Table of contents

In its 10th year, the International LISA Symposium of 2004 was the first to be organized by ESA. After the first Symposium at the Rutherford Appleton Laboratory in 1996, and subsequent Symposia at Caltech (1998), the Albert Einstein Institute in Golm (2000) and Penn State University (2002), ESA's European Space and Technology Centre (ESTEC) is proud to have hosted the 5th International LISA Symposium in 2004 in conjunction with the 38th ESLAB Symposium.

During these 10 years, we have seen the technology required for such ambitious space missions as LISA and LISA Pathfinder developing and maturing to a point where flightlevel hardware can be produced and tested. The technology demonstrator LISA Pathfinder has become a mission well established in the ESA programme and has entered its project implementation phase; the LISA mission is in the formulation phase.

At the same time, the preparations for LISA data analysis and first activities on data archives and LISA simulators have begun, indicating that LISA is regarded as more than just a mission far in the future.

The astrophysics of the sources of gravitational waves is emerging as a rapidly growing field that will become even more important in the coming years, when the focus of the activities on LISA and LISA Pathfinder will shift from making the missions possible to deriving scientific results from the data.

The 5th International LISA Symposium had presentations on all of the above topics, from the technology of LISA and LISA Pathfinder, LISA data analysis, and modelling and simulation, to the astrophysics of the sources. The programme included an overview of the activities at the ground-based detectors, with which LISA shares not only a common technological heritage but also the prospect of detecting gravitational waves in the next 10 years.

Such a conference would not be possible without the help of many people, not least the Scientific Organizing Committee, and the local organization, provided by ESA's conference bureau and Research and Scientific Support Department, that established the framework for an excellent and memorable conference. This having been set, it was up to the speakers and the participants to make the Symposium a success - a task that they performed spectacularly well.

The 6th International LISA Symposium in 2006 will be held in Annapolis, MD, USA, organized by NASA, an event to which I look forward with anticipation.

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.

The top-level requirement of the LISA Pathfinder mission is the verification of pure relative free fall between two test masses with an accuracy of about 3 × 10⁻¹⁴ m s⁻² Hz^−1/2 in a measurement bandwidth between 1 mHz and 30 mHz. The drag-free control system is one of the key technology elements that shall be verified. Its design is strongly connected to the overall system and experimental design, in particular, via the following issues: the differential test mass motion and thus the science measurements depend on the control system; design constraints, such as negative stiffness of test masses and electrostatic actuation cross-talk, have an impact on science and control system performance; derived requirements for control system components, in particular, the micro-propulsion system, must be within reasonable and feasible limits. In this paper, the control design approach is outlined and the system-related issues are addressed.

The LISA Technology Package (LTP), to be launched by ESA in 2008, is a technology demonstration mission in preparation for the LISA space-borne gravitational wave detector. A central part of the LTP is the optical metrology package (heterodyne interferometer with phasemeter) that measures the distance between two test masses with a noise level of 10 pm Hz^−1/2 between 3 mHz and 30 mHz and also the test mass alignment with a noise level of <10 nrad Hz^−1/2. An engineering model of the interferometer has been built and environmentally tested. Extensive functionality and performance tests were conducted. This paper reports on the successful test results.

The LISA Technology Package (LTP) uses laser interferometry to measure the changes in relative displacement between two inertial test masses. The goals of the mission require a displacement measuring precision of 10 pm Hz^−1/2 at frequencies in the 3–30 mHz band. We report on progress with a prototype LTP interferometer optical bench in which fused silica mirrors and beamsplitters are fixed to a ZERODUR® substrate using hydroxide catalysis bonding to form a rigid interferometer. The couplings to displacement noise of this interferometer of two expected noise sources—laser frequency noise and ambient temperature fluctuations—have been investigated, and an additional, unexpected, noise source has been identified. The additional noise is due to small amounts of signal at the heterodyne frequency arriving at the photodiode preamplifiers with a phase that quasistatically changes with respect to the optical signal. The phase shift is caused by differential changes in the external optical paths the beams travel before they reach the rigid interferometer. Two different external path length stabilization systems have been demonstrated and these allowed the performance of the overall system to meet the LTP displacement noise requirement.

The LISA Technology Package (LTP) will verify the performance of the inertial sensors that are being developed for the LISA mission. The position of the test masses will be read out by a heterodyning laser interferometer system with the phase of the detected signals also providing measurements of their angular alignment. The electronics required to measure the relative phases of the signals from the photo-detectors has been developed as part of an ESA contract and preliminary results of bench testing the unit are presented.

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 10⁻⁵ K Hz^−1/2.

