Silicon carbide telescopes for space based lasercom

A key component of space based lasercom terminals for earth-orbiting and deep space applications is the transmitter/receiver telescope. This paper describes the results of two lasercom transceiver telescopes designed and fabricated as technology demonstrations for the Jet Propulsion Laboratory. Both telescopes employ a variety of silicon carbide (SiC) technologies to address the specific stressing requirements of next-generation space-based lasercom telescope., Such telescopes require 20-30 cm apertures, afocal designs of 10-20X magnification, multiple channels for transmit and receive, and near-diffraction limited visible optical performance. They must have excellent stray light rejection to allow operation when the sun or other bright object is near the field of view, and they must maintain optical performance in the presence of harsh thermal conditions, including sun-in-the-aperture. Finally, next generation lasercom telescopes must be light weight and low cost if they are to replace traditional deep-space up- and down-links or be financially viable for commercial earth orbiting communication. SSG has employed a variety of SiC technologies to address these design challenges in the fabrication of two 30 cm aperture demonstration telescopes. Light weight, visible-level thermally stable mirrors have been fabricated in both hot pressed and castable forms of silicon carbide. Composite SiC in various forms has been employed to reduce structure weight and create passively athermal systems. Silicon clad surfaces have allowed ease of fabrication and finish. Thermal testing has demonstrated stability over temperature, and vibration testing is also planned for the second telescope.