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Temperature fluctuations are expected to be one of the limiting factors for gravitational-wave detectors in the very-low-frequency range. Here we report the characterization of this noise source in the LISA Pathfinder optical bench and propose a method to remove its contribution from the data. Our results show that temperature fluctuations are indeed limiting our measurement below one millihertz, and that their subtraction leads to a factor 5.6 (15 dB) reduction in the noise level at the lower end of the LISA measurement band (10-4 Hz), which increases to 20.2 (26 dB) at even lower frequencies, i.e., 1.5 X 10-5 Hz. The method presented here can be applied to the subtraction of other noise sources in gravitational-wave detectors in the general situation where multiple sensors are used to characterize the noise source. [ABSTRACT FROM AUTHOR]

Thermal conditions in the LTP, the LISA Technology Package, are required to be very stable, and in such environments precision temperature measurements are also required for various diagnostics objectives. A sensitive temperature gauging system for the LTP is being developed at IEEC, which includes a set of thermistors and associated electronics. In this paper, we discuss the derived requirements applying to the temperature sensing system, and address the problem of how to create in the laboratory a thermally quiet environment, suitable for performing meaningful on-ground tests of the system. The concept is a two-layer spherical body, with a central aluminium core for sensor implantation surrounded by a layer of polyurethane. We construct the insulator transfer function, which relates the temperature at the core to the laboratory ambient temperature, and evaluate the losses caused by heat leakage through connecting wires. The results of the analysis indicate that, in spite of the very demanding stability conditions, a sphere of outer diameter of the order 1 m is sufficient. We provide experimental evidence confirming the model predictions.

This is a short note reporting on the current state of development of the temperature sensors which are part of the LTP Diagnostics Subsystem on board the LISA Pathfinder mission (LPF). A thermal insulator has been designed which ensures sufficient stability of a set of eight NTC sensors (negative temperature coefficient of resistance or thermistors), and the front-end electronics has also been designed and manufactured. Tests have been performed which nearly approach the goal of a global stability of 10?5K Hz?1/2.

We report on the development of the LISA Technology Package (LTP) experiment that will fly onboard the LISA Pathfinder mission of the European Space Agency in 2008. We first summarize the science rationale of the experiment aimed at showing the operational feasibility of the so-called transverse-traceless coordinate frame within the accuracy needed for LISA. We then show briefly the basic features of the instrument and we finally discuss its projected sensitivity and the extrapolation of its results to LISA.

LISA is the upcoming space-based gravitational-wave detector. LISA Pathfinder, to be launched in the coming years, will be the in-flight test of the LISA arm, with a hardware (control scheme, sensors, and actuators) identical in design to LISA. LISA Pathfinder will collect a picture of all noise disturbances possibly affecting LISA, achieving the unprecedented pureness of geodesic motion of test masses necessary for the detection of gravitational waves. The first steps of both missions will crucially depend on a very precise calibration of the key system parameters. Moreover, robust parameters estimation has a fundamental importance in the correct assessment of the residual acceleration noise between the test masses, an essential part of the data preprocessing for LISA. In this paper, we present a maximum likelihood parameter estimation technique in time domain employed for system identification, being devised for this calibration, and show its proficiency on simulated data and validation through Monte Carlo realizations of independent noise runs. We discuss its robustness to nonstandard scenarios possibly arising during the real mission. Furthermore, we apply the same technique to data produced in missionlike fashion during operational exercises with a realistic simulator provided by European Space Agency. The result of the investigation is that parameter estimation is mandatory to avoid systematic errors in the estimated differential acceleration noise. [ABSTRACT FROM AUTHOR]