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Gravitational Reference Sensors (Ballroom A)
Thursday Chair: Giacomo Ciani
16:00 - 16:15 Henri Inchauspe
APC/Paris
Migrating LISAPathfinder noise results to the eLISA mission.Download
16:15 - 16:30 Antoine Petiteau
APC
Links between instrument developments and science with gravitational waves : the LISACode simulator, robust data analysis and calibration methods.Download
16:30 - 16:45 Koki Okutomi
Graduate University for Advanced Study, NAOJ
Development of Inertial Sensor for DECIGO Pathfinder
16:45 - 17:00 Franz Georg hey
Airbus Defense and Spance, Space Systems / Technische Universität Dresden
Development of a Micro-Thruster Test Facility which fulfils the LISA requirementsDownload
17:00 - 17:15 John Conklin
University of Florida
Testing new GRS technologies and configurations with the UF torsion pendulumDownload
17:15 - 17:30 Hang Yin for Zebing Zhou
Huazhong University of Science and Technology
Progress of surface potential measurement using a torsion pendulumDownload
17:30 - 17:45 Ignacio Mateos
Institut de Cičncies de l'Espai (IEEC-CSIC)
Progress on the design of the magnetic field measurement system for eLISADownload
17:45 - 18:00 Andreas Zoellner
Stanford University
Drag-free Technology Demonstration on a SmallSatDownload
Migrating LISAPathfinder noise results to the eLISA mission. Download
Henri Inchauspe - APC/Paris
The LISAPathfinder (LPF) mission will be launched in 2015 and its main results will become apparent in 2016. Among those are a study of the residual noise budget and a better evaluation of the impact of the different noise sources. Around 2020, the selection process of the ESA L3 mission will begin and the eLISA concept is a strong competitor for this. One of main parameters of this mission is its sensitivity curve which, at low frequency depends on the outcome of LPF. The APC group is therefore working on a (simplified) modeling of the eLISA constellation in order to evaluate the impact of the results of LPF on the expected sensitivity of eLISA. The talk will present the status of this work and will attempt to compare the results of this analysis with the present status of the eLISA sensitivity curve.
Links between instrument developments and science with gravitational waves : the LISACode simulator, robust data analysis and calibration methods. Download
Antoine Petiteau - APC
The long developments and studies that have been done on LISA and eLISA until now are either related to instrument developments and research on high level technologies, or related on data analysis and science with gravitational waves. These two aspects of the mission have been well studied independently but very few studies are making the link between them. But, since the mission is selected, it is necessary now to consider them coherently. In this talk, I will present several ongoing studies making this link : developments of LISACode toward more realistic simulations by modeling last instrument designs, more realistic noises, by connecting this numerical simulator to hardware experiments (LOTe) and by modeling most recent waveform; integration of LISAPathfinder results; potentialities for future MLDCs; robust data analysis methods that can be used either for instrument understanding or for gravitational wave data analysis; possible calibration procedures; tools to be provide to the large community.
Development of Inertial Sensor for DECIGO Pathfinder
Koki Okutomi - Graduate University for Advanced Study, NAOJ
DECIGO Pathfinder (DPF) is the first milestone mission for DECIGO (DECi-hertz Interferometer Gravitational wave Observatory), the future space gravitational-wave antenna of Japan which target is low-frequency gravitational waves around 0.1 Hz. DPF aims to verify some key technologies required for DECIGO such as precise measurement of position of a test-mass with laser interferometer, frequency stabilization of the laser source and drag-free control. We are developing an inertial sensor, which consists of a cubic test mass and enclosing electrodes for an electrostatic sensor and actuator. In this talk, we will present especially conceptual inertial sensor model with comb-like electrodes in order to reduce gas damping noise, in particular an increasing effect of so-called squeeze-film damping in test-mass housing, and secure enough electrostatic force for test-mass position control.
