Heinzel, Gerhard
Lade...
4 Ergebnisse
Gerade angezeigt 1 - 4 von 4
- Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Optical Metrology Terminal for Satellite-to-Satellite Laser Ranging(2022-01-24); ; ; Interferometric laser ranging is a powerful enabling technology for high-precision satellite-to-satellite tracking within the context of Earth observation, gravitational wave detection, and formation flying. Since the launch of the gravity field mission GRACE Follow-On in 2018, the onboard Laser Ranging Interferometer has successfully been operating as a technology demonstrator in a low-Earth orbit and has significantly enhanced the measurement accuracy compared to the former microwave instrument. Within the framework of this work, a new design concept for an optical instrument of this type is derived, allowing the location of the reference point and the external beam offset to be tuned independently of the integrated retroreflector. On this basis, optical design and construction of the "Optical Metrology Terminal" are carried out, resulting in a basically flight-representative instrument as it could be used in future gravity field missions. Experimental evaluation on elegant breadboard level demonstrated excellent tolerance against variations of the angle of incidence.Dissertation354 650 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Gravity Field Recovery from GRACE Satellite Data and Investigation of Sensor, Environment and Processing-Option Influences by Closed Loop Mission Simulation(2021-10-04); ; ; Die globale Vermessung des Gravitationsfeldes der Erde und dessen zeitliche Veränderung liefert eine einzigartige Messgröße der Erdbeobachtung: Gravitation, und davon abgeleitet Masseverteilung und Massetransport in der oberflächennahen Schicht der Erdkruste. Die Zeitliche Änderung des Gravitationsfeldes liefert Daten, die mittlerweile eine Grundlage für viele Geowissenschagften bilden und eien erheblichen Beitrag zum Verständnis des dynamischen Erdsystems, dessen Wasserkreislauf und des Klimawandels leisten. Die Messung der Gravitation und des Schwerefeldes wird allgemein als Gravimetrie bezeichnet. Sie ermöglicht die quantitative Messung von Masseänderungen, ob sichtbare oder unsichtbar, was durch keine andere Technik möglich ist. Insbesondere die GRACE (Gravity Recovery And Climate Experiment) Satellitenmission hat seit 2002 zu den großen Erfolgen der Satelliten-Gravimetrie beigetragen. Obwohl der Start der GRACE Satelliten nun schon fast 19 Jahre her ist, und mittlerweile die Nachfolgemission GRACE-FO mit dem selben Messprinzip die Vermessungszeitreihe fortführt, wird die Datenauswertung immer noch kontinuierlich verbessert. Im Rahmen dieser Arbeit wurde eine Software zur präzisen Orbit und Gravitationsfeld Bestimmung entwickelt. Dabei wird aus den beobachteten Messdaten entlang der Satellitenbahn ein globales Modell des Erd-Gravitationsfeldes in Form von sphärisch-Harmonischen abgeleitet. Dazu wurde in dieser Arbeit der klassische Ansatz der "Variational Equations" implementiert, welcher inzwischen als das Verfahren mit den genausten Ergebnissen betrachtet wird. Die Arbeit verfolgt zwei Hauptziele. Zuerst wird die GRACE Datenauswertung, also die Bestimmung monatlicher Gravitationsfelder mittels des implementierten Verfahrens untersucht. Ein Hauptaugenmerk ist dabei die Charakterisierung der Auswirkungen verschiedener Parameter und Varianten des Verfahrens auf die Ergebnisse. Des weiteren wird der Einfluss der verschiedenen Sensordaten und dessen Kalibrierung während des Verfahrens analysiert. Vor allem die Akzelerometerdaten, welche nicht-gravitative Beschleunigungen auf die Satelliten messen, werden detailliert studiert. Die größten Einflüsse auf die Ergebnisse haben die Gewichtung der verschiedenen Messdaten, sowie die neben dem Gravitationsfeld bestimmten Parameter. Diese sind hauptsächlich durch die Kalibrierung der Akzelerometer und die Unterteilung der monatlichen Datensätze definiert. Das zweite Ziel der Arbeit ist die komplette Simulation einer GRACE ähnlichen Satellitenmission samt Datenauswertung. Dazu wurden die beiden Satelliten samt aller relevanten Sensordaten und unter Berücksichtigung von Umwelt- und Sensormodellen simuliert. Mit der Simulation werden Effekte und Einflüsse jedes einzelnen Sensors und dessen Charakteristik, sowie verschiedener Observationsdaten und verschiedener Umwelteinflüsse auf die Ergebnisse untersucht. In der Simulation sind zu jeder Zeit das wahre Gravitationsfeld und die theoretisch perfekten Sensordaten als Referenz bekannt. Zudem bietet die Simulation den großen Vorteil jedes Sensor- und Umweltmodell einzeln ein- und auszuschalten. Mit dem Vergleich der realen GRACE Datenauswertung und den Ergebnissen der Simulation, werden Rückschlüsse auf die GRACE Daten und die Gravitationsfeldbestimmung gezogen aber andersherum auch die Modellierung validiert.Dissertation453 566 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Towards an Advanced LISA Payload Architecture Featuring In-Field Pointing and Spherical Proof Masses(2018-09-04); ; ; The prediction of gravitational waves in the early 20th century promised new means for observational astronomy, since they were expected to allow deeper insight into our universe. Recently, the first direct detection of gravitational waves by the earth based LIGO detectors - a major achievement along gravitational wave observation - confirmed the original prediction. This milestone elevated the interest in the development of enhanced as well as new detectors, which hopefully