Search

Pose estimation is critical for mobile robots to fulfill various tasks, such as path following or mapping the environment. This is usually accomplished by simultaneous localization and mapping (SLAM). However, computationally constrained systems, such as planetary rovers, rely on less intensive guidance navigation and control (GNC) solutions generally derived solely from visual odometry (VO), wheel odometry, and the onboard inertial measurement unit. Although providing adequate localization performances, the drift accumulated overtime is not compensated by loop closing capabilities, typical of SLAM. Usually, rovers send surface images to the ground station, and these images are used for multiple purposes, such as scientific and operational planning. The number of images is constrained by the communication bandwidth and power budget. The set of transmitted images can be used as a means to correct the robot’s trajectory in an off-line manner. In this work, a solution is presented to the problem of selecting the optimal set of viewpoints belonging to the planned path from which to capture and transmit images: 1) it guarantees accurate trajectory correction and 2) complies with the maximum number of images that can be transmitted to ground control given the available data budget. To this end, it is proposed: 1) a delocalized/decentralized sensor fusion approach based on pose graph optimization and structure from motion and 2) a strategy to select a minimal set of viewpoints along the trajectory that, given a tentative geometry of the environment and the global path that the rover must follow, minimizes the uncertainty of all the robot poses. Optimal camera viewpoint positions are selected as a function of the planned trajectory, the approximate scene geometry, and the maximum transmittable number of images. The proposed method has been tested on a dataset of stereo-images collected in a representative Martian environment, the ALTEC Mars Terrain Simulator (MTS), with the ExoMars testing rover (ExoTeR—European Space Agency, Paris, France, property). Rover stereo-images ground truth was given with millimetric accuracy by a motion capture (MC) system. [ABSTRACT FROM AUTHOR]

Monocular vision systems allow compact and resource-constrained vehicles to perform online state estimation through Structure from Motion approaches. However, it is needed to integrate additional information to obtain a metric scale for the estimated trajectory. We propose a minimalistic approach based on the sensor fusion between a monocular camera and a 1D LiDAR (LIght Detection And Ranging) rangefinder. A classical visual front-end, in charge of tracking the camera pose with respect to a map of landmarks, is paired with an optimization back-end where depth measurements constrain the distance between cameras and 3D points. The fusion methodology is based on a keyframe-wise search of correspondences between visual landmarks and projections of altimeter points. The differences between triangulated landmark depths and associated altimeter measurements are minimized using the iSAM2 incremental smoother. We test our algorithm in a variety of datasets comprising an outdoor scenario with accurate D-GPS ground truth evaluating both tracking accuracy and computational effort. Results show that our algorithm provides comparable performances to scale-aware RGB-D vision systems and obtains relative trajectory errors close to 0.5%. Furthermore, we propose and validate an extrinsic calibration pipeline to refer range measurements in the camera reference system which differs from common LiDAR-camera calibration algorithms due to the 5 Degrees of Freedom (DoF) nature of the single-point rangefinder and camera system. [ABSTRACT FROM AUTHOR]

We present a flexible sensor fusion approach to retrieve scale information in monocular visual odometry (VO) through integrating range measurements from a wide variety of depth sensors spanning from small-resolution time-of-flight (ToF) cameras to 2-D and potentially 3-D LiDARs. While many algorithms exist in literature for range-enhanced monocular VO, the majority of them are tailored for a specific sensor choice, limiting the integration on generic mobile systems. Our monocular VO algorithm builds on a standard front end, where the camera tracking is performed relative to a map of triangulated landmarks. The inherent scale ambiguity and drift in monocular perception are resolved by optimizing both the camera poses as well as the landmark map with the depth information provided by the range sensor. Performances have been tested on the custom data sets created with an experimental platform comprising a stereo camera, a low-resolution ToF camera, and a 2-D LiDAR. We present a detailed overview of the extrinsic calibration procedures including an ad hoc solution applicable to very low-resolution depth sensors. The proposed system is tested on short- and long-range motions, showing that: 1) performances in each of the tested configurations are on par or better than the state-of-the-art stereo systems and 2) it is sufficient to use a reduced number of range measurements to obtain a scaled trajectory accurately. [ABSTRACT FROM AUTHOR]

