This thesis project investigates navigational aspects of the upcoming JUICE (JUpiter ICy moons Explorer) mission, which is expected to deliver valuable data products for the scientific study of the Jovian system, and the three Galilean moons Europa, Ganymede and Callisto in particular. One such data product comes from the 3GM radio science payload, which is expected to contribute towards more accurate ephemerides of the Galilean moons and a refined study of their gravity fields. Accurate and reliable acquisition of these data depends greatly on the successful Guidance, Navigation and Control (GNC) operations, where an efficient GNC performance can unlock excess ∆V capabilities. It is the goal of this work to identify statistical ∆V savings from integration of in-mission radio science ephemeris improvements into the GNC operations. The resulting excess ∆V could be used to effectuate one of the mission enhancement and extension options (e.g. coverage of the Jupiter’s mid-high latitudes or a lower-altitude Ganymede orbit), the enablement of which ultimately motivates this thesis project. A navigational orbit determination (OD) framework was set up, modelled closely after the OD setup from the JUICE mission analysis team. An interface for simulating moon state knowledge updates from external ephemeris products was implemented. This setup was then extended to support a simplified statistical ∆V analysis. The external ephemeris products were modelled using an adopted high-fidelity OD setup with a coupled filter configuration, which simulates the uncertainty of in-mission ephemeris updates from the 3GM radio science data. These results were then used to simulate external ephemeris updates to the navigation OD and to evaluate their impact on the statistical ∆V expenditure. It was found that external moon ephemerides in general, and the simulated science data based OD solu- tion in particular, are not suitable for reducing the statistical ΔV cost of post-flyby correction manoeuvres. Within one to two encounters of a given flyby body, the nominal (update-free) navigation OD has improved moon state knowledge to a point where it no longer contributes significantly to size of the correction ma- noeuvres. To generate statistical ΔV savings, the moon state knowledge must be improved for the navigation of the mission’s first encounters. It was thus concluded that moon ephemeris improvements should not be provided from JUICE science data, but from observations that have been collected prior to mission. It was furthermore found that due to its extensive coverage, the navigation tracking data captures system informa- tion that the radio science data is less sensitive to. It could therefore be considered in the post-mission efforts to improve the high-accuracy ephemerides of the Galilean moons.

Interplanetary missions have relied on Radio Science (RS) for recovering gravity fields via detecting their signature on the spacecraft’s trajectory. Yet the weak gravitational fields of small bodies, coupled with the prominent influence of confounding accelerations, hinder the efficacy of this method. Meanwhile, quantum sensors based on Cold Atom Interferometry (CAI) have demonstrated absolute measurements with an inherent stability and repeatability, reaching the utmost accuracy in microgravity. This work addresses the potential of CAI-based Gradiometry (CG) as a means to strengthen the RS gravity experiment for small-body missions. Phobos represents an ideal science case as astronomic observations and recent flybys have conferred enough information to define a robust orbiting strategy, whilst promoting studies linking its geodesic observables to its origin. A covariance analysis was adopted to evaluate the contribution of RS and CG in the gravity field solution, for a mission duration of one week. The favourable observational geometry and the small characteristic period of the gravity signal add to the competitiveness of Doppler observables. Provided that empirical accelerations can be modelled below the nm/s2 level, RS is able to infer the 6x6 spherical harmonic spectrum to an accuracy of 0.1-1% w.r.t. the homogeneous interior values. If this correlates to a density anomaly beneath the Stickney crater, RS would suce to constrain Phobos’ origin. Yet, in event of a rubble pile or icy moon interior (or a combination thereof) CG remains imperative, enabling an accuracy below 0.1% for most of the 10x10 spectrum. Nevertheless, technological advancements will be needed to alleviate the current logistical challenges associated with CG operation. This work also reflects on the sensitivity of the candidate orbits with regards to dynamical model uncertainties, which are common in small-body environments. This brings confidence in the applicability of the identified geodetic estimation strategy for missions targeting other moons, particularly those of the Giant planets, which are targets for robotic exploration in the coming decades.

