Possible post-LISA science missions with gravitational reference sensors

Among the many interesting possibilities for types of future missions that would benefit strongly from LISA and LISA Pathfinder technology development, three will be discussed. They are in the fields of fundamental physics, Earth science, and gravitational wave astronomy. The first is a mission to measure the gravitational time delay due to the Sun from a spacecraft near the L-1 point of the Earth-Sun system. It would require gravitational reference sensors (GRSs) with roughly 10-13 [10-6 Hz/f] m/s2 /vHz performance at frequencies down to about 0.3 microHz. The second type of mission is future drag-free missions to measure time variations in the Earth s gravitational field. One example of such a mission will be described, with two satellites in the same polar orbit at about 300 km altitude. Changes in the roughly 50 km satellite separation would be measured with 10-14 or better accuracy, and spurious accelerations of the test masses in the GRS on each satellite would be the other main measurement accuracy limitation. The third mission is a possible moderately improved LISA follow-on mission aimed at being able to detect mergers of 10 solar mass black holes with IMBHs out to redshifts of about 10 in order to investigate the formation and growth of IMBHs in more detail than LISA will be able to achieve.