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Abstract:
The existence of gravitational waves is the most prominent of Einstein's predictions that has not yet been directly verified. The space projects LISA and (partially) ASTROD share their goal and principle of operation with the ground-based interferometers currently under construction: the detection and measurement of gravitational waves by laser interferometry. Ground and space detection differ in their frequency ranges, and thus the detectable sources. Towards low frequencies, ground-based detection is limited by seismic noise, and yet more fundamentally by 'gravity gradient noise', thus covering the range from a few Hz to a few kHz. On five sites worldwide, detectors of armlengths from 0.3 to 4 km are nearing completion. they will progressively be put in operation in the years 2002 and 2003. Future enhanced versions are being planned, with scientific data not expected until 2008, i.e. near the launch of the space project LISA. It is only in space that detection of signals below, say, 1 Hz is possible, opening a wide window to a different class of interesting sources of gravitational waves. The project LISA consists of three spacecraft in heliocentric orbits, forming a triangle of 5 million km sides. A technology demonstrator, designed to test vital LISA technologies, is to be launched, aboard a SMART-2 mission, in 2006. The proposed mission ASTROD will, among other goals, also aim at detecting gravitational waves, at even lower frequencies than LISA. Its later start will allow it to benefit from the expertise gained with LISA
