Spacecrafts

Motivation:

The sloshing behavior in the main tanks of a liquid rocket has a significant influence on its flight dynamics and can lead to the loss of the rocket in extreme cases. It is therefore important that these effects are taken into account when designing the controller for a rocket in order to guarantee the success of the mission. As part of this research project, an already non-linear simulation environment of the chair is to be expanded to include sloshing dynamics.

Task definition:

• Literature research on the modeling of fuel sloshing at different mission times (launch, stage separation, landing)

• Literature research on active/passive damping methods and their modeling

• Derivation of a model for propellant sloshing in the main tanks of a liquid rocket for v

• Implementation in a non-linear simulation environment in Matlab/Simulink

• Design of a controller for active damping of the propellant slosh

• Verification through reference missions

Contact person:

© M. Kretschmar

Research Assistant

Name

Dipl.-Ing. Frederik Thiele

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Organization Name

Chair of Flight Mechanics and Control

Chair of Flight Mechanics and Control

Address work

Visiting address:

WIK Windkanal, Room 18 Marschnerstraße 28

01307 Dresden

work Tel.

fax Fax

+49 351 463-38187

Motivation

Control systems for the autonomous landing of reusable rocket stages or on celestial bodies such as the moon or Mars must demonstrate a high degree of robustness and reliability. In most cases, test runs on the real object are not practically feasible without taking high financial risks due to a potential failure. The VTOL (Vertical Take-Off and Landing) test platform EAGLE (Environment for Autonomous GNC Landing Experiments) developed by the German Aerospace Center (DLR) offers the possibility of testing planned controller architectures ahead of time on a system with comparable, generally unstable system dynamics. In the future, the capabilities will be expanded to imitate the real behavior of spacecraft and thus verify the controllers designed for the mission.

The EAGLE's main thrust system currently consists of a kerosene-fueled turbine. This results in a high level of complexity in operation and maintenance, as well as in ensuring safe flight operations with high operating costs and low flexibility. For this reason, a conversion to a comparably powerful electric propulsion system is to be conceptually explored as part of this student project/diploma thesis. This should be able to be operated by built-in batteries, but also by cable if longer test campaigns with short distances are planned. The aim of the work is to find a configuration of a purely electrically powered EAGLE that represents an optimal compromise between capabilities and the effort/cost of the conversion.

Task description

• Analysis of the existing thrust system
• Research into the electrification of the thrust system
• Detailed comparison of possible conversion variants
• Selection and documentation of the best configuration

© S. Ellger

Research Assistant

Name

Dipl.-Ing. Carl-Johann Winkler

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Contact Information

Organization Name

Chair of Flight Mechanics and Control

Chair of Flight Mechanics and Control

Address work

Visiting address:

WIK Windkanal, room 18 Marschnerstraße 28

01307 Dresden

work Tel.

fax Fax

+49 351 463-38187

Motivation:

The Verification and Validation (V&V) of a spacecraft control system is a challenging and resource intensive process. The physical models of the spacecraft, which is used for the design of the controller, are subject to uncertain parameters (e.g. masses or moments of inertia are only given within an interval in an early design phase or they can vary throughout the mission). It is still necessary to characterize the stability or the performance of the control loop while considering those uncertainties. Besides worst-case analyses, probabilistic methods are in the focus of attention, which give a probability distribution of those characteristics based on the distributions of the uncertainties. Polynomial Chaos Expansion (PCE) is a method to approximate this distribution. PCE promises a significant increase in computational efficiency compared to Monte-Carlo simulations, which are the classical method of probabilistic analysis. Multiple approaches for the efficient calculation of PCE have been developed, each coming with their own pros and cons.

Task definition:

• Literature research on methods of PCE computation (focus on sparse/adaptive basis PCE)

• Implementation of some of those algorithms in Matlab

• Evaluation and comparison on a benchmark satellite mission

Contact person:

In-orbit rendezvous manoeuvres play a key role for various space missions, e.g., crewed missions and cargo delivery to space stations, in-orbit servicing of satellites or space debris removal. A necessary aspect to successfully perform such a manoeuvre is an appropriate guidance profile, which can be designed and optimized in advanced, calculated during flight or a combination of both. Such a profile has to meet various objectives, such as minimizing transfer duration and fuel consumption while providing sufficient safety margins and account for nonlinear orbital mechanics and uncertainties in the spacecrafts’ trajectories and dynamics.

This thesis shall focus on the “out of sight” phase of a rendezvous manoeuvre, which encompasses the phase until the relative position and velocity between both spacecraft is sufficiently small to perform the final approach using visual guidance. The calculation of an optimal guidance profile is to be implemented in MATLAB, and the impact of uncertainties on the resulting performance shall be discussed.

Task

• Overview of guidance and control approaches for rendezvous manoeuvres
• Literature review to “offline” and “online” calculation of guidance profiles for different objectives during the “out of sight” phase of rendezvous.
• Implementation of the calculation of selected approaches in MATLAB
• Discussion of the impacts of uncertainties and appropriate mitigation methods in the guidance or control design for rendezvous  

© M. Kretschmar

Research Assistant

Name

Dipl.-Ing. Frederik Thiele

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Contact Information

Organization Name

Chair of Flight Mechanics and Control

Chair of Flight Mechanics and Control

Address work

Visiting address:

WIK Windkanal, Room 18 Marschnerstraße 28

01307 Dresden

work Tel.

fax Fax

+49 351 463-38187

Guidance and control algorithms for guiding and controlling spacecraft form the basis of many space missions. Due to high demands on robustness, safety and reliability, complex dynamic relationships and a wide range of uncertainties must be taken into account in detail during their development. However, real tests are only possible to a very limited extent, particularly for economic, organizational and safety reasons. A capabilities simulation environment is therefore a central prerequisite for the development and validation of such algorithms. It must be able to propagate orbital and suborbital trajectories of several spacecraft in time and to map position-dependent environmental influences such as gravitational gradients, residual atmosphere or solar radiation with sufficient accuracy. As part of this work, a simulation environment is to be developed and evaluated for the Chair of Flight Mechanics and Control.

Task definition:

• Literature research on orbital mechanics and "in-orbit" environmental influences and their modeling
• Development of a modular simulation concept
• Implementation of the simulation framework in Matlab/Simulink
• Validation of the simulation using an example mission

© S. Ellger

Research Assistant

Name

Ms Emily Burgin M.Eng.

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Contact Information

Organization Name

Chair of Flight Mechanics and Control

Chair of Flight Mechanics and Control

Address work

Visiting address:

WIK Windkanal, room 18 Marschnerstraße 28

01307 Dresden

work Tel.

fax Fax

+49 351 463-38187