Emulating On-Orbit Interactions Using Forward Dynamics Based Cartesian Motion

The paper presents a novel Hardware-In-the-Loop (HIL) emulation framework of on-orbit interactions using on-ground robotic manipulators. It combines Virtual Forward Dynamic Model (VFDM) for Cartesian motion control of robotic manipulators with an Orbital Dynamics Simulator (ODS) based on the Clohessy Wiltshire (CW) Model. VFDM-based Inverse Kinematics (IK) solver is known to have better motion tracking, path accuracy, and solver convergency than traditional IK solvers. Therefore it provides a stable Cartesian motion for manipulator-based HIL on-orbit emulations. The framework is tested on a ROS-based robotics testbed to emulate two scenarios: free-floating satellite motion and free-floating interaction (collision). Mock-ups of two satellites are mounted at the robots' end-effectors. Forces acting on the mock-ups are measured through an in-built F/T sensor on each robotic arm. During the tests, the relative motion of the mock-ups is expressed with respect to a moving observer rotating at a fixed angular velocity in a circular orbit rather than their motion in the inertial frame. The ODS incorporates the force and torque values on the fly and delivers the corresponding satellite motions to the virtual forward dynamics model as online trajectories. Results are comparable to other free-floating HIL emulators. Fidelity between the simulated motion and robot-mounted mock-up motion is confirmed.Comment: Submitted to ICRA2023, for associated video, see: https://www.youtube.com/watch?v=N2KYCKJ4KM

Hardware-in-the-loop Proximity Operations in Cislunar Space

Space missions to Near Rectilinear Halo Orbits (NRHOs) in the Earth-Moon system are upcoming. A rendezvous technique in the cislunar space is proposed in this investigation, one that leverages coupled orbit and attitude dynamics in the Circular Restricted Three-body Problem (CR3BP). An autonomous Guidance, Navigation and Control (GNC) technique is demonstrated in which a chaser spacecraft approaches a target spacecraft in the southern 9:2 synodic-resonant L2 Near Rectilinear Halo Orbit (NRHO), one that currently serves as the baseline for NASA's Gateway. A two-layer control approach is contemplated. First, a nonlinear optimal controller identifies an appropriate baseline rendezvous path, both in position and orientation. As the spacecraft progresses along the pre-computed baseline path, optical sensors measure the relative pose of the chaser relative to the target. A Kalman filter processes these observations and offers precise state estimates. A linear controller compensates for any deviations identified from the predetermined rendezvous path. The efficacy of the GNC technique is tested by considering a complex scenario in which the rendezvous operation is conducted with a non-cooperative tumbling target. Hardware-in-the-loop laboratory experiments are conducted as proof-of-concept to validate the guidance algorithm, with observations supplemented by optical navigation techniques

Rendezvous in cislunar halo orbits: Hardware-in-the-loop simulation with coupled orbit and attitude dynamics

Space missions to Near Rectilinear Halo Orbits (NRHOs) in the Earth-Moon system are upcoming. A rendezvous technique in cislunar space is proposed in this investigation, one that leverages coupled orbit and attitude dynamics in the Circular Restricted Three-body Problem (CR3BP). An autonomous Guidance, Navigation, and Control (GNC) technique is demonstrated in which a chaser spacecraft approaches a target spacecraft in a sample southern 9:2 synodic-resonant L2 NRHO, one that currently serves as the baseline for NASA's Gateway. A two-layer guidance and control approach is contemplated. First, a nonlinear optimal controller identifies an appropriate baseline rendezvous path for guidance, both in position and orientation. As the spacecraft progresses along the pre-computed baseline path, navigation is performed through optical sensors that measure the relative pose of the chaser relative to the target. A Kalman filter processes these observations and offers state estimates. A linear controller compensates for any deviations identified from the predetermined rendezvous path. The efficacy of the GNC technique is tested by considering a complex scenario in which the rendezvous operation is conducted with an uncontrolled tumbling target. Hardware-in-the-loop laboratory experiments are conducted as a proof-of-concept to validate the guidance algorithm, with observations supplemented by optical navigation techniques

