Student theses

The LunarCobot project is investigating the deployment of heterogeneous robot teams on the lunar surface. Multi-robot operations and autonomous system networks enable complex mission profiles to be carried out through the use of multiple specialised robotic systems, which is particularly relevant for exploring challenging environments on the lunar surface. A key research focus of the project is on increasing the technology readiness level of various robotic technologies and modular exploration systems through further development of hardware and software, as well as the evaluation of these technologies in an analogue environment.

The aim of this work is to further develop the transceiver circuits of the Nanokhod microrover, which perform key functions relating to the rover’s communication and power supply. In order to prepare the existing laboratory setup of the transmission link for subsequent integration into the overall system, new PCB designs for the transceiver circuits must be developed and power-optimised components selected. Furthermore, the development is to be experimentally validated through precise measurements and integrated into the existing laboratory setup. In preparation for the integration of the rover into compact payload modules, the constraints of the analogue mission are to be taken into account, and innovative concepts for implementing the required transceiver electronics are to be developed and evaluated.

Tasks:
• Further development of the central interface for simultaneous data communication and power supply to the rover
• Design of a customised transceiver circuit to enable the transfer of laboratory set-ups into payload modules
• Detailed development and implementation of the new PCB design
• Measurement and characterisation of the developed electronics and test setup

The LunarCobot project is investigating the deployment of heterogeneous robot teams on the lunar surface. Multi-robot operations and autonomous system networks enable complex mission profiles to be carried out through the use of multiple specialised robotic systems, which is particularly relevant for exploring challenging environments on the lunar surface. A key research focus of the project is on increasing the technology readiness level of various robotic technologies and modular exploration systems through further development of hardware and software, as well as the evaluation of these technologies in an analogue environment.

The aim of this thesis is to further develop the contactless interface in the tether mechanism of the Nanokhod microrover. The rover is connected to a primary system via a 100 m long tether and uses an inductive coupler within the coil body to avoid the use of slip rings, which are prone to wear. The aim of the work is to adapt the converter and transformer circuit of the Wireless Power Transfer (WPT) module for integration into a rotating measurement setup that reproduces the geometric and dynamic boundary conditions of the coil winding. Subsequently, the simultaneous power and data transmission must be experimentally investigated and quantified. In the measurement setup, the effects of rotation, air gap and other interfering parameters are to be systematically identified, evaluated and documented in the form of measurement data.

Tasks:
• Further development of the transmission link from the primary system to the rover
• Design of a suitable measurement setup and implementation in a laboratory environment
• Adaptation and integration of the converter assembly into the measurement setup
• Characterisation of the measurement link during test operations

The LunarCobot project is investigating the deployment of heterogeneous robot teams on the lunar surface. Multi-robot operations and autonomous system networks enable complex mission profiles to be carried out through the use of multiple specialised robotic systems, which is particularly relevant for exploring challenging environments on the lunar surface. A key research focus of the project is on increasing the technology readiness level of various robotic technologies and modular exploration systems through further development of hardware and software, as well as the evaluation of these technologies in an analogue environment.

The aim of this work is to further develop the transceiver circuits of the Nanokhod microrover, which perform key functions relating to the rover’s communication and power supply. In order to prepare the existing laboratory setup of the transmission link for subsequent integration into the overall system, new PCB designs for the transceiver circuits must be developed and power-optimised components selected. Furthermore, the development is to be experimentally validated through precise measurements and integrated into the existing laboratory setup. In preparation for the integration of the rover into compact payload modules, the constraints of the analogue mission are to be taken into account, and innovative concepts for implementing the required transceiver electronics are to be developed and evaluated.

