provides a compression of 21 ... 36 pm at ambient temperature and 2...17 pm at operating temperature of  120K.  Selection of Bearing Material  The selection of the bearing material had to consider the demanding mechanical and environmental loads.  Among the bearing materials, firstly the traditional bearing materials AIS1 521 00 and corrosion resistant  AIS1 440C were studied. It turned out early that these materials do not have the required corrosion  resistance for exposure to salt fog. A preliminary salt environment test showed severe signs of corrosion  as expected for the AIS1 521 00, but also, although less severe, for the AIS1 440C.  For this reason it was decided to use a better corrosion resistant bearing steel for the bearings of the  gimbal: Cronidur 30. This material is a FAG-proprietary bearing steel that combines excellent corrosion  resistance with high strength and durability [l]. A standard grade of Cronidur 30 was chosen that is also  used on cryogenic applications of the U.S. space shuttle program. The corrosion resistance of this  material was demonstrated in a salt spray test according to the Ariane standard salt spray test procedure  that has a duration of 4 days. No signs of corrosions were visible.  Selection of Bearing Lubricant  Liquid lubrication was not possible as the gimbal operates at cryogenic temperatures. After a pre-selection  among available dry lubricants the following candidates were identified: sputtered MoS2, sputtered Ag  (Silver), sputtered Pb (Lead), blasted WS2 (trade name "Dicronite DL-5"), TIC coating, or an uncoated  design.  An early development test showed that sputterevhlead by ESTL, UK was the suitable solution. The results  of the tribological tests were presented on the 37 Aerospace Mechanisms Symposium [3].  Design of the Bearing Support  The design of the bearing support was driven by stringent envelope constraints and demanding stiffness  specifications. To cope with the high radial loads on the bearings, it was desired to find a design that  allows for a maximized pitch size diameter of the needles. A bearing support consuming little space was  necessary and leads to an unconventional design solution for the bearing support:  0  0 an un-divided yoke design, that requires axial insertion of the press-fit mounted outer rings, and  thin walled outer bearing rings and yokes.  The bearing support consists of a circular bore in housing that has varying stiffness along its  circumference: It is thin walled at the lateral faces and it is rigid at the top and at the bottom of the bearing.  Compression fits are used for the bearings to allow a design consuming little space while being more rigid  than a conventional, separated housing clamped by bolts.  Firstly the unequal stiffness distribution causes circularity deviations caused by changing cutting forces  during machining. The weaker sections of the bearing support exhibit a larger diameter than the rigid  sections caused by elastic deformation during the turning and grinding operations. These circularity  deviations were measured to be 4.. .8 pm.  Secondly, as described above, the bearing outer rings are situated within the bearing support using a  compression fit. This compression fit causes radial load on the bearing support. This radial load deforms  the bearing support made of titanium alloy. Deformation is larger in areas of the weaker sections than in  the areas of the rigid sections. This circularity deviation, caused by elastic deformation was calculated by  FEM analysis with 8 pm.  The compression fit causes the outer bearing ring to follow these circularity deviations, so above two  reasons lead to a circularity deviation of the race of the integrated bearing outer ring that has to be  considered for the dimensioning of the bearing clearance.  273