The Space Technology 7 (ST-7) payload, flying on the Laser Interferometer Space Antenna (LISA) Pathfinder (LPF) mission, will demonstrate drag-free control of a test mass with acceleration disturbances below 3 × 10⁻¹⁴ m s⁻² Hz^−1/2 over a frequency range of 1 mHz to 30 mHz. Low-frequency acceleration noise introduced by the electrostatic force needed to counter static mass distribution imbalance is expected to be a significant contributor to the acceleration noise budget. For this reason, the self-gravity (due to mass imbalance) is minimized by adding trim mass to bring the total differential acceleration between the two test masses due to self-gravity below 5 × 10⁻¹⁰ m s⁻² in any axis and the dc acceleration gradient due to self-gravity below 4 × 10⁻⁸ m s⁻² m⁻¹ in any axis of either test mass. A plan has been established to develop the distribution and placement of the compensation masses. Compensation for the self-gravity effects on the two test masses is handled in a two-step process. A nominal compensation mass is defined and incorporated early and is located very near the test masses. The final trimming for self-gravity occurs after the integration on the spacecraft with small mass added externally to the test-mass vacuum enclosures. The plan identifies three preliminary points in the hardware maturity where the trimming to the as-built configuration can take place: (1) during build-up of the sensor vacuum enclosure, (2) prior to delivery of the integrated ST-7 to Europe and (3) prior to environmental testing of the integrated LPF system. The sensitivity of the self-gravity to knowledge errors in the actual mass distribution is taken into account in the determination of final trimming opportunities and mounting locations.

Virgo is a French–Italian collaboration for the construction and operation of a 3 km long interferometric gravitational wave antenna. The construction of the detector is already completed and the commissioning is quite advanced, while the data taking is expected to start in 2005. In this paper, we report on the present status of Virgo and on the results of commissioning activity. In particular, we analyse the first four engineering runs (C1–C4) and discuss the sensitivity obtained in C4.

Since December 2003, the gravitational-wave detector GEO 600 has routinely operated in the dual recycled mode, using a lock acquisition scheme based on the detection of optical sideband power at the dark port. With the detector locking very robustly, the current commissioning work is entirely dedicated to sensitivity improvements. We give a brief overview of the GEO 600 detector, the implementation of dual recycling, and summarize recent work regarding the increase in the detector sensitivity.

The High Optical Power Test Facility for Advanced Interferometry has been built by the Australian Consortium for Interferometric Gravitational Astronomy north of Perth in Western Australia. An 80 m suspended cavity has been prepared in collaboration with LIGO, where a set of experiments to test suspension control and thermal compensation will soon take place. Future experiments will investigate radiation pressure instabilities and optical spring effects in a high power optical cavity with ∼200 kW circulating power. The facility combines research and development undertaken by all consortium members, whose latest results are presented.

The Schenberg gravitational wave detector is almost completed for operation at its site in the Physics Institute of the University of São Paulo, under the full support of FAPESP (the São Paulo State Foundation for Research Support). We have been working on the development of a transducer system, which will be installed after the arrival of all the microwave components and the completion of the transducer mechanical parts. The initial plan is to operate a CuAl6% two-mode parametric transducer in a first operational run at 4.2 K with nine transducers and an initial target sensitivity of h ∼ 2 × 10⁻²¹ Hz^−1/2 in a 50 Hz bandwidth around 3.2 kHz. Here we present details of this plan and some recent results of the development of this project.

The MiniGRAIL detector was improved. The sphere was replaced by a slightly larger one, having a diameter of 68 cm (instead of 65 cm), reducing the resonant frequency by about 200 Hz to around 2.9 kHz. The last four masses of the attenuation system were machined to increase their resonant frequency and improve the attenuation around the resonant frequency of the sphere. In the new sphere, six holes were machined on the TIGA positions for easy mounting of the transducers. During the last cryogenic run, two capacitive transducers and a calibrator were mounted on the sphere. The first transducer was coupled to a double-stage SQUID amplifier having a commercial quantum design SQUID as a first stage and a DROS as a second stage. The second transducer was read by a single-stage quantum design SQUID. During the cryogenic run, the sphere was cooled down to 4 K. The two-stage SQUID had a flux noise of about 1.6 μϕ₀ Hz^−1/2. The detector was calibrated and the sensitivity curve of MiniGRAIL was determined.

Overcoming laser frequency noise is a significant technical challenge for achieving the design sensitivity of the Laser Interferometer Space Antenna (LISA) gravitational wave detector. Arm-locking is a recently proposed technique for suppressing frequency noise in LISA and can be used in addition to the established techniques of pre-stabilization and time-delay interferometry. Incorporation of arm-locking into LISA could provide many benefits, however experimental verification and testing is needed. We present the progress of an experimental test of arm-locking which uses 10 km of optical fibre to generate a large propagation time delay, analogous to the propagation delay in LISA.

