  In the context of the Laser Interferometer Space Antenna (LISA), the laser
subsystems exhibit frequency fluctuations that introduce significant levels of
noise into the measurements, surpassing the gravitational wave signal by
several orders of magnitude. Mitigation is achieved via time-shifting
individual measurements in a data processing step known as time-delay
interferometry (TDI). The suppression performance of TDI relies on accurate
knowledge and consideration of the delays experienced by the interfering
lasers. While considerable efforts have been dedicated to the accurate
determination of inter-spacecraft ranging delays, the sources for onboard
delays have been either neglected or assumed to be known. Contrary to these
assumptions, analog delays of the phasemeter front end and the laser modulator
are not only large but also prone to change with temperature and heterodyne
frequency. This motivates our proposal for a novel method enabling a
calibration of these delays on-ground and in-space, based on minimal functional
additions to the receiver architecture. Specifically, we establish a set of
calibration measurements and elucidate how these measurements are utilized in
data processing, leading to the mitigation of the delays in the TDI Michelson
variables. Following a performance analysis of the calibration measurements,
proposed calibration scheme is assessed through numerical simulations. We find
that in the absence of the calibration scheme, the assumed drifts of the analog
delays increase residual laser noise at high frequencies of the LISA
measurement band. A single, on-ground calibration of the analog delays leads to
an improvement by roughly one order of magnitude, while re-calibration in space
may improve performance by yet another order of magnitude. Towards lower
frequencies, ranging error is always found to be the limiting factor for which
countermeasures are discussed.
