and speed testing have demonstrably met and exceeded life requirements in flight, with outlier units  completing lifetime >3 billion revs [31] suggests the approach may not only have been pragmatic for a  schedule requiring full development of spacecraft from contract to flight in ~27 months, but entirely  appropriate.  In summary we could state that whilst at component level the relationship between contact stress and life  is beginning to become clearer, to reduce the spread of results (in the above curve experimental results  may be a factor 10 higher or lower than predicted by the curve) more controlled tests are needed.   New Analysis and Measurement Techniques  Given the number of complexities and considerations applicable to the accelerated testing of fluid and solid  lubricated bearings, it is desirable to classify these considerations as likely to be of first or second order  significance such that in test definition first order effects would be accurately addressed, whereas  compromises could perhaps be made concerning full representativity for second order effects without  invalidating the whole test. In this respect, the use of quite sophisticated test techniques at component level  might inform mechanism/instrument level accelerated tests (in which inevitably the quality of data which  can be obtained may be relatively low).   In order to develop further the understanding of fluid, solid or self-lubricating lubricated bearings an  enhanced Advanced Bearing Test Rig (ABTR) facility has been developed (which traces its conceptual  heritage to the work of Ward [32]. This new bearing test rig enables simultaneous direct measurement of  lubricant film thickness, torque, preload, inner/outer ring electrical resistance and local temperature. The  bearing system used is compliantly preloaded (allowing compliance to be a test variable) and the lubricant  film thickness is determined by measurement of shaft motion from an on-axis high sensitivity capacitance  displacement transducer.   Measurements derived from this kind of setup include:  •Lubricating film thickness or torque evolution vs. speed or test duration (in time or frequency domain) •Improved bearing level understanding of solid-lubricated bearing performance – e.g. PVD film life, onset of transfer-film dominated behavior, effect of run-in, speed or environment on subsequent lubricant film behavior •Effect of preload compliance on lubricant performance •Cage stability (presence of cage whirl frequency in the FFT of torque) First data, presented below, relates to a Type 7004 bearing with preload 48 N (~820/707 MPa peak Hertz  stress at inner and outer raceway contacts), compliantly preloaded using a spring (compliance 1.7E-4 m/N).  All testing is in vacuum (<1E-5 mbar). In Figure 17 we show the mean torque and film thickness evolution  for a bearing lubricated only by transfer film formation from its PGM-HT cage (i.e. a self-lubricating bearing  without MoS 2 applied to balls or races initially). From this it can be seen that after an initially high peak,  some millions of revolutions are required for the torque and film thickness to become quasi-stable. If we  follow the evolution of this behavior further into the operational life of the bearing, we see that there are  periods of high and low torque which seem to be accompanied by increased PGM-HT film thickness.  Statistically the two parameters film thickness and torque are closely and positively correlated with a  coefficient of 0.83. The peak film thickness reached during run-in is around 2.5 µm (which correlates to the  1-3 µm transfer films found in the SOT trials above), however the mean film thickness seems to be around 0.5 µm when the bearing is stationary. It is also notable that the mean torque observed is a little higher than calculated, even assuming a friction coefficient, µ=0.4. This may be due to the relatively low preload used (hence perhaps not all balls are fully loaded as assumed in the bearing model), or to local changes in ball/raceway conformity due to the presence of the transfer film. NASA/CP—2018-219887 524