Electronic phase delay (EPD), a new technique for delaying the phase of a signal by an arbitrary amount, is presented as the basis for a model of the Laser Interferometer Space Antenna (LISA). The validity of EPD is demonstrated by constructing a synthetic interferometer (SI) with a single-arm time delay of 1 s. Schemes for studying the phase noise reduction techniques of arm-locking and time delay interferometry using EPD units are presented and discussed, with preliminary results for arm-locking. EPD can also be used as the basis for a bench-top model of LISA which will be used to study LISA interferometry and data analysis methods.

We present the first experimental confirmation of the so-called 'self-phase-locked delay interferometry'. This laser frequency stabilization technique consists basically in comparing the prompt laser signal with a delayed version of itself that has been reflected in another LISA satellite 5 × 10⁹ m away. In our table-top experiment, the phase of a voltage-controlled oscillator is stabilized by means of a control loop based on this technique. In agreement with the theory, the measured unity gain frequency is not limited by the inverse of the used delay (1.6 µs). In the time domain, the system also behaves as predicted, including the appearance of a quasi-periodic 'ringing' just after the lock acquisition, which decays exponentially. Its initial amplitude is smaller when the loop gain is slowly ramped up instead of suddenly switched on.

The long armlengths of the LISA interferometer, and the finite aperture of the telescope, lead to an optical power attenuation of ∼10⁻¹⁰ of the transmitted to received light. Simple reflection at the end of the arm is therefore not an optimum interferometric design. Instead, a local laser is offset phase locked to the weak incoming beam, transferring the phase information of the incoming to the outgoing light. This paper reports on an experiment to characterize a weak-light phase-locking scheme suitable for LISA in which a diode-pumped, Nd:YAG, non-planar ring oscillator (NPRO) is offset phase locked to a low-power (13 pW) frequency stabilized master NPRO. Preliminary results of the relative phase noise of the slave laser shows shot noise limited performance above 0.4 Hz. Excess noise is observed at lower frequencies, most probably due to thermal effects in the optical arrangement and phase-sensing electronics.

This paper presents some of the more topical results of a study into the LISA phase measurement system. This system is responsible for measuring the phase of the heterodyne signal caused by the interference of the laser beams between the local and far spacecraft. Interactions with the LISA systems that surround the phase measurement system imply additional non-trivial requirements on the phase measurement system.

Space-based optical systems must be made from lightweight materials which can withstand significant acceleration and temperature changes. Materials such as ZERODUR®, ULE® (Ultra Low Expansion material) and silica are all potentially suitable. Depending on the specific requirements of the optical system and the transmissive or reflective nature of the optical layout these materials can be used by themselves or together to fabricate optical benches. The geometrical layouts of these optical systems are often very complicated and the requirements for mechanical stability very stringent, thus jointing components presents a challenge. In this paper we present developments of a novel chemical bonding process, originally invented at Stanford University for bonding silica components for the optical telescope for the Gravity Probe B mission. Colloquially called silicate bonding, this process utilizes hydroxide catalysis to join optical components to optical mounts to obtain high stability whilst accommodating the requirement for precise alignment procedures.

We describe a compact interferometer, under development at the University of Birmingham, that could be employed as a zero-stiffness sensor for drag-free satellites. A prototype bench-top polarization-based homodyne interferometer is discussed that achieves a shot-noise limited displacement sensitivity of 3 × 10⁻¹² m Hz^1/2 above 60 Hz. We discuss a wavelength modulation technique that will render the interferometer more robust as it enables the absolute difference in interferometric armlengths to be determined.

In this paper, we analyse the application of an optical readout system to the gravitational reference sensor of LISA. The goal is not the replacement of the capacitive sensor with an optical one, but the integration of the optical sensor in the present design of LISA. The main motivation is the implementation of a back-up solution, so that there is a significant risk reduction for the mission in case the main sensor fails for some reason. Furthermore, an optical system is potentially more sensitive than the capacitive one for some degrees of freedom. In this paper, we report some preliminary experimental results on the sensitivity of the sensor and describe a possible set-up for the implementation according to the present design of the gravitational reference sensor.

LISA and the next generation of space-based laser interferometers require gravitational reference sensors (GRS) to provide distance measurements to picometre precision for LISA, and femtometre precision for the proposed Big Bang Observatory (BBO). We describe a stand-alone GRS structure that has the benefits of higher sensitivity and ease of fabrication. The proposed GRS structure enables high precision interferometric links in three-dimensional directions. The GRS housing provides the optical reference surface onto which the transmitted laser beam, and the independent received laser beam are referenced. The stand-alone GRS allows balanced optical probing of the distance of the proof mass relative to the housing at a power and wavelength that differ from the transmitted and received wavelengths and with picometre sensitivity without radiation pressure imbalance. The single parameter that reduces proof mass disturbance forces is the gap spacing. Optical readout allows the use of a large gap between the GRS housing and proof mass. We propose using rf-modulated optical interferometry to measure both relative displacement and absolute distance. Further we propose to use a reflective grating beamsplitter within the GRS and on the external optical bench. The reflective grating design eliminates the in-path transmissive optical components and the dn/dT related optical path effects, and simplifies the optical bench structure. Inside the GRS, a near-Littrow mounted grating enables picometre precision measurement at microwatts of optical power. Preliminary experimental results using a grating beamsplitter interferometer are presented, which demonstrate an optical sensing sensitivity of 30 pm Hz^−1/2.

