Hansjörg Dittus

OPTIS: a satellite-based test of special and general relativity

A new satellite-based test of special and general relativity is proposed. For the Michelson-Morley test we expect an improvement of at least three orders of magnitude, and for the Kennedy-Thorndike test an improvement of more than one order of magnitude. Furthermore, an improvement by two orders of magnitude of the test of the universality of the gravitational redshift by comparison of an atomic clock with an optical clock is projected. The tests are based on ultrastable optical cavities, lasers, an atomic clock and a frequency comb generator.

New powerful thermal modelling for high-precision gravity missions with application to Pioneer 10/11

The evaluation of about 25 years of Doppler data has shown an anomalous constant deceleration of the deep space probes Pioneer 10 and 11. This observation became known as the Pioneer anomaly (PA) and has been confirmed independently by several groups. Many disturbing effects that could cause a constant deceleration of the craft have been excluded as possible source of the PA. However, a potential asymmetric heat dissipation of the spacecraft surface leading to a resulting acceleration still remains to be analysed in detail. We developed a method to calculate this force with very high precision by means of finite element (FE) modelling and ray tracing algorithms. The elaborated method is divided into two separate parts. The first part consists of the modelling of the spacecraft geometry in FE and the generation of a steady state temperature surface map of the craft. In the second part, this thermal map is used to compute the force with a ray-tracing algorithm, which gives the total momentum generated by the radiation emitted from the spacecraft surface. The modelling steps and the force computation are presented for a simplified geometry of the Pioneer 10/11 spacecraft including radioisotope thermoelectric generators (RTG), equipment/experiment section and the high gain antenna. Analysis results how that the magnitude of the forces to be expected are non-negligible with respect to the PA and that more detailed investigations are necessary. The method worked out here for the first time is not restricted to the modelling of the Pioneer spacecraft but can be used for many future fundamental physics (in particular gravitational physics) and geodesy missions like LISA, LISA Pathfinder or MICROSCOPE for which an exact disturbance modelling is crucial.

Confronting Finsler space–time with experiment

Within all approaches to quantum gravity small violations of the Einstein Equivalence Principle are expected. This includes violations of Lorentz invariance. While usually violations of Lorentz invariance are introduced through the coupling to additional tensor fields, here a Finslerian approach is employed where violations of Lorentz invariance are incorporated as an integral part of the space–time metrics. Within such a Finslerian framework a modified dispersion relation is derived which is confronted with current high precision experiments. As a result, Finsler type deviations from the Minkowskian metric are excluded with an accuracy of 10−16.

On the possibility of measuring the Lense-Thirring effect with a LAGEOS-LAGEOS II-OPTIS mission

A space mission, OPTIS, has been proposed for testing the foundations of special relativity and post-Newtonian gravitation in the field of the Earth. The constraints posed on the original OPTIS orbital geometry would allow for a rather wide range of possibilities for the final OPTIS orbital parameters. This freedom could be exploited for further tests of post-Newtonian gravity. In this paper, we wish to preliminarily investigate if it would be possible to use the orbital data from OPTIS together with those from the existing geodetic passive laser-ranged LAGEOS and LAGEOS II satellites in order to perform precise measurements of the Lense–Thirring effect. With regard to this possibility, it is important to note that the drag-free technology which should be adopted for the OPTIS mission would yield a lifetime of many years for this satellite. It turns out that the best choice would probably be to adopt the same orbital configuration as the proposed LAGEOS-like LARES satellite and, for testing, select a linear combination including the nodes of LAGEOS, LAGEOS II and OPTIS and the perigee of OPTIS. The total systematic error should be of the order of 1%. The LARES orbital geometry should not be too much in conflict with the original specifications of the OPTIS mission. However, a compromise solution could also be adopted. A comparison with the new perspectives of measuring the Lense–Thirring effect with the existing laser-tracked satellites opened by the new gravity models from CHAMP and, especially, GRACE is made. It turns out that an OPTIS/LARES mission would still be of great significance because the obtainable accuracy would be better than that offered by a reanalysis of the currently existing satellites.

