Welcome to the 10th International LISA Symposium

GRACE Follow-On will replace the Gravity Recovery and Climate Experiment (GRACE) mission, which has been measuring Earth’s gravity field since 2002. Like GRACE, GRACE Follow-On will use a microwave link as its primary instrument to measure micron-level changes in the 200km separation of a pair of satellites in a following polar orbit. GRACE Follow-On will also include a 2-way laser-link, the Laser Ranging Interferometer (LRI), as a technology demonstrator package. The LRI is an NASA/German partnership and will demonstrate inter-spacecraft laser interferometry with a goal of 10 times better precision than the microwave instrument, or about 90 nm/rt(Hz) between 10 and 100 mHz. The similarities between the LRI and a single arm of Laser Interferometer Space Antenna (LISA) mean many of the required technologies will be the same. This talk will give an overview of the LRI and the status of the LRI instruments.

The Weak Equivalence Principle (WEP), which states the equality of the inertial and gravitational masses, is a cornerstone of General Relativity (GR). However, most theories beyond GR, such as modified gravitation theories that aim to explain the current acceleration of the Universe's expansion, or string theory-inspired theories that attempt to reconcile GR with Quantum Physics at small scale, predict a violation of the WEP in the range [1e-18, 1e-13]. The WEP being currently constrained at a few 1e-13, it is important to improve this limit so that new theories can be tested. MICROSCOPE is a French Space Agency funded mission that aims to test the WEP in space, down to an accuracy of 1e-15. It consists of a drag-free satellite which embarks two ultrasensitive electrostatic differential accelerometers. Each accelerometer is made up of two coaxial cylindrical proof masses whose motion is electrostatically constrained. In one (reference) accelerometer, the proof masses are made of the same material to demonstrate the experiment accuracy; they are made of different materials in the second accelerometer, which is used to test the WEP. The electric potential applied to keep the masses in equilibrium is a measure of the difference in the proof masses motion; hence, a non-zero applied potential is a measure of a WEP violation. The talk will present the scientific context and goals of the MICROSCOPE mission. Then the payload and the principle of the measurement will be described, before giving an update on the mission status.

To be submitted

Electrostatic inertial sensor has been employed for several space-based experiments to study spatial environments, map gravitational field of the Earth, and space gravitational experiments. Space electrostatic accelerometer or inertial sensor has been developed in our group since 2000 in order to push the space missions such as TISS (test of the Inversed-Square law in Space), TEPO (Test of Equivalence Principle in space with Optical readout), and the satellite gravity measurement. In this talk, we will give a report about the progress of the electrostatic accelerometer in our group, and measurement by three methods including high-voltage levitation, fiber suspension, and flight in space. A about 70g test mass is levitated by a high-voltage with output of about 900 V and frequency band larger than 11 kHz, and then six degree-of-freedom control strategy of the test mass are tested, and a sensitivity about 10-8 m/s2/Hz1/2 below 1 Hz, which is limited by the seismic noise in site. In order to directly verify the resolution and other performance of the inertial sensor, electrostatic controlled torsion pendulums, including one stage pendulum and two-stage pendulum, are developed. In this method, seismic noise effect is suppressed more than 80dB in low-frequency due to common-mode rejection, therefore, the electrostatic accelerometer or inertial sensor can be investigated at the level of 10-10m/s2/Hz1/2 and ever higher. Finally, an engineering accelerometer has been tested in flight in the end of 2013, and preliminary result in orbit is presented.