This paper concerns the effects of the build-up of electrical charge on the LISA test masses. Charge accumulates on the isolated test masses due to the bombardment of the spacecraft by galactic cosmic rays and solar particles. This will result in forces on the test masses, due to Coulomb and Lorentz interactions, which will disturb their geodesic motion. The three main disturbances associated with this charge are an increase in the test mass acceleration noise, coupling between the test mass and the spacecraft and the appearance of coherent Fourier components in the measurement bandwidth. These disturbances are estimated using the latest charging rate and noise predictions from GEANT4 for both the LISA mission and the technology demonstration mission, LISA Pathfinder, at different times in the solar cycle. The Coulomb disturbances are evaluated based on a detailed 3D, electrostatic, finite element model and submodels of the LTP sensor. These results are compared with those derived using the customary parallel plate approximation to calculate capacitances, and the accuracy of these approximations is assessed for typical parameter settings. The variation of the magnitude of charging disturbances as different parameters are changed, and the management of such disturbances are discussed.

We present detailed Monte Carlo simulations of test-mass charging caused by energetic cosmic rays in the LISA Pathfinder mission, using the GEANT4 software toolkit. This effect can lead to a variety of disturbances, threatening the goal of the mission—to achieve a low-frequency acceleration noise within an order of magnitude of that required for LISA. We calculate the test-mass charging rates and charging shot noise for different solar conditions, including solar energetic particle eruptions. Further simulations show that the inclusion of additional masses within the LTP inertial sensor, to balance the gravitational accelerations felt by the test masses, does not significantly alter the overall charging rates. The specifications of a particle monitor for LISA Pathfinder, which can detect variations in the energetic particle flux and enable correlation with test-mass charging, are also described.

Cosmic-ray and solar particles above 100 MeV penetrate the LISA experiment test masses. Consequently, electric charges accumulating there generate spurious Coulomb forces between the masses and the surrounding electrodes. This process increments the noise level of the experiment. We have estimated the amount of charge deposited per second on the LISA test masses by primary cosmic-ray protons at solar minimum and solar maximum and by solar energetic particle (SEP) events. This simulation has been carried out with the Fluka Monte Carlo program. A simplified geometry for the experiment has been considered. We have found an effective charge rate of 110 e s⁻¹ for primary protons at solar maximum and 150 e s⁻¹ at solar minimum between 0.1 and 1000 GeV. The amount of charge released by a medium intensity gradual event (7 May 1978) varies from 206 e s⁻¹ in the first few minutes to 4575 e s⁻¹ at the peak of the event. At the occurrence of medium or strong solar events, the LISA sensitivity curve at frequencies lower than 3 × 10⁻⁴ Hz is dominated by the noise due to the test-mass charging process.

Solar energetic particles and galactic cosmic rays with energies larger than 100 MeV cause progressive charging of the LISA experiment test masses. Consequently, Coulomb forces occur between the test masses and the surrounding conducting surfaces generating spurious signals that might be mistaken for gravitational wave signals. We have parametrized the energy spectra of galactic cosmic-ray nuclei and electrons near the LISA orbit in order to evaluate their role in the test-mass charging relative to the most abundant proton component. This work has been carried out using the FLUKA Monte Carlo program.

Galactic cosmic rays and solar energetic particles (SEPs) with energies larger than 100 MeV/n are able to penetrate and charge the test masses of the LISA experiment. As this process constitutes one of the major sources of noise for the experiment, a small telescope of silicon detectors will be located on board the LISA PathFinder and, possibly, the three LISA spacecraft. This device will allow us to monitor real-time galactic and solar cosmic-ray incident proton fluxes above 100 MeV. Moreover, spectral information will be provided up to an energy of 500 MeV. We propose to use the above instrument for the evaluation of the test mass charging process and the study of SEPs accelerated by coronal mass ejection (CME) propagation. Because of the peculiar orbit of the LISA spacecraft around the Sun, this experiment offers a unique chance to monitor an evolving CME contemporary at 2° (among spacecraft) and 20° (between LISA and Earth) intervals in longitude at once. These observations are of particular interest for both solar physics and space weather investigations. SEP event occurrence is not predictable and these events are particularly dangerous to astronauts and space equipment.

