Ulrich Walter

• PhD
• Professor (Full) at Technical University of Munich

This research explores an integrated control technique for a dual-armed space robot that has captured a tumbling satellite. The compliant behavior for safe manipulation in-orbit is achieved using the external impedance at the target level. First, considering the control moment constraints imposed on the target body, a fast detumbling strategy is pr...

ComPol is a proposed CubeSat mission dedicated to long-term study of gamma-ray polarisation of astrophysical objects. Besides spectral and timing measurements, polarisation analysis can be a powerful tool in constraining current models of the geometry, magnetic field structure and acceleration mechanisms of different astrophysical sources. The ComP...

The recent and significant enlargement of aerospace research at the Technical University of Munich presents a unique opportunity to forge synergistic and enduring ties within the aerospace community in Munich and beyond. By establishing a multi-institutional Space Missions Laboratory dedicated to a broad field of disciplines—ranging from astrophysi...

Determining how to grasp a non-cooperative target by applying a space robot is still a challenging issue, especially when the target is tumbling in space. This paper presents an optimal grasp planning strategy for a kinematically redundant space manipulator to capture an arbitrarily rotating target, such as a dysfunctional satellite or a piece of s...

This paper focuses on the motion planning to detumble and control of a space robot to capture a non-cooperative target satellite. The objective is to construct a detumbling strategy for the target and a coordination control scheme for the space robotic system in post-capture phase. First, the dynamics of the kinematically redundant space robot afte...

How to identify the mass properties and eliminate the unknown angular momentum of space robotic system after capturing a non-cooperative target is of great challenge. This paper focuses on designing an integrated control framework which includes detumbling strategy, coordination control and parameter identification. Firstly, inverted and forward ch...

Application of the multi-arm space robot will be more effective than single arm especially when the target is tumbling. This paper investigates the application of particle swarm optimization (PSO) strategy to coordinated trajectory planning of the dual-arm space robot in free-floating mode. In order to overcome the dynamics singularities issue, the...

Many people have had and still have misconceptions about the basic principle of rocket propulsion. Here is a comment of an unknown editorial writer of the renowned New York Times from January 13, 1920, about the pioneer of US astronautics, Robert Goddard, who at that time was carrying out the first experiments with liquid propulsion engines: “Profe...

The most important maneuver in space is the one to change the orbit of a space vehicle. Because the initial and final orbits are subject to a central gravitational potential such a S/C will transit between two Keplerian orbits. This is true not only for planetary orbits but also for interplanetary flights with the Sun as the central body.

So far, we have studied the two-body problem, in which one body moves under a central Newtonian force, as given by a gravitational field of a second body, a point mass.

This introductory text covers all the key concepts, relationships, and ideas behind spaceflight and is the perfect companion for students pursuing courses on or related to astronautics. As a crew member of the STS-55 Space Shuttle mission and a full professor of astronautics at the Technical University of Munich, Ulrich Walter is an acknowledged ex...

In Sect. 1.3.1, we found out that there are limits to the obtainable payload mass because of the finite structural mass. This limit is crucial for the construction of a rocket. If a rocket is to reach the low Earth orbit, a propulsion demand of about 9 km s⁻¹ has to be taken into account (see end of Sect. 6.4.7), which is at the limit of feasibilit...

In Chap. 7, we have looked at two point masses that were moving under their mutual gravitational influence. Formally speaking we were dealing with two bodies each with six degrees of freedom (three position vector components and three velocity vector components).

Electric propulsion engines differ from thermal engines in that, among other things, the propellant does not serve as an energy source to heat and accelerate the propellant mass in the combustion chamber. Rather acceleration is achieved by accelerating ions in an electric field, the energy of which needs to be provided externally by an electric cur...

The thrust from thermal propulsion engines, such as jet engines, results from the exhaust of propellant gases, which is achieved by the rapid expansion of the heated gas. The heat usually comes from the combustion of chemical propellants—which we will assume in the following without loss of generality—or from the supply of external heat, or from bo...

In fact, the first problem—to determine the orbit in the spheres of influence of different celestial bodies—is so serious that we cannot solve it exactly with analytical means. Hence, in practice, all interplanetary flights are determined only by complex numerical simulations. This enables one also to take even more complex situations into account,...

After ascent, we are now in outer space. How does a spacecraft move under the influence of the gravitational forces of the Sun, planets, and moons? This is the question we will deal with in this chapter, and we are pursuing general answers to it. Let us face reality from the start: The details of motions are usually very complicated and can be dete...

