  The Laser Interferometer Space Antenna (LISA) will observe gravitational
radiation in the milliHertz band by measuring picometer-level fluctuations in
the distance between drag-free proof masses over baselines of approximately
five million kilometers. The measurement over each baseline will be divided
into three parts: two short-arm measurements between the proof masses and a
fiducial point on their respective spacecraft, and a long-arm measurement
between fiducial points on separate spacecraft. This work focuses on the
technical challenges associated with these long-arm measurements and the
techniques that have been developed to overcome them.