Tasks:
• Further development of the central interface for simultaneous data communication and power supply to the rover
• Design of a customised transceiver circuit to enable the transfer of laboratory set-ups into payload modules
• Detailed development and implementation of the new PCB design
• Measurement and characterisation of the developed electronics and test setup

A space system is composed of two major building blocks: the flight segment and the ground segment. The flight segment can be a single satellite or space probe, but also a constellation of satellites, a space station or a landing vehicle. A ground segment can be decomposed into the following three major systems and subsystems:

• Ground Station Network / Communication
• Operations System (Command & Control, Mission Planning, Flight Dynamics, Tasking)
• Infrastructure (IT, Facilities & Accommodation, Simulator, Security)

While the flight segment is normally highly mission specific, the design of the ground segment systems is usually more generic. This is due to the fact that most ground segments are built to serve more than one mission. However, there are driving factors that affect the specification of the ground segment and therefore its elements, for example: traveling distance of the flight segment, concept of operation, number of spacecraft or the purpose and the type of the missions. All these factors drive the design and the infrastructure on ground that is necessary for the execution of the mission. University of Stuttgart and its Institute of Space System are planning to convert their existing ground segment into a Training and Research Space Operations Center (TSOC). TSOC shall also bundle satellite operation and ground system engineering competences under one roof.

During this work, a Phase 0 study for the striven ground segment (TSOC) shall be executed. This covers the specification, the development of a concept and a preliminary design based on top-level project goals. The work further makes the first steps towards a later project execution by identifying the stakeholders, executing trade-offs, creation of a work breakdown structure and cost estimation. The work shall be executed in close collaboration with TSOC project management and covers the following steps:

• Use Case Analysis
• Specification based on top-level requirements and goals
• Concept development and identification of major building blocks
• Preliminary System Design
• Where possible, selection of components
• Creation of a work breakdown structure for project execution
• Cost Estimation
• Documentation

For satellite operation a stable communication link is key. Most ground stations use parabolic antennas for the reception and the radiation of the RF signals. To close the radio link, it is necessary that the antenna accurately points at the orbiting satellite. This requires accurate orbit information about the operated satellite. Under certain circumstances (data outages, lack of external tracking capabilities) it might happen that this orbit information is not available or not accurate enough for the pointing control of the antenna dish. Under these circumstances the antenna must be able to track the satellite based on the radio signal received. For such a case, an RF-signal tracking chain shall be conceptualized. One method, for instance, is multimode mono-pulse tracking. The RF feed of the parabolic antenna is designed in a way that two modes are excited with the incoming signal, where magnitude and phase of both modes are related to the azimuth and elevation angle. The deviation between magnitude and phase of those two modes relates to the offset error of the line of sight.

The development of such an RF-signal tracking chain is an iterative process. First, a selection of suitable concepts must be made based on the targeted frequency bands, tracking requirements and other boundary conditions. Second, the signal processing chain must be designed and simulated. Based on the findings of the simulation, the design shall be iterated. This procedure must be repeated until the solution converges towards a design that fulfills the requirements. Besides the technical requirements that must be fulfilled, the solution must be compliant with a set of boundary conditions, which are performance, cost and the availability of the necessary hardware components.
· Familiarization with the concept of RF-signal tracking
· Specification and Identification of suitable tracking concepts
· Setup of an initial design
· Modeling and simulation of the signal tracking chain in MATLAB Simulink
· Design proposal and Iteration
· Documentation

When communicating with satellites in orbit, the antennas used on ground are mostly
large parabolic dish antennas. Those antennas, depending on their size, need to be
oriented towards the satellite with an accuracy of below 1°. To achieve such accuracies,
the antenna orientation on ground needs to be calibrated.
A common way to do this, is to receive signal from satellites with a known orbit and to
determine the offset between the known orbit and the antenna orientation. A big
disadvantage is, that the antennas can only be calibrated in the directions of known
satellites, that transmit over the antenna location in the same frequency band. And in
addition, the calibration can only be done, when those satellites pass over the ground
station.
To mitigate this disadvantage, a new way for calibration shall be developed. For this
purpose, star images shall be used. Using images of the night sky, the orientation of the
camera used for taken the image can be determined with arc second accuracy using
already existing algorithms. Using this this technique, a method and software for a full
antenna calibration shall be developed within this thesis.

