Algorithms for spacecraft formation flying navigation based on wireless positioning system measurements

Spacecraft formation flying navigation continues to receive a great deal of interest. The research presented in this dissertation focuses on developing methods for estimating spacecraft absolute and relative positions, assuming measurements of only relative positions using wireless sensors. The implementation of the extended Kalman filter to the spacecraft formation navigation problem results in high estimation errors and instabilities in state estimation at times. This is due tp the high nonlinearities in the system dynamic model. Several approaches are attempted in this dissertation aiming at increasing the estimation stability and improving the estimation accuracy. A differential geometric filter is implemented for spacecraft positions estimation. The differential geometric filter avoids the linearization step (which is always carried out in the extended Kalman filter) through a mathematical transformation that converts the nonlinear system into a linear system. A linear estimator is designed in the linear domain, and then transformed back to the physical domain. This approach demonstrated better estimation stability for spacecraft formation positions estimation, as detailed in this dissertation. The constrained Kalman filter is also implemented for spacecraft formation flying absolute positions estimation. The orbital motion of a spacecraft is characterized by two range extrema (perigee and apogee). At the extremum, the rate of change of a spacecraft’s range vanishes. This motion constraint can be used to improve the position estimation accuracy. The application of the constrained Kalman filter at only two points in the orbit causes filter instability. Two variables are introduced into the constrained Kalman filter to maintain the stability and improve the estimation accuracy. An extended Kalman filter is implemented as a benchmark for comparison with the constrained Kalman filter. Simulation results show that the constrained Kalman filter provides better estimation accuracy as compared with the extended Kalman filter. A Weighted Measurement Fusion Kalman Filter (WMFKF) is proposed in this dissertation. In wireless localizing sensors, a measurement error is proportional to the distance of the signal travels and sensor noise. In this proposed Weighted Measurement Fusion Kalman Filter, the signal traveling time delay is not modeled; however, each measurement is weighted based on the measured signal travel distance. The obtained estimation performance is compared to the standard Kalman filter in two scenarios. The first scenario assumes using a wireless local positioning system in a GPS denied environment. The second scenario assumes the availability of both the wireless local positioning system and GPS measurements. The simulation results show that the WMFKF has similar accuracy performance as the standard Kalman Filter (KF) in the GPS denied environment. However, the WMFKF maintains the position estimation error within its expected error boundary when the WLPS detection range limit is above 30km. In addition, the WMFKF has a better accuracy and stability performance when GPS is available. Also, the computational cost analysis shows that the WMFKF has less computational cost than the standard KF, and the WMFKF has higher ellipsoid error probable percentage than the standard Measurement Fusion method. A method to determine the relative attitudes between three spacecraft is developed. The method requires four direction measurements between the three spacecraft. The simulation results and covariance analysis show that the method’s error falls within a three sigma boundary without exhibiting any singularity issues. A study of the accuracy of the proposed method with respect to the shape of the spacecraft formation is also presented.

[Navigation and robotics of the lateral skull base]

Computer-aided microscopic surgery of the lateral skull base is a rare intervention in daily practice. It is often a delicate and difficult minimally invasive intervention, since orientation between the petrous bone and the petrous bone apex is often challenging. In the case of aural atresia or tumors the normal anatomical landmarks are often absent, making orientation more difficult. Navigation support, together with imaging techniques such as CT, MR and angiography, enable the surgeon in such cases to perform the operation more accurately and, in some cases, also in a shorter time. However, there are no internationally standardised indications for navigated surgery on the lateral skull base. Miniaturised robotic systems are still in the initial validation phase.

Exploiting Runtime Information in the IDE

Developers rely on the mechanisms provided by their IDE to browse and navigate a large software system. These mechanisms are usually based purely on a system's static source code. The static perspective, however, is not enough to understand an object-oriented program's behavior, in particular if implemented in a dynamic language. We propose to enhance IDEs with a program's runtime information (eg. message sends and type information) to support program comprehension through precise navigation and informative browsing. To precisely specify the type and amount of runtime data to gather about a system under development, dynamically and on demand, we adopt a technique known as partial behavioral reflection. We implemented navigation and browsing enhancements to an IDE that exploit this runtime information in a prototype called Hermion. We present preliminary validation of our experimental enhanced IDE by asking developers to assess its usefulness to understand an unfamiliar software system.

