60 During a recent ESA-f unded research program, the PFPE oil Fo mblin Z60 was highlighted as having  exceedingly low vapor pressure, with predicted oil loss by evaporation approximately three orders of  magnitude lower than that of Fomblin Z25 at room  temperature [1]. Subsequent bearing testing at ESTL  found the oil displayed similar lifetimes to those observed with Z25 bearings [2]. Friction coefficients were  demonstrated in the range 0.1 – 0.15, with the Z60 di splaying slightly higher torque, consistent with the  higher viscosity of this oil. During the work described in this paper, a detailed study of these oils was carried out to assess their comparative friction and lifetimes under differing conditions.  In addition to oils, this work program investigated  the performance of space-based grease lubricants,  focusing upon the MAPLUB grease range. The MAPLUB range provides a series of high performance  greases for space applications, developed in co llaboration with CNES (Centre National d'Etudes  Spatiales). These greases are available under a range of formulations, and are described using a 5-digit reference, e.g. PF100. Grease consistency depends upon both thickener and base oil, and is related to the grease’s deformation by an applied force.  • The two letters indicate the base oil  o PF for Perfluroropolyalkylether oil (Fomblin Z25)  o SH for Synthetic Hydrocarbon oil (NYE 2001A)  • The first two figures correspond to the grease consistency  o 10 for low consistency  o 05 for very low consistency  • The final figure specifies the type of additive filler  o 0 for PTFE only  o 1 for PTFE and molybdenum disulphide (MoS 2)   Due to a change in laws regarding CFC products, the formulation of these greas es has recently changed,  resulting in a change in product index (e.g. PF100-a changed to PF100-b). For the old (-a) greases, the PTFE was procured as a powder suspended in a solvent, whilst in the new (-b) formulation the PTFE is  procured as a dry powder [3]. It cannot be assumed t hat the performance of t hese new greases can be  extrapolated from the performance of the old, and thus a comparison study was required. The remaining  greases tested included Castrol Braycote 601EF, Braycote 601EF Micronic, and NYE Rheolube 2000.  The Braycote greases consist of Brayco 815Z oil suspended within a PTFE thickener, and have strong  heritage within the space industry. The Micronic  designation indicates the grease has been extruded  through a screen pack filter to remove PTFE parti cles larger than one micron. NYE Rheolube 2000 is a  sodium complex-soap-thickened, medium-visco sity MAC grease based upon the oil NYE 2001.    In addition, two commonly used solid lubricants were included within this study. The selected lubricants were sputtered MoS 2, and lead, applied as a thin film. Between them, these two lubricants account for a  large majority of solid lubrication for space and have a heritage of succ essful applications.   Scope of work

This paper covers the friction and lifetime performanc e of the space lubricants listed in Table 1 under  vacuum, assessed with a Spiral Orbit Tribometer.   Table 1. Lubricants covered within the scope of this work  Lubricant State Base Oil  Fomblin Z25 Oil --  Fomblin Z60 Oil --  NYE 2001 (with additives) Oil --  NYE 2001A (without additives) Oil --  MAPLUB PF100-a Grease Fomblin Z25  MAPLUB PF100-b Grease Fomblin Z25  MAPLUB PF101-a Grease Fomblin Z25  MAPLUB PF101-b Grease Fomblin Z25  NASA/CP-2010-216272