Experimental characterization of deployable outer barrel assemblies for large space telescopes

Several variations of large space-based observatories have been hypothesized using different approaches to deploying the primary and secondary mirrors on orbit. Careful consideration must also be given to the design and implementation of the shield that protects these observatories from thermal extremes, micro-debris, and controls stray light entry into the optical train. One approach to the shield architecture is use of an Optical Barrel Assembly (OBA), such as that used on the Hubble Space Telescope (HST). For space telescopes much larger than the HST, an OBA will need to be deployed or assembled to form an adequately large structure to fully shield both the primary mirror and secondary mirror. This paper describes the design, prototyping, characterization tests, and test results from two different OBA development efforts. The first design is a combined barrel and secondary mirror support structure. This system was designed for a fixed primary mirror and deploys straight upward along the optical axis, carrying the Secondary Mirror Assembly (SMA) with it. The second OBA design is of a structurally independent OBA that deploys out from behind the Primary Mirror Assembly (PMA) (itself deployed or assembled) and extends forward along the optical axis to completely enclose the optical train, pulling along the shroud material. Examples of both systems were built out of prototype materials, tested, and the test results were compared against modeled predictions of system performance. The designs, test procedures, and test results are presented along with recommendations for future work.