Rath, Hans J.

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Rath, Hans J.

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Rath, Hans J.

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Rendezvous with a Non-Cooperating Target
(2011-09-30)
Arantes, Gilberto Junior
;
Milagre da Fonseca, Ijar
;
Rath, Hans J.
;
Rath, Hans J.
Space robotics has a substantial interest in achieving on-orbit service (OOS) operations autonomously, i.e rendezvous and docking/berthing (RVDB) with failed, stranded or malfunction satellites. Visual navigation system has a wide area of applications. In the context of this thesis we investigate a visual navigation system for on-orbit service (OOS). The space servicing area has a very important appeal in space flight dynamics mainly in these days when the scientific community is deeply concerned with space debris and the risk those objects impose on other space missions and even on the ecosystem not to say risk on human life on ground. Moreover current database indicates regular opportunities for satellite servicing including on-orbit upgrades, repair and rescue of stranded satellites. Those satellites are classified as non-cooperative targets when under the goal of space cleaning or space maintenance by space tugs. A chaser spacecraft would have to have the capability to rendezvous and grasp a dead satellite or other space debris, taking it out of its orbit for the sake of fixing problems, refueling, or just for cleaning purposes, without any cooperation from the target vehicle. In this sense failed or dead satellites become non-cooperative targets that are not able to provide any information on their position and attitude and eventually are not capable of maneuvering to cooperate with the docking operation. Position and attitude here shall be understood as relative orbital position and relative attitude between the chaser and target space vehicles or chaser vehicles and other space objects. This thesis presents an algorithm developed for estimating the pose (position and attitude) and the motion (velocities) of a generic target satellite based on visual navigation. The algorithm gathers the strength of classical attitude estimation methods to obtain real-time applicability conditions when adopting a Kalman filter for sequential state estimation. The visual system is monocular and satellite model-based. Therefore, it does not rely on any marker attached to the target satellite. The navigation solution can be used for a vast category of applications such as space debris removal, servicing for stranded satellites, and interception of hostile objects. The approach is first tested with synthetic image data from a spacecraft object generated in virtual reality. A test-bed is used to simulate the on-orbit optical environment. A scaled satellite model and a CCD camera is employed in the test bed in order to evaluate the algorithm for real-time application. A combination of three dimensional (3D) model-based attitude estimation and filtering time series of images produce similar real time solution for the estimation problem and increases the reliability of the relative attitude and position results.
Dissertation
368 163
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High precision modelling of thermal perturbations with application to Pioneer 10 and Rosetta
(2012-01-13)
Rievers, Benny
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Dittus, Hansjörg
;
Rath, Hans J.
;
Rath, Hans J.
This thesis deals with the exact numerical determination of thermal recoil pressure (TRP) and solar radiation pressure (SRP) for complex satellite geometries. The basic equations for both perturbations are introduced and expanded into a generic numerical approach based on finite element modeling and ray-tracing. The method is applied to the missions Pioneer 10 and Rosetta. For Pioneer 10, it is found that the so-called Pioneer anomaly can fully be explained by the recoil resulting from anisotropic heat radiation. In case of Rosetta, observed discrepancies of ESAs SRP models are resolved as unmodeled TRP. Furthermore both SRP and TRP are analysed for the first Earth fly-by. Here both effects can be excluded as causes of the observed fly-by anomaly.
Dissertation
336 206
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Characterization of the Autoignition of Single Droplets of Fischer-Tropsch Fuels and Development of Surrogates
(2012-03-09)
Reimert, Manfredo
;
Thöming, Jorg
;
Dinkelacker, Friedrich
;
Rath, Hans J.
The autoignition behavior of single droplets of synthetic fuels produced by the Fischer-Tropsch process, such as GTL-Diesel and GTL-Kerosene, is the main focus of this study. For this, experiments are carried out under microgravity and normal gravity conditions with single droplets with an initial diameter of 0,7 mm in a high-temperature high-pressure chamber. Ignition delay times are determined for ambient pressures between 0,1 MPa < p < 1 MPa and ambient temperatures between 550 K < T < 950 K with the aid of a Michelson interferometer setup. The experimental data is fitted with two-term Arrhenius-type functions that represent the two main reaction mechanisms, the cool and hot flame. Furthermore the development of suitable surrogate fuels for these fuels is performed and the selection and formulation procedure for the components is shown. Surrogate fuels enable numerical calculations with detailed chemical reaction kinetics. The obtained data on the characterization of the aforementioned fuels is compared with data of related fuels, such as their mineral variants and other surrogates.
Dissertation
238 168
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Theoretische und experimentelle Untersuchungen zur Zündung einzelner Kohlepartikel
(2004-07-14)
Wendt, Christian
;
Triebel, Wolfgang
;
Rath, Hans J.
;
Rath, Hans J.
In theoretischen und experimentellen Grundlagenuntersuchungen an einzelnen Partikeln aus Kohle und ähnlichen Brennstoffen wird schwerpunktmäßig der prinzipielle Effekt der Partikelgröße und Form auf den Zündprozess studiert. Das mathematische Modell dieser Arbeit zur Partikelzündung basiert auf dem von Du und Annamalai veröffentlichten, eindimensionalen Modell und erweitert dieses vor allem um den intrapartikulären Wärme- und Stofftransport. Gute Übereinstimmung der durchgeführten Simulationen mit dem Modell von Du und Annamalai ist hinsichtlich der absoluten Zündverzugszeiten festzustellen. Im Rahmen dieser Arbeit wurde ein Experimentaufbau zur Laseraufheizung von Festbrennstoffpartikeln entwickelt, in welchem zur Bestimmung der ortsaufgelösten Oberflächentemperatur ein Thermographie-Verfahren auf Basis der Zwei-Wellenlängen Pyrometrie zum Einsatz kommt. Die hiermit durchgeführten Zündexperimente an Modellbrennstoffen für Kohle können mit der in dieser Arbeit entwickelten Theorie generell nachgebildet werden. Mikrogravitationsexperimente zur Zündung einzelner Braunkohlepartikel in einem erprobten Lampenofen zeigen eine Abhängigkeit des Zündprozesses von der Partikelform. Innerhalb der Messfehler stimmen die mit dem Modell dieser Arbeit berechneten, homogenen Zündverzugszeiten mit den gemessenen Zeiten überein. Das in den vorangegangenen Untersuchungen überprüfte Modell dieser Arbeit wird abschließend zur Vorhersage der Zündverzugszeiten von Zylindern gleicher spezifischer Oberfläche aber verschiedenen Länge/Durchmesser-Verhältnissen in einer heißen Umgebung genutzt. Im Gegensatz zu einem üblichen Ansatz, welcher die Partikelform durch einen Formfaktor basierend auf der spezifischen Oberfläche berücksichtigt und für die hier analysierten Zylinder gleiche Zündverzugszeiten vorhersagt, werden mit dem detaillierten Modell dieser Arbeit für technisch relevante Länge/Durchmesser-Verhältnisse deutlich verschiedene Zündverzugszeiten berechnet.
Dissertation
246 246

Rath, Hans J.

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