Development and Wear Evaluation of Titanium Spacesuit Bearings

Legacy EVA spacesuit designs have used stainless steel as a bearing material, which has proved to be a durable, but not optimal solution. Incorporating titanium bearings into the Z-2 Prototype Planetary Extravehicular Space Suit reduced mass by an estimated 23 lbs per suit system, without compromising the suit’s functionality. Testing conducted in 2014 proved that even in worst case conditions, Titanium bearings in the oxygen-rich environment of the suit did not pose an ignition hazard. Research conducted in 2016, and presented in the paper ICES-2016-60 “Development and Evaluation of Titanium Spacesuit Bearings”, has determined stress limits for titanium that allow satisfaction of the cycle life requirements of an exploration mission. In order to use these stress limits to create safe bearing designs, an analytical process must be developed to predict the contact pressures that exist in real spacesuit bearing races.

As a main load-carrying component of the suit, bearings must be capable of withstanding high loads arising from internal suit pressure and occupant motions. A majority of this loading is carried by axial restraint lines attached to the bearing races. These localized loads acting on the bearing races cause an uneven stress distribution amongst the bearing balls. Maximum stresses become even more difficult to predict as the bearing rotates and load paths misalign, causing stresses to redistribute. Localized point contact phenomena between the ball and bearing groove is too complex to model, so a means to take physical measurements using sensor film of race forces and link that information to FEA was developed. After the analysis was completed, new bearing designs were developed and the designs were cycle tested on specialized test machinery. The development of this analytical tool and testing method can be used to optimize future spaceflight and commercial bearing designs.