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In this paper an adaptive, disturbance-based sliding-mode controller for hypersonic entry vehicles is proposed. The scheme is based on high-order sliding-mode theory, and is coupled to an extended sliding-mode observer, able to reconstruct online the disturbances. The result is a numerically-stable control scheme, able to adapt online to reduce the error in presence of multiple uncertainties. The transformation of a highorder sliding-mode technique into an adaptive law by using the extended sliding-mode observer is, together with the multi-input, multi-output formulation for hypersonic entry vehicles, the main contribution of this paper. The robustness is veried with respect to perturbations in terms of initial conditions, atmospheric density variations, as well as mass and aerodynamic uncertainties. Results show that the approach is valid, leading to accurate disturbance reconstruction, to a better transient, and to good tracking performance, improved of about 50% in terms of altitude and range errors with respect to the corresponding standard sliding-mode control approach.

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The effect of sloshing on the controllability of a conventional aeroelastic launch vehicle Mooij, Erwin; Gransden, Derek I.

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Since before I can remember, I have had a near-obsession with everything related to outer space. Whether it was in the form of astronomy, science fiction, or actual space flight, something about the vast universe beyond the frail atmosphere of our home planet has always been able to capture my imagination. Therefore, I like to see this thesis not only as the final result of my six years of study at the Delft University of Technology, but also as the culmination of a life-long fascination with the topic.Sentimental reminiscing aside, I would like to spend a few words on the background of this thesis. When ESA released a call for proposals for the design of a GNC system for deorbiting the derelict Envisat in early 2013, it was originally envisioned that the Delft University of Technology would join forces with Dutch Space, now Airbus Defence & Space Netherlands, to submit such a proposal. Furthermore, such a proposal would permit room for an MSc thesis topic, and the MSc coordinator of our department, Ron Noomen, suggested me as a candidate. While the actual proposal itself unfortunately fell through, the thesis topic remained, along with the cooperation with Dutch Space, who graciously allowed me to use the GGNCSIM simulator libraries. With the actual mission to deorbit Envisat well underway, now is an exciting time to be working in the field of active debris removal! Of course, I could not have tackled this challenging thesis topic on my own, and owe a debt of gratitude to a great many people. First, and foremost, I would like to thank my direct supervisor at the Delft University of Technology for this thesis research, Erwin Mooij, for being an outstanding tutor as well as a great sounding board for my ideas. The discussions we had, both on and off topic, proved invaluable for the successful completion of the research and for the preservation of my peace of mind. I would also like to thank Ron Noomen, also of the Delft University of Technology, for proposing me as a candidate for this research in the first place. Furthermore, I would like to thank Marc Oort, Marcel Ellenbroek, and Lex Meijer, all of Dutch Space (forgive my use of the old name), for allowing me to use GGNCSIM, as well as attentively discussing my findings. Remaining in the space industry, I would like to thank Alexander Cropp, of ESA ESTEC, for patiently answering all my questions on the topic. To all my fellow graduate students in the MSc rooms at the faculty, thank you all for making the time I spent there unforgettable. Finally, I would like to thank my family, friends, and girlfried for supporting (and putting up with) me over the course of the past year: I wouldn't have been able to do it without you. ABSTRACTRecent years have seen a steep increase in research being performed towards active space debris removal: space debris has proven to be a very real threat to operational spacecraft, and studies indicate that the frequency of collisions will only increase if nothing is done to remove large pieces of debris. In particular, ESA has done stud...

Ben-Gurion University of the Negev, POB 653, 84105, Beer Sheva, Israel This paper investigates the efficacy of dual quaternion filtering in the realm of asteroid missions. The main contribution is the development of a dual quaternion relative navigation filter applied to asteroid circumnavigation. The simulated target asteroid is Kleopatra, a dog-bone shaped asteroid featuring a low potential highly-perturbed gravity field. The spacecraft is equipped with a navigation camera and a laser ranger for position sensing, and a star tracker and rate gyroscope for attitude sensing. The paper innovates in the methods for landmarks identification within a camera field-of-view, true range and ranging errors determination, and spacecraft gravity-gradient torque modeling. For the sake of comparison, a navigation filter based on a conventional pose representation using Cartesian coordinates position and attitude quaternion is developed and tested under the same conditions. The dual quaternion filter succeeds in estimating the relative pose with high accuracy, as well as the gyroscope drift and the asteroid angular rates. The latter depends on the frequency and geometry of the landmarks lines-of-sight detected within the camera field-of-view. Significant gains in the transients of the estimation errors are achieved by the dual quaternion filter, when compared to the conventional filter. The errors feature similar steady-state levels in both filters.

To limit the mass of the vehicle's thermal protection system, an optimal trajectory that minimizes the total integrated heat load should be flown. In essence this boils down to tracking the maximum heat-flux constraint for as long as possible. A straight-forward and simple implementation for this tracking system could be a (linear) output-feedback controller that has a fast response, although its robustness could be doubtful due to insufficient damping. A possible good alternative is a guidance-tracking system based on so-called simple adaptive control. Such a system can have excellent performance under the influence of rather large uncertainties, although its transient response can be sluggish at times. In this paper the performance of both tracking systems has been compared, as well as an integrated implementation to see whether the individual strong points of the tracking systems can be combined. The system under consideration is a hypersonic test vehicle that has to track a stagnation heat-flux constraint of 1,700 kW/m 2 . The results show that for a nominal mission the performance of the two individual systems is equal. A Monte-Carlo analysis indicates that the tracking error is smaller for the output-feedback controller, but due to its longer tracking time the total heat load is smaller for the adaptive system. Integrating the two systems yields a significant reduction of the tracking error, albeit at the expense of a larger guidance effort.