Augmenting Static Source Views in IDEs with Dynamic Metrics

Mainstream IDEs such as Eclipse support developers in managing software projects mainly by offering static views of the source code. Such a static perspective neglects any information about runtime behavior. However, object-oriented programs heavily rely on polymorphism and late-binding, which makes them difficult to understand just based on their static structure. Developers thus resort to debuggers or profilers to study the system's dynamics. However, the information provided by these tools is volatile and hence cannot be exploited to ease the navigation of the source space. In this paper we present an approach to augment the static source perspective with dynamic metrics such as precise runtime type information, or memory and object allocation statistics. Dynamic metrics can leverage the understanding for the behavior and structure of a system. We rely on dynamic data gathering based on aspects to analyze running Java systems. By solving concrete use cases we illustrate how dynamic metrics directly available in the IDE are useful. We also comprehensively report on the efficiency of our approach to gather dynamic metrics.

Tackling Software Navigation Issues of the Smalltalk IDE

The IDE used in most Smalltalk dialects such as Pharo, Squeak or Cincom Smalltalk did not evolve significantly over the last years, if not to say decades. For other languages, for instance Java, the available IDEs made tremendous progress as Eclipse or NetBeans illustrate. While the Smalltalk IDE served as an exemplar for many years, other IDEs caught up or even overtook the erstwhile leader in terms of feature-richness, usability, or code navigation facilities. In this paper we first analyze the difficulty of software navigation in the Smalltalk IDE and second illustrate with concrete examples the features we added to the Smalltalk IDE to fill the gap to modern IDEs and to provide novel, improved means to navigate source space. We show that thanks to the agility and dynamics of Smalltalk, we are able to extend and enhance with reasonable effort the Smalltalk IDE to better support software navigation, program comprehension, and software maintenance in general. One such support is the integration of dynamic information into the static source views we are familiar with. Other means include easing the access to static information (for instance by better arranging important packages) or helping developers re-locating artifacts of interest (for example with a categorization system such as smart groups).

Autumn Leaves: Curing the Window Plague in IDEs

Navigating large software systems is difficult as the various artifacts are distributed in a huge space, while the relationships between different artifacts often remain hidden and obscure. As a consequence, developers using a modern interactive development environment (IDE) are forced to open views on numerous source artifacts to reveal these hidden relationships, leading to a crowded workspace with many opened windows or tabs. Developers often lose the overview in such a cluttered workspace as IDEs provide little support to get rid of unused windows. AutumnLeaves automatically selects windows unlikely for future use to be closed or grayed out while important ones are displayed more prominently. This reduces the number of windows opened at a time and adds structure to the developer's workspace. We validate AutumnLeaves with a benchmark evaluation using recorded navigation data of various developers to determine the prediction quality of the employed algorithms.

Entwicklung eines Dispositionsleitstandes zur Bestimmung optimaler Torbelegungen in Stückgutspeditionsanlagen

