Design and fabrication of a lightweight 2-m telescope for the balloon-borne large-aperture submillimeter telescope: BLAST

Abstract

ABSTRACT Balloon borne instruments offer opportunities for astronomical observation in an environment that is superior to manyground observatories and less expensive than space borne observatories. BLAST is an infrared astronomical telescopethat will use a high altitude balloon as an observation platform. The BLAST telescope has a unique set of requirements:lightweight, low cost, zenith to horizon pointing, 10 arc-second pointing accuracy, high Strehl ratio far infrared/sub-milllimeter observation. The design of the BLAST telescope takes advantage of a pre-existing 2-m experimentallightweight carbon fiber mirror. Using this spherical primary, an aspheric secondary was designed to produce adiffraction limited telescope at 250 microns. The telescope metering structure was designed and fabricated using highstiffness, low mass, thermally stable carbon fiber. The secondary mirror was aggressively lightweighted and fabricatedusing state of the art diamond turning technology. Design was verified prior to manufacturing using finite elementstructural analyses in order to demonstrate compliance with the deflection requirements of the secondary mirror whenpointing zenith and near horizon. This paper will review the optical and opto-mechanical design, fabrication, integrationand alignment of the BLAST telescope.Keywords: infrared astronomy, carbon fiber composite, balloon borne telescope, lightweight mirror