This paper presents investigations toward the development of an inflated deformable rolling rover. The proposed novel locomotion system could find potential future use, for example, in scouting and exploration missions. The manufacturing procedure used to fabricate a preliminary prototype is presented in this paper. The prototype consists of a rigid frame and four dielectric elastomer actuator (DEA) sectors, which give the prototype a spherical shape. Analytical models are proposed to predict the electromechanical behavior of the DEA sectors and to estimate their effect on the prototype's dynamics. These models are validated through an experimental procedure. [ABSTRACT FROM PUBLISHER]

The Visible and Infrared Hyperspectral Imager (VIHI) is one of the three optical heads of the Spectrometers and Imagers for MPO BepiColombo Integrated Observatory SYStem (SIMBIO-SYS) experiment onboard European Space Agency's BepiColombo cornerstone mission to Mercury. The other two optical heads of SIMBIO-SYS are a stereo camera and a high-resolution image camera. The experiment is designed to scan the Hermean surface from a polar orbit with the three channels to map the physical, morphological, tectonic, and compositional properties of the planet. The main scientific objectives of SIMBIO-SYS are the study of Mercury's surface geology and stratigraphy, the surface composition, the regolith properties, the crustal differentiation, impact, and volcanic processes. The VIHI experiment uses a high-performance optical layout (Schmidt telescope and spectrometer in Littrow configuration) which allows investigating the 400–2000-nm spectral range with 256 spectral channels (6.25 nm/band sampling). The instrument has an instrument field of view (FOV) of 250 \mu\rad corresponding to a spatial scale of about 100 m/pixel at periherm and 375 m at apoherm. The instrument operates in pushbroom configuration, sampling the surface of Mercury with an FOV of 64 \times 0.25 mrad. The main technical challenges of this experiment are focal-plane design (cadmium–mercury–telluride thinned to improve the efficiency at visible wavelengths), short dwell time (from about 40 ms at equator to about 100 ms at poles), thermal control, mechanical miniaturization, radiation hardening, high data rate, and compression. A description of the internal calibration unit concept and functionalities is given. [ABSTRACT FROM AUTHOR]

In this paper, a detailed accuracy analysis for the orientation of an innovative open-chain pointing mechanism is carried out, employing methods for indirect measurements. The particular shape of the mechanism exhibits the advantage of high structural stiffness and different pointing accuracy in comparison with a standard orthogonal axes gimbal. With the aim of finding out advantages and drawbacks as regard the accuracy of the proposed pointing mechanism, an accuracy analysis is performed through three different methods of uncertainty expression and propagation based on the probability theory or the theory of evidence. The proposed pointing mechanism, in comparison with the standard orthogonal axes gimbal, exhibits a considerable lower uncertainty for two of the three Euler angles that are used for the end-effector orientation expression and a higher uncertainty for the third Euler angle. Thus, the proposed mechanism could be particularly suited for pointing directional antennas, allowing the employment of high-data-rate communication systems. This result is strengthened by the fact that the accuracy analysis was performed with different uncertainty expression and propagation methods, which take into account only random effects or both random and systematic effects. [ABSTRACT FROM AUTHOR]

Metrology is the theoretical and experimental interdisciplinary science of the measurement for each research and application field. In the aerospace field, metrology plays a fundamental role both for certification and for calibration of instrumentation. In addition, it drives the ideation and design of innovative instrumentation and experimental setups to reproduce on the ground aerospace environments. In this issue, we try to demonstrate this, highlighting the importance of measurement and instrumentation for all activities involved in aerospace. Aerospace projects need innovative and unique test and measurement solutions throughout the entire product life cycle, from modelling and simulation on a research and development bench to flight testing and operational applications. Innovation in aerospace technologies takes place at an increasingly fast pace, as does the development of test and measurement methodologies and technologies, and this is important for miniaturization and increasingly integrated solutions to minimize the necessary resources. Companies and researchers should focus on the development of the next generations of aerospace equipment and, in the meantime, must ensure their effectiveness before they are used in an operational context [ABSTRACT FROM AUTHOR]