Lasers, Clocks and Drag-Free Control

Part I Surveys: Fundamental Physics, Space, Missions and Technologies -- Claus Lammerzahl, Hansjorg Dittus General Theory of Relativity: Will it Survive the Next Decade? -- Orfeu Bertolami, Jorge Paramos, Slava G. Turyshev Is the Physics Within the Solar System Really Understood? -- Claus Lammerzahl, Oliver Preuss, Hansjorg Dittus Part II Theory Propagation of Light in the Gravitational Field of Binary Systems to Quadratic Order in Newtons Gravitational Constant -- Gerhard Schafer and Michael H. Brugmann On the Radar Method in General-Relativistic Spacetimes -- Volker Perlick A Universal Tool for Determining the Time Delay and the Frequency Shift of Light: Synges World Function -- Pierre Teyssandier, Christophe Le Poncin-Lafitte, Bernard Linet Unified Formula for Comparison of Clock Rates and its Applications -- C. Xu, X. Wu, and E. Bruning Gravity Tests and the Pioneer Anomaly -- Marc-Thierry Jaekel, Serge Reynaud Laser Ranging Delay in the Bi-Metric Theory of Gravity -- Sergei M. Kopeikin, Wei-Tou Ni Part III Technologies Measurement of the Shapiro Time Delay Between Drag-free Spacecraft -- Neil Ashby, Peter L. Bender Laser Transponders for High Accuracy Interplanetary Laser Ranging and Time Transfer -- John J. Degnan Unequal-arm Interferometry and Ranging in Space -- Massimo Tinto Technology for Precision Gravity Measurements -- RobertD. Reasenberg and J.D. Phillips Clocks and accelerometers for space tests of fundamental physics -- Lute Maleki, James M. Kohel, Nathan E. Lundblad, John D. Prestage, Robert J. Thompson, and Nan Yu Atom Interferometric Inertial Sensors for Space Applications -- Philippe Bouyer, Franck Pereira dos Santos, Arnaud Landragin and Christian J. Borde Drag-Free Satellite Control -- Stephan Theil Drag-free Control Design with Cubic Test Masses -- Walter Fichter, AlexanderSchleicher, Stefano Vitale Solar Sail Propulsion: An Enabling Technology for Fundamental Physics Missions -- Bernd Dachwald, Wolfgang Seboldt, Claus Lammerzahl Part IV Missions and Projects Testing Relativity with Space Astrometry Missions -- Sergei A. Klioner LISA, the Laser Interferometer Space Antenna, requires the ultimate in Lasers, Clocks, and Drag-Free Control -- Albrecht Rudiger, Gerhard Heinzel, and Michael Trobs Lunar Laser Ranging Contributions to Relativity and Geodesy -- Jurgen Muller, James G. Williams, Slava G. Turyshev Science, Technology and Mission Design for the Laser Astrometric Test Of Relativity -- Slava G. Turyshev, Michael Shao, Kenneth L. Nordtvedt, Jr. LATORs Measured Science Parameters and Mission Configuration -- Kenneth Nordtvedt OPTIS - High Precision Tests of Special and General Relativity in Space -- Claus Lammerzahl, Hansjorg Dittus, Achim Peters, Silvia Scheithauer, Stephan Schiller Testing Relativistic Gravity to One Part per Billion -- Wei-Tou Ni, Antonio Pulido Paton, and Yan Xia Exploring the Pioneer Anomaly: Concept Considerations for a Deep Space Gravity Probe Based on Laser Controlled Free Flying Reference Masses -- Ulrich Johann, Hansjorg Dittus, Claus Lammerzahl Pioneer Anomaly: What Can We Learn from LISA? -- Denis Defrere, Andreas Rathke

Testing the equivalence principle with atomic interferometry

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.

ASTROD and ASTROD I: Progress Report

Over the next decade the gravitational physics community will benefit from dramatic improvements in many technologies critical to the tests of gravity and gravitational-wave detection. The highly accurate deep space navigation, interplanetary laser ranging and communication, interferometry and metrology, high precision frequency standards, precise pointing and attitude control, together with the drag-free technologies will revolutionize the field of the experimental gravitational physics. Deep-space laser ranging will be ideal for gravitational-wave detection, and testing relativity and measuring solar-system parameter to an unprecedented accuracy. ASTROD I is such a mission with single spacecraft; it is the first step of ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) with 3 spacecraft. In this paper, we will present the progress of ASTROD and ASTROD I with emphases on the acceleration noises, mission requirement, charging simulation, drag-free control and low-frequency gravitational-wave sensitivity.

KINEMATICAL TEST THEORIES FOR SPECIAL RELATIVITY: A COMPARISON

A comparison of certain kinematical test theories for Special Relativity including the Robertson and Mansouri–Sext test theories is presented and the accuracy of the experimental results testing Special Relativity are expressed in terms of the parameters appearing in these test theories. The theoretical results are applied to the most precise experimental results obtained recently for the isotropy of light propagation and the constancy of the speed of light.

Testing the Universality of Free Fall for Charged Particles in Space

At first a short analysis of the notion of the Universality of Free Fall (UFF) for charged matter is given. Even if neutral bound systems of charged particles are in full accordance with the UFF, there is still a possibility that an isolated charge couples anomalously to gravitational fields. The experiment of Witteborn and Fairbank aimed at testing the UFF for electrons is shortly reviewed emphasizing the various additional disturbing gravity induced electromagnetic fields. Since these additional gravity induced fields are not very well under control, a space borne version of this experiment will reduce these disturbances considerably. The corresponding estimates for these kinds of tests in space are presented. As a result, gravity–induced stray field can be reduced considerably. Furthermore, also patch–effects can be reduced efficiently due to novel coating techniques. Therefore, due to microgravity conditions and new techniques the UFF for charged particles may be tested with much higher accuracy than in previous experiments.

High Sensitive DC SQUID Based Position Detectors for Application in Gravitational Experiments at the Drop Tower Bremen

Free fall tests for proving the Weak Equivalence Principle (WEP) have been rarely be done in history. Although they seem to be the natural experiments to test the equivalence of inertial and gravitational mass, best results for proofs of the WEP could be attained with torsion pendulum tests to an accuracy of 10-12. Pendulum tests are long term periodic experiments, whereas free fall tests on Earth can be carried out only for seconds causing certain limitations in principle. Nevertheless, very precise fall tests in the 10-12 to 10-13 range are possible and under preparation to be carried out on the Drop Tower Bremen for a free fall over 110 m. These tests require position detectors with an extremely high resolution in order to measure tiny displacements of freely falling test masses. Using SQUID-based sensing technique, the displacements can be determined with an accuracy of 2 x 10-14 m/√Hz. The SQUID system, developed and manufactured at Jena University, provides high sensitivity and extremely low intrinsic noise, especially at low frequencies. Some recent results are discussed.