The dc pointing directions for the LISA laser beams will be chosen to minimize the sensitivity of the measured arm lengths to jitter in the beam pointing. The earliest studies of the effects of wavefront distortion included only astigmatism and defocus, so that the desired dc beam pointing directions were on the axis for the transmitting telescopes. But, if other aberrations cause the dc pointing directions to be considerably off axis, some of the laser beam intensity will be lost. A brief study of this effect has been carried out. As examples, several cases with defocus, spherical aberration, and two components each of astigmatism and coma have been investigated. Within this class of models, pure astigmatism turned out to give the maximum sensitivity to beam pointing jitter, for a given rms wavefront distortion. Although further study is needed, it appears that the usually quoted requirements of 3 × 10⁻⁸ rad for the dc beam pointing offsets and 8 × 10⁻⁹ rad Hz^−1/2 for the pointing jitter are probably reasonable choices.

In the past decade, most effort in the study of supermassive black holes (BHs) has been devoted to measuring their masses. This led to the finding of the tight M_BH–σ relation, which indicates the existence of strong links between the formation of the BHs and of their host spheroids. Many scenarios have been proposed to explain this relation, and all agree on the key role of BHs' growth and feedback in shaping their host galaxies. However, the currently available observational constraints, essentially BH masses and galaxy photometry, are not sufficient to conclusively select among the alternatives. A crucial piece of information on black-hole formation is recorded in the orbital distribution of the stars, which can only be extracted from high-resolution integral-field (IF) stellar kinematics. The introduction of IF spectrographs with adaptive optics on large telescopes opens a new era in the study of BHs by finally allowing this key element to be uncovered. This information will be complementary to what will be provided by the LISA gravitational wave satellite, which can directly detect coalescing BHs. Here, an example is presented for the recovery of the orbital distribution in the centre of the giant elliptical galaxy M87, which has a well-resolved BH sphere of influence, using SAURON IF kinematics.

LISA will be able to detect gravitational waves from inspiralling massive black-hole (MBH) binaries out to redshifts z > 10. If the binary masses and luminosity distances can be extracted from the LISA data stream, this information can be used to reveal the merger history of MBH binaries and their host galaxies in the evolving universe. Since this parameter extraction generally requires that LISA observe the inspiral for a significant fraction of its yearly orbit, carrying out this programme requires adequate sensitivity at low frequencies, f < 10⁻⁴ Hz. Using several candidate low-frequency sensitivities, we examine LISA's potential for characterizing MBH binary coalescences at redshifts z > 1. The results underscore the need for more detailed work towards understanding the potential scientific value of the low-frequency part of LISA's sensitivity band.

We compute the expected low-frequency gravitational wave signal from coalescing massive black-hole (MBH) binaries at the centres of galaxies. We follow the merging history of halos and associated holes via cosmological Monte Carlo realizations of the merger hierarchy from early times to the present in a ΛCDM cosmology. MBHs get incorporated through a series of mergers into larger and larger halos, sink to the centre owing to dynamical friction, accrete a fraction of the gas in the merger remnant to become more massive, and form a binary system. Stellar dynamical processes dominate the orbital evolution of the binary at large separations, while gravitational wave emission takes over at small radii, causing the final coalescence of the system. We discuss the observability of inspiralling MBH binaries by a low-frequency gravitational wave experiment such as the planned Laser Interferometer Space Antenna (LISA), discriminating between resolvable sources and unresolved confusion noise. Over a three-year observing period LISA should resolve this GWB into discrete sources, detecting ≈90 individual events above a S/N = 5 confidence level, while expected confusion noise is well below planned LISA capabilities.

We present a report on the progress made in the development of computational techniques to evaluate the gravitational radiation generated by a particle orbiting a massive black hole to second perturbative order.

For a successful detection of gravitational waves by LISA, it is essential to construct theoretical waveforms in a reliable manner. We discuss gravitational waves from an extreme mass ratio binary system which is expected to be a promising target of the LISA project. The extreme mass ratio binary is a binary system of a supermassive black hole and a stellar mass compact object. As the supermassive black hole dominates the gravitational field of the system, we suppose that the system might be well approximated by a metric perturbation of a Kerr black hole. We discuss recent theoretical progress in calculating the waveforms from such a system.

We develop a method for analytically constructing highly accurate post-Newtonian (PN) templates for gravitational-wave signals emitted by compact binaries moving in inspiralling eccentric orbits. Employing an improved 'method of variation of constants', applied to 2PN accurate generalized quasi-Keplerian parametrization for the orbital motion, we combine three relevant time scales associated with the orbital period, periastron precession and radiation reaction, without treating the radiative time scale in an adiabatic manner. We explicitly implement our method to obtain 2.5PN accurate 'post-adiabatic' gravitational waveforms h_+,×. Using the 'effective one-body' approach, we define the domain of validity of our method. We also discuss how to extend our method to construct 'ready to use' search templates for gravitational waves from inspiralling eccentric orbits.

