424. A Bifilar Moment of Inertia Facility

Paper

Abstract

Most mass measurement facilities perform single functions. However, a facility for performing multiple mass properties measurements of rigid bodies, such as spacecraft components and/or assemblies weighing up to 1,000 pounds, is in operation at the NASA – Goddard Space Flight Center. It provides measurements of weight, center of gravity, moment of inertia, and product of inertia in a completely self-contained facility. Weight measurement is provided by a calibrated load cell mounted in the support system; center of gravity, by load cells’ arranged to determine the mechanical moment required to balance the weight moment of the test item: moment of inertia, through application of the bifilar pendulum; and product of inertia, by means of dynamic recording of force moments developed in torsional oscillation. A view into the background of spacecraft mass measurements at Goddard Space Flight Center is discussed. The advent of the second generation or observatory type scientific spacecraft pointed to the need for larger capacity and more accurate mass measurement facilities.. This need led to consideration of a multiple mass measuring facility instead of individual facilities for the separate operations. The development history of the facility is discussed, including problems encountered and their solutions. The historical treatment begins with the design specification and runs through the proposal, contractor’s development, installation, modifications, acceptance, and operational experience. A description of the facility is given with a functional discussion of the major components and assemblies. Built-in handling and maintenance aids are described. A test sequence for a typical sample spacecraft is described. Use of data sheets for recording test measurements is described, and the derivation of constants used in the data sheets is shown.