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Europa, the smallest of the Galilean satellites, is characterized by a young water-ice surface showing a rich structure of cracks, ridges and chaotic terrain. Below the ice shell a subsurface water-ocean might exist, which in Europa’s case would be in direct contact with the silicate mantle. This direct contact is important from an astrobiological perspective, as living organisms might have developed at places where a hot part of the mantle contacts the ocean. As a consequence, many scientists consider Europa as the planetary body with the largest probability to harbor life within our solar system. It is therefore of utmost importance to find out whether a subsurface ocean exists underneath the ice shell. One plausible method to determine the existence of an ocean is based on the measurement of the radial deformation induced by the eccentricity-tide acting on Europa. If an ocean is present in the interior, the radial deformation at the surface will be one to two orders of magnitude larger than in the case that an ocean is absent. Such a large difference in deformation can be detected from measurements performed by a dedicated orbiter. As a result, a mission to the Jovian system would be required. An alternative method to determine whether there is a subsurface ocean underneath the ice shell is based on establishing a connection between the shape of the lineaments observed on the surface and the acting stress fields. Stresses at the surface might be induced by several different mechanisms, from which only the two most important will be analyzed in this research: the eccentricity-tide acting on Europa and non-synchronous rotation (NSR) of the ice shell. The first mechanism, i.e. the eccentricity-tide, induces a highly variable stress field that explains the formation of cycloidal features even without taking into account NSR stresses. The second mechanism, i.e. NSR, induces a nearly static stress field that explains the formation of slightly-curved or global lineaments. As both types of lineaments exist on Europa’s surface, the strength of NSR stresses should have changed throughout the geological history of Europa. Such a change can be driven by a variable rate of non-synchronous rotation, which can be the result of thickness variations in the ice shell. One important result obtained in this research is that tensile stresses at the surface of models without a subsurface ocean are too small to originate a crack at the surface if NSR is not taken into account. If NSR stresses are added to the modeling of the stress field, tensile stresses only become large enough to break ice when the stress field is practically static. As a result, the existence of cycloidal features strongly suggests the existence of a subsurface ocean underneath the ice shell of Europa.

In November 2003 the Voyager 1 spacecraft pierced through the Solar system’s termination shock, followed by Voyager 2 in August 2007. These events marked the beginning of interstellar exploration by spacecraft, which caused a wave of renewed interest in the outer heliosphere throughout the scientific community. This thesis research investigated the feasibility of a mission to the Solar bow shock (the true interstellar boundary) at ∼200 AU from the Sun; twice as far as the Voyager spacecraft. The techniques used in designing its trajectory were standard gravitational-assist manoeuvres and/or a single close-proximity flyby with the Sun, and both low-thrust and high-thrust propulsion systems were investigated. Minimum time of flight and maximum spacecraft dry mass were primary objectives, whereas the number and quality of minor planet flybys were secondary objectives. A maximum on the time of flight of 15 years was upheld, extendible to a maximum of 25 years in case the first constraint could not be met or proved overly beneficial to the other objectives. This constraint necessitated upholding a maximum of 3 gravitational-assist manoeuvres, which gave rise to a search space of 146 unique flyby sequences. A novel optimization algorithm developed in this thesis (GODLIKE) identified 3 feasible sequences, which were only feasible in combination with a high-thrust propulsion system. The most promising sequence (Earth/Jupiter/Uranus/bow shock) proved capable of reaching the bow shock with minimal risk and impact on the spacecraft’s dry mass. The best result found requires a ∆V of 5.86 km/s and approaches approximately 14 minor planets to within 0.03 AU. The total time of flight could unfortunately not be kept below 15 years; technically feasible trajectories could only be generated for times of flight between 23 and 25 years. Despite the long time of flight, the results developed in this research do show that it is possible to traverse the entire heliosphere using time-proven and conventional means.