Task description of the Master thesis work:
- Research of all necessary components
- Develop Calibration Method
- Implementation of the Method
- Verification of the Method
- Documentation

Very Low Earth Orbits (VLEOs) offer benefits such as higher-resolution Earth observation, lower communication latency, and reduced launch costs. Operating in VLEO, however, is challenging due to increased atmospheric drag and the need for sustained propulsion. Atmosphere-Breathing Electric Propulsion (ABEP) systems address these challenges by using atmospheric particles for propulsion, reducing onboard propellant needs. In order to better develop these systems, it is essential to advance not only technological developments related to hardware, but also the development of appropriate simulation and design tools. While the focus in this regard has so far been primarily on either an assessment of the orbital mechanics aspects and associated dynamic dependencies (e.g. atmospheric variability, satellite aerodynamics etc.) or on the design of the spacecraft itself, a true evaluation can only be made by taking a holistic view. The objective of this thesis is to lay the groundwork for a comprehensive, modular design and dimensioning framework for an ABEP spacecraft, embedding dynamic dependencies into the design process.

Motivation:
The growing use of small satellite constellations in Low Earth Orbit (LEO) for purposes such as earth observation, communication and other commercial services presents significant potential for business opportunities and technological advancements. However, it is also accompanied by challenges, such as the need for de-orbiting and disposal of satellites at their end-of-life with a low-risk probability of causing property damage or casualties on the ground. This is ensured during the development of the satellites using numerical tools such as ESA’s SCARAB software, which analyzes demisability. Additionally, plasma wind tunnel (PWT) experiments provide a valuable opportunity to study the demise behavior of materials and structures in plasma environments relevant to re entry. Past studies have revealed that glass fiber reinforced polymers (GFRPs) as used in printed circuit boards (PCBs) are resistant to high temperatures and demise worse than expected. In order to improve the understanding of demise processes and calibrate numerical models, experimental PWT studies are performed within the SKALE project. One critical parameter for the description of demise processes is temperature and its spatial distribution on test objects. Therefore, the specimens are to be equipped with thermocouples. The surface temperature can be measured using pyrometers and thermal imaging cameras. The resulting measurement data can then be compared to the numerical simulation results for validation and verification purposes.
Task Description:
• Introduction to uncontrolled re-entry, PWT testing, and the SCARAB simulation software
• Set-up of a test plan for the demise of PCB samples
• Preparing and assisting PWT experiments
• Numerical rebuilding of PWT experiments in SCARAB
• Analysis of measurement data and comparison to simulation results
• Documentation

The Collaborative Research Centre 1667 “Advancing Technologies of Very Low-Altitude Satellites (ATLAS)”, funded by the German Research Foundation DFG, addresses the fundamental scientific and engineering challenges of rendering Very Low Earth Orbit (VLEO, about 200 km to 450 km altitude) accessible. ATLAS Project A06 investigates methods of exploiting the aerodynamic forces for orbit control. To deal with the inherent uncertainties in the environmental conditions in VLEO, robust optimization and planning methods are required. This thesis shall contribute to the implementation of a planning routine that is robust to the uncertainties. To investigate different approaches how uncertainties may be considered in the planning processes, a comprehensive literature review is planned. Suitable methods shall be selected and implemented for a simple reference system. Based on this, strengths and weaknesses shall be identified and compared. The most promising approach shall then be used to develop a robust planning routine by subsequently increasing the level of complexity, eventually being able to apply it to satellite orbit control including both aerodynamic drag and lift. The results will contribute to the future realization of practical aerodynamic orbit control for satellites in VLEO.

Pulsed, gas-fed electric propulsion systems such as quasi steady-state magnetoplasmadynamic thrusters are a promising option for future small satellite missions but pose significant challenges for accurate thrust characterization e.g. due to parasitic forces introduced by propellant feed lines. Indirect measurement methods where the thruster plume imparts its impulse on a target that is connected to a thrust balance solve this problem, but introduce new challenges regarding the impulse transfer from the plume to the target. Many approaches that try to avoid this problem exist in literature. Most try to minimize reflection and sputtering via the target design. Some then assume perfect impulse transfer in their thrust model, while others take inelastic processes like phonons into account.

At the Institute of Space Systems, a new model is developed for indirect thrust measurements. It uses a simple planar target and does not rely on minimizing reflection or sputtering via target design. Instead, molecular dynamics simulations are used to determine the impulse transfer efficiency, including reflection, sputtering, and inelastic processes. In this work, the simulation approach shall be validated using suitable experiments and supplementary molecular dynamics simulations.