No abstract

The top-level requirement of the LISA Pathfinder mission is the verification of pure relative free fall between two test masses with an accuracy of about 3 × 10 −14 m s −2 Hz −1/2 in a measurement bandwidth between 1 mHz and 30 mHz. The drag-free control system is one of the key technology elements that shall be verified. Its design is strongly connected to the overall system and experimental design, in particular, via the following issues: the differential test mass motion and thus the science measurements depend on the control system; design constraints, such as negative stiffness of test masses and electrostatic actuation cross-talk, have an impact on science and control system performance; derived requirements for control system components, in particular, the micropropulsion system, must be within reasonable and feasible limits. In this paper, the control design approach is outlined and the system-related issues are addressed.

No abstract

LISA, the Laser Interferometer Space Antenna, will be launched by NASA and ESA in the 2014 timeframe and will be the first gravitational wave observatory for the many fascinating sources at low frequencies (down to 10 −5 Hz). One of the challenges is to perform precision laser interferometry over a distance of 5 million km. This paper describes recent developments in the interferometer design.

Future drag-free missions for space-based experiments in gravitational physics require a Gravitational Reference Sensor with extremely demanding sensing and disturbance reduction requirements. A configuration with two cubical sensors is the current baseline for the Laser Interferometer Space Antenna (LISA) and has reached a high level of maturity. Nevertheless, several promising concepts have been proposed with potential applications beyond LISA and are currently investigated at HEPL, Stanford, and EADS Astrium, Germany. The general motivation is to exploit the possibility of achieving improved disturbance reduction, and ultimately understand how low acceleration noise can be pushed with a realistic design for future mission. In this paper, we discuss disturbance reduction requirements for LISA and beyond, describe four different payload concepts, compare expected strain sensitivities in the "low-frequency" region of the frequency spectrum, dominated by acceleration noise, and ultimately discuss advantages and disadvantages of each of those concepts in achieving disturbance reduction for space-based detectors beyond LISA.