We now want to tackle the problem of solving the equation of rocket motion Eq. ( 1.1.7). As will be seen in Sect. 2.1, even for many simple cases it can be solved only by numerical methods. Since this is not the objective of this book, we will treat only those important cases that can be analyzed analytically. This will give rise to an important ch...

Now that we know the technical and physical properties of a rocket and the general equation of motion, which governs its flight, we are ready for a mission to the planets in our solar system. Before we investigate the rocket’s motion in interplanetary space, it first has to ascent in Earth’s gravitational field through the atmosphere. As will be sh...

After a spaceflight, the planetary entry (a.k.a. reentry for entry into Earth’s atmosphere) of a spacecraft is subject to the same aerodynamic and physical laws and equations (see Eqs. (6.3.6) and (6.3.7)) as ascent. One might therefore infer that the circumstances of both situations are the same.

To delineate the general trajectory of a body mathematically or graphically one needs an observational space reference frame. In physics a reference frame is meant to be a concrete realization of a conceptional reference system with a choice of a coordinate system—meaning: a system of coordinates, such as rectangular (Cartesian), polar, or cylindri...

In this section we derive some useful formulas for the design of satellite missions.

The ultimate goal of this chapter is to determine the temperature equilibrium distribution inside a spacecraft (S/C) as a result of the thermal equilibrium with its space environment. Knowing these inside temperatures is essential when designing a S/C, as most components only work reliably within certain temperature ranges: batteries lose capacity...

The general motion of a perfectly rigid body is the superposition of translation and rotation. We talked about translation under the influence of a gravitational field and possible external perturbations in the previous chapters. Now we want to have a look at the rotational behavior of a body.

In this paper, we analyze the trajectory and body attitude data of Felix Baumgartner’s supersonic free fall through the atmosphere on October 14, 2012. As one of us (UW) was scientific advisor to the Red Bull Stratos team, the analysis is based on true body data (body mass, wetted pressure suit surface area) and actual atmospheric data from weather...

The project CopKa at the Technical University of Munich investigates the possibilities of enhancing the situation awareness during emergency and rescue situations (both routine and major incidents) in a coordination centre, while decreasing the workload of the rescue crew. In the envisioned CopKa scenario, video and telemetry data from different da...

The objective of this paper is to establish a detumbling strategy and a coordination control scheme for a kinematically redundant space manipulator post-grasping a rotational satellite. First, the dynamics of the kinematically redundant space robot after grasping the target is presented, which lays the foundation for the coordination controller des...

Water scarcity and contamination of clean water have been identified as major challenges of the 21st century, in particular for developing countries. According to the International Water Management Institute, about 30% of the world's population does not have reliable access to clean water. Consequently, contaminated water contributes to the death o...

This paper presents the fundamental work on the attitude control design using solely magnetic actuation for the MOVE-II mission. Two control modes are primarily considered: detumbling and sun pointing control. Regarding the sun pointing control, two approaches are discussed. The first is the Spin Stabilized Sun Pointing Control (SSPC) which provide...

Time–cost trade-offs arise when organizations seek the fastest product development (PD) process subject to a predefined budget, or the lowest-cost PD process within a given project deadline. Most of the engineering and project management literature has addressed this trade-off problem solely in terms of crashing—options to trade cost for time at th...

Water scarcity and contamination of clean water have been identified as major challenges of the 21 st century, in particular for developing countries. According to the International Water Management Institute, about 30 percent of the world´s population does not have reliable access to clean water. Consequently, contaminated water contributes to the...

The platform for resource observation and in situ prospecting for exploration, commercial exploitation, and transportation (PROSPECT) instrument package is under development by the European Space Agency for the upcoming Luna-27 mission to the lunar south pole. The purpose of the instrument is to detect and quantify volatiles on the lunar surface wi...

This paper proposes a guidance scheme for autonomous docking between a controlled spacecraft and an uncontrolled tumbling target in circular orbit. The onboard trajectory planning consists of a direct optimization method based on the inversion of the system dynamics. The trajectory components of the controlled spacecraft are imposed by using polyno...

This paper presents a pose estimation procedure for tracking attitude and position of a noncooperative tumbling spacecraft during rendezvous and docking maneuvers. The key aspect of the method is that the current state of the target spacecraft is estimated in real-time using a low-resolution depth-image of the scene and a known model of the vehicle...

In this paper, a transient thermal simulation approach is used to characterize the heat flux and heat flux rates between the lunar surface and a moving spacesuit model. Five different lunar-surface settings are simulated with craters and boulders at three solar elevation angles (θ=2, 10, 90 deg). Heat fluxes and rates are evaluated for different pa...

