D. Hoyland

The LTP experiment on the LISA Pathfinder mission

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 Pathfinder: the experiment and the route to LISA

LISA Pathfinder (LPF) is a science and technology demonstrator planned by the European Space Agency in view of the LISA mission. As a scientific payload, the LISA Technology Package on board LPF will be the most precise geodesics explorer flown as of today, both in terms of displacement and acceleration sensitivity. The challenges embodied by LPF make it a unique mission, paving the way towards the space-borne detection of gravitational waves with LISA. This paper summarizes the basics of LPF, and the progress made in preparing its effective implementation in flight. We hereby give an overview of the experiment philosophy and assumptions to carry on the measurement. We report on the mission plan and hardware design advances and on the progress on detailing measurements and operations. Some light will be shed on the related data processing algorithms. In particular, we show how to single out the acceleration noise from the spacecraft motion perturbations, how to account for dynamical deformation parameters distorting the measurement reference and how to decouple the actuation noise via parabolic free flight.

Update on quadruple suspension design for Advanced LIGO

We describe the design of the suspension systems for the major optics for Advanced LIGO, the upgrade to LIGO—the Laser Interferometric Gravitational-Wave Observatory. The design is based on that used in GEO600—the German/UK interferometric gravitational wave detector, with further development to meet the more stringent noise requirements for Advanced LIGO. The test mass suspensions consist of a four-stage or quadruple pendulum for enhanced seismic isolation. To minimize suspension thermal noise, the final stage consists of a silica mirror, 40 kg in mass, suspended from another silica mass by four silica fibres welded to silica ears attached to the sides of the masses using hydroxide-catalysis bonding. The design is chosen to achieve a displacement noise level for each of the seismic and thermal noise contributions of 10^(−19) m/√Hz at 10 Hz, for each test mass. We discuss features of the design which has been developed as a result of experience with prototypes and associated investigations.

LISA Pathfinder: mission and status

LISA Pathfinder, the second of the European Space Agencys Small Missions for Advanced Research in Technology (SMART), is a dedicated technology demonstrator for the joint ESA/NASA Laser Interferometer Space Antenna (LISA) mission. The technologies required for LISA are many and extremely challenging. This coupled with the fact that some flight hardware cannot be fully tested on ground due to Earth-induced noise led to the implementation of the LISA Pathfinder mission to test the critical LISA technologies in a flight environment. LISA Pathfinder essentially mimics one arm of the LISA constellation by shrinking the 5 million kilometre armlength down to a few tens of centimetres, giving up the sensitivity to gravitational waves, but keeping the measurement technology: the distance between the two test masses is measured using a laser interferometric technique similar to one aspect of the LISA interferometry system. The scientific objective of the LISA Pathfinder mission consists then of the first in-flight test of low frequency gravitational wave detection metrology. LISA Pathfinder is due to be launched in 2013 on-board a dedicated small launch vehicle (VEGA). After a series of apogee raising manoeuvres using an expendable propulsion module, LISA Pathfinder will enter a transfer orbit towards the first Sun?Earth Lagrange point (L1). After separation from the propulsion module, the LPF spacecraft will be stabilized using the micro-Newton thrusters, entering a 500?000 km by 800?000 km Lissajous orbit around L1. Science results will be available approximately 2 months after launch.

The LISA Pathfinder Mission

In this paper, we describe the current status of the LISA Pathfinder mission, a precursor mission aimed at demonstrating key technologies for future space-based gravitational wave detectors, like LISA. Since much of the flight hardware has already been constructed and tested, we will show that performance measurements and analysis of these flight components lead to an expected performance of the LISA Pathfinder which is a significant improvement over the mission requirements, and which actually reaches the LISA requirements over the entire LISA Pathfinder measurement band.

Sensors and actuators for the Advanced LIGO mirror suspensions

We have developed, produced and characterized integrated sensors, actuators and the related read-out and drive electronics that will be used for the control of the Advanced LIGO suspensions. The overall system consists of the BOSEMs (a displacement sensor with an integrated electromagnetic actuator), the satellite boxes (the BOSEM readout and interface electronics) and six different types of coil-driver units. In this paper, we present the design of this read-out and control system, we discuss the related performance relevant for the Advanced LIGO suspensions, and we report on the experimental activity finalized at the production of the instruments for the Advanced LIGO detectors.

Testing LISA drag-free control with the LISA technology package flight experiment

The LISA test masses must be kept fre eo fs tray acceleration noise to within 3 × 10 −15 ms −2 Hz −1/2 in order to obtain the low-frequency gravitational wave sensitivity goal. The LISA technology package (LTP) is a dedicated ESA flight experiment for testing the drag-free control technology that must ensure purity of free fall in the LISA mission. We present here a brief description of the LTP experimental configuration, specific measurements to be performed and the requirements that must be met in order to demonstrate the LTP stray acceleration upper limit goal of 3 × 10 −14 ms −2 Hz −1/2 at 1 mHz.

Data analysis for the LISA Technology Package

The LISA Technology Package (LTP) on board the LISA Pathfinder mission aims to demonstrate some key concepts for LISA which cannot be tested on ground. The mission consists of a series of preplanned experimental runs. The data analysis for each experiment must be designed in advance of the mission. During the mission, the analysis must be carried out promptly so that the results can be fed forward into subsequent experiments. As such a robust and flexible data analysis environment needs to be put in place. Since this software is used during mission operations and effects the mission timeline, it must be very robust and tested to a high degree. This paper presents the requirements, design and implementation of the data analysis environment (LTPDA) that will be used for analysing the data from LTP. The use of the analysis software to perform mock data challenges (MDC) is also discussed, and some highlights from the first MDC are presented.

Construction and testing of the optical bench for LISA Pathfinder

eLISA is a space mission designed to measure gravitational radiation over a frequency range of 0.1–100 mHz (European Space Agency LISA Assessment Study Report 2011). It uses laser interferometry to measure changes of order 10 pm/ √ Hz in the separation of inertial test masses housed in spacecraft separated by 1 million km. LISA Pathfinder (LPF) is a technology demonstrator mission that will test the key eLISA technologies of inertial test masses monitored by laser interferometry in a drag-free spacecraft. The optical bench that provides the interferometry for LPF must meet a number of stringent requirements: the optical path must be stable at the few pm/ √ Hz level; it must direct the optical beams onto the inertial masses with an accuracy of better than ±25 μm, and it must be robust enough not only to survive launch vibrations but to achieve full performance after launch. In this paper we describe the construction and testing of the flight optical bench for LISA Pathfinder that meets all the design requirements.

Interferometry for the LISA technology package LTP: an update

This paper gives an update on the status of the LISA technology package (LTP) which is to be launched in 2009 by ESA as a technology demonstration mission for the space- borne gravitational wave observatory LISA. The dominant noise source in the interferometer prototype has been investigated and improved such that it is now comfortably below its budget at all frequencies.