Lessons from a Space Lab -- An Image Acquisition Perspective

peer reviewedThe use of Deep Learning (DL) algorithms has improved the performance of vision-based space applications in recent years. However, generating large amounts of annotated data for training these DL algorithms has proven challenging. While synthetically generated images can be used, the DL models trained on synthetic data are often susceptible to performance degradation, when tested in real-world environments. In this context, the Interdisciplinary Center of Security, Reliability and Trust (SnT) at the University of Luxembourg has developed the 'SnT Zero-G Lab', for training and validating vision-based space algorithms in conditions emulating real-world space environments. An important aspect of the SnT Zero-G Lab development was the equipment selection. From the lessons learned during the lab development, this article presents a systematic approach combining market survey and experimental analyses for equipment selection. In particular, the article focus on the image acquisition equipment in a space lab: background materials, cameras and illumination lamps. The results from the experiment analyses show that the market survey complimented by experimental analyses is required for effective equipment selection in a space lab development project.R-AGR-3874 - BRIDGES/20/14755859 MEET-A - LMO Contrib (01/01/2021 - 31/12/2023) - AOUADA Djamil

Safety-enhanced human-robot interaction control of redundant robot for teleoperated minimally invasive surgery

In this paper, a teleoperation control of a 7- DoF robot manipulator for Minimally Invasive Surgery (MIS), which guarantees a safety-enhanced compliant behavior in the null space, is described. The redundancy of the manipulator is exploited to provide a flexible workspace for nurses or other staff (assisting physicians, patient support). The issue with safety and accurate surgical task execution may arise in the presence of human-robot interaction. Based on the implemented impedance control of tele-operated MIS tasks, a safety enhanced constraint is applied on the compliant null space motion. At the same time, the control approach integrates an adaptive fuzzy compensator to guarantee the accuracy of the surgical tasks during the uncertain human-robot interaction. The performance of the proposed algorithm is verified with virtual surgical tasks. The results showed that the compliant null space motion is constrained in a safe area, and also that the accuracy of tooltip is improved, providing a flexible and safe collaborative behavior in the null space for human-robot interaction during surgical tasks

Zero-G Lab: A multi-purpose facility for emulating space operations

peer reviewedDuring orbital rendezvous, the spacecraft typically approach in the same orbital plane, and the phase of the orbit eventually aligns. Potential rendezvous and docking missions need to be emulated and tested in an on-ground facility for micro-gravity research prior to meeting the harsh conditions of space environment. For orbital docking, the velocity profile of the two spacecraft must be matched. The chaser is placed in a slightly lower orbit than the target. Since all these tasks are quite complex and the realization of space missions are very expensive, any space-related hardware or software's performance must be tested in an on-ground facility providing zero gravity emulation before initiating its operation in space. This facility shall enable emulation conditions to mimic pseudo zero gravity. It is of critical importance to be equipped with all the necessary ”instruments and infrastructure” to test contact dynamics, guidance, navigation and control using robotic manipulators and/or floating platforms. The Zero-G Laboratory at the University of Luxembourg has been designed and built to emulate scenarios such as rendezvous, docking, capture and other interaction scenarios between separate spacecraft. It is equipped with relevant infrastructure including nearly space-representative lightning conditions, motion capture system, epoxy floor, mounted rails with robots, capability to integrate on-board computers and mount large mock-ups. These capabilities allow researchers to perform a wide variety of experiments for unique orbital scenarios. It gives a possibility to perform hybrid emulations with robots with integrated hardware adding pre-modeled software components. The entire facility can be commanded and operated in real-time and ensures the true nature of contact dynamics in space. The Zero-G Lab also brings great opportunities for companies/startups in the space industry to test their products before launching the space missions. The article provides a compilation of best practices, know-how and recommendations learned while constructing the facility. It is addressed to the research community to act as a guideline to construct a similar facility