Super-ASTROD: probing primordial gravitational waves and mapping the outer solar system

Super-ASTROD ( Super Astrodynamical Space Test of Relativity using Optical Devices, or ASTROD III) is a mission concept with four spacecraft in 5 AU orbits together with an Earth-Sun L1/L2 spacecraft ranging optically with one another to probe primordial gravitational waves with frequencies 0.1 mu Hz-1 mHz, to test fundamental laws of spacetime and to map the outer-solar-system mass distribution and dynamics. In this paper we address its scientific goals, orbit and payload selection, and sensitivity to gravitational waves.