Flight Dynamics Operations of the TanDEM-X Formation

Since end of 2010 the German TerraSAR-X and TanDEM-X satellites are routinely operated as the first configurable single-pass Synthetic Aperture Radar interferometer in space. The two 1340 kg satellites fly in a 514 km sun-synchronous orbit. In order to collect sufficient measurements for the generation of a global digital elevation model and to demonstrate new interferometric SAR techniques and applications, more than three years of formation flying are foreseen with flexible baselines ranging from 150 m to few kilometers. As a prerequisite for the close formation flight an extensive flight dynamics system was established at DLR/GSOC, which comprises of GPS-based absolute and relative navigation and impulsive orbit and formation control. Daily formation maintenance maneuvers are performed by TanDEM-X to counterbalance natural and artificial disturbances. The paper elaborates on the routine flight dynamics operations and its interactions with mission planning and ground-station network. The navigation and formation control concepts and the achieved control accuracy are briefly outlined. Furthermore, the paper addresses non-routine operations experienced during formation acquisition, frequent formation reconfiguration, formation maintenance problems and space debris collision avoidance, which is even more challenging than for single-satellite operations. In particular two close approaches of debris are presented, which were experienced in March 2011 and April 2012. Finally, a formation break-up procedure is discussed which could be executed in case of severe onboard failures

The technique and imagery of Yuan san-ch'u.

In the following analysis of forty-six songs I have attempted to describe the genre of san-ch'u as it was practised by writers of the Yuan Dynasty. To accomplish this I felt the most significant points were technique of composition and the manner in which it produced effective imagery. Although critical appraisal is an inevitable part of any analysis, here it is used as often to shed light on the appreciation of a song within the original circum-stances of its composition and performance as it is to make general comparisons with other poetry. I felt it legitimate to praise songs that are interesting as poems but have usually qualified any criticism of those that are not good by modern critical standards because it is often our lack of essential information, specifically the music to which it was written, that makes some san-ch'u appear mediocre to us now. To have judged the songs solely as poetry would have given a distorted view of the genre as it existed in the Yuan Dynasty. In every way as essential as the description of san-ch'u is the need to outline certain aspects of poetic composition that are characteristic of san-ch'u and Chinese poetry in general, aspects that a Chinese reader is able to take for granted but without an understanding of which a foreign student of Chinese poetry can hardly progress beyond the meanings of words alone. Although a great share of the work has taken the form of studies in technique, i.e. metre, rhyme, colour, repetition patterning and figuration, I have aimed at seeking out and remarking on the poetic effects and imagery that the various techniques are able to produce

Eine qualitative Studie: der individuelle Umgang mit Problemen in den Lebenswelten von Schülern und Schülerinnen mit Lernbehinderungen

