LISA mission and system design

A gravitational-wave observatory is recommended as the seventh cornerstone in ESA's long-term programme in space science, known as 'Horizon 2000 Plus'. A concept for such a gravitational-wave mission, LISA, was studied within ESA in order to assess its feasibility and technological requirements. Six spacecraft in a triangular configuration form a laser interferometer with baselines of 5 x 10(6) km. This interferometer will orbit the Sun at a heliocentric radius of approximately I AU, following the Earth at an angular distance of 20 degrees. Launch of all six spacecraft will be with an Ariane 5 launch vehicle and jettisonable propulsion modules will place the spacecraft in their respective orbits. All six spacecraft are identical and accommodate a payload module which houses a test mass with capacitive sensors, a transmit-receive telescope and lasers. The interferometer arms are determined by the test masses and the spacecraft; must shield the test mass from all extraneous disturbances, requiring a 'drag-free' control system which uses electric thrusters to make the spacecraft follow the test mass.