An adaptive Backstepping attitude control law based on Immersion and Invariance (I&I) is developed for the TU Delft FAST-D micro-satellite. Tackling both system uncertainties and disturbances, a general additively disturbed rotational dynamics model is considered. In the I&I framework the parameters to be estimated are typically constant. Here, however, a family of I&I-Backstepping controllers is shown to be input-to-state stable for a class of strict-feedback systems with time-varying uncertainties. This novel result allows the design of an I&I attitude controller for the spacecraft model considered. The developed control law shows superior performance with respect to Standard (non-adaptive) and Tuning Functions adaptive Backstepping controllers under nominal and heavily perturbed conditions.
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