Development of a Micro-Thruster Test Facility which fulfils the LISA requirements Download
Franz Georg hey - Airbus Defense and Spance, Space Systems / Technische Universität Dresden
In the context of investigations for a sufficient attitude control thruster for eLISA, we have developed a thruster test facility which consists of a highly precise thrust balance coupled with plasma diagnostics. In parallel to the test facility development, investigations to down scale a Highly Precise Multistage Plasma Thruster (HEMP-T) are also being carried out. The thruster has been used to demonstrate the measurement capabilities of the facility. The setup allows a parallel operation of all instruments and can also be used for other types of µN propulsion systems including cold gas thrusters. The thrust balance consists of two pendulums. As read out a heterodyne laser interferometer is used. Differential wave front sensing enables the measurement of the pendulum tilt which, via suitable calibration using an electrostatic comb, can be converted to a thrust. The whole setup is a symmetric configuration enabling a common-mode rejection of the dominant noise sources (e.g. seismic noise etc.). The thrust balance has a demonstrated precision of 0.1 µN/sqrt(Hz). Based on our unique design, this precision can be attained down to 1e-3. Thus, the measurement setup is especially suitable for characterising the thrust noise of potential eLISA propulsion candidates. We will give an overview of the design, the present performance, and the future plans.
Testing new GRS technologies and configurations with the UF torsion pendulum Download
John Conklin - University of Florida
LISA will directly observe gravitational waves in the 0.1 mHz to 1 Hz frequency band which hosts signals from the most interesting sources, including super-massive black hole mergers anywhere in the Universe, compact galactic binaries, and extreme mass ratio inspirals. With the recent discovery of B-mode polarization in the CMB, the July 2015 launch of LISA Pathfinder (LPF), the expected direct detection of high-frequency gravitational waves by aLIGO before 2019, and the selection of The Gravitational Universe for the European Space Agency’s L3 science theme, this should be considered the gravitational wave decade. LISA has consistently been ranked in the top two of future large space missions in the last two Decadal Surveys, and advancing LISA’s technology readiness in the next four years is critically important for ensuring that it becomes the highest ranked mission in the 2020 Decadal Survey. LISA will use laser interferometry will measure picometer changes in the distances between free falling test masses separated by millions of kilometers caused by gravitational waves. A test mass and its associated sensing, actuation, charge control and caging subsystems are referred to as a gravitational reference sensor (GRS).  Following a successful demonstration of the baseline LISA GRS by LPF, the measurement principle will be carried forward, but improvements in the electronic and optical sensing and control system, the charge control system, and other components are possible over the next ten years. These improvements will lead to cost savings and potential noise reductions. The UF LISA group has constructed the UF Torsion Pendulum to increase U.S. competency in this critical area and to have a facility where these new technologies can be developed and evaluated. This presentation will introduce this facility, show some preliminary results, and describe its future role in developing technology for LISA.
Progress of surface potential measurement using a torsion pendulum Download
Zebing Zhou - Huazhong University of Science and Technology
Surface potential variation of the test mass is one of main noises for space gravitational experiments such as the LISA project, which should be carefully investigated. A scheme has been proposed for measuring surface potential distribution base on a electrostatic-controlled torsion balance. A gold coated K9 glass test mass with a size of 100mm×40mm×8mm and a mass of about 80g is suspended from a tungsten wire with a diameter of 25 micrometer and a length of about 0.35m, and a Au coated K9 glass source mass with a surface area of 5mm×5mm acts as the source conductor, which can be moved by a translational stage in order to be able to probe the surface charge distribution of the test mass. Two pair of capacitive electrodes are used to measure and then control the test mass, in this case, the control voltage applied on the electrodes can provide the information of the charge variation between the probe and test mass. According to our design, both of temporal and spatial variations in surface potential of the test mass could be measured. The current static experiments show that resolution of the controlled torsion pendulum reaches 7×10-14 Nm/Hz1/2, and corresponding voltage measurement level comes to about 15V/Hz1/2 at 0.03Hz. The scanning experiment, which wants to investigate spatial variations in surface potential of the test mass, is being carried out.