Understanding the fate of merging supermassive black holes in galactic mergers, and the gravitational wave emission from this process, are important LISA science goals. To this end, we present results from numerical relativity simulations of binary black hole mergers using the so-called Lazarus approach to model gravitational radiation from these events. In particular, we focus here on some recent calculations of the final spin and recoil velocity of the remnant hole formed at the end of a binary black hole merger process, which may constrain the growth history of massive black holes at the core of galaxies and globular clusters.

The Laser Interferometer Space Antenna (LISA) mission, a space-based gravitational wave detector, uses laser metrology to measure distance fluctuations between proof masses aboard three sciencecraft. The total acceleration disturbance to each proof mass is required to be below 3 × 10⁻¹⁵ m s⁻² Hz^−1/2 at 0.1 mHz. Self-gravity noise due to sciencecraft distortion and motion is expected to be a significant contributor to the acceleration noise budget. To minimize these effects, the gravitational field at each proof mass must be kept as small, flat and constant as possible. It is estimated that the static (non-fluctuating) self-gravity acceleration must be kept below 5 × 10⁻¹⁰ m s⁻² with a gradient below 3 × 10⁻⁸ s⁻² in order to meet the required noise levels. Most likely it will not be possible to directly verify that the LISA sciencecraft meets these requirements by measurements; they must be verified by models. The LISA integrated modelling team developed a new self-gravity tool that calculates the gravitational forces and moments on the proof masses to aid in the design and verification of the LISA sciencecraft. We present here an overview of the tool and the latest self-gravity results calculated using the current baseline design of LISA.

The Laser Interferometer Space Antenna (LISA) mission, a space-based gravitational wave detector, uses laser metrology to measure distance fluctuations between proof masses aboard three spacecraft. The total acceleration disturbance to each proof mass is required to be below 3 × 10⁻¹⁵ m s⁻² Hz^−1/2 at 0.1 mHz. Optical path length variations on each optical bench must be kept below about 40 pm Hz^−1/2 over 1–100 mHz. Noise due to spacecraft thermal distortions, temperature difference variations across the proof mass housing and other thermal effects are expected to be significant contributors to these noise budgets. The LISA Integrated Modelling team developed a detailed thermal model that is currently being used to drive the design of LISA. Several new thermal analysis techniques are also being developed in order to achieve model accuracies to LISA levels. We present here an overview of the LISA thermal design and modelling efforts. The latest thermal results calculated using the current baseline design of LISA are also discussed.

The Laser Interferometer Space Antenna (LISA) mission is a space-borne gravitational wave detector consisting of three sciencecraft in heliocentric orbit. Each sciencecraft is delivered to its operational orbit by a propulsion module. Because of the strict thermal and mass balancing requirements of LISA, the baseline mission concept requires that the propulsion module separate from the sciencecraft after delivery. The only propulsion system currently included in the sciencecraft design are micronewton level thrusters, such as field emission electric propulsion (FEEP) or colloid thrusters, that are used to balance the 30–40 µN of solar radiation pressure and provide the drag-free and attitude control of the sciencecraft. Due to these thrusters' limited authority, the separation of the propulsion module from the sciencecraft must be well controlled to not induce a large tip-off rotation of the sciencecraft. We present here the results of a study of the propulsion module separation system requirements that are necessary to safely deliver the three LISA sciencecraft to their final operational orbits.

The Laser Interferometer Space Antenna mission is a planned gravitational wave detector consisting of three spacecraft in heliocentric orbit. Laser interferometry is used to measure distance fluctuations between test masses aboard each spacecraft to the picometre level over a 5 million km separation. The disturbance reduction system comprises the pointing and positioning control of the spacecraft, electrostatic suspension control of the test masses and point-ahead and acquisition control. This paper presents an approach for the acquisition control of the LISA formation. The approach establishes one link at a time. For each link, it defocuses the incoming beams to make its light detectable by the receiving spacecraft. Simulations are performed to demonstrate the feasibility of the proposed approach.

The Laser Interferometer Space Antenna (LISA) mission is planned to measure gravitational waves by using a constellation of three spacecraft which stay at the points of an equilateral triangle revolving around the Sun for a period of at least five and up to 8.5 years. This mission description tells how the spacecraft are launched together and then separately transferred to their constellation positions using chemical propulsion to perform manoeuvres along the way. The paper further gives characteristics of the operational orbits (contrary to common perception, for example, the LISA configuration has no net rotation in inertial space), and discusses navigation and the effects of errors in the delivery to the constellation. The particular mission described here is the LISA Baseline 1 mission, which is based on operational orbits that minimize the average rate of change of the lengths of the arms of the triangular constellation over the five-year nominal mission. The launch period for mission described here is in December 2010, which is earlier than the launch period that will actually be used by the LISA project, so this mission must be considered only as characteristic of the mission architecture and not as a final plan.

