High precision modelling of thermal perturbations with application to Pioneer 10 and Rosetta

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

Atom Interferometry in Space: Thermal Management and Magnetic Shielding

Atom interferometry is an exciting tool to probe fundamental physics. It is considered especially apt to test the universality of free fall by using two different sorts of atoms. The increasing sensitivity required for this kind of experiment sets severe requirements on its environments, instrument control, and systematic effects. This can partially be mitigated by going to space as was proposed, for example, in the Spacetime Explorer and Quantum Equivalence Principle Space Test (STE-QUEST) mission. However, the requirements on the instrument are still very challenging. For example, the specifications of the STE-QUEST mission imply that the Feshbach coils of the atom interferometer are allowed to change their radius only by about 260 nm or 2.6E-4% due to thermal expansion although they consume an average power of 22 W. Also Earth's magnetic field has to be suppressed by a factor of 10E5. We show in this article that with the right design such thermal and magnetic requirements can indeed be met and that these are not an impediment for the exciting physics possible with atom interferometers in space.Comment: v2: minor changes to agree with published version; 8 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

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

Gravitomagnetic Clock Effect: Using GALILEO to explore General Relativity

All experiments to date are in remarkable agreement with the predictions of Einstein's theory of gravity, General Relativity. Besides the classical tests, involving light deflection, orbit precession, signal delay, and the gravitational redshift, modern technology has pushed the limits even further. Gravitational waves have been observed multiple times as have been black holes, arguably amongst the most fascinating objects populating our universe. Moreover, geodetic satellite missions have enabled the verification of yet another prediction: gravitomagnetism. This phenomenon arises due to the rotation of a central body, e.g., the Earth, which is dragging spacetime along. One resulting effect on satellite orbits is the observed Lense-Thirring effect. Another predicted, yet unverified, effect is the so-called gravitomagnetic clock effect, which was first described by Cohen and Mashhoon as the proper time difference of two counter-revolving clocks in an orbit around a rotating mass. A theoretical framework is introduced that describes a gravitomagnetic clock effect based on a stationary spacetime model. An incremental definition of a suitable observable follows, which can be accessed via orbit data obtained from the European satellite navigation system Galileo, and an implementation of the framework for use with real satellite and clock data is presented. The technical requirements on a satellite mission are studied to measure the gravitomagnetic clock effect at the state-of-the-art in satellite laser ranging and modelling of gravitational and non-gravitational perturbations. Based on the analysis within this work, a measurement of the gravitomagnetic clock effect is highly demanding, but might just be within reach in the very near future based on current and upcoming technology.Comment: 13 pages, 3 figures, 3 supplemental page

Astrodynamical Space Test of Relativity using Optical Devices I (ASTROD I) - A class-M fundamental physics mission proposal for Cosmic Vision 2015-2025: 2010 Update

This paper on ASTROD I is based on our 2010 proposal submitted for the ESA call for class-M mission proposals, and is a sequel and an update to our previous paper [Experimental Astronomy 23 (2009) 491-527; designated as Paper I] which was based on our last proposal submitted for the 2007 ESA call. In this paper, we present our orbit selection with one Venus swing-by together with orbit simulation. In Paper I, our orbit choice is with two Venus swing-bys. The present choice takes shorter time (about 250 days) to reach the opposite side of the Sun. We also present a preliminary design of the optical bench, and elaborate on the solar physics goals with the radiation monitor payload. We discuss telescope size, trade-offs of drag-free sensitivities, thermal issues and present an outlook. ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test General Relativity with an improvement in sensitivity of over 3 orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of the solar system; and to measure the time rate of change of the gravitational constant with an order of magnitude improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is envisaged as the first in a series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way, two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth, to achieve the ASTROD I goals.Comment: 15 pages, 11 figures, 1 table, based on our 2010 proposal submitted for the ESA call for class-M mission proposals, a sequel and an update to previous paper [Experimental Astronomy 23 (2009) 491-527] which was based on our last proposal submitted for the 2007 ESA call, submitted to Experimental Astronom

Design of a dual species atom interferometer for space

Atom interferometers have a multitude of proposed applications in space including precise measurements of the Earth's gravitational field, in navigation & ranging, and in fundamental physics such as tests of the weak equivalence principle (WEP) and gravitational wave detection. While atom interferometers are realized routinely in ground-based laboratories, current efforts aim at the development of a space compatible design optimized with respect to dimensions, weight, power consumption, mechanical robustness and radiation hardness. In this paper, we present a design of a high-sensitivity differential dual species $^{85}$Rb/$^{87}$Rb atom interferometer for space, including physics package, laser system, electronics and software. The physics package comprises the atom source consisting of dispensers and a 2D magneto-optical trap (MOT), the science chamber with a 3D-MOT, a magnetic trap based on an atom chip and an optical dipole trap (ODT) used for Bose-Einstein condensate (BEC) creation and interferometry, the detection unit, the vacuum system for $10^{-11}$ mbar ultra-high vacuum generation, and the high-suppression factor magnetic shielding as well as the thermal control system. The laser system is based on a hybrid approach using fiber-based telecom components and high-power laser diode technology and includes all laser sources for 2D-MOT, 3D-MOT, ODT, interferometry and detection. Manipulation and switching of the laser beams is carried out on an optical bench using Zerodur bonding technology. The instrument consists of 9 units with an overall mass of 221 kg, an average power consumption of 608 W (819 W peak), and a volume of 470 liters which would well fit on a satellite to be launched with a Soyuz rocket, as system studies have shown.Comment: 30 pages, 23 figures, accepted for publication in Experimental Astronom