Im operativen Betrieb einer Stückgutspeditionsanlage entscheidet der Betriebslenker bzw. der Disponent in einem ersten Schritt darüber, an welche Tore die Fahrzeuge zur Be- und Entladung andocken sollen. Darüber hinaus muss er für jede Tour ein Zeitfenster ausweisen innerhalb dessen sie das jeweilige Tor belegt. Durch die örtliche und zeitliche Fahrzeug-Tor-Zuordnung wird der für den innerbetrieblichen Umschlagprozess erforderliche Ressourcenaufwand in Form von zu fahrenden Wegstrecken oder aber Gabelstaplerstunden bestimmt. Ein Ziel der Planungsaufgabe ist somit, die Zuordnung der Fahrzeuge an die Tore so vorzunehmen, dass dabei minimale innerbetriebliche Wegstrecken entstehen. Dies führt zu einer minimalen Anzahl an benötigten Umschlagmittelressourcen. Darüber hinaus kann es aber auch zweckmäßig sein, die Fahrzeuge möglichst früh an die Tore anzudocken. Jede Tour verfügt über einen individuellen Fahrplan, der Auskunft über den Ankunftszeitpunkt sowie den Abfahrtszeitpunkt der jeweiligen Tour von der Anlage gibt. Nur innerhalb dieses Zeitfensters darf der Disponent die Tour einem der Tore zuweisen. Geschieht die Zuweisung nicht sofort nach Ankunft in der Anlage, so muss das Fahrzeug auf einer Parkfläche warten. Eine Minimierung der Wartezeiten ist wünschenswert, damit das Gelände der Anlage möglichst nicht durch zuviele Fahrzeuge gleichzeitig belastet wird. Es kann vor allem aber auch im Hinblick auf das Reservieren der Tore für zeitkritische Touren sinnvoll sein, Fahrzeuge möglichst früh abzufertigen. Am Lehrstuhl Verkehrssysteme und -logistik (VSL) der Universität Dortmund wurde die Entscheidungssituation im Rahmen eines Forschungsprojekts bei der Stiftung Industrieforschung in Anlehnung an ein zeitdiskretes Mehrgüterflussproblem mit unsplittable flow Bedingungen modelliert. Die beiden Zielsetzungen wurden dabei in einer eindimensionalen Zielfunktion integriert. Das resultierende Mixed Integer Linear Programm (MILP) wurde programmiert und für mittlere Szenarien durch Eingabe in den Optimization Solver CPlex mit dem dort implementierten exakten Branch-and-Cut Verfahren gelöst. Parallel wurde im Rahmen einer Kooperation zwischen dem Lehrstuhl VSL und dem Unternehmen hafa Docking Systems, einem der weltweit führenden Tor und Rampenhersteller, für die gleiche Planungsaufgabe ein heuristisches Scheduling Verfahren sowie ein Dispositionsleitstand namens LoadDock Navigation entwickelt. Der Dispositionsleitstand dient der optimalen Steuerung der Torbelegungen in logistischen Anlagen. In dem Leitstand wird planerische Intelligenz in Form des heuristischen Schedulingverfahrens, technische Neuerungen in der Rampentechnik in Form von Sensoren und das Expertenwissen des Disponenten in einem Tool verbunden. Das mathematische Modell sowie der Prototyp mit der integrierten Heuristik werden im Rahmen dieses Artikels vorgestellt.

[Second victim : Critical incident stress management in clinical medicine]

BACKGROUND Critical incidents in clinical medicine can have far-reaching consequences on patient health. In cases of severe medical errors they can seriously harm the patient or even lead to death. The involvement in such an event can result in a stress reaction, a so-called acute posttraumatic stress disorder in the healthcare provider, the so-called second victim of an adverse event. Psychological distress may not only have a long lasting impact on quality of life of the physician or caregiver involved but it may also affect the ability to provide safe patient care in the aftermath of adverse events. METHODS A literature review was performed to obtain information on care giver responses to medical errors and to determine possible supportive strategies to mitigate negative consequences of an adverse event on the second victim. An internet search and a search in Medline/Pubmed for scientific studies were conducted using the key words "second victim, "medical error", "critical incident stress management" (CISM) and "critical incident stress reporting system" (CIRS). Sources from academic medical societies and public institutions which offer crisis management programs where analyzed. The data were sorted by main categories and relevance for hospitals. Analysis was carried out using descriptive measures. RESULTS In disaster medicine and aviation navigation services the implementation of a CISM program is an efficient intervention to help staff to recover after a traumatic event and to return to normal functioning and behavior. Several other concepts for a clinical crisis management plan were identified. CONCLUSIONS The integration of CISM and CISM-related programs in a clinical setting may provide efficient support in an acute crisis and may help the caregiver to deal effectively with future error events and employee safety.