9 research outputs found
Subtraction-noise projection in gravitational-wave detector networks
In this paper, we present a successful implementation of a subtraction-noise
projection method into a simple, simulated data analysis pipeline of a
gravitational-wave search. We investigate the problem to reveal a weak
stochastic background signal which is covered by a strong foreground of
compact-binary coalescences. The foreground which is estimated by matched
filters, has to be subtracted from the data. Even an optimal analysis of
foreground signals will leave subtraction noise due to estimation errors of
template parameters which may corrupt the measurement of the background signal.
The subtraction noise can be removed by a noise projection. We apply our
analysis pipeline to the proposed future-generation space-borne Big Bang
Observer (BBO) mission which seeks for a stochastic background of primordial
GWs in the frequency range Hz covered by a foreground of
black-hole and neutron-star binaries. Our analysis is based on a simulation
code which provides a dynamical model of a time-delay interferometer (TDI)
network. It generates the data as time series and incorporates the analysis
pipeline together with the noise projection. Our results confirm previous ad
hoc predictions which say that BBO will be sensitive to backgrounds with
fractional energy densities below Comment: 54 pages, 15 figure
In-Orbit Performance of the GRACE Follow-on Laser Ranging Interferometer
The Laser Ranging Interferometer (LRI) instrument on the Gravity Recovery and Climate Experiment (GRACE) Follow-On mission has provided the first laser interferometric range measurements between remote spacecraft, separated by approximately 220 km. Autonomous controls that lock the laser frequency to a cavity reference and establish the 5 degrees of freedom two-way laser link between remote spacecraft succeeded on the first attempt. Active beam pointing based on differential wave front sensing compensates spacecraft attitude fluctuations. The LRI has operated continuously without breaks in phase tracking for more than 50 days, and has shown biased range measurements similar to the primary ranging instrument based on microwaves, but with much less noise at a level of 1 nm/Hz at Fourier frequencies above 100 mHz. © 2019 authors. Published by the American Physical Society
GRACE-Follow On Laser Ranging Interferometer: German contribution
The Gravity Recovery and Climate Experiment (GRACE) is a joint US/German
mission that has been mapping the Earth's gravity �eld since 2002 by measuring the distance
variations between two spacecraft using a micro-wave link. GRACE is reaching the end of its
lifetime. For this reason and in order to minimize data gaps, an almost identical mission will be
launched in 2017. This mission is called GRACE-Follow On (GRACE-FO) and it will include
an additional instrument as a technological demonstrator to monitor distance changes between
the spacecraft. This instrument is the Laser Ranging Interferometer (LRI), which is based on
heterodyne laser interferometry at 1064nm and takes advantage of many technologies developed
for LISA. In this paper a short overview of the current status of the German contribution is
presented
Laser link acquisition demonstration for the GRACE Follow-On mission
We experimentally demonstrate an inter-satellite laser link acquisition scheme for GRACE Follow-On. In this strategy, dedicated acquisition sensors are not required-instead we use the photodetectors and signal processing hardware already required for science operation. To establish the laser link, a search over five degrees of freedom must be conducted (± 3 mrad in pitch/yaw for each laser beam, and ± 1 GHz for the frequency difference between the two lasers). This search is combined with a FFT-based peak detection algorithm run on each satellite to find the heterodyne beat note resulting when the two beams are interfered. We experimentally demonstrate the two stages of our acquisition strategy: a ± 3 mrad commissioning scan and a ± 300 μrad reacquisition scan. The commissioning scan enables each beam to be pointed at the other satellite to within 142 μrad of its best alignment point with a frequency difference between lasers of less than 20 MHz. Scanning over the 4 alignment degrees of freedom in our commissioning scan takes 214 seconds, and when combined with sweeping the laser frequency difference at a rate of 88 kHz/s, the entire commissioning sequence completes within 6.3 hours. The reacquisition sequence takes 7 seconds to complete, and optimizes the alignment between beams to allow a smooth transition to differential wavefront sensing-based auto-alignment.This work was supported in part under the Australian Government’s Australian Space
Research Programme, grants from the Australian Research Council, and by the “Deutsche
Forschungsgemeinschaft” (DFG) through the Cluster of Excellence QUEST (Centre for Quantum
Engineering and Space-Time Research)
LASER RANGING INTERFEROMETER ON GRACE FOLLOW-ON
The Gravity Recovery and Climate Experiment (GRACE) is a successful Earth observation mission launched
in 2002 consisting of two identical satellites in a polar low-Earth orbit [1]. The distance variations between
these two satellites are measured with a Micro Wave Instrument (MWI) located in the central axis. In data postprocessing
the spatial and temporal variations of the Earth’s gravitational field are recovered, which are among
other things introduced by changing groundwater levels or ice-masses [2, 3, 4, 5]. The Laser Ranging
Interferometer (LRI) on-board the GRACE Follow-On (GFO) mission, which will be launched in 2017 by the
joint collaboration between USA (NASA) and Germany (GFZ), is a technology demonstrator to provide about
two orders of magnitude higher measurement accuracy than the initial GRACE MWI, about 80 nm/√Hz in the
measurement band between 2 mHz and 0.1 Hz. The integration of the LRI units on both GFO S/C has been
finished in summer 2016.
The design as well as the functional, performance, and thermal-vacuum tests results of the German LRI flight
units will be presented