Thermal Mathematical Models (TMMs) are used to predict the thermal behavior of satellite structures in orbit. However, due to inherent uncertainties in these models, physical testing is necessary to achieve reliable predictions. While these tests are critical, they often introduce uncontrolled uncertainties, such as heat leaks and measurement errors, making the correlation process complex and time-consuming. To address these challenges, this thesis proposes an alternative testing methodology that reduces uncertainties in thermal test data by using the phase shifts between temperature responses from oscillatory heat loads for TMM correlation. By comparing the measured and predicted phase shifts, thermal model parameters such as conductance or capacitance can be effectively correlated. The results demonstrate that this methodology is largely insensitive to uncontrolled conductive heat leaks, allowing the correlation process to focus only on key thermal parameters. This approach improves the reliability of thermal test data and streamlines the correlation process. Moreover, its potential application in ambient conditions offers a promising testing solution for early-phase model correlation.

With the advent of Reusable Launch Vehicles (RLVs) on the European launch market, the German Aerospace Centre (DLR)’s In-Air Capturing (IAC) recovery technique promises a competitive reduction in launch costs. Central to this IAC procedure is the Aerodynamically Controlled Capturing Device (ACCD), which is deployed from a Towing Aircraft (TA) by means of a tether. It intercepts a returning RLV, and provides a structural interface between the TA and RLV during tow-back. Once in the vicinity of a landing site, the ACCD releases the towing connection, and the RLV lands autonomously. Whereas the aerodynamic shell of the ACCD has been defined and studied in the past, an in-depth exploration of its electromechanical design space has not been performed previously. This work proposes a systems engineering approach to fill the corresponding design gap, based on the definition of key requirements and risks characterizing the ACCD’s functionalities, and its operational environment.

First, the behaviour of the ACCD as part of a larger towing system is analysed. For this, a two-dimensional (2D), quasi-steady-state Towing Model is developed, enabling a swift exploration of the ACCD’s design space, as well as a preliminary estimation of extreme tow-back loads. This Towing Model shows that the ACCD’s towing position relative to the TA is highly sensitivity to the ACCD’s Centre of Gravity (CoG); in order to stay clear of the TA’s disturbing wake zone, a maximum allowable CoG position of 1 m behind the vehicle’s nose is defined. Additionally, a significant pitch control authority is demonstrated, indicating substantial manoeuvrability. Finally, a study of extreme tow-back conditions results in the definition of a 300 kN axial towing design load - representing a 72% increase compared to previous estimates.

Next, the ACCD’s relative navigation system is studied, used to estimate the position and attitude of the RLV. A comparison between state-of-the-art systems is made, and the so-called VisNav solution is proposed - with a sensor attached to the RLV, and active beacons mounted on the ACCD. In order to identify a representative configuration for this system, a geometric VisNav Model is developed, analysing the visibility of beacons from the sensor’s Point of View (PoV). Based on comparative studies performed with this model, a design with three asymmetric rings of twelve beacons is proposed. Combined with Global Navigation Satellite System (GNSS) and Inertial Navigation System (INS) data, this configuration enables relative position and attitude estimation with an accuracy of 20 cm and 1°.

A representative electromechanical design for the ACCD is then proposed, based on results from the foregoing design space exploration. On the one hand, the selection of Commercial-off-the-Shelf (COTS) avionics is covered, as well as a preliminary dimensioning of the vehicle’s power system. Here, the ACCD’s actuators are identified to be the main drivers of its electronic design in terms of Size, Weight and Power (SWaP) footprint. Additionally, the feasibility of a battery-powered design is demonstrated. On the other hand, a Computer-Aided Design (CAD) study of mechanical subassemblies is performed, which are further analysed in terms of extreme operational loads. Most noticeably, a separation of the docking and release systems is proposed, as combining both into a single mechanism is deemed infeasible, due to the continuous presence of significant towing loads. Based on the presented design, a Bill of Materials (BoM) for the ACCD is established, yielding a total functional mass of 159.14 kg. Because of the substantial impact of the vehicle’s wings and docking system on its overall CoG, an additional 16.3 kg trim mass is required to reach the desired CoG position. Compared to previous studies, the final estimate for the ACCD’s total mass has increased by 33%.

Concluding the study, compliance with the vast majority of the postulated design requirements is demonstrated, while a number of future improvements and complementary studies are identified. These include an aerodynamic redesign and shortening of the ACCD’s shell, to eliminate the need for a trim mass. Additionally, prototyping of this unique vehicle is highly recommended, in order to further study its behaviour, and validate the theoretical design proposed in this work.

