ESA GNC Conference Papers Repository
Analysis of ITÜ NXG I Next Generation Technology Demonstrator from a Controls Perspective
Precise formation-flying control of free-flying satellites and monolithic flexible multi-body structures is an enabling technology for next generation controlled aperture missions such as on-orbit assembly and repair of spacecraft. All of these require unprecedented levels of precision in terms of relative navigation and control including precision orbit and attitude control of light weight-flexible structures Our previous work identified technology drivers and requirements for these next generation missions (e.g. XEUS, DARWIN) and proposed a low-cost test-bed ?TÜ-NXG I to demonstrate key technologies for relative metrology, navigation, robust control of flexible monolithic structures and formation flying control of two spacecraft. ?TÜ-NXG I is a pack of two nano-satellites (each 20cm cubes with approximately 10 kg of mass) launched joined together. Once in space, it includes a progressive three main control and navigation tests. One of these tests involve precise navigation (0.0001m relative, 0.05 deg) and control (0.001m, 0.1 deg) of a monolithic formation separated with a 2 meter flexible rod connecting them. This work focuses on the control system design and relative position and attitude analysis of the monolithic flexible structure mode. First we present the dynamical modelling of such a monolithic flexible structure, and then show a robust control system design for coordinated attitude control and vibration suppression of the on-board metrology experiments. The modelling approach hinges on the flexible multi-body structure form in which the satellites are modelled as two rigid bodies connected by an Euler-Bernoulli beam. The inertial reference frame is located at one of the bodies and is in orbit around the Earth. Control system design is performed through a regulation approach in quadratic form. The paper is concluded with a discussion on results and plans of future activity for rapid maturation of key components and technologies through various precursor pico-satellite missions.