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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

LISA Propulsion Module Separation Study

The Laser Interferometer Space Antenna (LISA) mission is a space-borne gravitational wave detector consisting of three spacecraft in heliocentric orbit. Each spacecraft is delivered to it operational orbit by a propulsion module. Because of the strict thermal and mass balancing requirements of LISA, the baseline mission concept requires that the propulsion module separate from the sciencecraft after delivery. The only propulsion system currently baselined for the sciencecraft are micronewton level thrusters, such as FEEP or colloid thrusters, that are used to balance the 30-40 microN of solar radiation pressure and provide the drag-free and attitude control of the spacecraft. Due to these thrusters limited authority, the separation of the propulsion module from the sciencecraft must be well controlled to not induce a large tip-off rotation of the sciencecraft. We present here the results of a design study of the propulsion module separation system that is shown to safely deliver the LISA sciencecraft to its final operational orbit.

Merkowitz, Stephen↗
NASA NTRS2005

Observing Massive Black Hole Binary Coalescences with LISA

Massive black hole binary coalescences are among the most important astrophysical sources of gravitational waves to be observed by LISA. The ability to observe and characterize such sources with masses approximately equal to 105 M/odot and larger at high redshifts is strongly dependent on the sensitivity of LISA in the low frequency (0.1 mHz and below) regime. We examine LISA's ability to observe these systems at redshifts up to z approximately equal to 10 for various proposed values of the low frequency sensitivity, under current assumptions about the merger rates. The discussion will focus on the astrophysical information that can be gained by these observations.

Centrella, Joan↗
NASA NTRS2006

LISA Framework for Enhancing Gravitational Wave Signal Extraction Techniques

This paper describes the development of a Framework for benchmarking and comparing signal-extraction and noise-interference-removal methods that are applicable to interferometric Gravitational Wave detector systems. The primary use is towards comparing signal and noise extraction techniques at LISA frequencies from multiple (possibly confused) ,gravitational wave sources. The Framework includes extensive hybrid learning/classification algorithms, as well as post-processing regularization methods, and is based on a unique plug-and-play (component) architecture. Published methods for signal extraction and interference removal at LISA Frequencies are being encoded, as well as multiple source noise models, so that the stiffness of GW Sensitivity Space can be explored under each combination of methods. Furthermore, synthetic datasets and source models can be created and imported into the Framework, and specific degraded numerical experiments can be run to test the flexibility of the analysis methods. The Framework also supports use of full current LISA Testbeds, Synthetic data systems, and Simulators already in existence through plug-ins and wrappers, thus preserving those legacy codes and systems in tact. Because of the component-based architecture, all selected procedures can be registered or de-registered at run-time, and are completely reusable, reconfigurable, and modular.

Thompson, David E.↗
NASA NTRS2008

LISA: Astrophysics Out to z Approximately 10 with Low-Frequency Gravitational Waves

This viewgraph presentation reviews the Laser Interferometer Space Antenna (LISA). LISA os a joint ESA-NASA project to design, build and operate a space-based gravitational wave detector. The 5 million Kilometer long detector will consist of three spacecraft orbiting the Sun in a triangular formation. Space-Time strains induced by gravitational waves are detected by measuring changes in the separation of fiducial masses with laser interferometry. LISA is expected to detect signals from merging massive black holes, compact stellar objects spiraling into super massive black holes in galactic nuclei, thousands of close binaries of compact objects in the Milky way and possible backgrounds of cosmological origin.

Stebbins, Robin T.↗
NASA NTRS2008

Science requirements for LISA

Historically, gravitational wave antennas have been characterized by their detection capability. This is measured in terms of signal-to-noise ratio, and implies a rate of false positives and false negatives. But to do useful astrophysics, one would like to measure - or more properly, estimate - astrophysical parameters of the gravitational wave sources. In the interest of strengthening the connection between science objectives and a specific instrument performance, the LISA community has reformulated the Laser Interferometer Space Antenna (LlSA) science requirements around the anticipated uncertainty in astrophysical parameter estimation. The rationale for this characterization of LlSA and a summary of the astrophysics and fundamental physics that LISA can do will be given. LISA will be able to make precision measurements of sources out to z approximately equal to 10.

Stebbins, Robin T.↗
NASA NTRS2008

LISA Parameter Estimation using Numerical Merger Waveforms

Coalescing supermassive black holes are expected to provide the strongest sources for gravitational radiation detected by LISA. Recent advances in numerical relativity provide a detailed description of the waveforms of such signals. We present a preliminary study of LISA's sensitivity to waveform parameters using a hybrid numerical/analytic waveform describing the coalescence of two equal-mass, nonspinning black holes. The Synthetic LISA software package is used to simulate the instrument response and the Fisher information matrix method is used to estimate errors in the waveform parameters. Initial results indicate that inclusion of the merger signal can significantly improve the precision of some parameter estimates. For example, the median parameter errors for an ensemble of systems with total redshifted mass of 10(exp 6) deg M solar mass at a redshift of z is approximately 1 were found to decrease by a factor of slightly more than two when the merger was included.