Stiff and transparent materials are essential across industries such as aerospace, defense, and consumer electronics. Traditional materials like glass and ceramics, while effective, have limitations due to brittleness, high density, and low impact resistance. Consequently, there is a demand for lightweight, durable materials with favorable optical properties. Fiber-reinforced polymers (FRPs) offer high strength-to-weight ratios and greater impact resistance than glass and ceramics. Given the low light absorption of glass fibers in the visible spectrum, transparent glass fiber-reinforced polymers (TGFRPs) show promise as replacements for traditional transparent materials.

This thesis explores two main aspects: (1) optimizing TGFRP transparency through manufacturing parameters and (2) leveraging TGFRP transparency for damage detection and stress analysis. In the first phase, findings demonstrate that achieving high surface smoothness and maximizing light transmission within the green spectrum (520–600 nm) are crucial for enhancing TGFRP transparency. This is best controlled via post-curing, a more stable approach than adding methyl methacrylate (MMA) as suggested in existing literature. Sizing was also found to play a critical role in transparency, ensuring optimal bonding between glass fibers and the matrix. Additionally, minimizing the number of glass fiber fabric layers improved transparency by reducing transmission losses across visible wavelengths.

The second phase investigated the transparency of TGFRP for visualizing internal damage and stress distributions. Confocal microscopy was used to observe cracks at various depths within TGFRP samples, while image processing techniques, such as thresholding, were employed to calculate crack density. The results indicate that a higher crack density corresponds to reduced light transmittance across the visible range. However, some limitations were encountered, as cracks and scratches on the upper layers cast shadows on the lower layers, complicating the detection of deeper damage.

During tensile testing of open-hole specimens, significant opacity changes were observed in high-strain regions, suggesting that opacity correlates with localized stress. Digital image correlation (DIC) and grayscale histogram analysis provided insights into the strain thresholds at which opacity changes begin. Future work could build on this by examining the extent to which opacity changes are due to refractive index variations alone, independent of crack formation, using these strain levels as a baseline.

Furthermore, verifying the reversibility of opacity changes through post-test spectrophotometry could position TGFRPs as highly effective materials for developing innovative and reliable non-destructive testing, damage detection, and stress visualization methods in glass fiber-reinforced polymer composites.

Recent studies have shown the feasibility of (quasi-)pole-sitter orbits at Mars and Venus, which involves a satellite positioned along or near the polar axis of a planet in order to have a continuous, hemispherical view of the planet's polar regions. In order to further demonstrate the feasibility of this mission concept, this thesis investigates time-optimal solar sail transfers to these (quasi-)pole-sitters. In particular, (quasi-)pole-sitters which are achievable when assuming solar sail technology expected in a near- to mid-term time-frame. To reduce mission operational cost, the objective of this research is to minimize the time required for the transfer, which requires the solution to an optimal control problem. Initial guess solutions for this optimal control problem are provided through two completely different techniques, in order to compare and validate the individual performances: first, a technique derived from dynamical systems theory (a type of grid search) and second, a genetic algorithm. Subsequent optimization using a direct pseudospectral algorithm results in time-optimal transfers to the considered Mars (quasi-)pole-sitters that span 2.61 and 2.72 years, and 1.07 and 1.19 years to the considered Venus (quasi-)pole-sitters. Effects due to variations in performance of the ideal sail, non-ideal sail properties, and Earth departure orbit are investigated. In addition, this paper demonstrates that a genetic algorithm is well suited to generate initial guesses for similar interplanetary transfers in the inner solar system. It provides initial guesses that outperform the more conventional grid search technique, in terms of feasibility of the initial guess transfers, as well as in computation time and ease of implementation.

The use of Taylor Series Integration (TSI) for the propagation of spacecraft trajectories and its combination with the relatively unknown Unified State Model (USM) coordinate system, resulting in the TSI-USM propagator, is known to allow fast propagation of interplanetary low-thrust trajectories. Unfortunately, the TSI-USM propagator is a problem-specific method, which is detrimental for its use in evolutionary algorithms.

In this thesis, a method was developed to generalize the TSI-USM propagator. The TSI-USM was generalized to allow the propagation of a spacecraft trajectory in a central gravitational field subject to any pre-set thrust profile, without the need to adapt the internal working of the propagator. The three-dimensional thrust profile should be specified a priori, and with respect to time, by the user or by an evolutionary algorithm. The method used to generalize the TSI-USM requires the coefficients of the cubic spline interpolation of the pre-set thrust profile to compute the recurrence relations of the TSI-USM.

Results show that, although the method indeed generalizes the TSI-USM, it is less accurate and requires more CPU time for a given accuracy than existing RK8(7)13M-based propagators. From this result, it can be expected that future attempts to generalize the TSI-USM propagator, without sacrificing its accuracy and computational speed, will be challenging.

the aim of this thesis is to regard all aspects concerning mass optimization with respect to small satellite structures and deployers, specifically aimed at the DelfiPQ PocketQube mission.