Design considerations for composite materials used in the Mars Observer Camera

Abstract

The Mars Observer Camera (MOC) is one of several instruments aboard the Mars Observer Spacecraft, which is scheduled to launch in September 1992, and begin monitoring the Martian surface (from Martian orbit) in December 1993. The MOC is the only instrument, however, that will record visual images of the surfe of Mars. The MOC comprises three separate optical systems: the Narrow-Angle system, for relaying high-resolution images of the Martian surface to Earth; the Red Wide-Angle system, for relaying limb-to-limb images in the 575 to 625 nanometer spectral range; and the Blue Wide-Angle system, for relaying limb-to-limb images in the 400 to 450 nanometer spectral range. The Mars Observer Project is conducted by the Jet Propulsion Laboratory (JPL), while the MOC experiment is conducted by the Arizona State University (ASU). Responsibility for the MOC instrument design, fabrication, integration, and test lies with the California Institute of Technology (Caltech). Perkin-Elmerts Applied Optics Operations (now OCA Applied Optics) and Composite Optics' involvement in the MOC program began in Iate-1986 when Caltech awarded this team a contact to fabricate the MOC Engineering Model and, later, two Right Models (one being a spare) based on the novel approach of utilizing graphite/epoxy composites for a majority of the MOC structure to achieve minimum weight. Since a majority of the structure is made of graphite/epoxy, including the sensitive metering structure between the pnmary and secondary mirrors of the Narrow-Angle system, charterizing the MOC structure became mandatory. Major concerns during the design of the MOC were not only structural integrity (designing the MOC such that its lightweight strucwre would withstand the shock and vibration of launch) and thermal stability (maintaining focus during the extreme thermal environment in Martian orbit), but also hygroscopic issues (paphite/epoxy absorbs atmospheric moisture and expands, causing defocus). This paper also briefly addresses the methods employed to reduce stray light from the walls of the graphite/epoxy structure.