Abstract This study investigates the use of the non-linear model predictive control (NMPC) strategy for a kinematically redundant space robot to approach an un-cooperative target in complex space environment. Collision avoidance, traditionally treated as a high level planning problem, can be effectively translated into control constraints as part o...

Project management theory provides insufficient insight on the effects of crashing and overlapping in product development (PD) projects. The scholarly literature largely assumes that networks of project activities are acyclical. PD projects are iterative, however, and the time-cost implications of managerial actions, such as activity crashing and o...

This paper investigates the application of the inverse dynamics in the virtual domain method to Euler angles, quaternions, and modified Rodrigues parameters for rapid optimal attitude trajectory generation for spacecraft reorientation maneuvers. The impact of the virtual domain and attitude representation is numerically investigated for both minimu...

This paper presents the on-orbit results and the lessons learned from First-MOVE (Munich Orbital Verification Experiment), the first CubeSat mission of the Institute of Astronautics (LRT) at the Technische Universität München (TUM). The development of the satellite started as a student project in 2006. First-MOVE was launched on November 21st 2013....

Orbital robotics is receiving growing attention worldwide for applications in servicing and repositioning of partially or fully defective satellites. In this paper, we present the scope and main results of a four-year research project, which aimed at developing necessary robotic technologies for such applications. The scope is two-fold, since we ad...

This study investigates the impact of communication link constraints in the transmission of streaming video feedback on spacecraft teleoperation system performance. A final approach and docking scenario with an uncooperative, rotating target was set up, in which operators in three experiment series were presented with different video frame rate lev...

The requirements for the design of rovers and sample collecting devices for the Moon are driven by the harsh and diverse thermal lunar environment. Local lunar surface temperatures are governed by boulders and craters. The present work quantifies the changes in solar and infrared heat fluxes q̇Sol and q̇IR impinging on a rover or a sample collectin...

This paper investigates the application of particle swarm optimization (PSO) strategy to trajectory planning of the kinematically redundant space robot in free-floating mode. Due to the path dependent dynamic singularities, the volume of available workspace of the space robot is limited and enormous joint velocities are required when such singulari...

In this paper we present the Virtual Habitat (V-HAB) model, which simulates on a system level the dynamics of entire mission scenarios for any given life support system (LSS) including a dynamic representation of the crew. We first present the V-HAB architecture. Thereafter we validate in selected case studies the V-HAB submodules. Finally, we demo...

This paper reports on a series of experiments that were conducted on a partial-g parabolic flight campaign to determine key parameters of hoppers, designed for regolith sampling, science experiments, or in situ resource utilization (ISRU) processes on Moon or Mars. A major problem related to these applications is the clogging of feeding and conveyi...

The rapid increase of available Ka-band and Ku-band transponders in orbit proves that these frequency bands will be in common use in the near future. However, compared to the Ku-band and lower frequencies, Ka-band transmission is much more sensitive to atmospheric moisture. To determine its impact, we have measured the beacon (27.5 GHz) signal of t...

This paper investigates the utilization of deployable and expandable structures for communication purposes and solar power generation on CubeSats. We present the design and on-orbit results of the flight-proven solar-panel release mechanism of the first satellite of Technische Universität München First-MOVE, as well as the preliminary design of a s...

The authority over search and rescue operations (SAR) rests to the so-called rescue coordination center in the Federal Republic of Germany. An essential element for the coordination of SAR operations in general is the communication between rescue workers and the rescue coordination center. A detailed description of the situation at a remote place,...

We present a new method, its development, implementation, and verification, for calculating the transient thermal interaction between lunar regolith and moving spacecraft travelling across the surface of the Moon. Regolith temperatures can be determined for lunar landscapes as defined by laser altimeter remote sensing data refined with local crater...

The Institute of Astronautics (LRT – Lehrstuhl Raumfahrttechnik) at Technische Universitaet Muenchen has a strong background in inter-satellite communication. The efforts were driven by the need of developing key methods and hardware for controlling robotic space applications by a user on ground. In this framework, research was conducted to control...

We present the results of experiments conducted on a series of parabolic flights to determine the compaction of lunar regolith samples under the influence of reduced gravity. The two regolith simulants, JSC-1A and NU-LHT-2M, showed decreased compaction in lower gravity. On average the sample volumes expanded up to 108% under Martian and 114% under...

The change of thermal-optical properties caused by lunar dust on optical instruments, surface coatings, seals and spacesuit garments has been the subject of numerous theoretical and experimental studies over the past decades. Surface-craft, such as rovers or astronauts in spacesuits, stir up dust due to their own movement. Dust particles also move...

