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  • 1
    Article
    Article
    Language: English
    In: CEAS Space Journal, 2017, Vol.9(1), pp.1-2
    Description: To access, purchase, authenticate, or subscribe to the full-text of this article, please visit this link: http://dx.doi.org/10.1007/s12567-017-0146-8 Byline: Hansjorg Dittus (1) Author Affiliation: (1) German Aerospace Center (DLR), Cologne, Germany Article History: Registration Date: 26/01/2017 Online Date: 09/02/2017
    Keywords: Engineering ; Aerospace Technology and Astronautics ; Engineering;
    ISSN: 1868-2502
    E-ISSN: 1868-2510
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  • 2
    Language: English
    In: Physical review letters, 08 December 2017, Vol.119(23), pp.231101
    Description: According to the weak equivalence principle, all bodies should fall at the same rate in a gravitational field. The MICROSCOPE satellite, launched in April 2016, aims to test its validity at the 10^{-15} precision level, by measuring the force required to maintain two test masses (of titanium and platinum alloys) exactly in the same orbit. A nonvanishing result would correspond to a violation of the equivalence principle, or to the discovery of a new long-range force. Analysis of the first data gives δ(Ti,Pt)=[-1±9(stat)±9(syst)]×10^{-15} (1σ statistical uncertainty) for the titanium-platinum Eötvös parameter characterizing the relative difference in their free-fall accelerations.
    Keywords: Astrophysics - Instrumentation And Methods For Astrophysics ; Astrophysics - Cosmology And Nongalactic Astrophysics ; General Relativity And Quantum Cosmology;
    ISSN: 00319007
    E-ISSN: 1079-7114
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  • 3
    Language: English
    In: Advances in Space Research, 15 August 2016, Vol.58(4), pp.644-677
    Description: The Weak Equivalence Principle (WEP) is at the basis of General Relativity – the best theory for gravitation today. It has been and still is tested with different methods and accuracies. In this paper an overview of tests of the Weak Equivalence Principle done in the past, developed in the present and planned for the future is given. The best result up to now is derived from the data of torsion balance experiments by Schlamminger et al. (2008). An intuitive test of the WEP consists of the comparison of the accelerations of two free falling test masses of different composition. This has been carried through by Kuroda & Mio (1989, 1990) with the up to date most precise result for this setup. There is still more potential in this method, especially with a longer free fall time and sensors with a higher resolution. Providing a free fall time of 4.74 s (9.3 s using the catapult) the drop tower of the Center of Applied Space Technology and Microgravity (ZARM) at the University of Bremen is a perfect facility for further improvements. In 2001 a free fall experiment with high sensitive SQUID (Superconductive QUantum Interference Device) sensors tested the WEP with an accuracy of (Nietzsche, 2001). For optimal conditions one could reach an accuracy of with this setup (Vodel et al., 2001). A description of this experiment and its results is given in the next part of this paper. For the free fall of macroscopic test masses it is important to start with precisely defined starting conditions concerning the positions and velocities of the test masses. An Electrostatic Positioning System (EPS) has been developed to this purpose. It is described in the last part of this paper.
    Keywords: Equivalence Principle ; Electrostatic Positioning System ; Free Fall Experiment ; Drop Tower ; Inertial Sensor ; Satellite Mission ; Engineering ; Astronomy & Astrophysics ; Physics
    ISSN: 0273-1177
    E-ISSN: 1879-1948
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  • 4
    Language: English
    In: Physical review letters, 07 December 2018, Vol.121(23), pp.231102
    Description: On August 22, 2014, the satellites GSAT-0201 and GSAT-0202 of the European GNSS Galileo were unintentionally launched into eccentric orbits. Unexpectedly, this has become a fortunate scientific opportunity since the onboard hydrogen masers allow for a sensitive test of the redshift predicted by the theory of general relativity. In the present Letter, we describe an analysis of approximately three years of data from these satellites including three different clocks. For one of these, we determine the test parameter quantifying a potential violation of the combined effects of the gravitational redshift and the relativistic Doppler shift. The uncertainty of our result is reduced by more than a factor 4 as compared to the values of Gravity Probe A obtained in 1976.
    Keywords: General Relativity And Quantum Cosmology;
    ISSN: 00319007
    E-ISSN: 1079-7114
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  • 5
    Language: English
    In: Classical and Quantum Gravity, 2012, Vol.29(18), p.184003 (12pp)
    Description: The weak equivalence principle (WEP), that is, the universality of free fall, states that all point-like neutral particles in a gravitational field fall in the same way. This is the basis of the geometrization of the gravitational interaction. Together with further requirements on the behavior of point particles, light propagation and clocks one can show that gravity is modeled by a Riemannian geometry. Since in the quantum domain all objects are extended, it is not clear whether the notion of a WEP in the quantum domain makes sense at all. We show that for matter wave interferometry the notion of WEP still can be given a meaning. We give a short overview over schemes which allows a violation of the WEP and emphasize that there are also schemes which show that there might be violations of the WEP in the quantum regime which are not present classically. This makes a test of the WEP with quantum matter necessary. We also give a brief outline of the efforts made for testing the WEP with interferometry with cold atoms in the Bremen drop tower carried out by the QUANTUS and PRIMUS collaboration.
