Ulf Bestmann

Evaluation of a double equipped MEMS IMU based on real flight trial scenarios

The Inertial Measurement Unit (IMU) investigated within the presented work consists of two (optional three) dissimilar sets of MEMS accelerometers and gyros, respectively. Both sets are mounted in one enclosure and thus are subject to the same calibration procedure. Different combinations of these dual sensor sets can be used to exploit the complementary sensor properties, e.g. measurement range, resolution and noise characteristics as well as to benefit from redundancy in airborne applications.

A Flight State Estimator that Combines Stereo-Vision, INS, and Satellite Pseudo-Ranges

This paper presents a flight state estimator which couples stereo vision, inertial (INS), and global navigation satellite system (GNSS) data. The navigation filter comes with different operation modes that allow loosely coupled GNSS/INS positioning and, for difficult conditions, improvements using visual odometry and a tighter coupling with GNSS pseudo-range (PSR) data. While camera systems are typically used as an additional relative movement sensor to enable positioning without GNSS for a certain amount of time, the PSR data filtering allows to use satellite navigation also when less than four satellites are available. This makes the filter even more robust against temporary dropouts of the full GNSS solution. The application is the navigation of unmanned aircraft in disaster scenarios which includes flights close to ground in urban or mountainous areas. The filter performance is evaluated with sensor data from unmanned helicopter flight tests where different conditions of the GNSS signal reception are simulated. It is shown that the use of PSR data improves the positioning significantly compared to the dropout when the signals of less than four satellites are available.

Observability of integrated navigation system states under varying dynamic conditions and aiding techniques

The performance of integrated navigation systems not only depends on the quality of the used inertial measurement unit (IMU) and aiding sensor information, but also on the correct observation of the systems state vector. As a classical example, an integration filter shows a good performance if it manages to estimate the sensor errors properly. As the observability varies with the current system states as well as the quality of the aiding information, a meaningful characterization of the systems performance is difficult to obtain. The aim of this paper is to analyze the impact of the influences named above on the observability of the system model that is part of the navigation filter. For linear and linearized systems, e.g. Kalman Filter and Extended Kalman Filter, different measures of observability can be derived from control theory. This paper will show the necessary basic algorithms and methods to evaluate a systems observability. Based on these insights an evaluation of a standard filter model of an integrated navigation system is performed. Therefore, different dynamic conditions as well as aiding information are taken into account. The main focus of this work lies on the examination of real flight data and correlation between system states and their observability. Based on these investigations this paper presents a detailed view on the assessment and first results towards a better characterization of IMU performance.

Stand-Alone Ship-Relative Navigation System Based on Pseudolite Technology

Automatic landing on a ship requires a navigation system that provides not only information of the global position of the ship rather, the relative position and attitude between aircraft and ship are required. Additionally, information of the current ship motion should be available, in order to select a favorable point in time for touchdown. In this paper we introduce a navigation system that provides the required navigation data and which can be used for automatic landings or to alleviate the workload of a pilot. The system consists of a pseudolite infrastructure onboard the ship and corresponding receivers onboard the aircraft, it needs no additional information and is independent of space-related navigation systems. The paper gives an overview of the latest navigation systems for the purpose of ship landings. Furthermore, we present the utilized filter algorithm for improved measurements. Simulation results show the capability of the proposed system and it is shown that its precision and accuracy are sufficient for automatic landings.

The far-infrared space interferometer study IRASSI: motivation, principle design, and technical aspects

