LARGE PIONNERING SCIENTIFIC EXPERIMENT PROJECT LISA or extreme-mass-ratio inspirals- as well as cosmological sources. Furthermore, such an instrument can observe the inspiral of compact binaries that will eventually be detected on Earth, but much earlier in time- from a few hours to up to a year- well before they enter the audio-frequency band of groundbased detectors. After decades of development and the successful demonstration of free-falling test-mass technology with ESA’ s LISA Pathfinder mission [ 4 ], the Laser Interferometer Space Antenna( LISA) was selected in 2017 [ 5 ] as the L3 mission of ESA’ s Cosmic Vision program and formally adopted in 2024. Launch is planned in the mid-2030s [ 6 ]. LISA consists of three spacecraft( S / C) forming an equilateral triangle with 2.5-million-km sides in a heliocentric orbit( Fig. 1). Together they act as a giant space-based Michelson interferometer, with a third arm providing independent measurements of the two GWs polarizations and system redundancy. The formation is centered in the ecliptic plane, 1 AU from the Sun and about 20 ° behind Earth. Its plane is inclined by 60 °, and the S / C orbits are designed to preserve the triangular configuration throughout the year, making the formation appear to rotate once per year around its center. Each S / C houses two free-falling test masses( TM), one at the end of each arm( Fig. 2). A drag-free control system adjusts the S / C position to follow the TMs, ensuring they remain in near-perfect free fall and serve as inertial references. Along every arm, two laser beams are continuously exchanged between S / C. By comparing the phase of the received light with that of the local laser, LISA measures
Figure 1. LISA mission orbit( not to scale): three S / C in an equilateral triangle of 2.5 million km arm, trailing on heliocentric orbit, behind the Earth at ~ 50 million km.
tiny distance variations projected along the arms— variations that directly reveal the passage of GWs through the three-satellite constellation. The three S / C will be launched from the Guiana Space Centre in Kourou, aboard an Ariane 6.4. The scientific payload is composed of subsystems developed by sixteen European partners- space agencies, laboratories and industry – together with NASA, under ESA leadership. OHB System AG serves as Industrial Prime Contractor, leading a consortium in which Thales Alenia Space Italy is a core team member responsible, among others, of avionics and telecommunications.
Figure 2. LISA measures pm distance variations between free-falling test masses situated at the end of each arm, using laser beams exchanged between the satellites.
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