Alternative opto-mechanical architectures for the LISA instrument

As part of the on-going LISA Mission Formulation study under ESA contract, EADS Astrium has recently suggested and investigated a variety of novel LISA payload architectures utilizing so-called "In-Field Pointing" for accommodation of seasonal constellation dynamics. Here, the annual variation in the angle between the interferometer arms of roughly ±1° is compensated by steering the lines of sight of the individual telescopes with a small actuated mirror located in an intermediate pupil plane inside the telescopes. This introduces a certain flexibility for the overall payload configuration and allows for very compact designs. In particular, it enables a "single active proof mass" mode with a true cold redundancy between a nominal and a backup GRS system on board each spacecraft, and thus enhances mission robustness.