Andreas Fleischner’s research while affiliated with Technical University of Munich and other places

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. The proposed procedure exploits the iterative closest point algorithm implemented in closed-loop fashion. In order to guarantee stability of the solution, the current pose of the target is predicted onboard by propagating the last estimated state using a dedicated dynamics model of the maneuver. The tracking procedure is initialized with a fast template matching algorithm that determines attitude and position of the target without prior information on its state. The capabilities of the proposed procedure are demonstrated using a full degrees-of-freedom hardware simulator. In these experiments, the Microsoft Kinect v2 sensor is employed for real-time acquisition of the target spacecraft depth image. The results demonstrate the effectiveness of the proposed procedure during docking maneuvers to a noncooperative tumbling target. However, prediction of the current target pose is crucial for algorithm robustness. Nomenclature Symbols C = principal body-fixed Cartesian coordinate system of the chaser spacecraft d = distance of the target spacecraft center of mass from the centroid of D, m D = point cloud of the target spacecraft measured by the rendezvous sensor, m H = Hill's Cartesian coordinate system l = position of the rendezvous sensor with respect to the chaser spacecraft center of mass, m p = position of the target spacecraft center of mass with respect to the rendezvous sensor, m q T = quaternion of the attitude of the coordinate system T with respect to H q T-S = quaternion of the attitude of the coordinate system T with respect to S q* = solution (attitude) of the Iterative Closest Point procedure r = position of the chaser spacecraft center of mass with respect to the target center of mass, m B A R = rotation matrix from the coordinate system A to the system B R(q) = rotation matrix defined by the unit quaternion vector q S = Cartesian coordinate system of the chaser spacecraft rendezvous sensor T = principal body-fixed Cartesian coordinate system of the target spacecraft t = solution (translation) of the Iterative Closest Point procedure, m X = point cloud of the reference target spacecraft geometry defined in the coordinate system S, m D μ = position of the centroid of the point cloud D, m Δθ = sampling angular step for the template matching procedure, rad Superscript a s = vector a whose components are expressed in the coordinate system s (s = H, C, T) X cp = closest point of the point cloud X to the points of D, m

This paper details the development and experimental evaluation of a head-up display for teleoperation of spacecraft proximity operations, both in a software-based simulation environment and in a hardware proximity operations simulator. The results show that attitude head-up displays are generally beneficial to operator performance in rendezvous and docking tasks, and that an outside-in attitude representation is superior to an inside-out system. The display reference coordinate system to be used in relative maneuvering tasks is, furthermore, the local horizontal system. A comparison of different configurations of trajectory prediction displays yielded no results.

Rendezvous and docking with uncooperative target objects are driving capabilities for future robotic on-orbit servicing and space debris removal systems. A teleoperation system augments a robotic system with the perception, cognition, and decision capabilities of a human operator, which can lead to a more capable and more flexible telerobotic system. The ThirdEye system was developed in order to support the human operator in the complex relative navigation task of final approach and docking. It provides the operator with a flexible camera vantage point which can be positioned freely in the relevant space around and between the chaser and target spacecraft. The primary and secondary camera views, an attitude head-up display, and a trajectory prediction display are integrated into an intuitive graphical user interface. A validation study was conducted to evaluate the effects of this ThirdEye system on the performance of the teleoperation system during final approach and docking with uncooperative, rotating targets. The results of this study show that the ThirdEye system increases the overall task success rate by $15$ and improves operator situation awareness, without having negative impact on the usage of system resources. The partial failure rates are decreased by hbox{20--30%}. In high-difficulty scenarios, the operator task load is increased due to the dual task of teleoperating the camera arm and the spacecraft in tandem, which leads to a minor increase in failure rate in these scenarios.

Upcoming space missions in the fields of on-orbit servicing and space debris removal will face highly complex tasks which require significant increases in complexity and capability of spacecraft systems, as well as increased dexterity of manipulators. In order to provide methods and technologies allowing real-time teleoperation in orbit, the Institute of Astronautics (LRT) at the Technical University Munich (TUM) is researching different technologies that will be needed for this new type of spacecraft mission operations. With the on-orbit servicing scenario as leading example mission, the main focus lies in developing technologies needed for teleoperated close-range proximity operations including inspection and docking maneuvers.

The objectives of on-orbit servicing (OOS) missions include manipulation, proximity operations and inspection of target satellites. Therefore the servicer satellite often has to be teleoperated at low latency for several minutes to fulfill these tasks. That means communication plays a crucial role for OOS missions because real time teleoperation including high data rates has to be realized. So the communication path from front end sensors on the servicer spacecraft to the operator on ground has to be optimized and the latency time has to be minimized. Furthermore a long access time from the ground station is required because continuous communication with the satellite is mandatory for most of the OOS tasks. This can be realized by an inter-satellite link via a geostationary relay satellite, which has the advantage that a satellite in Low Earth Orbit (LEO) can be accessed from one ground station for about half an orbit. To evaluate both, the requirement of a long access time from the ground station as well as the need of a short latency time, an end to end communication scenario was implemented at the Institute of Astronautics (LRT) at the Technische Universität München (TUM). This scenario includes different spacecraft sensors (e.g. stereo cameras, LIDAR systems), a Ka-Band ground station and man machine interfaces. This paper describes the setup of a realistic simulation of a communication path from a data source to an operator via space-link. Furthermore the method of latency measuring depending on the data source is described. The communication architecture is embedded in a spacecraft simulator to simulate On-Orbit Servicing scenarios like Space Debris removal and target inspection.

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 institute in the future. In the paper, the state of development is described, but emphasis is on the requirements for high reliability of the First-MOVE satellite and how robustness drives the actual design of the satellite.

This paper presents results and experiences gathered from the VECTOR (Verification of Concepts for Tracking and Orientation) experiment within the REXUS sounding rocket program. A novel dynamic spiral tracking (DST) concept for the tracking of fastmoving objects, such as sounding rockets, is introduced. The method is based on conical motion of the antenna around the vector to its anticipated target as well as the measurement and processing of the received signal strength from the rocket-borne radio transmitter. In addition to the tracking experiment, a hardware implementation of an on-board real-time video compression system for space missions based on the CCSDS standard was tested. In order to meet the specified real-time compression performance, a FPGA hardware implementation was developed.

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 real-time operation of space robots. Such operations imply unpredictable, interactive control of the space robot and hence significantly restrain the applicability of classical ahead mission planning. Especially direct or indirect effects of platform maneuvers or actuator reactions on the space robot's attitude and dynamics are considered to be critical. As a result from the unplanned change in attitude or angular velocity of the space robot's base, several operative constrains like communication antenna pointing might be violated, leading to signal loss, instrument damage or even loss of the spacecraft. A real-time space robotics simulator was developed in order to identify these problems and to test and evaluate the proposed concepts and solutions. This simulator is based on multi-body dynamics and relative kinematics models implemented in MATLAB/Simulink. A highly generic approach allows adapting the simulation to different scenario and spacecraft configurations. In addition, realistic visualization and real-time simulation capabilities allow operator-in-the-loop tests to evaluate the closed loop performance of different operator support concepts. The simulator architecture, identified operative constrains and simulation results are presented and discussed. Copyright ©2010 by the International Astronautical Federation. All rights reserved.