Optical telescope design for a space-based gravitational-wave mission

Space-based gravitational-wave observatories will systematically study the source-rich band of gravitational waves from 0.0001 Hz to 1 Hz. All current designs require propagation of a laser beam from one spacecraft to another over immense distances. An optical telescope is needed for efficient power delivery and its design is driven by the interferometric displacement sensitivity requirements. Here we describe the design for a catoptric telescope that meets those requirements, emphasizing differences from the usual specifications for high quality image formation, and discuss design trade-offs as well as early results from research into scattered light suppression and modeling that may enable alternative designs.