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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]

In situ measurements by an atmospheric entry probe allow for sounding and investigating atmospheric composition, structure and dynamics deep into the atmosphere of a Giant planet. In this paper, we describe an Atmospheric Structure Instrument (ASI) for an entry probe at Uranus and/or Neptune. The scientific objectives, the measurements and the expected results are discussed in the framework of a future opportunity for an NASA-ESA joint mission to the Ice Giant planets. [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 a novel solution for the inverse kinematics of redundant space manipulators, which is aimed at locally minimizing the dynamic disturbances transferred to the spacecraft during trajectory tracking maneuvers. The solution is based on a constrained least-squares approach and is suitable for real-time implementation. To formulate the problem as a function of dynamic variables, the inverse kinematics at the acceleration level is considered. The proposed solution is introduced in the context of a more general theory, including the classical pseudoinverse, the extended task-space, and the task priority solutions. Moreover, the introduction of joint acceleration constraints in order to take into account the physical limits of the manipulator joints and the relaxing of the end-effector tracking requirements have been studied, and their influence on the minimization performance has been assessed. The experimental validation of the proposed solutions, with an insight on the effect of joint flexibility on their performance, has been carried out for a planar three-degrees-of-freedom manipulator. Two test cases have been considered, in which the number of force and torque reaction components to be controlled are equal to or greater than the available degree of redundancy. [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]

After having observed the planets from his house in Padova using his telescope, in January 1611 Galileo wrote to Giuliano de Medici that Venus is moving around the Sun as Mercury. Forty years ago, Giuseppe Colombo, professor of Celestial Mechanics in Padova, made a decisive step to clarify the rotational period of Mercury. Today, scientists and engineers of the Astronomical Observatory of Padova and of the University of Padova, reunited in the Center for Space Studies and Activities (CISAS) named after Giuseppe Colombo, are busy to realize a stereo camera (STC) that will be on board the European (ESA) and Japanese (JAXA) space mission BepiColombo, devoted to the observation and exploration of the innermost planet. This paper will describe the stereo camera, which is one of the channels of the SIMBIOSYS instrument, aiming to produce the global mapping of the surface with 3D images. [ABSTRACT FROM PUBLISHER]

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]

The entry, descent and landing of Schiaparelli, the ExoMars Entry, descent and landing Demonstrator Module (EDM), offered a rare (once-per-mission) opportunity for in situ investigations of the martian environment over a wide altitude range. The aim of the ExoMars AMELIA experiment was to exploit the Entry, Descent and Landing System (EDLS) engineering measurements for scientific investigations of Mars' atmosphere and surface. Here we present the simulations, modelling and the planned investigations prior to the Entry, Descent and Landing (EDL) event that took place on 19th October 2016. Despite the unfortunate conclusion of the Schiaparelli mission, flight data recorded during the entry and the descent until the loss of signal, have been recovered. These flight data, although limited and affected by transmission interruptions and malfunctions, are essential for investigating the anomaly and validating the EDL operation, but can also contribute towards the partial achievement of AMELIA science objectives. [ABSTRACT FROM AUTHOR]

An improved approach for the measurement of the relative pose between a target and a chaser spacecraft is presented. The selected method is based on a single camera, which can be mounted on the chaser, and a plurality of fiducial markers, which can be mounted on the external surface of the target. The measurement procedure comprises of a closed-form solution of the Perspective from n Points (PnP) problem, a RANdom SAmple Consensus (RANSAC) procedure, a non-linear local optimization and a global Bundle Adjustment refinement of the marker map and relative poses. A metrological characterization of the measurement system is performed using an experimental set-up that can impose rotations combined with a linear translation and can measure them. The rotation and position measurement errors are calculated with reference instrumentations and their uncertainties are evaluated by the Monte Carlo method. The experimental laboratory tests highlight the significant improvements provided by the Bundle Adjustment refinement. Moreover, a set of possible influencing physical parameters are defined and their correlations with the rotation and position errors and uncertainties are analyzed. Using both numerical quantitative correlation coefficients and qualitative graphical representations, the most significant parameters for the final measurement errors and uncertainties are determined. The obtained results give clear indications and advice for the design of future measurement systems and for the selection of the marker positioning on a satellite surface. [ABSTRACT FROM AUTHOR]