While a paradigm shift in space industry has already started involving “mass production” of higher standardized, large distributed systems such as constellations, there are no effective solutions existing for the “mass removal” of satellites. Many indicators point to a further increase in the space traffic in Earth orbit in the near future, which could imply new dynamics in the evolution of the space debris environment. Even in case of diligent compliance with the Inter-Agency Space Debris Coordination Committee (IADC) mitigation guidelines, the growth in space traffic complicates its management and drastically increases the probability of accidents and system failures. NASA scientist Donald J. Kessler proposed a scenario in which the density of objects in low Earth orbit is high enough that collisions between objects could cause a cascade that renders space unusable for many generations. Therefore, a reliable and affordable capability of removing or servicing non-functional objects is essential to guarantee sustainable access to Earth orbit. Recently, the CubeSat design standard introduced a new class of cost-efficient small spacecraft and thereby offers a potential solution to the active debris removal (ADR) problem. The development of a novel “CubeSat-compatible” ADR technology has significant advantages such as the use of commercial off-the-shelf parts, reduced launch cost, and reduced design efforts. This thesis presents –in the frame of an ADR mission– an approach to advanced rendezvous and docking with non-cooperative targets via CubeSat. It covers the design process of simulation systems used for verification purposes, the ideation and implementation of novel guidance, control, and docking techniques, as well as their verification and evaluation. The outcome of this research is a series of validated software tools, processes, technical devices, and algorithms for automated approach and docking, that have been tested in simulation and with prototype hardware.

This book focuses on the theory and design methods for guidance, navigation, and control (GNC) in the context of spacecraft rendezvous and docking (RVD). The position and attitude dynamics and kinematics equations for RVD are presented systematically in accordance with several different coordinate systems, including elliptical orbital frame, and recommendations are supplied on which of these equations to use in different phases of RVD. The book subsequently explains the basic principles and relative navigation algorithms of RVD sensors such as GNSS, radar, and camera-type RVD sensors. It also provides guidance algorithms and schemes for different phases of RVD, including the latest research advances in rapid RVD. In turn, the book presents a detailed introduction to intelligent adaptive control and proposes corresponding theoretical approaches to thruster configuration and control allocation for RVD. Emphasis is placed on the design method of active and passive trajectory protection in different phases of RVD, and on the safety design of the RVD mission as a whole. For purposes of verification, the Shenzhou spacecraft’s in-orbit flight mission is introduced as well. All issues addressed are described and explained from basic principles to detailed engineering methods and examples, providing aerospace engineers and students both a basic understanding of, and numerous practical engineering methods for, GNC system design in RVD.

Rendezvous and docking missions have been a mainstay of space exploration from the Apollo program through present day operations with the International Space Station. There remains a growing interest in several mission types that not only rely on rendezvous and docking, but also rely on maneuvering spacecraft once docked. For example, there is active interest in orbital debris removal, on-orbit assembly, on-orbit refueling, and on-orbit servicing and repair missions. As these missions become more and more popular, the number of rendezvous and docking class operations will increase dramatically. Current methods focus on performing rendezvous and docking to very well-known targets and in very well-known conditions. Inherent to these new mission types, however, is an increasing element of uncertainty to which new guidance and control architectures will need to be robust. As guidance and control techniques become more robust, a corresponding tradeoff in performance can typically be experienced. This thesis attempts to address the uncertainties in rendezvous and docking operations while maintaining a probabilistically optimal level of performance. There are two main focuses in the thesis: spacecraft trajectory optimization and reference-tracking controller selection. With respect to trajectory optimization, the goal is to nd probabilistically optimal trajectories given large uncertainties in mission critical parameters, such as knowledge of an obstacle's position, while knowing that the trajectory is able to be replanned onboard the spacecraft when higher precision information is obtained. This baseline optimal trajectory and subsequently replanned trajectories are then followed by an optimally determined set of reference-tracking controllers. These controllers are selected and scheduled throughout the phases of the mission based on the probabilistically expected performance in the presence of noise and uncertain parameters. This process is explored through its implementation on a generic problem setup for rendezvous, docking, and joint maneuvering. Results specfic to this problem and associated analysis motivate the use of probabilistic planning in future space missions. Specically, the thesis shows that fuel and tracking performance can be improved if multi-stage missions are planned continuously through phase transitions and without the use of waypoints. Furthermore, under the presence of large uncertainties, the techniques in this thesis produce better expected fuel and tracking performance than traditional trajectory planning and controller selection methods.

