Laser Interferometer Space Antenna
LISA (Laser Interferometer Space Antenna) is the large-class mission of the European Space Agency’s (ESA) long-term Cosmic Vision programme for the observation of gravitational waves. It will be the first space-based gravitational wave detector.
LISA is a three-arm interferometer consisting of a constellation of three identical satellites, placed at the vertices of an equilateral triangle with 2.5 million km sides, linked in pairs by laser beams.
LISA will orbit the Sun, trailing the Earth by 20°, with each satellite following its own heliocentric orbit. The plane of the constellation is tilted by 60° with respect to the ecliptic (see figure opposite). The triangular formation is maintained almost rigidly and rotates around its centre with the orbital frequency of one cycle per year.
The orbits of each satellite are designed to keep the constellation as “rigid” as possible, with variations in the inter-satellite distances limited to about 1% at most. The system’s dynamics induce variations of the triangular angles of about ±1 degree, while the constellation’s orbits maintain a constant angle relative to the Sun. This ensures a thermally stable environment and, more importantly, allows the solar panels to continuously capture sunlight to charge the onboard batteries of each satellite.
LISA is designed to measure spacetime variations caused by passing gravitational waves thanks to the redundancy of its interferometric arms. These measurements are performed in a frequency band inaccessible to ground-based interferometers (limited by arm length and Earth’s gravity gradient), between 0.1 mHz and 1 Hz. In terms of performance, LISA aims to reach a sensitivity of ΔL/L ~10⁻²¹, corresponding to distance variations of only a few hundred picometres over the 2.5 × 10⁶ km arm length.
LISA at Irfu
The LISA-Irfu group formally joined the LISA consortium in 2018. It is composed of researchers and engineers from five departments: DAp, DEDIP, DIS, DPhN, and DPhP.
Its members are involved in:
- data analysis to contribute to the LISA Data Challenges and advanced data processing techniques,
- multi-messenger observational astrophysics across all wavelengths,
- stellar astrophysics focused on binary population synthesis,
- cosmology,
- fundamental physics related to dark matter, alternative theories of gravity, and physics beyond the Standard Model,
- the development of ultra-stable metrology instruments to qualify the OGSE (Optical Ground Support Equipment) for the AIVT (Assembly, Integration, Validation and Tests) of the MOSA (Moving Optical Sub-Assembly, each satellite payload includes two MOSAs),
- the interface between the LISA performance model and the design of TDI (Time Delay Interferometry) algorithms, which enable the reconstruction of Michelson-type interferometers from LISA data.
Irfu is also strongly involved in the organisation and leadership of the project at both national and international levels.