Launch Load Resistant Spacecra ft Mechanism Bearings Made From NiTi Superelastic Intermetallic Materials Christopher DellaCorte*and Lewis E. Moore III** Abstract Compared to conventional bearing materials (tool steel and ceramics), emerging Superelastic Intermetallic Materials (SIMs), such as 60NiTi, have significantly lower elastic modulus and enhanced strain capability. They are also immune to atmospheric corrosion (rusting). This offers the potential for increased resilience and superior ability to withstand static indentation load without damage. In this paper, the static load capacity of hardened 60NiTi 50-mm-bore ball bearing races are measured to correlate  existing flat-plate indentation load capacity data to an actual bearing geometry through the Hertz stress  relations. The results confirmed the validity of using the Hertz stress relations to model 60NiTi contacts;60NiTi exhibits a static stress capability (~3.1 GPa) between that of 440C (2.4 GPa) and REX20(3.8 GPa) tool steel. When the reduced modulus and extended strain capability are taken into account,  60NiTi is shown to withstand higher loads than other bearing materials. To quantify this effect, a notional space mechanism, a 5-kg mass reaction wheel, was modeled with respect to launch load capability when  supported on standard (catalogue geometry) design 440C; 60NiTi and REX20 tool steel bearings. For this  application, the use of REX20 bearings increased the static load capability of the mechanism by a factor  of three while the use of 60NiTi bearings resulted in an order of magnitude improvement compared to the  baseline 440C stainless steel bearings. Introduction Spacecraft experience violent (shaking) and sustained (acceleration) inertial forces during launch  because of the unsteady combustion provided by rocket propulsion systems (Ref. 1). Though each different launch vehicle presents a different vibration signature to its cargo, the launch load environments  share certain characteristics. The launch loads are made up of a fairly steady average acceleration load of 3 to 6 g’s plus a dynamic load that varies from 3 g’s to over 9 g’s depending upon whether the rocket utilizes solid propellants, liquid propellants, or a combination of the two. In addition, spacecraft  mechanisms often must endure additional shock-type loads during deployment where the sudden release  of spring energy and the use of pyrotechnic charges are encountered. Such high environmental loads can lead to structural damage and payload damage, especially for  delicate hardware. In response to these challenges, the space launch community has developed detailed design guidelines and testing protocols to mitigate negative outcomes (Ref. 1). One approach is to add  design margin to flight hardware so that the damage load threshold is well above expected launch loads. This tends to add weight and expense. Another approach is to provide isolation of sensitive mechanisms  to shield them from the launch environment. Such isolation systems can themselves be heavy and costly.In most instances, a combination of both approaches is used. Clearly, the development of more  intrinsically robust mechanisms offers a path to ameliorate this issue. Inside space mechanisms, the contacts between balls and races in ball bearings are a primary  vulnerability for launch load damage. Spacecraft mechanisms rely on ball bearings for smooth and low friction operation of a wide array of systems such as deployment mechanisms, pointing gimbals and flywheels used in gyroscopes and reaction wheels. If a bearing raceway surface is dented by a static  *NASA Glenn Research Center, Cleveland, OH  **NASA Marshall Space Flight Center, Huntsville, AL /g51/g85/g82/g70/g72/g72/g71/g76/g81/g74/g86/g3/g82/g73/g3/g87/g75/g72/g3/g23/g21/g81/g71/g3/g36/g72/g85/g82/g86/g83/g68/g70/g72/g3/g48/g72/g70/g75/g68/g81/g76/g86/g80/g86/g3/g54/g92/g80/g83/g82/g86/g76/g88/g80/g15/g3/g49/g36/g54/g36/g3/g42/g82/g71/g71/g68/g85 /g71/g3/g54/g83/g68/g70/g72/g3/g41/g79/g76/g74/g75/g87/g3/g38/g72/g81/g87/g72/g85/g15/g3/g48/g68/g92/g3/g20/g23/g16/g20/g25/g15/g3/g21/g19/g20/g23/g3 73