LISA R&D

Home page of the Experiment:

http://sci.esa.int/home/lisa

http://lisa.jpl.nasa.gov/whatis.html

LISA, Laser Interferometer Space Antenna for the detection of Gravitational waves, is a project aimed at placing in a heliocentric orbit, a constellation of three spacecraft acting as a gravitational wave antenna for signals in the frequency range between 0.1 mHz and 0.1 Hz.

The orbits of three spacecraft are adjusted such that they form an equilateral triangle with a side of 5x106 km revolving around the sun and rotating in its own plane. Inside each of the three spacecraft, there are two 1 kg test-masses kept in "free fall" by keeping any non-gravitational force acting onto them at <3 10-15 N/Hz1/2. A key point of this free fall is a "drag-free" control loop that keeps the spacecraft centered onto the test-masses by using a proper relative displacement detector and a set of micro-Newton thrusters. Each test-mass forms, together with one placed in a different spacecraft, the end mirror of a 5x106 km arm-length laser interferometer that then measure the distance between the two test masses with a goal resolution of 40 pm/Hz1/2. The three resulting interferometers form a gravitational wave detector similar to the Earth-based ones like VIRGO and LIGO, but with an additional redundant arm and a 5x106 km arm-length instead of a few kilometers.

LISA targets at detecting with signal to noise ratios in excess of 500, galactic binaries of which basically everything is known. This kind of sources will act as standard candles for LISA and there is no uncertainty about the detection of their signal. In addition to that LISA will search for the signals coming from super-massive black holes binaries formed during merger of galaxies. Many of these signal are predicted during the 2-year minimum lifetime of LISA with signal to noise ratios in excess of 100 for binaries at z 1-3. Other potential sources for LISA are stellar-mass black holes falling into a super-massive one, a probe of the gravitational field at the event horizon that constitute a unique experiment in gravitational physics in the strong field limit.

LISA is a Cornerstone mission of the European Space Agency (ESA) and is in the strategic plans of NASA. It is foreseen as a 50%-50% collaborative experiment between Europe and the USA with a launch in 2010-2011. Prior to the launch of the mission, both agencies plan for a launch of an in-flight test of the relevant technology, i.e. the free-falling test mass with all connected instrumentation, around 2005.

The present INFN experiment deals with a R&D study of the test-mass and the related displacement sensor and with the development of a torsion pendulum based test bench to assess the level of disturbances affecting the test-mass.

INFN and ASI are the supporting agencies for the Italian participation to LISA. In particular INFN has been supporting the Gravitational Wave Group at Trento that constitutes the core of the Italian participation. Out of the 10 European Members of the ESA/NASA Joint Lisa International Science Team (LIST) 2 are Italians and are both INFN associates.