First, the data from the three spacecraft with their independent free-running clocks must be synchronized to nanosecond accuracy based on the ranging timestamps, and the interspacecraft distances must be extracted simultaneously. We have begun to develop optimal filters for this purpose, which are similar to Kalman filters but non-standard because the real time of a raw measurement is not known a priori but instead contaminated by the clock offsets which are in turn part of the unknown state vector. Next in the processing chain is the well-established technique of time-delay interferometry (TDI). All existing publications are based on an outdated LISA layout and are oversimplified in some aspects like the absolute ordering of frequencies. We have begun to rewrite the equations for more realistic scenarios and will perform numerical simulations for verification.
The demonstration of offset phase locking with sub-nW power levels and a study of an alternative LTP-like frequency stabilization scheme as fallback option for LISA is also part of our research. The largest project here is the testing of a complete breadboard of the LISA optical bench, for which we have a contract with ESA as part of a team with Astrium, Glasgow and TNO. Our role is to build the test equipment and perform the tests.