MOVE II is a 2U CubeSat currently under development at Technische Universität München (TUM). The main objective of the MOVE II mission is to measure the flux of magnetically trapped antiprotons with kinetic energies below 80 MeV inside the South Atlantic Anomaly (SAA). Several theoretical models have been published in the last 20 years describing t...

This study investigates the use of nonlinear model predictive control (NMPC) for the approach of a space redundant manipulator to an un-cooperative target satellite in space. The objective is to evaluate the performance of the predictive controller for the approaching task and to investigate the need and feasibility of incorporating constraints int...

This paper presents a new distributed real- Time simulation architecture based on Data Distribution Service (DDS) for space robotic tele-operation tasks. The objective of this paper is to make the simulation architecture open for collaborative tele-operation research and provide the operator an intuitive view of space robotic tele-operation in a wi...

This study focuses on a modeling scheme that uses the concepts of graph theory and spatial notation for calculating the joint-space dynamics of tree structure space manipulator. The objective is to investigate the forward and inverse multibody dynamics algorithms which are relevant to the development of appropriate trajectory planning and control a...

This study, relevant to the development of appropriate trajectory planning and control algorithms, focuses on a modeling scheme that uses the concepts of graph theory and spatial notation for calculating the joint-space dynamics of tree structure space manipulator systems. Firstly, the configuration description of space manipulators using graph the...

This article describes how to measure a three-dimensional antenna radiation pattern and the most effective method to achieve this. We present a new automated three-dimensional measurement scheme, inspired by the seed pattern of a sunflower seed head, where the seed placements are arranged in a way, so that rotational symmetry is obtained in order t...

This paper describes the concept for an End-to-End test environment using the developed Ka-Band inter-satellite antenna in combination with the Ka-band mock-up system of the Institute of Astronautics (LRT – Lehrstuhl Raumfahrttechnik) at Technische Universitaet Muenchen. As the Ka-Band mock-up is an outdoor 3-axis attitude simulator facility, the p...

We investigated if lunar regolith simulant JSC-1A can be "loaded" with hydrogen, nitrogen and the noble gases helium and argon in an attempt to simulate solar wind implanted particles (SWIP) by means of ion implantation. For that purpose we exposed specifically pretreated JSC-1A material to an energetic ion beam of 150 keV of these elements until t...

This work focused on modeling the transient thermal behavior of objects on the surface of the Moon. We determined the impact of the lunar environment, such as latitude, craters, boulders, and slopes, on the core temperatures of specific objects. In particular, we investigated a human in an EVA-suit, an exploration rover, and a highly integrated spa...

Rendezvous & Docking will be an essential part for many future spaceflight activities, like manned or unmanned exploration of the Moon or Near Earth Objects (NEOs), a Mars Sample Return mission, as well as On-Orbit Servicing or Space Debris Removal activities. While autonomy is expected to play a major role in future Rendezvous & Docking, human ope...

Real-time Tele-operation (RTTO) is a control concept for tasks in which in-situ manipulations by humans are not feasible (e.g. dangerous environmental conditions), and autonomous control is demanding due to complex tasks and unforeseeable problems arising during mission conduct. Possible applications of RTTO in space vary from debris removal, using...

We discuss the possibility of an autonomous navigation system for spacecraft that is based on pulsar timing data. Pulsars are rapidly rotating neutron stars that are observable as variable celestial sources of electromagnetic radiation. Their periodic signals have timing stabilities comparable to atomic clocks and provide characteristic temporal si...

The Institute of Astronautics (IA, Lehrstuhl Raumfahrttechnik / LRT) at Technische Universität München has a strong background in inter-satellite communication. The efforts were driven by the need of developing key methods and hardware for controlling robotic space applications by a user on ground. In this framework, research was conducted to contr...

Using a variable temperature scanning tunnelling microscope we have observed both the lattice and the triple charge density wave (CDW) in 1T-TaS2. We obtained images of the nearly-commensurate (NC) phase between 350 and 200 K and the triclinic (T) phase between 220 and 280 K. We analysed the images to determine the local angle of rotation of the CD...

In this paper the case is made for the necessity of a dynamic thermal tool for surface operations called the Thermal Moon Simulation (TherMoS). Lunar surface temperature models are compared and established thermal softwares are discussed. The major shortcomings of these existing models and software tools, with regard to celestial body surface opera...

Usually, positions of spacecraft on interplanetary or deep space missions are determined by radar tracking from ground stations, a method by which uncertainty increases with distance from Earth. As an alternative, a spacecraft equipped with e.g. an X-ray telescope could determine its position autonomoulsy via onboard analysis of X-ray pulsar signal...

