The primary objective of the subsystem discussed in this report is to continuously estimate the transfer-response of the system using the position measured by the interferometer, in order to accomplish adapted model inverted control using a dynamically updating model. In addition, this subsystem design incorporates a controller that is crucial for obtaining undisturbed position measurements. This is achieved through a feedback loop that is controlling the DC operating point of the interferometer such that it is at its quadrature point.