This thesis studies the dynamics of Phobos, Mars’ bigger moon, as part of the preparation for coming Phobos-bound missions. Existing observations have not been able to properly constrain the interior of the two Martian moons in general and Phobos in particular, being therefore inconclusive about their origin and formation. Thus, on-site measurements with the aid of Phobos landers is planned for the near future. In particular, this thesis focuses on the couplings between Phobos’ translational and rotational dynamics. Their effect in state propagation is quantitatively described and their impact on parameter estimation is assessed. For this, the trajectory of Phobos has been computed by propagating a given initial state in two ways. A first manner integrates Phobos’ translational and rotational equations of motion simultaneously; a second manner integrates Phobos’ translational equations of motion alone, and assumes that Phobos is in a fully-locked configuration with a once-per-orbit longitudinal libration. A first part of the results is an analysis of the differences between these two solutions, in terms of position and orientation. A second part of the solution is the analysis of least-squares estimations, by which the uncoupled model is fit to observations taken from the coupled trajectory. In doing so, the best way in which the uncoupled model can imitate the coupled model by changing some dynamical parameters is found. The results are analyzed in terms of estimation post-fit residuals - the final differences between the coupled and uncoupled solutions - and differences between the parameter estimates and the true parameters. These parameters comprise mostly the once-per-orbit libration amplitude and the quadrupole gravity field, all of which provide information of Phobos’ interior. The outcome of this thesis is a detailed and quantitative study of the extent to which an uncoupled model can imitate a coupled model and how the differences generated by couplings are absorbed into modifications of estimated parameters to keep the to trajectories as similar as possible. This provides a preliminary approximation of the type of true errors that state-of-the-art estimations contained in their fitted solutions.

Interactions between tidal migration and the encounter of mean motion resonances (MMRs) have widely been used in attempts to explain unexpectedly young surfaces and high free eccentricities of moons. A driving variable in this process is the planetary quality factor (Q$), which has so far been assumed to be constant throughout the system. However, data showing faster migration rates for moons farther from the primary indicate otherwise. The proposed mechanism behind this phenomenon is resonance locking, which uses steep localised dips in Qp to explain why certain moons migrate faster than expected. These dips evolve along with the primary, and a secondary may reach the same migration rate, "locking" with a frequency mode. This thesis aims to provide a better understanding of the orbital evolution of pairs of moons in MMRs under the influence of the resonance locking mechanism, from the process of capture into a resonance lock, to the possibility of breaking the MMR. In this context, the differences between first- and second-order MMRs are examined. A higher order numerical model has been developed that combines the effects of tidal migration and MMRs with the newly proposed resonance locking mechanism. It is used to examine a variety of scenarios and test the behaviour of a pair of moons when the inner moon is in a resonance lock. Additionally, the stability of the 2:1 and 3:1 e-type resonances when encountering a mode are examined. It was found that the |Im(k2,p)| required to enter the resonance lock can reach values 50% higher than expected from theory, due to oscillations in mean motion caused by the interactions with the second moon. A substantial growth in eccentricity can be experienced, potentially growing indefinitely provided both the resonance lock and MMR are maintained. Finally, while it is unlikely that a resonance lock has caused an MMR to break in the past of our Solar System due to the lower masses, it may occur for heavier exoplanets. It can be concluded that resonance locking mechanism provides an alternative explanation for high free eccentricities and unexpected surface features. However, to better predict whether moons have been or are affected by a mode, for the Galilean moons data from the upcoming JUICE and Europa Clipper missions are needed. Finally, Juno has already helped constrain some of Jupiter's internal properties, and will continue to do so during the remainder of its mission, which may aid characterisation of the mode characteristics.

The Ganymede Circular Orbit Phase (GCO-500) of the JUICE mission will be the first time a moon beyond Earth’s will be orbited for an extended period of 9 months. This orbit phase, due to its close proximity, opens the window to more accurately determine the spacecraft orbit and thereby unambiguously characterize the interiors of the Galilean moons. Ganymede is believed to harbor an internal ocean and will help understand the habitability of icy worlds in the outer solar system. In this study results of a sensitivity analysis are presented which investigate the settings of a model developed for the GCO-500 phase. The model aims to realistically emulate the JUICE mission concept, by specifically focusing on the radio science experiment 3GM, responsible for estimating the gravity field. The model also includes non-gravitational accelerations which are accounted for by the High Accuracy Accelerometer (HAA).