A prerequisite to accomplish a system simulation is to have a system model holding all necessary project information in a centralized repository that can be accessed and edited by all parties involved. At the Institute of Astronautics of the Technische Universitaet Muenchen a modular approach for modeling and dynamic simulation of satellite systems...

In this paper we report on the development of a dynamic MATLAB SIMULINK® model for the water and electrolyte balance inside the human body. This model is part of an environmentally sensitive dynamic human model for the optimization and verification of environmental control and life support systems (ECLSS) in space flight applications.An ECLSS provi...

MOVE (Munich Orbital Verification Experiment) is a program of the Institute of Astronautics (LRT) at the Technische Universität München (TUM), which aims on building pico-satellites with university students mainly for educational purposes. First-MOVE shall create a robust platform as a starting point for sophisticated satellite missions of the inst...

Our exploration group at the Technical University of Munich (TUM) has investigated the dynamic stability of Life Support Systems (LSS) on a system level since 2006 and builds on an even longer LSS heritage. The main body of this investigation was the development of the "Virtual Habitat" (V-HAB) dynamic LSS simulation software. In its final version,...

The collaborative research center SFB453 (www.sfb453.de) aims to realize high-fidelity telepresence and teleaction systems. Telepresence and teleaction systems extend the human workspace to remote locations in order to overcome barriers like distance, scaling, danger or the human skin. Using a human-system interface the human operator controls a re...

The major part of the recent research efforts in the field of robotic on-orbit servicing (OOS) has been spent on pursuing autonomous systems, such as Orbital Express or ETS-VII. TU Munich's Institute of Astronautics (LRT) considers the degree of flexibility required of an OOS system to be only achievable by keeping human operators in the loop, by m...

You have a flat tire. You will have to buy a new car!" While on earth, nobody would follow such advice; in space, there are few other options than to replace a malfunctioning spacecraft. There are no repair shops and gas stations in the earth orbit. Because of the lack of so-called on-orbit servicing (OOS) opportunities, some malfunctioning spacecr...

The Exploration group of the Institute of Astronautics (LRT) of the Technische Universitüt a München focuses on long-term scenarios and sustainable human presence in space. One of the enabling technologies in this long-term perspective is in-situ resource utilization (ISRU). When dealing with the prospect of future manned missions to Moon and Mars...

This paper defines and analyzes problems in complying with operative constrains during telepresent space robot missions and proposes methods to support the ground operator during teleoperation. Numerous possible scenarios, like on-orbit servicing of an uncooperative spacecraft with indefinite knowledge of its current state, call for telepresent rea...

Upcoming space missions utilizing hyperspectral or other high-resolution sensors will generate a vast amount of data in orbit. The average communication duration between a spacecraft in low Earth orbit (LEO) to a dedicated ground station is short and in addition, due to the high amount of data to be transferred at link times, a high-performance com...

One of main tasks within the antenna development program LISA is to optimize manufacturing technologies to be applied best to Ka-band multifeed arrays. NC-milling, Cu electroforming, direct laser sintering (DLMS) of aluminium and laser sintering of plastics are being developed/evaluated. Some interest also is put on CFRP technology. The paper prese...

In an ideal case telepresence achieves a state in which a human operator can no longer differentiate between an interaction with a real environment and a technical mediated one. This state is called transparent telepresence. The applicability of telepresence to on-orbit servicing (OOS), i.e., an unmanned servicing operation in space, teleoperated f...

In an ideal case telepresence achieves a state in which a human operator can no longer differentiate between an interaction with a real environment and a technical mediated one. This state is called transparent telepresence. The applicability of telepresence to on-orbit servicing (OOS), i.e., an unmanned servicing operation in space, teleoperated f...

On-Orbit Servicing (OOS), meaning inspection, upgrade, repair, replenishment or maneuvering of a spacecraft on orbit, promises to be a capability with the potential to change the way space business is conducted, for manufacturers, operators, and insurers. The Institute of Astronautics (LRT) of Technische Universitaet Muenchen (TUM) is investigating...

A major challenge in telepresent on-orbit servicing is providing the human operator with all the information required to gain the situational awareness required to safely and effectively perform complex servicing tasks in the remote orbital environment. One support tool is a dedicated robotic camera arm. This will be teleoperated independent of bot...

Spacecrafts are the only complex engineering systems without hands-on maintenance and repair-supporting infrastructure. Though occasionally there have been Space-Shuttle-based servicing missions, such as the Solar Maximum Repair Mission (SMRM) in 1984, usually on-orbit mainten-ance procedures are not foreseen for an individual spacecraft. However,...