Rotating Boson Stars in 5 Dimensions

We study rotating boson stars in five spacetime dimensions. The boson fields consist of a complex doublet scalar field. Considering boson stars rotating in two orthogonal planes with both angular momenta of equal magnitude, a special ansatz for the boson field and the metric allows for solutions with nontrivial dependence on the radial coordinate only. The charge of the scalar field equals the sum of the angular momenta. The rotating boson stars are globally regular and asymptotically flat. For our choice of a sixtic potential the rotating boson star solutions possess a flat spacetime limit. We study the solutions in flat and curved spacetime.Comment: 17 pages, 6 figure

High precision orbit simulations for geodesy and fundamental physics missions

Orbit propagation including detailed environment models as well as system models is the basis for generating mock data sets for developing appropriate data analysis procedures in case of scientific and geodesy space missions. They allow to determine in virtual space the sensitivity of involved instruments and, furthermore, they help to optimize mission scenarios before their final design. It has been shown that the best gravitational redshift test is only possible if the correct modeling of the solar radiation pressure as well as interactions with magnetic fields and temperature effects are included in the data analysis process. Additionally, high precision simulations allow for the calibration of instruments in preparation for data analysis procedures, e.g. accelerometers on board of the GRACE satellites. The HPS (Hybrid Simulation Platform for Space Systems) developed from DLR and ZARM, University of Bremen, deals with all of these aspects. As a modular and generic tool it can be adapted to various scenarios of mission concepts and layouts. This talk will present examples of the usage of HPS in the context of instrument calibration, orbit propagation for studying the environmental influences on the satellite's orbit, and data analysis improvement on behalf of mock data sets

Rotating Boson Stars and Q-Balls

We consider axially symmetric, rotating boson stars. Their flat space limits represent spinning Q-balls. We discuss their properties and determine their domain of existence. Q-balls and boson stars are stationary solutions and exist only in a limited frequency range. The coupling to gravity gives rise to a spiral-like frequency dependence of the boson stars. We address the flat space limit and the limit of strong gravitational coupling. For comparison we also determine the properties of spherically symmetric Q-balls and boson stars.Comment: 22 pages, 18 figure

AOCS for future multi-satellite geodesy missions

Missions like GRACE and GRACE-FO have successfully established a continuous time series of data for Earth gravity field estimation. The continuous observation of Earths gravitational field is essential for the understanding of Earths mass transportation and climate change. Since GRACE-FO is already in service and the demand of more accurate data series arises, new Mission concepts need to be investigated to guarantee the continuation of the data time series and to increase the accuracy of Earths gravity field estimation. The German Aerospace Center (DLR) Institute for Satellite Geodesy and Inertial Sensing and the ZARM, University of Bremen are developing a Multi-Purpose Space Mission Simulator in the scope of the DFG Collaborative Research Center 1464 TerraQ. The simulation platform is capable of modelling for the atmospheric, magnetic, radiative, and gravitational environment in orbit and their coupling into system and sensor-specific effects. This work focuses on extending the simulation environment with an attitude control system to investigate next-generation gravimetry mission (NGGM) concepts with multiple satellites. The attitude control system should be modeled in three parts: Sensors, State Estimator and Controller, and Actuators. The aim is to model a realistic attitude control system. Thus, the performance of different satellite constellation approaches, such as pendulum orbits, bender orbits, and swarm constellations can be examined with the help of the simulator. Requirements for the AOCS subsystem will be derived to evaluate the feasibility of such mission concepts and sensors. This paper presents the current status of the research

GRACE Follow-On Accelerometer Data Recovery by High-Precision Environment Modelling

The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) satellites are equipped with high-precision three-axis accelerometers to measure all non-gravitational accelerations acting on the satellites. The accelerometer data are mainly used to account for the influence of these accelerations in the gravity-field-recovery process. Unfortunately, after only one month in orbit the accelerometer on one of the two satellites produced decreasingly accurate measurements. Due to this, the GRACE-D accelerometer data have to be replaced by artificial data. The procedure for the official GRACE-FO Science Data System (SDS) data products is a so called transplant of GRACE-C data. As an alternative approach, we present a modelling method, where the GRACE-D accelerometer data are based on high-precision non-gravitational force and disturbance modelling. We compare our modelled data to thruster-free accelerometer data derived from the official SDS data products. With this, we can evaluate the performance and show details of our approach. For example, the influence of an in-situ drag-coefficient estimation based on Sentman’s approach. In contrast to other GRACE-FO accelerometer-data-recovery approaches, no transplant of data is incorporated. This work is part of the Collaborative Research Center 1464 TerraQ and funded by DFG

Investigation of future geodesy mission concepts for their feasibility and requirements to the AOCS subsystem

Missions like GRACE and GRACE-FO have successfully established a continuous time series of data for Earth gravity field estimation. The continuous observation of Earths gravitational field is essential for the understanding of Earths mass transportation and climate change. Since GRACE-FO is already in service and the demand of more accurate data series arises, new Mission concepts need to be investigated to guarantee the continuation of the data time series and to increase the accuracy of Earths gravity field estimation. The German Aerospace Center (DLR) Institute for Satellite Geodesy and Inertial Sensing, as well as ZARM University of Bremen, is developing a simulation environment called the Hybrid Simulation Platform for Space Systems (HPS) to examine future geodesy satellite mission concepts. The simulation platform is capable of modelling for the atmospheric, magnetic, radiative, and gravitational environment in orbit and their coupling into system and sensor-specific effects. This work focuses on next-generation gravimetry mission (NGGM) concepts with multiple satellites and different satellite constellation approaches, such as pendulum orbits, bender orbits and swarm constellations, being examined with the help of the HPS simulator. In addition, new quantum sensors are considered to measure Earths gravitational field which put increased requirements on the AOCS subsystem, especially when considering drag-free control concepts. Requirements for the AOCS subsystem will be derived to evaluate the feasibility of such mission concepts and sensors. In parallel, collaborations with experts in orbit propagation and quantum sensors are being established within the scope of the German Collaborative Research Center TerraQ focusing on the improvement of Gravity field determination both on ground and space level. This paper presents the current status of the research

Charged boson stars and black holes

We consider boson stars and black holes in scalar electrodynamics with a V-shaped scalar potential. The boson stars come in two types, having either ball-like or shell-like charge density. We analyze the properties of these solutions and determine their domains of existence. When mass and charge become equal, the space-times develop a throat. The shell-like solutions need not be globally regular, but may possess a horizon. The space-times then consist of a Schwarzschild-type black hole in the interior, surrounded by a shell of charged matter, and thus a Reissner-Nordström-type space-time in the exterior. These solutions violate black hole uniqueness. The mass of the black hole solutions is related to the mass of the regular shell-like solutions by a mass formula of the type first obtained within the isolated horizon framework