Science Case for LISA Pathfinder

1. Science Case for LISA Pathfinder Paul McNamara LISA Pathfinder Project Scientist 30th & 31st January 2007

2. Why LISA Pathfinder? • The science case for LISA is extremely compelling and has continually been highly ranked by independent review boards • However, both ESA and NASA believed that the risk was too high to fly LISA with an unproven measurement concept • LISA Pathfinder was instigated by ESA to test the concept of low-frequency gravitational wave detection • The LPF development has shown that the technologies required for LISA are difficult, but not impossible • LPF has already solved many of the challenges associated with low frequency gravitational wave detection With LISA Pathfinder, ESA paves the way for LISA and future fundamental physics missions

3. Foundations of General Relativity • The most basic assumption of General Relativity is that free-particles follow geodesics unless acted upon by an unbalanced force The definition of geodesics in Einstein’s “The Meaning of Relativity” • ALL missions aimed at demonstrating an aspect of GR rely on geodesics • LISA Pathfinder will be the first mission to demonstrate that free particles do indeed follow geodesics at such an unprecedented level • Requires that the free-particle is measured with respect to another free-particle!

4. Mission Concept

5. Science demonstrated with LPF • Geodesic motion of free particles • Pico-meter/nano radian laser metrology to free falling mirrors • Nano-metre three-body “formation flying” • 2nd TM and spacecraft servoed to follow primary TM (to better than 10pm/Hz and 2nm/Hz at 1mHz respectively) • Materials physics • Test mass magnetic properties • Patch field effects • Thermal effects • Precision modelling of cosmic ray charging • Correlate test mass charge with models and on-board particle detector

6. Goal of LPF • To put test mass into (almost) perfect free-fall • Spurious accelerations kept to less than • Current best “on-orbit” performance by GRACE: • LPF will demonstrate ~TWO orders of magnitude better performance than has been, or is currently planned to be (with the exception of LISA), demonstrated on-orbit! • MICROSCOPE should demonstrate ~10-12ms-2/Hz at 1mHz

7. Performance of LPF

8. Comparison of missions

9. LPF Legacy • The main output of LPF is the physics model of the free falling test mass and its environment • Model of the electromagnetic and gravitational interactions at play when dealing with extremely small forces and low acceleration levels • This physical model will be used to extrapolate to the parameter ranges relevant to a host of other missions • e.g. LISA, Pioneer Anomaly, SSI, etc • The models (updated with on-orbit data) are designed to be plugged into the spacecraft/environment simulators of future missions

10. Missions: Fundamental Physics [1] • LISA • LATOR (Cassini) • ASTROD • Microscope (FEEPS)

11. Future missions: Fundamental Physics [2] Probable submission to the Cosmic Vision AO (among others in FP): • GAUGE • Pioneer Anomaly? • Fundamental Physics Explorer

12. Missions: Earth Observation • GRACE (Launched 17/3/2002) • GOCE (Launch 2007) • SSI (GRACE/GOCE follow-on mission) • Re-use of LTP inertial sensor AND laser interferometry

13. Conclusions • LISA Pathfinder will be the first mission with the specific goal of demonstrating geodesic motion of a free-particle • LISA Pathfinder is the first step in the development of low frequency gravitational wave telescopes • The science and technology knowledge gained from LISA Pathfinder will be re-used in future missions • With the descope of the NASA provided DRS, the LTP is the ONLY inertial sensor planned to be flown, and gives Europe a significant lead in this and related fields. The LISA Pathfinder platform allows future fundamental physics missions to become reality More information on the Science Case for LPF can be found in: LISA Pathfinder: Einstein’s Geodesic Explorer [ESA-SCI(2007)1]

14. LTP on LPF