The laser phase noise is one of the dominant noises for the gravitational wave detector LISA. Since it is impossible to maintain equal distances among spacecraft, the time-delay interferometric (TDI) techniques are used to eliminate the laser phase noise along with optical bench noise. In this work, we estimate the effects due to the Sagnac phase by taking the realistic model for LISA orbital motion. We extend the algebraic formalism to include the effects due to the Sagnac phase.

The inspirals of stellar-mass compact objects into supermassive black holes are some of the most important sources for LISA. Detection techniques based on fully coherent matched filtering have been shown to be computationally intractable. We describe an efficient and robust detection method that utilizes the time–frequency evolution of such systems. We show that a typical extreme mass ratio inspiral (EMRI) source could possibly be detected at distances of up to ∼2 Gpc, which would mean ∼tens of EMRI sources can be detected per year using this technique. We discuss the feasibility of using this method as a first step in a hierarchical search.

We have computed the gravitational wave emission arising from the coalescence of several close white dwarf binary systems. In order to do so, we have followed the evolution of such systems using a smoothed particle hydrodynamics code. Here we present some of the results obtained so far, paying special attention to the detectability of the emitted gravitational waves. Within this context, we show which could be the impact of individual merging episodes for LISA.

In the context of star capture by a black hole, a new noticeable difference between the Brans–Dicke theory and the general relativity gravitational radiation is pointed out. This feature stems from the non-stationarity of the black-hole state, barring Hawking's theorem.

For future configurations, we study the relation between the abatement of the noise sources and the signal-to-noise ratio (SNR) for coalescing binaries. Our aim is not the proposition of a new design, but an indication of where in the bandwidth or for which noise source a noise reduction would be most efficient. We take VIRGO as the reference for our considerations, solely applicable to the inspiralling phase of a coalescing binary. Thus, only neutron stars and small black holes of a few solar masses are encompassed by our analysis. The contributions to the SNR given by final merge and quasi-normal ringing are neglected. It is identified that (i) the reduction in the mirror thermal noise band provides the highest gain for the SNR, when the VIRGO bandwidth is divided according to the dominant noises; (ii) there exists a specific frequency at which lies the largest potential increment in the SNR, and the enlargement of the bandwidth, where the noise is reduced, produces a shift of such an optimal frequency to higher values; (iii) the abatement of the pendulum thermal noise provides the largest, but modest, gain, when noise sources are considered separately. Our recent astrophysical analysis of event rates for neutron stars leads to a detection rate of one every 148 or 125 years for VIRGO and LIGO, respectively, while a recently proposed and improved, but still conservative, VIRGO configuration would provide an increase to 1.5 events per year. Instead, a bi-monthly event rate, similar to advanced LIGO, requires a 16 times gain. We analyse the 3D (pendulum, mirror, shot noises) parameter space showing how such a gain could be achieved.

The Brazilian spherical antenna (Schenberg) is planned to detect high frequency gravitational waves (GWs) ranging from 3.0 kHz to 3.4 kHz. There is a host of astrophysical sources capable of being detected by the Brazilian antenna, namely: core collapse in supernova events; (proto)neutron stars undergoing hydrodynamical instability; f-mode unstable neutron stars, caused by quakes and oscillations; excitation of the first quadrupole normal mode of 4–9 solar mass black holes; coalescence of neutron stars and/or black holes; exotic sources such as bosonic or strange matter stars rotating at 1.6 kHz; and inspiralling of mini black-hole binaries. We here address our study in particular to neutron stars, which could well become f-mode unstable producing therefore GWs. We estimate, for this particular source of GWs, the event rates that in principle can be detected by Schenberg and by the Dutch Mini-Grail antenna.

Several processes active in the very early universe are thought capable of generating gravitational waves at frequencies above 1 MHz. These include parametric amplification of quantum fluctuations during inflation and bubble cavitation during first-order phase changes. Predictions of the likely spectra of such radiation often show peaks in the MHz to GHz region, far beyond the range of either bar detectors or interferometers and so other detection methods must be developed. A correlation detector based on these principles is being commissioned at Birmingham.

We outline the design, construction and testing of a field effect neutralizer, which provides a source of up to 6 mA of electron emission to maintain charge neutrality for the LISA Pathfinder mission spacecraft. The low mass, low power neutralizer uses silicon field emitter arrays and has been engineered for integration into the LISA Pathfinder micro-propulsion system. The silicon emitters are constructed using micro-fabrication techniques and electron beam lithography to ensure uniformity and precise control of emitter location. Control of the manufacture processes, plasma-enhanced vapour deposition, wet and dry plasma etch and various coatings, has been optimized to achieve robust reproducible devices suitable for space use.