Single-Stage-To-Orbit (SSTO) launch vehicles are capable of reaching orbit while being potentially fully reusable. A technology capable of enabling SSTO access to space is the air-breathing engine, which has a high specific impulse and low thrust-over-weight (T/W) ratio compared to conventional rocket engines. This necessitates the use of a Horizontal Take-off and Horizontal Landing (HTHL) launch vehicle with a lifting surface, which enables banking maneuvers that can manipulate the orbital Right Ascension of the Ascending Node (RAAN) that the space plane achieves. This means that the space plane is capable of advancing or delaying its time of launch, while still achieving a similar orbital RAAN. This effectively increases the launch window even if a precise orbit insertion is necessary. This thesis answers the question what the fuel-optimal ascent trajectory is for a space plane that would extend its launch window. In order to answer this question, the full six DoF equations of motion have been defined to simulate the ascent trajectory of a space plane. Additionally, a robust Guidance and Control system is developed that can use the nonlinear translational and rotational equations of motion. For several launch times, ranging from two hours earlier to two hours later than the nominal launch time, the ascent trajectory has been optimized that included a banking maneuver. It was found that at the cost of propellant, it is possible to have a launch time delayed are advanced by as much as two hours, which means that the space plane can manipulate the RAAN by ± 30 degrees. The extra propellant cost can be related to increased drag losses during the banking maneuver.

The Mars Ascent Vehicle will bring samples back from the surface of Mars to its low orbit in 2031. Its preliminary design has been performed by NASA, defining it as a two-stage solid propellant rocket. However, a research gap exists in finding what the optimum solid rocket motors geometries are to bring the Martian samples to a target orbit between 300km and 375km above Mars. To this extent, the ascent and propellant burn have been modelled, allowing for variation in the geometry of the motors, but also in the launch and separation angles, and in thrust vectoring control. This model has been incorporated into an optimisation, from which a minimum lift-off mass of 343kg was found, 57kg less than required. In the process, 18 thousand different solutions have been found that satisfy all requirements, would the priority shift from the mass of the vehicle to for instance the burn time, or the final altitude.

As part of the ESA mission to Jupiter and Ganymede carried out by the Jupiter Icy Moons Explorer (JUICE) spacecraft, the Ganymede Laser Altimeter (GALA) will determine the topography and detect Ganymede’s tidal degree-2 signal in order to investigate the existence of a subsurface ocean and constrain its thickness. To deliver successful measurements GALA is to be calibrated for its misalignment with an accuracy of at least 14 arcsec. This misalignment cannot be measured on ground since it will be subject to vibrations, microgravity and settling after launch. Thus this calibration is to be performed while JUICE is on its interplanetary cruise to Jupiter. This thesis aims to answer the question how this calibration can be performed using laser ranging to an Earth-based ground station. This calibration procedure consists of a scan performed by JUICE with a size as large as the maximum expected misalignment found at 333 arcsec. A model for the attitude during laser ranging was developed to be used to simulate the distribution and intensities of the laser pulses transmitted by GALA. During this scan of several hours and with a shot frequency of 30 Hz, the ground station will be able to detect 500 to 1500 pulses. This result was validated with the real life MLA and Hayabusa experiments already performed. The spatial distribution of these detected pulses is used to reconstruct the Gaussian pulse shape of the laser pulses. By determining its peak intensity, the ground station location can be estimated which is used to measure the misalignment. This estimation procedure was found to be robust and reliable enough to be incorporated in the simulation tool that can be run many times to achieve a statistically significant result on the estimation error. Since the estimation is based on the spatial distribution, the main drivers for the accuracy are the slew rate, scan pattern, distance, detection threshold and attitude model. These were investigated for their influence on the calibration and used to find their optimal values. The trajectory of JUICE was analysed for the most optimal opportunities given various constrains to perform a laser ranging campaign leading to a selection of options to be analysed. Using the simulation it was found that interplanetary laser ranging can be used to calibrate GALA by employing 8-10 hours of scanning at a distance no further than around 0.5 AU by using ground station characteristics such as found at Wettzell with a telescope diameter of 0.75 metres and optical and quantum efficiencies of 0.5 and 0.2 respectively. For the most optimal opportunity, laser ranging will be performed at a distance of 0.39 AU for 10 hours with a slew rate of 0.0055 deg/s. This leads to a 2 sigma calibration residual of 3.62 arcsec resulting in a total calibration error of 11 arcsec. This confirms the assumption that a calibration accuracy of 14 arcsec is possible and thus a successful laser altimetry mission can be performed by GALA.