    Keywords: Quantum Gravity ; Equivalence Principle ; Drop Towers ; Cold Atoms ; Clocks ; Gravitational Fields ; Interferometry ; Matter Waves ; Quantum Physics (So) ; Atomic and Molecular Physics (Ah);
    ISSN: 0264-9381
    E-ISSN: 1361-6382
    Source: IOPscience (IOP Publishing)
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  • 6
    Language: English
    In: Acta Astronautica, 2011, Vol.68(1), pp.28-33
    Description: MICROSCOPE is a French space mission for testing the weak equivalence principle (WEP). The mission goal is the determination of the Eötvös parameter with an accuracy of 10 . The French space agency CNES is responsible for the satellite which is developed and produced within the Myriade series. The satellite's payload T-SAGE (Twin Space Accelerometer for Gravitation Experimentation) is developed and built by the French institute ONERA. It consists of two high-precision capacitive differential accelerometers. One accelerometer is used as reference sensor with two test masses of platinum, the science sensor contains a platinum and a titanium proof mass. The detection of the test mass movement and their control is done via a complex electrode system. As a member of the MICROSCOPE performance team, the German department ZARM will be involved in the data analysis of the MICROSCOPE mission. For this purpose, mission simulations and the preparation of the mission data evaluation in close cooperation with the French partners CNES, ONERA and OCA are realised. The development status of the simulation tool which will represent the complex spacecraft dynamics and all error sources in order to design and test data reduction procedures is presented and some features are discussed in detail.
    Keywords: Microscope ; Microgravity ; Simulation ; Equivalence Principle ; Accelerometer ; Engineering
    ISSN: 0094-5765
    E-ISSN: 1879-2030
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  • 7
    Language: English
    In: Space Science Reviews, 2010, Vol.151(1), pp.123-133
    Description: Electromagnetic radiation emitted from a source carries momentum. Thus, the dissipation of waste thermal energy can produce disturbance forces on spacecraft surfaces if the energy is not dissipated in a symmetric pattern. This force can be computed for a plate element as the quotient of the radiated power in normal direction and the speed of light. Depending on mission and spacecraft design the resulting surface forces have to be included into the disturbance budget. At ZARM an elaborated method for the exact modeling of the disturbances caused by heat radiation was developed which can be used for any satellite mission with high requirements on perturbation knowledge (e.g. LISA, LISA pathfinder, MICROSCOPE). The method which will be presented in this paper is based on raytracing and finite element (FE) thermal analysis. As a demonstration of the potential of the method, preliminary results acquired with a test case model of the Pioneer 10/11 Radioisotopic Thermal Generators (RTGs) will be shown.
    Keywords: Disturbance modeling ; Heat dissipation ; FEM
    ISSN: 0038-6308
    E-ISSN: 1572-9672
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  • 8
    Language: English
    In: Microgravity Science and Technology, 2010, Vol.22(4), pp.539-549
    Description: The Bremen drop tower at the Center of Applied Space Technology and Microgravity (ZARM) provides high quality micro-g condition needed for many high precision tests. This is even more improved by the development of a free flyer technology. This new technology is used for a free fall test of the MICROSCOPE differential accelerometers which only can work with a residual acceleration disturbance level below 25 nano-g in the high resolution mode. The French MICROSCOPE space mission for testing the Weak Equivalence Principle is scheduled for 2012/2013. The free fall accelerometer test campaign at ZARM is an important part of the pre-mission test program. In this article the new free flyer technology, its performance as well as the accelerometer tests are described.
    Keywords: Microgravity ; Drop tower ; Free flyer ; MICROSCOPE ; Accelerometer ; Weak eqiuvalence principle
    ISSN: 0938-0108
    E-ISSN: 1875-0494
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  • 9
    Language: English
    In: Acta Astronautica, 2010, Vol.66(3), pp.467-476
    Description: The dissipation of thermal energy can produce disturbance forces on spacecraft surfaces if the energy is not dissipated in a symmetric pattern. This force can be computed as the quotient of the radiated power and the speed of light for a plate surface element. Depending on mission and spacecraft design the resulting surface forces have to be included into the disturbance budget. At ZARM (Center of Applied Space Technology and Microgravity) a raytracing algorithm was developed that allows the computation of the resulting force for complex spacecraft geometries. The method is based on the modeling of the spacecraft geometry in finite elements (FEs). Using an FE-solver the surface temperatures of the satellite can be derived with geometry and material parameters using heat sources/sinks as constraints. The outgoing radiation force is computed including reflectivity and absorption between all elements of the model. As an example for the method a test case model of the radio isotope thermal generators (RTGs) of Pioneer 11 is processed with this force computing method. The results show that detailed thermal modeling for the whole craft is necessary as the simplified test case results in a force that is non-negligible with respect to the pioneer anomaly.
    Keywords: Thermal Recoil Force ; Thermal Modeling ; Finite Elements ; Disturbance Modeling ; Pioneer Anomaly ; Engineering
    ISSN: 0094-5765
    E-ISSN: 1879-2030
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  • 10
    Language: English
    In: Microgravity Science and Technology, 2010, Vol.22(4), pp.529-538
    Description: The realization of a Bose Einstein condensate in the Bremen drop tower as achieved by the QUANTUS collaboration in 2007 has added a new field to microgravity research: the study of freely evolving degenerate quantum gases at largely extended evolution times. Here we give an outlook on some experiments that could be done with such ultra-cold quantum gases in this unique laboratory and on other microgravity platforms to study fundamental physics questions. In particular we consider experiments that could employ the increased precision of matter wave interferometers in microgravity to search for low-energy phenomena of quantum gravity.
    Keywords: Fundamental physics ; Precision measurements ; Quantum gravity ; Matterwave optics
    ISSN: 0938-0108
    E-ISSN: 1875-0494
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