Markus Wilde

Effects of Multivantage Point Systems on the Teleoperation of Spacecraft Docking

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 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.

Experimental Characterization of Inverse Dynamics Guidance in Docking with a Rotating Target

The performance of an inverse dynamics guidance and control strategy is experimentally evaluated for the planar maneuver of a “chaser” spacecraft docking with a rotating “target.” The experiments were conducted on an air-bearing proximity maneuver testbed. The chaser spacecraft simulator consists of a three-degree-of-freedom autonomous vehicle floating via air pads on a granite table and actuated by thrusters. The target consists of a docking interface mounted on a rotational stage with the rotation axis perpendicular to the plane of motion. Given a preassigned trajectory, the guidance and control strategy computes the required maneuver control forces and torque via an inverse dynamics operation. The recorded data of 150 experimental test runs were analyzed using two-way analysis of variance and post hoc Tukey tests. The metrics were maneuver success, vehicle mass change, maneuver duration, thruster duty cycle, and maneuver work. The results showed that the guidance and control algorithm provided robust p...

A robotic camera arm for increased situational awareness in telepresent on-orbit servicing

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 Munichs 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 means of telepresence. However, the absence of important sensory input, such as acoustic and tactile information and peripheral vision, the lack of reference points for discerning orientations, distances and velocities, and the unfamiliar behavior and motion of objects in space reduce the situational awareness of the human operator. In order to provide the human operator with additional visual input and to enable him/her to take up vantage points which would not be available by means of platform-fixed or manipulator-fixed sensors, the utility of a dedicated robotic camera arm is investigated which will be used by the human operator for judging relative attitude and position of chaser and target vehicle and for viewing the remote work site from otherwise unattainable angles and over obstacles. The stereo video stream delivered by this so-called “Third Eye” will be superimposed with head-up display type graphics in order to provide the operator with attitude and position cues. These enable him/her to integrate the additional visual information into his mental model of the surroundings. Operator performance and maneuver safety is also supported by the projection of laser grids onto the surfaces of the target satellite, thereby facilitating attitude and position determination during station keeping.1 2

Evaluation of Head-Up Displays for teleoperated Rendezvous & Docking

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 operators on the ground will still perform either real-time monitoring or actual control of the interceptor vehicle during its final approach. In order to enable the operator to perform these functions effectively and safely, a proximity operations Head-Up Display (HUD) was designed, providing attitude and trajectory prediction information in a number of different attitude projections, coordinate systems and display methods. The different configurations were compared in user studies to evaluate their performance in a number of test scenarios. The results show that an attitude HUD is a valuable addition to a teleoperation man-machine interface, with the outside-in attitude representation showing the greatest benefit for operator efficiency. The choice of coordinate system however has a small effect on the quality of target relative position estimates. Operators perform marginally better using a reference system based on the local horizontal plane than with one using the orbital plane. The different trajectory prediction display methods evaluated cause no measurable difference in maneuver guidance efficiency.

ORION: A simulation environment for spacecraft formation flight, capture, and orbital robotics

The Florida Institute of Technology developed the Orbital Robotic Interaction, On-orbit servicing, and Navigation (ORION) laboratory for the testing of spacecraft guidance, navigation, and control systems for spacecraft proximity maneuvers, and autonomous or telerobotic capture. ORION combines the precise kinematics simulation and large load-bearing capacity of a Cartesian robotic system with the vehicle dynamics simulation capabilities of an air-bearing flat-floor setup, with all vehicles in the simulation being tracked by an optical tracking system. The vehicles can simulate the kinematics and dynamics aspects of three-dimensional formation flight, final approach of uncooperative target objects, and capture. In addition to spacecraft maneuvers, ORION will also serve experiments and tests in the domains of unmanned aerial vehicles and terrestrial robots. This paper describes the design and capabilities of the six degrees of freedom maneuver kinematics simulator of the ORION lab, and the six degrees of freedom air-bearing vehicles for the flat-floor. Furthermore, the paper provides examples of the ongoing research activities: the development and test of capture tools for space debris objects, the project Assessment, Diagnostics, Corrections and Ground Testing of RINGS (Resonant Inductive Near-field Generation Systems), and the development and validation of a distributed virtual sensor for deflection, rate of rotation and acceleration of flexible structures based on fiber Bragg sensor arrays.

