Achieving geodetic motion for LISA test masses: ground testing results

Area of Science:

• Astrophysics
• Gravitational Wave Detection
• Space Mission Technology

Background:

• Space-based gravitational wave observatories require highly pure orbits for reference test masses.
• The Laser Interferometry Space Antenna (LISA) mission relies on precise test mass motion for low-frequency gravitational wave detection.
• Understanding and mitigating forces acting on test masses is critical for mission sensitivity.

Purpose of the Study:

• To investigate disturbing forces on a test mass within a LISA capacitive position sensor.
• To establish upper limits on sensor force noise contributions.
• To measure the sensor's electrostatic stiffness and detect stray biases.

Main Methods:

• Utilized a torsion pendulum with a torque noise floor below 10 fN m/sqrt(Hz) from 0.6 to 10 mHz.
• Performed detailed studies on forces affecting a test mass in a simulated LISA environment.
• Implemented methods for detecting and compensating electrostatic biases.

Main Results:

• Placed an upper limit on the contribution of sensor forces to test mass noise.
• Measured the electrostatic stiffness of the LISA capacitive position sensor with 5% accuracy.
• Successfully detected and compensated stray direct current (dc) electrostatic biases at the millivolt level.

Conclusions:

• The torsion pendulum study provides crucial data for understanding and minimizing noise sources in LISA.
• Accurate measurement of electrostatic stiffness and bias compensation are vital for achieving LISA's scientific goals.
• The findings contribute to ensuring the orbital purity necessary for low-frequency gravitational wave detection.