Progress on the design of the magnetic field measurement system for eLISA Download
Ignacio Mateos - Institut de Cičncies de l'Espai (IEEC-CSIC)
Magnetic sensors are necessary devices to map the magnetic field and gradient at the location of the test masses in eLISA, with the primary goal of assessing the contribution of the magnetic effects to the acceleration noise budget. Our previous experience with the design of the magnetic diagnostics system for LISA Pathfinder indicates that the critical issues are the accuracy of the magnetic field map reconstruction and the sensitivity of the sensors at sub-milli-Hertz frequencies. Taking into consideration the more demanding requirements for eLISA, we need to enhance the performance of the LISA Pathfinder magnetic subsystem using different magnetic sensing techniques. Here, we present the ongoing research to find alternatives in the magnetic field monitoring in order to develop criteria for the best choice of magnetic sensors for eLISA.
Drag-free Technology Demonstration on a SmallSat Download
Andreas Zoellner - Stanford University
The core instrument of LISA consists of a long arm interferometer and a free floating test mass enclosed in a drag-free system. The goal of the drag-free system is to shielded the test mass against all external non-gravitational forces and to keep the distance between the test mass and the satellite in tight bounds. The distance between the test mass and the satellite is measured with a short arm interferometer, the long arm interferometer then completes the displacement measurement between two such test masses on far away satellites. Drag-free technology can be used for several applications besides gravitational wave detection such as geodesy, aeronomy, and other fundamental physics experiments. A number of drag-free system designs have been proposed since the first drag-free satellite was flown in 1972. One such design, the Modular Gravitational Reference Sensor (MGRS), is in development at Stanford since 2004. The MGRS can be scaled in size according to the requirements of a specific mission. It is designed around a single spherical test mass and an optical readout of the test mass position. Only the most demanding missions such LISA need a picometer sensitivity of the test mass displacement. Most mission scenarios only require a sensitivity of about 1 nm. In that case one can omit the short arm interferometer module and use a simpler readout system, the Differential Optical Shadow Sensor (DOSS). It is primarily designed to provide a displacement measurement for the drag free controller and is intended to provide a nanometer scale measurement over a large dynamic range. The MGRS further includes 1) a UV LED system to eliminate any difference in electrical potential between the test mass and the surrounding housing in order to reduce electrostatic forces on the test mass, 2) a caging system to hold the test mass during launch and release it once the satellite reaches its designated orbit, 3) a thermal shield designed to maintain a temperature stability of 10-6 K at the orbital period, and 4) thrusters to counteract the external forces and maintain the relative position between spacecraft and test mass. Thruster size is an important design variable. The thrusters must have sufficient dynamic range to make the micro-scale adjustments needed to preserve drag-free operation and to overcome the external forces encountered in low earth orbit. The operational lifetime (number of firings) of the thrusters may also constrain the duration of the mission. Initial analysis and simulation indicates that on-off thrusters with thrust on the order of 100 micro-Newtons and a bit size on the order of 100 ms should be sufficient for drag-free operation of a SaudiSat. The modularity of the MGRS allows for a parallel technology maturation. The UV LED system is going to be space qualified on a SaudiSat mission scheduled for launch in June 2014. The caging system is being tested on microgravity parabolic flights as part of NASA's flight opportunity program. The DOSS system was selected to fly on a CubeSat as part of the ELaNa program. We will highlight the progress of the technology maturation leading towards a drag-free mission on a SaudiSat bus. This mission will demonstrate drag-free technology on a small spacecraft at a fraction of the cost of previous drag-free missions. The target acceleration noise is 10e-12 m/sec^2. With multiple such satellites a GRACE-like mission with improved sensitivity and potentially improved spatial and temporal resolution can be achieved.