 6
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    Experimental Determination of Load Carrying Capacity of Point Contacts at Zero Entrainment Velocity (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: A capacitance technique was used to monitor the film thickness separating two steel balls of a unique tribometer while subjecting the ball-ball contact to highly stressed, zero entrainment velocity (ZEV) conditions. All tests were performed under a N2 purge (R.H. 〈 1.0%) and utilized 52100 steel balls (R(sub a) = 0.02 mm). Tribometer operations and capacitance-to-film-thickness accuracy were verified by comparing the film thickness approximations to established theoretical predictions for test conditions involving pure rolling. Pure rolling experiments were performed under maximum contact stresses and entrainment velocities of 1.0 GPa and 1.0 m/s to 3.0 m/s, respectively. All data from these baseline tests conformed to theory. ZEV tests were initiated after calibration of the tribometer and verification of film thickness approximation accuracy. Maximum contact stresses up to 0.57 GPa were supported at zero entrainment velocity with sliding speeds from 6.0 to 10.0 m/s for sustained amounts of time up to 28.8 minutes. The protective lubricating film separating the specimens at ZEV had a thickness between 0.10 and 0.14 mm (4 to 6 min), which corresponds to an approximate L-value of 4. The film thickness did not have a strong dependence upon variations of load or speed. Decreasing the sliding speed from 10.0 m/s to 1 m/s revealed a rapid loss in load support between 3.0 and 1.0 m/s. The formation of an immobile film formed by lubricant entrapment is discussed as an explanation of the load carrying capacity at these zero entrainment velocity conditions, relevant to the ball-ball contact application in retainerless ball bearings.
    Keywords: Fluid Mechanics and Heat Transfer
    Type: NASA/TM-1999-208848 , E- 11469 , NAS 1.15:208848
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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