enable the discovery of new aspects of our universe. One of these new detectors is the planned Laser Interferometer Space Antenna (LISA) space mission, which will represent a giant interferometer for the observation of gravitational waves in space. LISA consists of three satellites, which are arranged in a triangular formation and form three interferometer arms. The detection will be performed via interferometric, inter-satellite laser distance metrology between free-flying proof masses, which act as the end points of the interferometer arms and will change their relative distances with respect to each other when a gravitational wave is passing. However, the strain amplitudes of gravitational waves are small and so will be the distance changes between the proof masses (in the order of a few tens of a picometer), which makes their detection very challenging. LISA will expand the currently available measurement bandwidth covered by the earth based detectors to lower frequencies, hence enabling the detection of new gravitational wave sources. In the baseline LISA payload architecture, changes in the angles of the triangular spacecraft formation, caused by the individual orbital mechanics of the spacecraft, are compensated by pointing of the whole telescope assemblies. This concept is called telescope pointing. During the LISA mission formulation study a new, alternative LISA payload architecture was developed and theoretically investigated. This concept features in-field pointing in order to compensate for these changes in spacecraft formation. The in-field pointing architecture offers potential savings in mass, volume and power consumption as well as potential improvements in measurement performance of the metrology instrument, compared to telescope pointing. Nonetheless, the technical realisation of the IFP concept in compliance with the requirements is highly demanding. This thesis covers two different and potentially limiting aspects concerning the realisation of an advanced LISA payload architecture including in-field pointing. The first one is part of the detailed investigations of the required wide-field telescope, suffering from mirror topography induced (optical) path length changes, so called piston, due to active beam steering and walking of the laser beam over the surfaces of subsequent telescope mirrors. This specific effect and its impact on the LISA measurement performance is investigated in more detail based on experimental measurements as well as a theoretical model. The second aspect investigated in this thesis is a novel concept for a LISA like inertial sensor, which features a spherical proof mass in combination with an all optical read-out. This concept represents an elegant solution for a low-noise, fully drag-free inertial sensor system, which could further increase the measurement performance of the LISA metrology instrument. In particular, the presented investigations include the development of a measurement setup for generating a detailed surface map of spherical proof masses, in order to calibrate its topography with respect to the sphere's centre of mass. First results of one-dimensional topography measurements of a SPM dummy are presented, representing a first step towards the generation of a complete two-dimensional surface map. Both topics are based on picometer-precision interferometric topography measurements, utilising highly sensitive heterodyne techniques. A major advantage of this measurement principle is its non-tactile nature, hence avoiding damage of the examined surfaces, while offering high levels of accuracy and reproducibility.Dissertation468 290 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Laser Ranging Interferometry for Future Gravity Missions : Instrument Design, Link Acquisition and Data Calibration(2017-01-13); ; ; The presented study aims to improve the design solution adopted for the Laser Ranging Instrument of the GRACE Follow-On mission in terms of instrument layout, algorithms for the laser link acquisition and techniques for mitigating the range measurement noise. The first part of this work describes viable layout solutions of a heterodyne interferometer employed for intra-satellite range metrology and the major noise contributions which degrade the overall accuracy of the instrument. Together with the optical layout of the instrument, novel design concepts of the instrumenta s subsystems are also analyzed and tested. Precisely, a phasemeter designed to autonomously acquire and track a heterodyne signal with low signal-to-noise ratio in a frequency band that spans from 1MHz to 25MHz is presented. Particular attention is also dedicated to the mathematical modeling of the steering mirror dynamics and to the enhancement of its pointing performance by means of feedforward control. In the second part of this work, solutions for autonomously acquiring a laser signal buried in noise are analyzed and put in relation with the boundary constraints of the acquisition problem. The acquisition algorithms presented and the robustness of their design is verified mainly using numerical simulations. Experimental tests have also been performed for validating the simulation hypothesis and verifying their compliancy to a realistic mission scenario. The last part of this work describes a calibration algorithm which has been developed for minimizing, during data post-processing, the noise due to the tilt-to-piston coupling which represents one of the highest contributors to the overall measurement noise.Dissertation420 192