This thesis work has been motivated by the growing interest in small-spacecraft small-body missions and more specifically inspired by a proposed mission to the largest Martian Trojan (5261) Eureka. This binary asteroid represents a promising target for a planetary mission, as a better understanding of its formation and evolution would provide valuable insights into the history of both the Martian system and binary asteroids. This work has focused on identifying orbital designs which would optimise the geodetic parameters estimate, and thus best help characterise the asteroid's internal structure. The orbit determination solutions have been computed from simulated tracking data in various orbital configurations. To compensate the highly perturbed nature of the binary asteroid's environment, pseudo-periodic solutions identified around Eureka have been used as stable initial conditions for the spacecraft orbits. As Eureka's shape, gravity field and rotational state are not well characterised yet, large resulting uncertainties have been accounted for. They have been propagated to assess the robustness of the spacecraft orbits and subsequent orbit determination solutions to dynamical mismodelling, in order to eventually limit the science risk of the mission. For single CubeSat configurations, an optimal semi-major axis has been identified, being the one closest to the asteroid before orbital instability would start deteriorating the orbit determination solution. Non-equatorial retrograde orbits have been found to provide the lowest formal errors for geodetic parameters. Moreover, the benefit of simultaneously deploying two or even three CubeSats around the asteroid has been demonstrated. In both the two and three CubeSats configurations, promising orbital designs have been identified. They provide an estimation of the geodetic parameters which is accurate enough to bring insights into Eureka’s internal structure, and has been proven to be robust to dynamical mismodelling. The methodology developed in this work is of interest to design other small-spacecraft small-body missions, and optimise their achievable geodetic parameters estimate. Additionally, Eureka's dynamical model and the large uncertainties assigned to it have been mostly based on models available for other binary asteroids. This brings confidence in the possible applicability of the identified optimal orbital designs to CubeSats missions targeting other binary asteroids.

In 2022, ESA plans to launch the JUICE (JUpiter ICy moons Explorer) mission which will spend at least three years making detailed observations of Jupiter and three of its largest moons, Ganymede, Callisto and Europa. These moons are currently a hot topic within the science community as their interiors might include oceans consisting of liquid water. These oceans could provide life, but at the moment little is known about the exact composition and structure of these interiors. Only Earth based observations and a few fly-by’s have been performed to measure the characteristics of these moons. The JUICE mission will provide more detailed information on the moons through fly-by’s. This thesis research will focus on Ganymede as JUICE will be the first human-developed satellite to orbit thismoon. Ganymede stands out as a potential scientific target due to several specific reasons; the most remarkable being it’s intrinsic magnetic field. Only two other solid bodies within the Solar System generate such a magnetic dipole field (Earth andMercury). The complex interactions of this magnetic fieldwith Jupiter’smagnetic field are unique and could provide a lot of new knowledge when studied. Measurements from Galileo and the Hubble space telescope suggest that a subsurface layer of (saline) water is present within the moons interior. Saline water could be a good conductor of electricity, generating the magnetic field. The magnetic field of Ganymede could also point towards a complex core, which is another possibility for the generation of this field. It could be that the core of Ganymede consists of liquid, iron rich elements which generate and maintain this magnetic field. Unfortunately, current models of the gravitational potential field and the interior of Ganymede are still uncertain. A precise gravitationalmodel of Ganymede could provide a lot of information about this interior. An orbiter or in-situ probes are required to achieve high precision gravitational potential field models. JUICE is expected to obtain a model of Ganymede’s gravitational potential field of at least degree and order 15. This thesis will provide insight in how different possible internal density distributions of Ganymede influence the gravitational potential field of the moon. Thisway,when JUICE obtains more information on the gravitational potential field of Ganymede, variations within this field can directly be utilized to determine what interior aspects could cause these variations. From 44 billion 1D homogeneous models considered during this research, only 260 adhered to current known characteristics of Ganymede. Certain elements and water phases are present in all models: a pure iron or iron-sulfide core, a silicon mantle, an ice VI layer together with an liquid ocean and a outer crust consisting of Ice Ih. Dependent on the exact layer thicknesses within a model, intermediate ice phases, ice III and V, can also be present. Layer correlations between the 260 models were analyzed and fourteen models where selected for further research. These models were combined with different boundary and density variations to obtain different 3D heterogeneous models. Gravitational potential simulations for spherical harmonics coefficients up to order/degree 48 were performed. It was found that several relations exist between gravitational potential field data and internal density distributions within Ganymede. If one can effectively correct gravitational potential field signals for measurable components within Ganymede’s interior, several sets of internal structures emerge. Furthermore, taking into account the established limitations and correlations between layers, the gradient of the gravitational signal power over spherical harmonics degree can be directly related to the thickness of an interiors ocean. Several distinguishable models show that the presence of ice III, and to a lesser extent ice V, increase the gravitational signal power of a model. When combined with the correlations found between internal layers during this research, one could even establish an accurate first order approximate of Ganymede’s internal composition. These results, together with measurements performed by JUICE, will provide numerous new insights on Ganymede’s frozen enigma.

