Abstract:
The Laser Interferometer Space Antenna (LISA) is a space mission jointly
proposed to NASA and ESA, and aimed to detect and study low-frequency
(millihertz) gravitational radiation.
LISA will use coherent laser beams exchanged between three remote
drag-free spacecraft, and will rely on measurements performed by multiple
Doppler readouts. These incorporate frequency standards used to heterodyne
phase differences between the received and transmitted laser beams. By
properly time-shifting and linearly combining the Doppler data one
can remove the phase fluctuations of the lasers, the mechanical vibrations
of the optical benches, and the phase fluctuations of the frequency
standards while preserving the gravitational wave signal.
All these observables show different couplings to gravitational waves and
to the various remaining LISA instrumental noises, and offer redundancy
against loss of any two of the one-way Doppler links. Moreover, by
comparing the "Michelson interferometer" observable with the
fully-symmetric Sagnac observable, one can unambiguously discriminate
between the on-flight instrumental noise and the Galactic gravitational
wave background from binary systems, making its unambiguous observation
possible.