A Flexible Image Processing Framework for Vision-based Navigation Using Monocular Image Sensors

On-Orbit Servicing (OOS) encompasses all operations related to servicing satellites and performing other work on-orbit, such as reduction of space debris. Servicing satellites includes repairs, refueling, attitude control and other tasks, which may be needed to put a failed satellite back into working condition. A servicing satellite requires accurate position and orientation (pose) information about the target spacecraft. A large quantity of different sensor families is available to accommodate this need. However, when it comes to minimizing mass, space and power required for a sensor system, mostly monocular imaging sensors perform very well. A disadvantage is- when comparing to LIDAR sensors- that costly computations are needed to process the data of the sensor. The method presented in this paper is addressing these problems by aiming to implement three different design principles; First: keep the computational burden as low as possible. Second: utilize different algorithms and choose among them, depending on the situation, to retrieve the most stable results. Third: Stay modular and flexible. The software is designed primarily for utilization in On-Orbit Servicing tasks, where- for example- a servicer spacecraft approaches an uncooperative client spacecraft, which can not aid in the process in any way as it is assumed to be completely passive. Image processing is used for navigating to the client spacecraft. In this specific scenario, it is vital to obtain accurate distance and bearing information until, in the last few meters, all six degrees of freedom are needed to be known. The smaller the distance between the spacecraft, the more accurate pose estimates are required. The algorithms used here are tested and optimized on a sophisticated Rendezvous and Docking Simulation facility (European Proximity Operations Simulator- EPOS 2.0) in its second-generation form located at the German Space Operations Center (GSOC) in Weßling, Germany. This particular simulation environment is real-time capable and provides an interface to test sensor system hardware in closed loop configuration. The results from these tests are summarized in the paper as well. Finally, an outlook on future work is given, with the intention of providing some long-term goals as the paper is presenting a snapshot of ongoing, by far not yet completed work. Moreover, it serves as an overview of additions which can improve the presented method further

Control Strategy of Hardware-in-the-Loop Simulator EPOS 2.0 for Autonomous Docking Verification

This paper briefly describes the hybrid simulator system called European Proximity Operation Simulator (EPOS 2.0) and the development of the hardware-in-the-loop (HIL) docking simulation concept. A critical requirement for the docking simulation of this HIL simulator is that the 6-DOF robots in the loop have to exactly mimic the dynamic response of the two satellites during a contact operation. The main challenges to meet this requirement are in the stiffness of the robots, which is unlike that of the satellites, as well as the time delay in the HIL simulator. The paper mainly presents the impedance parameter identification concept for matching the impedance between the satellites impact model and the EPOS robots. In addition it presents the contact dynamics model used, and the control strategies to meet the requirements of the docking simulator. Finally it presents the preliminary results and future work

GNC Systems Development in Conjunction with a RvD Hardware-in-the-Loop Simulator

In the last years several satellite projects started providing on-orbit servicing capabilities. This means that an on-orbit servicing spacecraft approaches to a client satellite, captures it, takes over the attitude and orbit control and possibly performs additional maintenance tasks. One of the critical phases of such a mission is to ensure a safe and reliable rendezvous and docking (RvD) process. Especially this phase has to be analyzed, simulated and verified in detail. For the special case of verification of rendezvous and docking sensors and systems, DLR has built a new hardware-in-the-loop simulator capable of testing and verifying rendezvous and docking subsystems. This simulator is known as the European Proximity Operations Simulator (EPOS). It is part of the German Space Operations Center (GSOC) located near Weßling. After completion of the baseline simulator concept in 2009, the facility is going to be used for the first time for an internal research project concentrating on a CCD-based rendezvous and docking sensor. This leads to results of both the research project and information about the facility in operation. The paper presents first results and provides insight into ongoing work and projects as well as an outlook of future things to come

Rendezvous Simulation for On-Orbit Servicing Missions Using Advanced Robotic Technology

Increasing complexity and costs of satellite missions promote the idea of extending the operational lifetime or improving functionalities/performance of a satellite in orbit instead of simply replacing it by a new one. Further, satellites in orbit can severely be affected by aging or degradation of their components and systems as well as by consumption of available resources. These problems may be solved by satellite on-orbit servicing (OOS) missions. One of the critical issues of such a mission is to ensure a safe and reliable Rendezvous and Docking (RvD) operation performed autonomously in space. Due to the high risk associated with an RvD operation, it must be carefully analyzed, simulated and verified in detail before the real space mission can be launched. This paper describes a ground-based hardware-in-the-loop RvD simulation facility. Designed and built on 2-decade experience of RvD experiment and testing, this unique, high-fidelity simulation facility is capable of physically simulating the final approach within 25-meter range and the docking/capture process of an on-orbital servicing mission. Additionally this paper presents first results of hardware in the loop simulations for a rendezvous process to a non-cooperative target

