Brief Introduction

Gravitational radiation has the potential of providing a powerful new window on the universe for observing the behavior of astronomical systems under conditions of strongly non-linear gravity and super-high velocities. Because of seismic and gravity gradient noise on Earth, searches for gravitational radiation at frequencies lower than 10 Hz must be done in space. The frequency range 10^-4 to 1 Hz contains many of the most astrophysically interesting sources. In this band, predicted emission includes that associated with the formation or coalescence of massive black holes in galactic nuclei. LISA is a constellation of three spacecraft that uses laser interferometry to precisely measure distance changes between widely separated freely falling test masses housed in each spacecraft. The spacecrafts are at the corners of an equilateral triangle 5x10⁶ km on a side in heliocentric orbit. LISA should observe low frequency gravitational radiation from likely sources out to cosmological distances, and would be an important complement to the ground-based experiments already being operated. LISA is a NASA/ESA mission and is expected to launch at the beginning of the next decade.