Last Update: October 2000

LISA R&D

Collaboration:

Trento, Perugia

ESA, NASA, ASI

# 1. Goal of the experiment

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 5 106 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 centred 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 mirrors of a 5 106 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 5 10-6 km arm-length instead of a few kilometres.

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

# 2. Physics achievement in 2000

After a study phase to assess the most relevant source of noise, we have designed and built an inertial sensor with 100 µm precision machining, for overall functionality testing of the design and of the electronics (Fig. 1). We have performed a few tests on the fabrication technology of the electrode housing for a 3 µm precision machined prototype. The technology uses a composite Mo Ceramic construction (Fig.2). The results have been satisfactory. As a consequence we have now designed a prototype based on this technology which is currently under fabrication (Fig. 3). We have designed a torsion pendulum test bench (Fig. 5) including a vacuum chamber (Fig. 6) and a micro-positioning system (Fig. 7 and 8) for the test-mass. The pendulum is now under assemblage. We have designed and built the readout electronics including an oscillator, a Blumlein bridge, a preamplifier and a PSD. We have performed a full noise calculation for the readout electronics. Preliminary tests agree quantitatively with the calculation. We have also a preliminary design of a low frequency suspension loop, a key feature for LISA, with a numerical simulation of its performance.

Fig.1 | Fig.2 | Fig.3 | Fig.4
Fig.5 | Fig.6 | Fig.7 | Fig.8

3. INFN contribution to the experiment in terms of manpower and financial support

The group is composed of 5 researchers associated to INFN.

Financial support: 46 Mlit

# 4. Number of Publication in refereed journals

3 strictly related to the project

# 5. Number of talks to conferences

7, all invited.

# 6. Number of undergraduate and doctoral thesis in the experiment

1 graduate student

# 7. Leadership role in the experiment

Member of the core ESA science team

Member of the international LISA team (ESA/NASA)

Prime contractor ESTEC/Contract n. 13691/99/NL/FM(SC), “drag-free satellite for ELITE” (Lisa technology demonstration) with Imperial College, Rutherford Appleton Laboratory and Birmingham University.

Subcontractor to ASTRIUM, LISA System Level Study, ESA

Chair, ESA's Fundamental Physics Advisory Group. Member of ESA Space Science Advisory Committee.

# 8. Innovative instruments

Development of a gravitational sensor for LISA.

Development of a torsion pendulum based test bench for parasitic forces.

# 9. Competing experiments

There are no competing experiments. There is a general consensus that ground based experiments that search for waves in the audio band are complementary to LISA as they look for a rather different kind of gravitational wave sources.

# 10. International committees that have reviewed the experiment.

LISA has been chosen by ESA's SPC has a cornerstone mission in fundamental physics. Has been confirmed in this status by many external and internal reviews. LISA has been endorsed by a series of panels of the NSF and NASA in the USA.