Currently one of the major drawbacks of interplanetary travel is the cost of these types of missions. Mission to extra-terrestrial bodies require a large amount of propellant to complete, which often takes up a large part of the mass budget of the spacecraft. This requires larger launchers to be used to get the spacecraft into the required orbit, which increases the cost of these missions. An often used method to decrease the propellant used during an interplanetary mission is the gravity assist. The gravity assist uses the gravitational influence of a planetary body to increase its heliocentric velocity. This is done by exchanging some of the planets momentum as it orbits the Sun to the spacecraft. The increase in velocity is limited by several factors: the gravitational influence of the body, the closest distance possible between the body and the spacecraft, and the orientation of the planetary bodies relative to each other. A new method has been proposed by McRonald (1990) called the aerogravity assist, which improves upon the gravity assist by increasing the angle over which the spacecraft can turn using the aerodynamic forces it experiences while travelling through the atmosphere of the planetary body. This increase in the velocity bending angle increases the heliocentric velocity compared to the gravity assist, and also allows for changes in inclination of the interplanetary orbit using less propellant. This report investigates both the atmospheric and interplanetary trajectory of the aerogravity assist, and combines them to understand the benefit of the aerogravity assist for interplanetary trajectories. A modular simulation environment is designed using the TU Delft Astrodynamics Toolbox to simulate the atmospheric trajectory of the aerogravity assist. This simulator allows the selection of different types of acceleration and environment models. The waverider is selected to be the vehicle used during the aerogravity assist, as it is able to obtain high lift-over-drag ratios which reduce the drag losses during the atmospheric section of the maneuver. The specific aerodynamic characteristics and heating models of the selected vehicle are evaluated and incorporated into the simulator. From this simulation environment, the optimal atmospheric trajectories were investigated using an optimization algorithm. It was found that this specific problem is extremely sensitive to the selected optimization algorithm, the tuning parameters of the optimization algorithm, and the objecive and decision variables that are used. The MOEA/D algorithm was selected to find the optimal atmospheric trajectories for Mars, Earth, and Venus, where the objective variables were chosen to be the atmospheric bending angle and the incoming and out-going inclination difference. It was found that using the angle-of-attack and bank angle as control variables, an atmospheric bending angle of 120.5 degrees and an inclination difference of 0.2 degrees could be obtained at Mars. Using the control action instead of the inclination difference as objective variable at Mars showed that the atmospheric bending could be increased to 151.2 degrees while maintaining an inclination difference of below 3 degrees, and smoothed the trajectory in the process. For Earth and Venus the same optimization scheme was employed. They were able to obtain atmospheric bending angles between 70 and 50 degrees, while obtaining inclination differences below 1.5 degrees. For Venus, the heat load was also optimized instead of the inclination difference and it was found that the peak heat flux decreased by around 1000 W/cm$^2$, while decreasing the atmospheric bending angle by around 10 degrees. A mission planner was designed to be able to investigate the effect of the aerogravity assist on interplanetary trajectories. To increase the accuracy of this mission planner, the numerically found atmospheric trajectories are used to determine the possible interplanetary trajectories. Pareto fronts were created for Mars, Earth, and Venus for a range of incoming velocities that showed the possible velocity bending angles and out-going velocities that can be achieved using an aerogravity assist. These Pareto fronts were then implemented in the mission planner to determine the influence of the AGA on an interplanetary trajectory. Several different interplanetary trajectories were investigated using both gravity and aerogravity assists. It was found that due to the fact that for Earth and Venus higher velocities are needed to travel through the atmosphere, the aerogravity assist would lose too much velocity and thus not improve upon the gravity assist. However, for Mars an increase was found of 4 km/s compared to the gravity assist for a trajectory to Saturn using fly-by's at Mars and Jupiter. Taking into account the extra mass of the thermal protection system, the decrease of mass was found to be around 60 percent, which could be used to lower the cost of the launcher or increase the scientific output of the mission by adding instruments to the payload.