The LISA mission is a planned gravitational wave observatory in spacethat will use inter spacecraft laser links to measure their relative distancechanges. In the current baseline implementation, each spacecraft will utilize two optical subsystems. This approach requires an optical connectionbetween the two subsystems, planned as a fiber-based connection. Theseoptical fibers are prone to disturbances by external factors. Thus, it wasfound that fiber dynamics will limit the phase performance of this connection, the "backlink." The primary contributors in the scope of LISAare fiber backscatter and phase signals induced by temperature or motionof the backlink fiber.A new transportable measurement setup was developed to obtain valuesfor these fiber dynamics. Additional equipment was implemented to measure the temperature and motion effects: a temperature modulator and amotion simulator. The effects of ionizing radiation on the backscatteredsignal were investigated since backscattered light is one of the primaryfactors limiting the performance and not yet tested for changes in therelevant environment.Four types of fibers were tested in backscatter and temperature couplingproperties: the successor of the fibers in the LISA pathfinder mission, apolarizing fiber, and later two types of fibers with larger core diameters.It was necessary to switch to these large core fiber candidates to prevent stimulated Brillouin scattering from arising. These new fiber typesshowed less backscatter than the previous candidates. All tested typesshowed no change in the backscattered power under increasing exposureto ionizing radiation within the expected levels of LISA. Therefore, nodegradation of the backlink’s performance is expected over the missionduration.Temperature-to-phase coupling of the fiber candidates was measured, andit was found that the new fibers offer lower temperature coupling. Thislower coupling makes the backlink less prone to phase noise induced bytemperature fluctuations. The motion mock-up simulates a LISA-likefiber motion to estimate the phase coupling of this fiber motion which isless than 1 rad=°.Lastly, the measured coupling factors and the updated backscatter numbers were implemented in an existing simulation of the backlink’s performance. These simulations show that the change in fiber type is beneficialfor the backlink’s performance as the noise decreases. Adding the motioninto these simulations also reveals that the coupling found is low enoughto be negligible and not change the performance significantly.The ongoing "Three-Backlink experiment" and the future backlink engineering model studies can be used to verify the impact of these dynamicson the performance experimentally.