Hans Strauch

Michael Erhard, Hans Strauch

In this paper we present the basic features of the flight control of the SkySails towing kite system. After introduction of coordinate definitions and basic system dynamics we introduce a novel model used for controller design and justify its main dynamics with results from system identification based on numerous sea trials. We then present the controller design which we successfully use for operational flights for several years. Finally we explain the generation of dynamical flight patterns.

Michael Erhard, Hans Strauch

Energy harvesting based on tethered kites benefits from exploiting higher wind speeds at higher altitudes. The setup considered in this paper is based on a pumping cycle. It generates energy by winching out at high tether forces, driving an electrical generator while flying crosswind. Then it winches in at a stationary neutral position, thus leaving a net amount of generated energy. The focus of this paper is put on the flight control design, which implements an accurate direction control towards target points and allows for a flight with an eight-down pattern. An extended overview on the control system approach, as well as details of each element of the flight controller, are presented. The control architecture is motivated by a simple, yet comprehensive model for the kite dynamics. In addition, winch strategies based on an optimization scheme are presented. In order to demonstrate the real world functionality of the presented algorithms, flight data from a fully automated pumping-cycle operation of a small-scale prototype are given. The setup is based on a 30m$^2$ kite linked to a ground-based 50kW electrical motor/generator by a single line.

Hans Strauch, Klaus Luig, Samir Bennani

The cost associated with developing flight control forms a significant part of the overall development cost. The increased demand for greater functionality and for extending the domain of applicability of future launchers leads to higher complexity of the GNC algorithms. Furthermore, there is also a need for a responsive design methodology, which can quickly adapt to changes in the requirements during the development process. These demands are stretching the current,largely manual, development process, which is fragmented in the different disciplines and activities concerning modelling, algorithm design, software coding, implementation on the avionics platform and the associated testing at the different stages. The model-based-design (MBD) philosophy presents an attractive solution in addressing the multi-disciplinary nature of the flight algorithm design task. In terms of design process, this materializes in a tight coupling between the modelling, the design and the analysis activities.An integrated design framework for the GNC development for future launcher upper stages has been realized.

Christina Jetzschmann, Hans Strauch, Samir Bennani

This paper presents a model based experimental investigation to demonstrate the usefulness of an active damping strategy to manage fluid sloshing motion in spacecraft tanks. The active damping strategy is designed to reduce the degrading impact on maneuvering and pointing performance via a force feedback strategy. Many problems have been encountered until now, such as instability of the closed loop system, excessive consumption in the attitude propellant or problems for engine re-ignition in upper stages. Mostly, they have been addressed in a passive way via the design of baffles and membranes, which on their own have mass and constructive impacts. Active management of propellant motion in launchers and satellites has the potential to increase performance on various levels. This paper demonstrates active slosh management using force feedback for the compensation of the slosh resonances. Force sensors between tank and the carrying structure provide information of the fluid motion via the reaction force. The control system is designed to generate an appropriate acceleration profile that leads to desired attenuation profiles in amplitude, frequency and time. Two robust control design methods, one based on $μ$ design and the other on parametric structured design based on non-smooth optimization of the worst-case $H_{\infty}$ norm, are applied. The controller is first tested with a computational fluid dynamics simulation in the loop. Finally a water tank mounted on a Hexapod with up to $1100$ liter is used to evaluate the control performance. The paper illustrates that is possible to actively influence sloshing via closed loop.

Michael Erhard, Hans Strauch

We present the sensor setup and the basic navigation algorithm used for the flight control of the SkySails towing kite system. Starting with brief summaries on system setup and equations of motion of the tethered kite system, we subsequently give an overview of the sensor setup, present the navigation task and discuss challenges which have to be mastered. In the second part we introduce in detail the inertial navigation algorithm which has been used for operational flights for years. The functional capability of this algorithm is illustrated by experimental flight data. Finally we suggest a modification of the algorithms as further development step in order to overcome certain limitations.