Here we describe the mission design for SMART-2/LISA Pathfinder. The best trade-off between the requirements of a low-disturbance environment and communications distance is found to be a free-insertion Lissajous orbit around the first collinear Lagrange point of the Sun–Earth system (L₁), 1.5 × 10⁶ km from Earth. In order to transfer SMART-2/LISA Pathfinder from a low Earth orbit, where it will be placed by a small launcher, the spacecraft carries out a number of apogee-raise manoeuvres, which ultimatively place it to a parabolic escape trajectory towards L₁. The challenges of the design of a small mission are met, fulfilling the very demanding technology demonstration requirements without creating excessive requirements on the launch system or the ground segment.

End-to-end (E2E) modelling and simulation, i.e. verifying the science performance of LISA Pathfinder (spacecraft and payload), is mandatory in order to minimize mission risks. In this paper, focus is on two particular applications of the E2E performance simulator currently being developed at EADS Astrium GmbH: the opto-dynamical stability and the self-gravity disturbance stability analysis. The E2E models applied here comprise the opto-dynamical modelling of the optical metrology systems (OMS) laser interferometry, the thermo-elastic distortion modelling of the OMS optical elements and the self-gravity disturbance model accounting for structural distortions. Preliminary analysis results are presented in detail, identifying shortcomings of the current LISA technology package (LTP) mounting baseline. As a consequence, the design is now being revised.

This paper addresses the problem of compensating self-gravity for the LISA Technology Package. Massive components onboard the spacecraft produce a gravitational imbalance on the free-falling test masses. We present here a compensation scheme to reduce the gravitational forces, torques, stiffness and cross-talk to values within requirements. Gravitational analysis and subsequent compensation are needed to limit the gravitational imbalances in order to reduce the force noise and force gradients associated with the electrostatic actuation that must compensate any residual gravitational imbalances. Starting from an educated guess based on simple Newtonian arguments, we present the approximate shapes of a compensation block solution which minimizes the residual gravitational imbalance and stiffness while adding a minimum of mass.

A torsion pendulum allows ground-based investigation of the purity of free fall for the LISA test masses inside their capacitive position sensor. This paper presents recent improvements in our torsion pendulum facility that have both increased the pendulum sensitivity and allowed detailed characterization of several important sources of acceleration noise for the LISA test masses. We discuss here an improved upper limit on random force noise originating in the sensor. Additionally, we present new measurement techniques and preliminary results for characterizing the forces caused by the sensor's residual electrostatic fields, dielectric losses, residual spring-like coupling and temperature gradients.

Achieving the low frequency LISA sensitivity requires that the test masses acting as the interferometer end mirrors are free-falling with an unprecedented small degree of deviation. Magnetic disturbances, originating in the interaction of the test mass with the environmental magnetic field, can significantly deteriorate the LISA performance and can be parametrized through the test mass remnant dipole moment and the magnetic susceptibility χ. While the LISA test flight precursor LTP will investigate these effects during the preliminary phases of the mission, the very stringent requirements on the test mass magnetic cleanliness make ground-based characterization of its magnetic properties paramount. We propose a torsion pendulum technique to accurately measure on the ground the magnetic properties of the LISA/LTP test masses.

This paper proposes a data analysis method to reduce the binary confusion noise. We analyse characteristics of the binary confusion noise in a wavelet space and extract a typical level of this noise. Using this level, we reduce the binary confusion noise and drive an approximate form of a burst signal subject to the confusion noise. We show that our method can reduce the influence of confusion noise and obtain an approximate waveform of the desired signal with high accuracy.

We derive a time-delay interferometric (TDI) combination that has zero-response to a gravitational wave signal. This combination, which we have called the zero-signal solution, is a two-parameter family of linear combinations of the generators of the TDI space that has null gravitational wave response when its two parameters coincide with the values of the angles of the source location in the sky. Remarkably, the zero-signal solution does not rely on any assumptions about the gravitational waveform, and in fact it works for waveforms of any kind.

A torsion pendulum facility for a ground-based performance test of the inertial sensor for ASTROD-1 has been constructed. The twist motion of the test mass is monitored and servo-controlled. The sensitivity of the electrostatic servo-controlled actuator is calibrated based on the elastic torque of the torsion fibre, and the torque resolution of the servo-controlled torsion pendulum comes to 2 × 10⁻¹¹ N m Hz^−1/2 from 1 mHz to 0.1 Hz, which is likely limited by the seismic noise, electronic noise and the cross coupling between the translation and twist modes.