Variations in the LISA mission

Before the design of LISA is frozen, it is important to consider whether changes in the design or in the mission operations would bring scientific benefits. I suggest here three possible changes: improving the shot-noise-limited sensitivity by either employing more light or larger mirrors; changing the arm-length during the mission; and inserting a fourth spacecraft into one of the arms to produce two fully independent interferometers whose noise would not be correlated. One benefit of these changes would be to significantly improve LISA's sensitivity to a cosmological background of gravitational waves. They would get LISA to within a factor of ten of the energy density upper limit of simple inflation, and they would allow LISA to verify that the window between 0.1 and 1.0 Hz is quiet enough to use it for exploring the cosmological background.