Bearing sphere for SOFIA telescope: a challenge for design and manufacturing

Supporting the Telescope structure is done via a Bearing Sphere in a Hydraulic bearing which is part of the SOFIA Suspension system. Frictionless bearing requires a sphere with varying stiffness in defined directions and a smooth and wear resistant surface giving also corrosion resistance against humidity and hydraulic fluid. Weight restrictions and through penetration by the Nasmyth Tube required a highly sophisticated design and manufacturing techniques. The 1.2 m sphere is cast from nodular cast iron, machined and coated by electrodeposition with a sulfamate nickel coating on the outer bearing sphere surfaces. The sphere represents a one of a kind construction unique in stiffness to mass ratio. The design as well as manufacturing philosophy of the sphere are presented.