(ed.). Gravitational waves (IOP, 2001)(422s).

116 LISA: A proposed joint ESA–NASA gravitational-wave missionThe possibility of making sensitive gravitational-wave measurements at lowfrequencies by laser interferometry between freely floating test masses in widelyseparated spacecraft appears to have been first suggested in print about 1972 [1,2].More extensive discussions started in 1974. An initial proposal similar to thatfor the LISA mission was presented at the Second International Conference onPrecision Measurement and Fundamental Constants in 1981 [3], and at the ESAColloquium on Kilometric Optical Arrays in Space in 1984 [4]. Work on theconcept was supported initially by the National Bureau of Standards, and later inthe USA by NASA. However, the concept became much better defined and widelyknown in the 1993–1994 period, when more extensive studies were carried out inEurope under ESA support. Since then, further studies have been carried out byboth ESA and NASA of a proposed joint ESA–NASA mission, that could fly asearly as 2010 if all goes well.The currently proposed mission is described in section 1 of this chapter. Thisincludes the overall antenna and spacecraft design, the optics and interferometrysystem, the free mass sensors, the required micronewton thrusters for thespacecraft, and the mission scenario. The emphasis will be on aspects of theantenna that are quite different from those for ground-based detectors. Section 2describes the main scientific results that seem likely to be obtained by LISA.This includes unique new information on three major astrophysical questionsconcerning MBHs and a nearly ideal test of general relativity, as well as thedetection of thousands of compact binaries in our Galaxy. In addition, somespeculations will be given on possible future prospects for gravitational-waveobservations in space after the LISA mission.Much more information on most of the above subjects can be found in ‘LaserInterferometer Space Antenna’, the Proceedings of the Second InternationalLISA Symposium [5], in the LISA Pre-Phase A Study [6], and in a special issueof Classical and Quantum Gravity [7], which is the Proceedings of the FirstInternational LISA Symposium. More recent information from the 1999–2000ESA Industrial Study of the LISA mission is being provided in the report of thatstudy and in several papers in the Proceedings of the Third International LISASymposium (Albert Einstein Institute, Potsdam, 11–14 July 2000).10.1.2 Overall antenna and spacecraft designThe basic geometry is shown schematically in figure 10.1. Three spacecraft forman equilateral triangle 5000 000 km on a side, and laser beams are sent both waysalong each side of the triangle. A Y-shaped thermal shield inside each spacecraftcontains the sensitive parts of the scientific payload, consisting of two separateoptical assemblies mounted in the two top arms of the Y, so that they are aimedalong the two adjacent sides of the triangle. The spacecraft instrumentation and acover over the sunward side of the spacecraft are not shown.Each spacecraft is in a one year period solar orbit with an eccentricity e ofabout 0.01 and an orbit inclination to the ecliptic of 3 0.5 × e [8]. By choosing