Robust optical design for optimal performance of the MERLIN lidar instrument

The optical design for the MERLIN instrument was driven by a concept which ensures reliable, high performance operation of the bi-static DIAL, consisting of separate transmitter (TX) and receiver paths (RX). The MERLIN satellite is a secondary passenger payload on the launcher. As such, the satellite places many constraints on the instrument, pertaining to the power, mass and volume allowable. The available resources force the MERLIN instrument to have passive thermal control while necessitating a very compact design due to the demanding envelope constraints. This creates a large operational temperature range with thermal gradients on the structure, requiring an extremely robust optical design in a compact envelope. Typically, a compact envelope requirement drives an optical design towards tight tolerances, which is in contradiction with a large operational temperature range. The robust optical design, for the RX- and TX-paths, employs several passive measures and an active pointing control for RX and TX co-alignment. These actions are necessary to ensure good instrument performance, despite the demanding environmental requirements. Presented here will be selected load case examples for the entire design and analysis chain, from the instrument performance model towards optical, structural and thermal design.