Sub-Femto-gFree Fall for Space-Based Gravitational Wave Observatories: LISA Pathfinder Results

Abstract

We report the first results of the LISA Pathfinder in-flight experiment. The results demonstrate that two free-falling reference test masses, such as those needed for a space-based gravitational wave observatory like LISA, can be put in free fall with a relative acceleration noise with a square root of the power spectral density of 5.2±0.1 fm s^{-2}/sqrt[Hz], or (0.54±0.01)×10^{-15} g/sqrt[Hz], with g the standard gravity, for frequencies between 0.7 and 20 mHz. This value is lower than the LISA Pathfinder requirement by more than a factor 5 and within a factor 1.25 of the requirement for the LISA mission, and is compatible with Brownian noise from viscous damping due to the residual gas surrounding the test masses. Above 60 mHz the acceleration noise is dominated by interferometer displacement readout noise at a level of (34.8±0.3) fm/sqrt[Hz], about 2 orders of magnitude better than requirements. At f≤0.5 mHz we observe a low-frequency tail that stays below 12 fm s^{-2}/sqrt[Hz] down to 0.1 mHz. This performance would allow for a space-based gravitational wave observatory with a sensitivity close to what was originally foreseen for LISA.

Gravitational wave detection with optical lattice atomic clocks

“…In each satellite the lattice confining the clock atoms is created using the standing wave formed by retroreflecting a magic wavelength laser [11][12][13] off of a mirror mounted on a free-floating reference mass, such that the atoms are strongly confined in the reference frame of the free mass and are therefore in free fall, despite their confinement. Drag-free masses have been studied in great detail by the LISA collaboration, and this technology is currently undergoing testing and verification in the LISA Pathfinder space mission [42,43]. The phase of the clock lasers in each satellite is kept referenced to the same mirror using interferometry [44] to cancel out any relative motion of the lasers or optics with respect to the atoms.…”

“…This noise has been carefully analyzed by the LISA collaboration [18,19,42,43], and a 1=f 2 scaling of the sensitivity is anticipated up to a frequency cutoff of ∼3 mHz. Our detector experiences the same acceleration noise, resulting in the same scaling of the signal-to-noise ratio.…”

Capacitive sensing of test mass motion with nanometer precision over millimeter-wide sensing gaps for space-borne gravitational reference sensors

“…Capacitive sensing, often in combination with optical metrology [1][2][3], is used to provide the reference signals for the drag-free control system of a spacecraft [1][2][3][4][5]7]. In this paper we report on the performance of the capacitive sensing system on board the LISA Pathfinder spacecraft.…”

“…Capacitive sensing is an established technique for the measurement of test mass (TM) motion in high precision space-borne experiments for the detection of gravitational waves [1][2][3], tests of the equivalent principle [4][5][6] and measurements of relativistic effects on precessing gyroscopes [7]. Capacitive sensing, often in combination with optical metrology [1][2][3], is used to provide the reference signals for the drag-free control system of a spacecraft [1][2][3][4][5]7].…”

“…LISA Pathfinder [1,2,8,9] (LPF) is an European Space Agency mission dedicated to the demonstration of free-fall of a TM to the level required for the implementation of the future space-borne gravitational wave (GW) observatory, LISA [3] (Laser Interferometer Space Antenna). Moving to space is advantageous for a GW observatory as there is no seismic gravitational noise that limits the low frequency sensitivity of the ground based GW observatories.…”