Verification of Placement Precision and Stability for the GEMS Telescope Optical Boom

摘要

A new variant of the venerable Coilable boom has been designed, built, and tested to validate the challenging structural requirements of the GEMS X-Ray Polarimeter deployable focal length spacecraft observatory. Until its cancellation by NASA in mid-2012, the Gravity and Extreme Magnetism SMEX (GEMS) X-ray polarimeter mission, led by the Goddard Space Flight Center (GSFC) was built around this new boom design which, thanks to its compact stowage and low mass, enabled the use of a relatively affordable, small launch vehicle. The work performed to date has established a completed Flight design, refined and validated by ground testing of a flight-like Engineering Test Unit (ETU), which demonstrated extremely tight deployed placement repeatability. Over dozens of ground deployments, this ETU deployed its 45-kg optical payload simulator to the same position at 3.8 m of linear extension within a 0.025 mm standard deviation, in all translational degrees of freedom (DOFs). In addition to the hardware ground testing, detailed thermal-structural analysis was performed which predicted orbital thermal distortions (including eclipse) on the order of 0.1 mm in all translational DOFs, and 5 arcsec in all rotational DOFs.