Concept and Feasibility Evaluation of Distributed Sensor-Based Measurement Systems Using Formation Flying Multicopters

Unmanned aerial vehicles (UAVs) have been used for increasing research applications in atmospheric measurements. However, most current solutions for these applications are based on a single UAV with limited payload capacity. In order to address the limitations of the single UAV-based approach, this paper proposes a new concept of measurements using tandem flying multicopters as a distributed sensor platform. Key challenges of the proposed concept are identified including the relative position estimation and control in wind-perturbed outdoor environment and the precise alignment of payloads. In the proposed concept, sliding mode control is chosen as the relative position controller and a gimbal stabilization system is introduced to achieve fine payload alignment. The characterization of the position estimation sensors (including global navigation satellite system and real-time kinematics) and flight controller is carried out using different UAVs (a DJI Matrice M600 Pro Hexacopter and Tarot X4 frame based Quadcopter) under different wind levels. Based on the experimental data, the performance of the sliding mode controller and the performance of the gimbal stabilization system are evaluated in a hardware-in-the-loop simulation environment (called ELISSA). Preliminary achievable control accuracies of the relative position and attitude of subsystems in the proposed concept are estimated based on experimental result

Survey of the Current Activities in the Field of Modeling the Space Debris Environment at TU Braunschweig

The Institute of Space Systems at Technische Universität Braunschweig has long-term experience in the field of space debris modeling. This article reviews the current state of ongoing research in this area. Extensive activities are currently underway to update the European space debris model MASTER. In addition to updating the historical population, the future evolution of the space debris environment is also being investigated. The competencies developed within these activities are used to address current problems with regard to the possibility of an increasing number of catastrophic collisions. Related research areas include, for example, research in the field of orbit determination and the simulation of sensor systems for the acquisition and cataloging of orbital objects. In particular, the ability to provide simulated measurement data for object populations in almost all size ranges is an important prerequisite for these investigations. Some selected results on the distribution of space debris on Earth orbit are presented in terms of spatial density. Furthermore, specific fragmentation events will be discussed

Development of Dynamical Visual Environment for Maritime Helicopter Real-Time Flight Simulation

A visual environment for maritime helicopter real-time flight simulation is presented and evaluated. For offshore helicopter operations, simulators have to replicate the flight through obstacle scenery (e.g. radio masts, cranes, rotating wind turbine blades…), and landing on a helideck with limited visual cues due to the natural environment. Poor modeling of moving obstacles or helidecks further increases the problems the pilots are faced to, resulting in "false learning" close to moving obstacles and helidecks. The paper focuses on the development and implementation of an Offshore-Scenario, taking into account complexity, real-time ability, and realism. Based on a thorough investigation of maritime helicopter operations, an Offshore-Scenario which depicts the situation off German coast, was defined. It includes several dynamical components such as rotating wind turbine blades, wind generated waves, and moving ships and is therefore suitable for simulating common offshore helicopter operations. The decks and visual sea models within simulators are usually not realistic, with the helideck having a sinusoidal motion and the visual wave model moving independently. Contrary to the common practice, in this work, the deck motion is modeled as a response to the wave excitation

HOST Versionsvergleich

Die Abteilung Hubschrauber des Institutes für Flugsystemtechnik verwendet das Hubschraubersimulationsprogramm HOST (Helicopter Overall Simulation Tool). Es werden damit Trimrechnungen, Zeitbereichssimulationen und Linearisierungen für vielfältige Hubschrauberkonfigurationen durchgeführt. Die Aufgabe dieser Arbeit ist es, ein Matlab Tool zu erstellen, mit dem HOST Versionen untereinander verglichen werden können. Da HOST in regelmäßigen Abständen durch eine neue Version ersetzt wird, muss es möglich sein, die Ergebnisse verschiedener Rechenfälle untereinander vergleichen zu können. Der Vergleich soll dabei über den Plot bestimmter Parameter innerhalb von einem Diagramm erfolgen. Durch die Auswertung repräsentativer Größen wie den Steuern, den Lagewinkeln, den Bewegungen und den Beschleunigungen des Hubschraubers kann so sehr schnell ermittelt werden, ob unterschiedliche HOST Versionen identische Ergebnisse liefern. Weiterhin kann der Versionsvergleich auch als reines Plottool verwendet werden

Modification of Space Debris Trajectories through Lasers: Dependence of Thermal and Impulse Coupling on Material and Surface Properties

Environmental pollution exists not only within our atmosphere but also in space. Space debris is a critical problem of modern and future space infrastructure. Congested orbits raise the question of spacecraft disposal. Therefore, state-of-the-art satellites come with a deorbit system in cases of low Earth orbit (LEO) and with thrusters for transferring into the graveyard orbit for geostationary and geosynchronous orbits. No practical solution is available for debris objects that stem from fragmentation events. The present study focuses on objects in LEO orbits with dimensions in the dangerous class of 1 to 10 cm. Our assumed method for the change of trajectories of space debris is laser ablation for collision avoidance or complete removal by ground-based laser systems. Thus, we executed an experimental feasibility study with focus on thermal and impulse coupling between laser and sample. Free-fall experiments with a 10 ns laser pulse at nominally 60 J and 1064 nm were conducted with GSI Darmstadt’s nhelix laser on various sample materials with different surfaces. Ablated mass, heating, and trajectory were recorded. Furthermore, we investigated the influence of the sample surface roughness on the laser-object interaction. We measured impulse coupling coefficients between 7 and 40 µNs/J and thermal coupling coefficients between 2% and 12.5% both depending on target fluence, surface roughness, and material. Ablated mass and changes in surface roughness were considered via simulation to discriminate their relevance for a multiple shot concept

Pancreatic surgery outcomes: multicentre prospective snapshot study in 67 countries

Background: Pancreatic surgery remains associated with high morbidity rates. Although postoperative mortality appears to have improved with specialization, the outcomes reported in the literature reflect the activity of highly specialized centres. The aim of this study was to evaluate the outcomes following pancreatic surgery worldwide.Methods: This was an international, prospective, multicentre, cross-sectional snapshot study of consecutive patients undergoing pancreatic operations worldwide in a 3-month interval in 2021. The primary outcome was postoperative mortality within 90 days of surgery. Multivariable logistic regression was used to explore relationships with Human Development Index (HDI) and other parameters.Results: A total of 4223 patients from 67 countries were analysed. A complication of any severity was detected in 68.7 percent of patients (2901 of 4223). Major complication rates (Clavien-Dindo grade at least IIIa) were 24, 18, and 27 percent, and mortality rates were 10, 5, and 5 per cent in low-to-middle-, high-, and very high-HDI countries respectively. The 90-day postoperative mortality rate was 5.4 per cent (229 of 4223) overall, but was significantly higher in the low-to-middle-HDI group (adjusted OR 2.88, 95 per cent c.i. 1.80 to 4.48). The overall failure-to-rescue rate was 21 percent; however, it was 41 per cent in low-to-middle-compared with 19 per cent in very high-HDI countries.Conclusion: Excess mortality in low-to-middle-HDI countries could be attributable to failure to rescue of patients from severe complications. The authors call for a collaborative response from international and regional associations of pancreatic surgeons to address management related to death from postoperative complications to tackle the global disparities in the outcomes of pancreatic surgery (NCT04652271; ISRCTN95140761)