The far-infrared (FIR) regime is one of the few wavelength ranges where no astronomical data with sub-arcsecond spatial resolution exist yet. Also medium-term satellite projects like SPICA, Millimetron or OST will not resolve this malady. For many research areas, however, information at high spatial and spectral resolution in the FIR, taken from atomic fine-structure lines, from highly excited CO and especially from water lines would open the door for transformative science. These demands call for interferometric concepts. We present here first results of our feasibility study IRASSI (Infrared Astronomy Satellite Swarm Interferometry) for an FIR space interferometer. Extending on the principal concept of the previous study ESPRIT, it features heterodyne interferometry within a swarm of 5 satellite elements. The satellites can drift in and out within a range of several hundred meters, thereby achieving spatial resolutions of <0.1 arcsec over the whole wavelength range of 1–6 THz. Precise knowledge on the baselines will be ensured by metrology employing laser frequency combs, for which first ground-based tests have been designed by members of our study team. In this contribution, we first give a motivation how the science requirements translated into operational and design parameters for IRASSI. Our consortium has put much emphasis on the navigational aspects of such a free-flying swarm of satellites operating in relatively close vicinity. We hence present work on the formation geometry, the relative dynamics of the swarm, and aspects of our investigation towards attitude estimation. Furthermore, we discuss issues regarding the real-time capability of the autonomous relative positioning system, which is an important aspect for IRASSI where, due to the large raw data rates expected, the interferometric correlation has to be done onboard, quasi in real-time. We also address questions regarding the spacecraft architecture and how a first thermomechanical model is used to study the effect of thermal perturbations on the spacecraft. This will have implications for the necessary internal calibration of the local tie between the laser metrology and the phase centres of the science signals.

Flugroboter. Ein Überblick über technologische und operationelle Entwicklungen und Trends

Zusammenfassung Technologische Fortschritte in den Kernbereichen der Luftfahrt- und Informationstechnologie wie z. B. dem Leichtbau, der Aerodynamik, der Antriebs- und Energiespeichertechnik sowie der Flugsysteme haben der Entwicklung von autonomen und oftmals miniaturisierten Fluggeräten erheblichen Vortrieb geliefert. In Verbindung mit neuen Methoden der automatisierten Luftfahrzeugführung erobern Flugroboter in bisher ungeahntem Ausmaß neue Anwendungsfelder. Der vorliegende Artikel soll einen kurzen Überblick über Trends in der Entwicklung dieser Systeme bieten. Abstract Significant progress in aerospace and computer sciences has enabled a rapid development of autonomous airborne systems. Light weight structures, efficient aerodynamics, new propulsion and energy storage systems as well as advanced aircraft systems are accelerating this trend. In combination with matured capabilities of autonomous situation assessment and flight guidance and control techniques new domains for applying unmanned aerial vehicles are being explored. This article provides a high level view on trends and technologies.

Mobile ad-hoc communication in machine swarms for relative positioning based on GNSS-raw data exchange

The increasing automation of mobile working machines and the progressive use of more than one machine up to machine swarms for cooperative tasks demands information about the relative position between the machines as well as between the machines and their attachments. This is especially necessary and important when carrying out tasks on distributed machines in a formation. Examples for application are parallel harvesting process in agricultural business or the cooperative search for survivors after a snow slide or e.g. an earthquake in urban scenarios. Moreover, it is very important to ensure relative position information in case of partial failure or a poor reception of the GNSS receiver, for example to avoid the collision between the machines. Options to handle this problem are the coupling of Global Navigation Satellite System (GNSS) measurements with measurements of an Inertial Measurement Unit (IMU). A further improvement or stabilization can be done by vision based systems, like 2D- or 3D-camera system using methods of optical flow for motion estimation. Another possibility for improvement for determining the swarm geometry, which will be described in this paper, is the so called swarm positioning method. This method is based on the exchange of the measured GNSS raw data, i.e. range measurements, between each participant in the swarm using a mobile ad-hoc network. Additionally, GNSS raw measurements and inertial measurements are coupled using multiple filters in order to detect degraded GNSS measurements and exclude these from further data processing. The challenge of the mobile ad-hoc network is the time variant network structure and the small available transmission rate in combination with a high demand for quick data exchange. The requirement to respond very flexibly to changes in topology and to compensate the loss of individual network participants as well as to spontaneously integrate further participants forbids the use of a fixed coordinator. Therefore different routing algorithms have to be combined and developed to ensure an information exchange in various scenarios.