Utility of Head-Up Displays for Teleoperated Rendezvous and Docking

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.

Technology development for real-time teleoperated spacecraft mission operations

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.

Equations of Motion of Free-Floating Spacecraft-Manipulator Systems: An Engineer's Tutorial

The paper provides a step-by-step tutorial on the Generalized Jacobian Matrix (GJM) approach for modeling and simulation of spacecraft-manipulator systems. The General Jacobian Matrix approach describes the motion of the end-effector of an underactuated manipulator system solely by the manipulator joint rotations, with the attitude and position of the base-spacecraft resulting from the manipulator motion. The coupling of the manipulator motion with the base-spacecraft are thus expressed in a generalized inertia matrix and a GJM. The focus of the paper lies on the complete analytic derivation of the generalized equations of motion of a free-floating spacecraft-manipulator system. This includes symbolic analytic expressions for all inertia property matrices of the system, including their time derivatives and joint-angle derivatives, as well as an expression for the generalized Jacobian of a generic point on any link of the spacecraft-manipulator system. The kinematics structure of the spacecraft-manipulator system is described both in terms of direction-cosine matrices and unit quaternions. An additional important contribution of this paper is to propose a new and more detailed definition for the modes of maneuvering of a spacecraft-manipulator. In particular, the two commonly used categories free-flying and free-floating are expanded by the introduction of five categories, namely floating, rotation-floating, rotation-flying, translation-flying, and flying. A fully-symbolic and a partially-symbolic option for the implementation of a numerical simulation model based on the proposed analytic approach are introduced and exemplary simulation results for a planar four-link spacecraft-manipulator system and a spatial six-link spacecraft manipulator system are presented.

CERBERUS: Prototype for an Agile Inspection and Servicing Satellite Using Thrust-Vectoring Cold-Gas Propulsion

This paper presents the current status of project Cerberus: the development and testing of a prototype for an agile inspection and servicing satellite using thrust-vectoring cold-gas propulsion. The Cerberus concept uses a set of three cold-gas thrusters controlled on twodegree-of-freedom (2DOF) mechanisms mounted on three sides of a hexagonal structure, 120° apart, providing the spacecraft with 6DOF. A set of two modular small robotic manipulators, each with 5DOF, enables Cerberus to capture and manipulate its targets. The robotic manipulators are mounted to two surfaces of the hexagon, while the bottom surface is used to mount the vehicle on a test platform. Cerberus was designed to be tested in the Orbital Robotics Interaction, On-orbit servicing, and Navigation (ORION) laboratory at Florida Institute of Technology, where an OptiTrack motion tracking system is used in conjunction with on-board optical sensors and laser rangefinders for guidance, navigation, and control.

Modified sliding control for tumbling satellite capture with robotic arm

The capability to capture uncooperative, tumbling space objects is a critical requirement for any on-orbit servicing or space debris removal system. For successful capture, the chaser spacecraft must be able to navigate to the target and reach the desired grasping or docking feature. In order for the forces during grasping on both the grasping mechanism and the target object not to exceed structural limits, the chaser must perform formation flight with low relative velocity for the duration of the capture process. This paper presents a robust control approach for the capture of an uncooperative, tumbling target based on the Clohessy-Wiltshire equations of motion. As the capture maneuver must be tuned to accommodate the capabilities of the capture mechanism, a conceptual design for a possible grasping mechanism is also presented. The capabilities of this mechanism help define the constraints of the numerical simulations of the capture maneuvers.