MERLIN: design of an IPDA LIDAR instrument

The Methane Remote Sensing LIDAR Mission (MERLIN) is a joint French–German cooperation on the development, launch and operation of a climate monitoring satellite, executed by the French Space Agency CNES and the German DLR Space Administration. It is focused on global measurements of the spatial and temporal gradients of atmospheric methane (CH4) with a precision and accuracy sufficient to constrain methane fluxes significantly better than with the current observation network. Airbus Defence and Space GmbH was selected by the German DLR Space Administration as the industrial prime contractor for the mission phase C/D, to build the MERLIN Payload, which is the first realization of such an instrument for space. This presentation will concentrate on the architecture and the optical design of the MERLIN Payload, 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. 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. Further details of the instrument development status during the ongoing phase C will be shown by an overview of the current hardware and design status of the major subsystems.