Non-cooperative spacecrafts are those current or future assets in orbit which have lost their control authority in one or more degrees of freedom and cannot convey any information concerning their position, attitude or rates to facilitate Rendezvous and Docking/Berthing (RVD/B) process. A growing field of study in space research is to develop On-Orbit Servicing (OOS) technology capable of dealing with these space- crafts, called targets, which are designed without any intention to be serviced. To render services such as repair, refuel or removal of the target from orbit, the chaser spacecraft should exhibit sophisticated RVD/B technology for formation fly and final stage docking/berthing operations of the mission. Assuming that the terminal capture operations of the target are to be performed by a suitable manipulator system on-board chaser, this study relies upon proven technology and outlines guidance and control methodologies to achieve rendezvous during proximity phases. The entry gate of chaser after phasing can be defined at a distance of about 5 km in ± V-bar direction from the target in its orbit. To account for errors in modeling, navigation or actuation, proximity range operations from the entry gate are decomposed into three different subphases as far range, inspection or fly around and closer approach. From the entry gate and along the path of the chaser two hold points are defined: first to initiate an inspection and the second, which is close to the safe zone defined around the target, to initiate a capture. The chaser is assumed to perform a station keeping maneuver at the second hold point until initial conditions for the capture are met. Possible scenarios pertaining to the behavior of the target in a circular orbit are considered and guidance schemes for different subphases are presented using a combination of Hill-Clohessy-Willtshire (HCW) solution, elliptical fly around, glides- lope algorithm etc. Relative controllers both for position and attitude of the chaser are also presented. A Linear Quadratic (LQ) controller for relative position and a Proportional Integral Derivative (PID) controller for relative attitude with angular velocity constraints are chosen to track down the error to achieve rendezvous and attitude synchronization with the non-cooperative target. A comparative analysis between different guidance trajectories for important parameters such as time, fuel usage, minimum absolute distance and the maximum radial distance from the target is presented. Verification of the proposed guidance and control methods is done by applying them to two different case studies: the first study incorporating a stabilized target in Geostationary Earth Orbit (GEO) and the second, with a spinning target in Low Earth Orbit (LEO). The methods presented here are general and provide a simulator to the chaser to perform rendezvous analysis with non-cooperative targets. To achieve RVD/B, the study proposes a careful combination of guidance solutions for different phases of proximity operations, and for different scenario’s of the target encountered by the chaser.

Mots-clés de l'auteur: space ; satellite ; cubesat ; rendezvous ; docking ; vision-based navigation ; robust control ; H-infinity ; mu-synthesis ; mu-analysis.

Includes the proceedings from the 7th IAASS Conference, "Space Safety is No Accident," held in Friedrichshafen, Germany, in October 2014. The 7th IAASS Conference, “Space Safety is No Accident” is an invitation to reflect and exchange information on a number of topics in space safety and sustainability of national and international interest. The conference is also a forum to promote mutual understanding, trust and the widest possible international cooperation in such matters. The once exclusive “club” of nations with autonomous sub-orbital and orbital space access capabilities is becoming crowded with fresh and ambitious new entrants. New commercial spaceports are starting operations and others are being built. In the manned spaceflight arena a commercial market is becoming a tangible reality with suborbital spaceflights and government use of commercial services for cargo and crew transportation to orbit. Besides the national ambitions in space, the international cooperation both civil and commercial is also gaining momentum. In the meantime robotic space exploration will accelerate and with it the need to internationally better regulate the usage of nuclear power sources. Space-bound systems and aviation traffic will share more and more a crowded airspace, while aviation will increasingly rely on space-based safety-critical services. Finally, most nations own nowadays space assets, mainly satellites of various kinds and purposes, which are under the constant threat of collision with other spacecraft and with the ever increasing number of space debris. Awareness is increasing internationally (as solemnly declared since decades in space treaties) that space is a mankind asset and that we all have the duty of caring for it. Without proactive and courageous international initiatives to organize space, we risk to negate access and use of space to future generations.

The capability to rendezvous and dock with tumbling objects has become prominent with increased interest in active debris removal, satellite servicing, and in-space assembly. Guidance and control algorithms have been developed in the literature to allow for a spacecraft to capture an uncooperative and tumbling object under several constraints such as collision avoidance, speed bounds, and thruster saturation. However, current algorithms for this capability do not address plume impingement due to thrusters, which can lead to damage to the target object, and can require the use of nonlinear solvers that neither guarantee convergence of a solution nor be deployed in real-time using current computational capabilities of spacecraft. This thesis presents a quasi-analytical guidance algorithm that allows for a spacecraft to soft-dock with a target, avoids plume impingement, and allows for real-time generation of trajectories with low computational expense. Several test cases compare the solution from this algorithm against a solution using pseudospectral methods and show similar performance at less than 0.1% computational cost, and an example scenario for docking with the the European Space Agency’s ENVISAT is presented. Additionally, a discrete transport trajectory optimizer is presented for use as a first cut solution to transporting several components to the same halo orbit for in-space assembly.