Currently, the student amateur rocket association Delft Aerospace Rocket Engineering (DARE), is designing a small sounding rocket to carry payloads to over 50 km, the Stratos II. Proper operation of this rocket will require an on-board position and attitude determination system. In this thesis, it will be researched how this position and attitude determination can be performed. In essence, the research can be divided into three main topics: simulation, measurement and estimation. Flight estimation is the main goal of the research, while simulation and measurements are prerequisites to estimation. A measurement system with low-cost sensors has been designed and built, and during calibration the performance of these sensors has been established. This measurement system has flown in an actual small sounding rocket, the Stratos II concept launcher, and acceleration, angular velocity and atmospheric pressure data have been acquired. Several estimators have been researched, from which the extended Kalman filter was selected as the most suitable to estimate the position and attitude. The accelerometer and gyroscope measurements are used to propagate the state, and the other measurement data to improve the state estimate, and to estimate various noise factors of the sensors. Measurements are generated from simulations of nominal and non-nominal flights, with nominal and non-nominal sensors, to verify the performance of the estimator. It was found that both the flight trajectory, as well as sensor noise factors such as bias and non-orthogonality strongly affect the estimation result. As only coarse requirements on the position and attitude determination system are available, it cannot be concluded with certainty that the developed measurement system and estimator are suitable for the Stratos II. However, preliminary analysis performed in this thesis, indicates that this is the case. Furthermore, in this thesis clear guidelines are established to improve the estimator performance, should the developed system not satisfy the final requirements.

The optimization of high-thrust interplanetary trajectories continues to draw attention. Especially when both Multiple Gravity Assists (MGA) as well as Deep Space Maneuvers (DSMs) are included, the optimization is typically very difficult. The search space may be characterized by a large number of minima and is furthermore very sensitive to small deviations in the decision vector. Various options are available to model these high-thrust trajectories. The trajectory may be modeled using a simple MGA trajectory model as well as using models including DSMs. Both a position and a velocity formulation variant may be adopted and also unpowered or powered swing-bys may be used. These trajectory models were implemented to study the effect of both DSM as well as powered swing-bys. Especially the option to perform DSMs proved to be vital for obtaining good trajectories. Also powered swing-bys may improve the efficiency of the trajectory. The velocity formulation variant proved to be much easier to optimize than the position formulation model. By analyzing the sensitivity and dependency of the various parameters in both models, a proposal for an even better trajectory model is suggested. Also regarding the optimization of these trajectories many options are available. Especially metaheuristics have proven to be very successful in optimizing these trajectories. Various studies have shown the importance of proper tuning of the basic versions of these metaheuristics, which is however often overlooked. This study applied a very rigorous tuning scheme to find the optimal settings for DE, GA and PSO. The results clearly reveal the superiority of DE above other methods. The tuned variants of DE outperformed other settings by one or multiple orders of magnitude, revealing the importance of this tuning scheme. The tuned variants of DE helped to improve a large number of instances in the Global Optimization Trajectory Problem (GTOP) database of ESA. Also the efficiency of these DE variants was shown to be competitive with, and sometimes better than, the best algorithms encountered in literature.

This dissertation describes the integration of accelerometer measurements of LEO-satellites in GPS-based orbit determination.

This thesis presentation will discuss stability assessments of orbits around asteroids, with in particular the asteroid Eros. The gravity field of an asteroid can be estimated using different techniques. For the thesis work presented the Polyhedron, Spherical Harmonic Expansion and Triaxial Ellipsoid methods are implemented on the Eros case. The differences in performance of the different gravity field modelling techniques will be discussed. The irregularity of the gravity field of Eros will have consequences on the orbital stability of satellites orbiting Eros, the influence of this irregularity will be estimated. Furthermore, the influence of the Solar Radiation Pressure and Third-body Perturbing forces on the stability of orbits around Eros will be determined. With the help of the Monte Carlo method and the Particle Swarm Optimization method a search is performed to find stable orbits within the vicinity of Eros.

The research can be placed in the framework of designing methods for complex systems focused on the conceptual design phase of the systems’ life-cycle. More specifically, the methods presented in the dissertation belong to the category of Operational Research methods. They aim at the creation of design and analysis tools in support of the engineering team during conceptual design activities. Even though the proposed methods are referred to space-systems applications throughout the dissertation, they are easily extendable also to other engineering applications. This aspect makes the research of great theoretical and practical interest also outside the aerospace industry. A powerful methodology was developed that is typical of more specialist applications (for more detailed design phases) and that is flexible and fast to execute at the same time as required for a conceptual design phase of a complex system.