Bei Beobachtungen in der beruflichen Praxis wurde deutlich, dass Schüler (und Schülerin-nen) und Lehrer (und Lehrerinnen) oftmals im Unterricht gegenseitig ihre Handlungen in Frage stellen. Diese Infragestellungen werden unter Anderem als 'Unterrichtsstörungen' beschrieben. Auf dem Hintergrund des leitenden Menschenbildes des Radikalen Konstruk-tivismus (von Glasersfeld), des Sozialen Konstruktionismus (Gergen) und der These, dass ein adäquater Einbezug der Schülerpersönlichkeiten in das Unterrichtsgeschehen Unter-richtsstörungen und kommunikative Missverständnisse verringern können und der indivi-duelle Lernerfolg ansteigen kann, wurde die Frage gestellt, wie ein Einbezug von Schülern und Schülerinnen mit Lernbehinderungen in die Themen- und Zielvorstellungen von Un-terricht aussehen könnte.Ausgehend von einem konstruktivistisch-systemischen Verständnis über 'Lernbehinderun-gen' (Werning und Schmetz) sowie basierend auf der Prämisse, dass über die Teilhabe an Alltagserfahrungen in den individuellen Lebenswelten der Schüler und Schülerinnen Rück-schlüsse über die Bedürfnisse, und auch über die vorhandenen Kompetenzen zur Nutzung bei der Planung und Durchführung von Unterricht möglich sind, wurde im Rahmen der Modernitätstheoretischen Kinderforschung unter Hinzuziehung von Elementen der Bio-graphieforschung und den Ausführungen über sozialrandständige, armutsgefährdete Kinder als methodischer Weg die (erweiterte) Einzelfallstudie unter Verwendung des Narrativen Interviews und der Teilnehmenden Beobachtung gewählt, um wissenschaftliche Erkennt-nisse zu erlangen.Über die verschiedenen Analyseschritte der Auswertungsmethode des Zirkulären De-konstruierens von Jaeggi u.a. (1998) kristallisierte sich 'die individuelle Problembewälti-gung in den Bereichen der verbalen Kommunikation und der Nutzung von Problemlöse-strategien als allen Jugendlichen gemeinsame Herausforderung ihres alltäglichen Lebens' (Schlepp-Pellny 2003, 15) heraus.Die Analyse des individuellen Umgangs mit Problemen von drei Jugendlichen 'mit Lern-behinderungen' zeigte auf, welche Inhalte, Begegnungen, Gespräche usw. den Jugendlichen subjektiv bedeutsam waren, welche Kompetenzen sie im Umgang mit individuellen Prob-lemen aufweisen konnten und in welchen Bereichen (u.a. insbesondere im Bereich der problemorientierten verbalen Argumentation und der Empathiefähigkeit) Förderbedarf bestand.Aus den ermittelten Informationen wurde, ausgehend von der Vorstellung, dass Lehrper-sonen eine besondere Verantwortung für das Gelingen von unterrichtlichen Vorstellungen und Zielen sowie für die den Unterricht begleitenden und begründenden sozialen Bedürf-nisse haben, ein Anforderungsprofil für den Unterricht in der Schule für Lernbehinderte erstellt. Darüber hinaus wurde auf der Basis des Unterrichtsprinzips zum vollständigen Lernen nach Peterßen (1999) das Modell des Kompetenzgeleiteten Unterrichts (KGU) ent-wickelt. Als Beleg zur Umsetzbarkeit des KGU schließt die Arbeit mit exemplarischen Unterrichtsbausteinen, welche den Einbezug der Schülerkompetenzen einerseits und die Förderbedürfnisse andererseits gewährleisten und demonstrieren. Bei der Beschreibung der angestrebten Förderziele wurden im zweiten Teil der vorliegenden Dissertation wesentli-che Prinzipien der sonderpädagogischen Theorie und Praxis (u.a.: Auswahl von lebensbe-deutsamen Themen und Zielen, didaktische Reduktion, Differenzierung) begründet und berücksichtigt. Alle Analyseschritte, die zur Entstehung der Dissertation und ihrer Ergebnisse beigetragen haben und nicht im Hauptteil der Dissertation abgedruckt sind, sind im dritten Teil der Studie (Anhang) aufgeführt

Flight Dynamics Experience on Target Orbit Acquisition and Maintenance Operations for Germany's Hyperspectral Satellite Mission EnMAP

The Environmental Mapping and Analysis Program (EnMAP) is a German hyperspectral satellite mission that aims at monitoring and characterizing Earth's environment on a global scale. The satellite was successfully launched with SpaceX's Falcon 9 Transporter-4 mission on April 1st, 2022. This paper elaborates on the in-flight results obtained during the EnMAP Launch and Early-Operations Phase (LEOP) and the first months of the commissioning phase. Besides the flight dynamics operations, this paper addresses the repeat ground-track orbit control concept and discusses novel flight dynamics functionalities implemented to optimize the scientific return of the EnMAP mission, such as microservices for fast data exchange between the flight dynamics and mission planning systems

