Introduction

Abstract

Following initial experimental attempts in the 1960s to detect gravitational radiation through the change of length of a test bar, a number of prototype detectors were set up in the 1970s using laser interferometers to measure the separation of suspended test masses. These experiments with arm lengths of 3 to 40 m developed into schemes to build large gravitational wave observatories in several countries. At the same time the ideas for carrying out such interferometer experiments in space began to be developed. A space experiment offers the possibility of escaping from the low frequency background noise that is present on Earth due to seismic and atmospheric processes. It also offers the possibility of a very long path length which relaxes the requirements on position measurement noise. A space experiment thus opens up the possibility of searching for signals at high strain sensitivity, <10-30 Hz-1/2, in the low frequency range of 10-4 - 1 Hz. It is thought that this range will contain sources that will be detected with certainty and at a high signal-to-noise ratio, enabling gravitational theory to be tested in the strong gravitational fields that surround compact objects as well as providing astrophysical data on the sources themselves. In 1992 the ESA's science programme commenced a study of the Satellite Test of the Equivalence Principle (STEP). This heralded an upsurge of interest in fundamental physics in ESA programmes which was strengthened by a proposal for LISA in 1993. After a number of assessment studies, LISA was included in 1995 as a cornerstone mission in ESA's Horizons 2000 programme. The purpose of the First International LISA Symposium was to discuss the LISA mission and the astrophysical observations which it can make together with the relevant gravitational theory. Included in the programme were papers on the technology needed for LISA and also reports on recent progress and developments in ground based detectors of gravitational radiation. Following the launch failure of ESA's cluster mission in June 1996 pressures on the Horizons 2000 programme have increased which may result in cornerstone missions such as LISA being delayed. It is unlikely that the high-frequency instruments being built on Earth will address to a significant degree the astrophysics and gravitational theory which will be studied with LISA. So it is important that every effort is made to launch LISA and thus open the low frequency window for gravitational radiation as soon as possible. A new study of LISA is in progress which takes advantage of new technology to reduce the number and cost of the space craft and this will be dealt with fully at the second International LISA Symposium which will be held in Hannover, 5 - 9 October 1998. This special issue contains the papers from the 1996 Symposium that were submitted for publication. The papers have been refereed in accordance with the policy of the Classical and Quantum Gravity editorial board. The Symposium was organised by the Space Science department at CLRC's Rutherford Appleton Laboratory. Sponsorship for the meeting and this publication was provided by Matra Marconi Space and the Gravitational Research Groups at the Universities of Glasgow, Hannover and Potsdam. Thanks are due to the members of the local Organizing Committee, the Science Programme Committee and others who acted as referees. M C W Sandford Scientific Programme Committee P Bender (JILA, USA) A Brillet (Orsay, France) K Danzmann (Hannover, Germany) J Hough (Glasgow, UK) Y Jafry (ESTEC, The Netherlands) M Sandford (RAL, UK) B Schutz (Cardiff, UK/Potsdam, Germany) D Shoemaker (MIT, USA) K Thorne (CalTech, USA) R Weiss (MIT, USA) Local Organizing Committee M Caldwell S Clelland M C W Sandford N D Valentine