A fundamental limitation for using fiber reinforced polymer composites in fabrication of reflective mirror substrates for space telescopes is the fiber print through phenomenon. Because of fiber print through, the typical surface roughness of composite substrates is orders of magnitude higher than what's required for IR and visible optics. This paper presents and demonstrates a new approach to overcome this inherent problem with composites, thus allowing these materials to be considered for mirrors operating in the IR and possibly the visible range of the electromagnetic spectrum.
Surface plates and blocking tools are commonly made of granite because of its good stability. But how stable is the granite, and which type of material is optimal? We have explored several materials and manufacturing processes for a 4-m aspheric reference surface that would serve as a tool for laying up composite optics. In this paper, we discuss the materials selection, stability to thermal and moisture effects, and parameters for processing the surface to give sub-micron accuracy and stability.
In the light of the recent successes in utilizing CFRP composites for fabrication of ultra-lightweight, micron- accuracy reflectors for space telescopes, this paper provides a recent assessment of the main factors influencing dimensional stability of composites. Two recent examples of all-composites reflector designs that demonstrate the validity of the composites choice for this type of space applications are presented.
The Far Infrared and Submillimeter Telescope (FIRST), is an ESA cornerstone mission, that will be used for photometry, imaging and spectroscopy in the 80 to 670 micrometer range. NASA, through the Jet Propulsion Laboratory (JPL), will be contributing the telescope and its design to ESA. This paper will discuss the work being done by JPL and Composite Optics, Incorporated (COI), the developer of the primary mirror technology. Optical and mechanical constraints for the telescope have been defined by ESA and evolved from their trade studies. Design drivers are wave front error (10 micrometer rms with a goal of 6 micrometer rms), mass (260 kg), primary mirror diameter (3.5 m) and f number (f/0.5), and the operational temperature (less than 90 K). In response to these requirements a low mass, low coefficient of thermal expansion (CTE) telescope has been designed using carbon fiber reinforced polymer (CFRP). This paper will first present background on the JPL/COI CFRP mirror development efforts. After selection of the material, the next two steps, that are being done in parallel, are to demonstrate that a large CFRP mirror could meet the requirements and to detail the optical, thermal and mechanical design of the telescope.