ATTITUDE CONTROL on GRACE FOLLOW-ON Experiences from the first years in orbit

The two satellites for the GRACE* Follow-on mission were successfully launched in May 2018 on a polar orbit at an altitude of 491 km. The mission continues the measurements of the gravity field of the Earth (with emphasis on the time variability) and also delivers radio occultation measurements. The twin satellites are kept at a relative distance of 170 to 270 km and act as probes in the gravity field of the Earth. The inter-satellite distance is measured by a microwave tracking system to an accuracy of 1 μm. A laser ranging interferometer is added as a technology demonstration. Stable and accurate relative pointing, as well as the minimization of disturbance torques, is required in order to optimize scientific results. This poses stringent demands upon attitude control. The performance of the GRACE Follow-on attitude control system will be presented, as well as the special actions and changes that became necessary as the mission evolved. A short description of the sensors and actuators used for attitude control is given and improvements with respect to GRACE are discussed in some more detail. The operational modes are described with a focus on the so-called nominal fine-pointing mode, in which the front-ends point towards each other in order to enable microwaveand laser-ranging. The third Section opens with a description of special tasks, such as the fine-tuning of the control and monitoring parameters and the complex determination of the satellite’s center of gravity. A comparison is made with a tracking model based upon the fuel expenditure from the two tanks that can be determined independently. Several series of involved tests with manual thruster firings were performed in order to characterize the response of the accelerometers to thruster actuations. A description of the design of the tests, their execution and results is presented. A switch to the redundant instrument was made five months after launch on one of the satellites. The consequences for attitude control are discussed in Section 4. A method that was developed to cope with a situation where also the redundant GPS receiver would become unavailable is discussed in detail. Conclusions and an outlook for the upcoming years of operations are presented in the last Section

Initial Results from the TechnoSat in-Orbit Demonstration Mission

Until now, Technische Universität Berlin successfully developed, built and operated sixteen satellites ranging from several single unit CubeSats to a 56 kg Earth observation mission. The recently launched TechnoSat mission has the primary objective to demonstrate and test novel small satellite technologies and components in Low Earth Orbit. To this end, the 20 kg spacecraft carries seven payloads. One payload, for example, is the fluid-dynamic actuator developed by Technische Universität Berlin. This novel attitude actuator is based on momentum storage via a liquid metal that is accelerated using an electromagnetic pump. The secondary mission objective of TechnoSat is the in-orbit verification of the newly developed satellite platform TUBiX20 of Technische Universität Berlin. This platform bases on a modular systems design and provides scalability regarding selected performance parameters, which allows for tailoring of the platform towards individual mission requirements. TechnoSat was launched into a 600 km Sun-synchronous orbit on the 14th of July 2017. Since then, experiments are successfully conducted regularly with all payloads and the analysis of the collected data is in progress. This paper presents first orbit results of the TechnoSat mission focusing on selected technology demonstration payload

Five Years of SMARTnet: Data, Processing, and Improvements

SMARTnet, operated by the Astronomical Institute of the University of Bern (AIUB) and the German Aerospace Center (DLR), went online and open to the public in 2017 with two telescope stations located in Zimmerwald, Switzerland, and Sutherland, South Africa. Over its five-year operational timespan, new partners have joined while one partner left, leaving telescope stations distributed today in Australia, South Africa, and Europe. All stations combined, 9 telescopes are actively providing data to the network. New contributors are currently in the applicant phase and will, together with further stations planned by DLR, enhance the network’s capabilities. The retrieved data is used for research, collision warnings, catalogue maintenance or for deriving data products, which can be sold to third parties. For the aforementioned points, the Backbone Catalogue of Relational Debris Information (BACARDI) was developed at DLR. BACARDI processes input data received from SMARTnet to data products such as ephemerides and orbit information for telescope observation planning, and attempts to detect new objects where an association of observations to already known objects is unsuccessful. To better operate the telescope stations, a dedicated software, called SMARTies, is under development in a joint project by AIUB and DLR. With this software, the telescope stations operations can be optimized to increase the daily data acquisition. It is planned to release SMARTies as Open Source software. To avoid deteriorating accuracy of the orbital information, ephemerides forecasted by BACARDI are combined with the planning tool “Optimal Catalog Maintenance and Survey Tasking” (OMST), which will help keeping all resident space objects in the data base. Furthermore, OMST will allow to search for new objects in the vicinity of the telescopes’ field of view in so-called “dead-times”. A short introduction to SMARTnet and its requirements is given, followed by some products retrieved from SMARTnet data. Also, the complete end-to-end chain from observations to processing, forecast, and its feed-back loop to observations is presented. Lastly, selected campaigns of some of the telescopes are presented. As part of non-regular observations, supporting observations can be acquired in case of special events (e.g. DART)

TerraSAR-X/TanDEM-X Formation Control - First Results from Commissioning and Routine Operations

This paper describes the TerraSAR-X / TanDEM-X formation control concept, which bases on the relative eccentricity / inclination vector separation method, implemented within GSOC’s flight dynamics system. The paper specifically elaborates on the results obtained during the first six month of the formation flying mission showing the safe and precise automated ground-control of the space-borne radar interferometer