Design and Performance Evaluation of a UWB Communication and Tracking System for Mini-AERCam

NASA Johnson Space Center (JSC) is developing a low-volume, low-mass, robotic free-flying camera known as Mini-AERCam (Autonomous Extra-vehicular Robotic Camera) to assist the International Space Station (ISS) operations. Mini-AERCam is designed to provide astronauts and ground control real-time video for camera views of ISS. The system will assist ISS crewmembers and ground personnel to monitor ongoing operations and perform visual inspections of exterior ISS components without requiring extravehicular activity (EAV). Mini-AERCam consists of a great number of subsystems. Many institutions and companies have been involved in the R&D for this project. A Mini-AERCam ground control system has been studied at Texas A&M University [3]. The path planning and control algorithms that direct the motions of Mini-AERCam have been developed through the joint effort of Carnegie Mellon University and the Texas Robotics and Automation Center [5]. NASA JSC has designed a layered control architecture that integrates all functions of Mini-AERCam [8]. The research described in this report is part of a larger effort focused on the communication and tracking subsystem that is designed to perform three major tasks: 1. To transmit commands from ISS to Mini-AERCam for control of robotic camera motions (downlink); 2. To transmit real-time video from Mini-AERCam to ISS for inspections (uplink); 3. To track the position of Mini-AERCam for precise motion control. The ISS propagation environment is unique due to the nature of the ISS structure and multiple RF interference sources [9]. The ISS is composed of various truss segments, solar panels, thermal radiator panels, and modules for laboratories and crew accommodations. A tracking system supplemental to GPS is desirable both to improve accuracy and to eliminate the structural blockage due to the close proximity of the ISS which could at times limit the number of GPS satellites accessible to the Mini-AERCam. Ideally, the tracking system will be a passive component of the communication system which will need to operate in a time-varying multipath environment created as the robot camera moves over the ISS structure. In addition, due to many interference sources located on the ISS, SSO, LEO satellites and ground-based transmitters, selecting a frequency for the ISS and Mini-AERCam link which will coexist with all interferers poses a major design challenge. To meet all of these challenges, ultrawideband (UWB) radio technology is being studied for use in the Mini-AERCam communication and tracking subsystem. The research described in this report is focused on design and evaluation of passive tracking system algorithms based on UWB radio transmissions from mini-AERCam

Proximity operations of a miniature inspector satellite using emulated computer vision

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008.Includes bibliographical references (p. 115-117).If a micrometeoroid, a piece of space junk, launch debris, or a major system failure impacts the Crew Exploration Vehicle (CEV), it can cause life-threatening damage. Past International Space Station (ISS) and Space Shuttle repair missions have shown that inspection of a damaged system is crucial for planning the EVA to repair it. To assist the CEV team with inspection and contingency planning, an inspector satellite can be an essential tool. This thesis presents the idea of using a miniature satellite to inspect the CEV for damage while flying in formation. In this research, the satellite test bed SPHERES has been used to develop, demonstrate, and flight-test an inspector-satellite operations design and controller. The design utilizes an autonomous control algorithm that combines Linear Quadratic Regulator (LQR) and Artificial Potential Field (APF) control. This controller is designed to navigate through waypoints, follow the contours of an inspected spacecraft's surface, avoid obstacles, operate in real-time onboard the inspector satellite, work with or without a-priori knowledge of the inspected spacecraft's geometry, interface with a computer-vision system, and handle the loss of computer-vision information. Since the SPHERES camera system is currently under development, computer vision data was emulated using the current SPHERES global metrology. Results from simulations and successful flight tests aboard the ISS are discussed.by Christine Marie Edwards.S.M

Autonomous control of a free-flying space robot

The ongoing requirement for the assembly of large space structures has made a call for astronauts to work in partnership with a new generation of free-flying robotic vehicles. This thesis develops the control methodology for a flying robot designed to operate autonomously onboard crewed spacecraft in pressurized or vacuum microgravity environments. The controller will provide the robot with decision-making capabilities, allowing it to navigate autonomously within the vicinity of a large space structure and complete a number of tasks. The controller design uses a behavioural 'Braitenberg' approach to avoid collisions and achieve useful task objectives such as reaching goal destinations, collecting randomly positioned objects, refuelling and following moving targets. The incorporation of manual input is developed to allow external control over the automated robotic vehicle. The suite of behaviours are given a variable weighting, to provide a versatile control methodology with seamless transition between behaviours, and in addition, integration of cue-deficit techniques to optimise the behavioural control when confronted with conflicting choices - such as the need to refuel whilst searching out a goal. The model is enhanced by the addition of a camera tool to complement the third person viewpoint with the ability to point the robot's camera optical axis in any desired orientation, providing tracking and fixed-pointing capabilities with possible uses in video conferencing. The camera tool incorporates an attitude controller (using potential functions) to bring the robot to rest at the desired goal orientation, or track moving targets. In summary, this thesis documents the development of a novel control methodology which integrates high-level behaviour based autonomy with low level translation and rotational control

Estimation of magnet separation for magnetic suspension applications

This thesis describes a form of non-contact measurement using two dimensional hall effect sensing to resolve the location of a moving magnet which is part of a ‘magnetic spring’ type suspension system. This work was inspired by the field of Space Robotics, which currently relies on solid link suspension techniques for rover stability. This thesis details the design, development and testing of a novel magnetic suspension system with a possible application in space and terrestrial based robotics, especially when the robot needs to traverse rough terrain. A number of algorithms were developed, to utilize experimental data from testing, that can approximate the separation between magnets in the suspension module through observation of the magnetic fields. Experimental hardware was also developed to demonstrate how two dimensional hall effect sensor arrays could provide accurate feedback, with respects to the magnetic suspension modules operation, so that future work can include the sensor array in a real-time control system to produce dynamic ride control for space robots. The research performed has proven that two dimensional hall effect sensing with respects to magnetic suspension is accurate, effective and suitable for future testing