Using Advanced Industrial Robotics for Spacecraft Rendezvous and Docking Simulation

One of the most challenging and risky missions for spacecraft is to perform Rendezvous and Docking (RvD) autonomously in space. To ensure a safe and reliable operation, such a mission must be carefully designed and thoroughly verified before a real space mission can be launched. This paper describes a new, robotics-based, hardware-in-the-loop RvD simulation facility which uses two industrial robots to simulate the 6-DOF dynamic maneuvering of the docking satellites. The facility is capable of physically simulating the final approaching within 25-meter range and the entire docking/capturing process in a satellite on-orbit servicing mission. The paper briefly discusses the difficulties of using industrial robots for HIL contact dynamics simulation and how these problems are solved

Hardware-in-the-loop Rendezvous Simulation using a Vision Based Sensor

One of the critical issues of a satellite On-Orbit Servicing (OOS) mission is to ensure a safe and reliable Rendezvous and Docking (RvD) process. This most risky part of the mission must be carefully analyzed, simulated and verified before the mission can be launched. This paper focuses on the utilization of the new RvD simulation facility called EPOS 2.0 (European Proximity Operations Simulator) to establish a hardware-in-the-loop (HIL) simulation of a close-range rendezvous process. As navigation sensor a monocular camera is used to measure the relative position and orientation of a mock-up of a Geo-stationary target satellite. A new developed image processing algorithm tracks the outer edges of the satellite body under different illumination conditions. The complex software functionality for relative guidance, navigation and control (GNC) and for the satellite dynamics is developed under Matlab/Simulink environment and auto-coded with Real Time Workshop

Hardware-in-the-Loop Rendezvous Simulation Involving an Autonomous Guidance, Navigation and Control System

The rendezvous process is a key technology in multi-spacecraft missions like on-orbit servicing missions. An active spacecraft (chaser) approaches a passive spacecraft (target) in its orbit by performing controlled orbit and attitude maneuvers. The paper presents an autonomous guidance, navigation and control system for rendezvous using a monocular camera as vision-based sensor for relative navigation. Image processing algorithms and navigation filters are employed to get accurate information about the relative position and attitude between the two spacecrafts. The rendezvous sensor and the entire GNC system is tested and verified at DLR's robotic-based test bed European Proximity Operations Simulator 2.0

ON-ORBIT SERVICING MISSIONS AT DLR / GSOC

The German Space Operation Centre (GSOC) is presently involved in the preparation of two On-Orbit Servicing Missions DEOS and OLEV which are presented in this paper. Additionally, we describe potential applications for this mission including space debris removal. Since there are many new challenges in the context of Rendezvous & Docking manoeuvres the ground segment design requires new concepts. We present our solutions in the field of Approach Navigation and Teleoperation. Finally, an integrated system test including GSOC’s new European Proximity Operations Simulator (EPOS) facility is described

Visual Navigation For On-Orbit Servicing Missions

Increasing complexity and costs of satellite missions promote the idea of looking for opportunities to extend the operational lifetime or to improve the performance of a satellite instead of simply replacing it by a new one. Satellites in orbit can severely be affected by ageing, limited fuel source, or degradation of their hardware components. Also the disposal of spacecraft after the end of lifetime will play a more and more important role in the future, especially, if the involved orbits are of strategic importance. Therefore, satellite on-orbit servicing (OOS) has increasingly caught the interests of both satellite developers and users. One of the critical issues of a satellite on-orbit servicing mission is to ensure a safe and reliable Rendezvous and Docking (RvD) process. DLR is developing new navigation algorithms using standard camera systems and advanced 3D sensor systems like PMD (Photonic Mixing Device). Furthermore DLR has built a new and more advanced RvD simulation facility called EPOS 2.0 (European Proximity Operations Simulator). The facility uses robotic manipulators to generate the relative motion between two satellites and allows full RvD test and simulation capabilities for OOS missions up to a range of 25m

Rendezvous Involving a Non-Cooperative, Tumbling Target - Estimation of Moments of Inertia and Center of Mass of an Unknown Target

Safe approach and docking to a non-cooperative, tumbling target satellite is one of the main critical issues in on-orbit servicing missions. Knowledge of the inertia properties of the target spacecraft is a prerequisite for many rendezvous and docking aspects. In this paper we propose a method to estimate the center of mass and moments of inertia using optical sensor data. For that, kinematic equations of motion and the conservation of the angular momentum are employed to estimate the unknown quantities with least squares methods. Observability and limitations are discussed and results gained from computer simulations involving different test cases are presented