Thorpe, J. I.↗
NASA NTRS2008

Frequency-Tuneable Pre-Stabilized Lasers for LISA via Sideband Locking

Laser frequency noise mitigation is one of the most challenging aspects of the LISA interferometric measurement system. The unstabilized frequency fluctuations must be suppressed by roughly twelve orders of magnitude in order to achieve a stability sufficient for gravitational wave detection. This enormous suppression will be achieved through a combination of stabilization and common-mode rejection. The stabilization component will itself be achieved in two stages: pre-stabilization to a local optical cavity followed by arm-locking to some combination of the inter-spacecraft distances. In order for these two stabilization stages to work simultaneously, the lock-point of the pre-stabilization loop must be frequency tunable. The current baseline stabilization technique, locking to an optical cavity, does not provide tunability between cavity resonance, which are typically spaced by 100s of MHz. Here we present a modification to the traditional Pound-Drever-Hall cavity locking technique that allows the laser to be locked to a cavity resonance with an adjustable frequency offset. This technique requires no modifications to the optical cavity itself, thus preserving the stability of the frequency reference. We present measurements of the system stability, demonstrating that the pre-stabilization level satisfies LISA requirements. We also present a demonstration of a phase-lock loop which utilizes the tunable sideband locking technique as a pre-stabilizations tage. The performance of the pre-stabilized phase-lock-loop indicates that the tunable sideband technique will meet the requirements as an actuator for arm-locking in LISA.

Thorpe, James Ira↗
NASA NTRS2008

Rightsizing LISA

The LISA science requirements and conceptual design have been fairly stable for over a decade. In the interest of reducing costs, the LISA Project at NASA has looked for simplifications of the architecture, at downsizing of subsystems, and at descopes of the entire mission. This is a natural activity of the formulation phase, and one that is particularly timely in the current NASA budgetary context. There is, and will continue to be, enormous pressure for cost reduction from both ESA and NASA, reviewers and the broader research community. Here, we review the rationale for the baseline architecture. and report recent efforts to find simplifications and other reductions that might lead to savings. A few possible simplifications have been found in the LISA baseline architecture. In the interest of exploring cost sensitivity, one moderate and one aggressive descope have been evaluated; the cost savings are modest and the loss of science is not.

Stebbins, Robin T.↗
NASA NTRS2008

LISA Technology Development at GSFC

The prime focus of LISA technology development efforts at NASA/GSFC has been in LISA interferometry, specifically in the area of laser frequency noise mitigation. Laser frequency noise is addressed through a combination of stabilization and common-mode rejection. Current plans call for two stages of stabilization, pre-stabilization to a local frequency reference and further stabilization using the constellation as a frequency reference. In order for these techniques to be used simultaneously, the pre-stabilization step must provide an adjustable frequency offset. Here, we report on a modification to the standard modulation/demodulation techniques used to stabilize to optical cavities that generates a frequency-tunable reference from a fixed-length cavity. This technique requires no modifications to the cavity itself and only minor modifications to the components. The measured noise performance and dynamic range of the laboratory prototype meets the LISA requirements.

Thorpe, James Ira↗
NASA NTRS2009

Rightsizing LISA

The LISA science requirements and conceptual design have been fairly stable for over a decade. In the interest of reducing costs, the LISA Project at NASA has looked for simplifications of the architecture, at downsizing of subsystems, and at descopes of the entire mission. This is a natural activity of the formulation phase, and one that is particularly timely in the current NASA budgetary context. There is, and will continue to be, enormous pressure for cost reduction from both ESA and NASA, reviewers and the broader research community. Here, the rationale for the baseline architecture is reviewed, and recent efforts to find simplifications and other reductions that might lead to savings are reported. A few possible simplifications have been found in the LISA baseline architecture. In the interest of exploring cost sensitivity, one moderate and one aggressive descope have been evaluated; the cost savings are modest and the loss of science is not.

Stebbins, Robin T.↗
NASA NTRS2009

Data Analysis for the LISA Pathfinder Mission

The LTP (LISA Technology Package) is the core part of the Laser Interferometer Space Antenna (LISA) Pathfinder mission. The main goal of the mission is to study the sources of any disturbances that perturb the motion of the freely-falling test masses from their geodesic trajectories as well as 10 test various technologies needed for LISA. The LTP experiment is designed as a sequence of experimental runs in which the performance of the instrument is studied and characterized under different operating conditions. In order to best optimize subsequent experimental runs, each run must be promptly analysed to ensure that the following ones make best use of the available knowledge of the instrument ' In order to do this, all analyses must be designed and tested in advance of the mission and have sufficient built-in flexibility to account for unexpected results or behaviour. To support this activity, a robust and flexible data analysis software package is also required. This poster presents two of the main components that make up the data analysis effort: the data analysis software and the mock-data challenges used to validate analysis procedures and experiment designs.

Thorpe, James Ira↗
NASA NTRS2009

Black-hole Merger Simulations for LISA Science

The strongest expected sources of gravitational waves in the LISA band are the mergers of massive black holes. LISA may observe these systems to high redshift, z>10, to uncover details of the origin of massive black holes, and of the relationship between black holes and their host structures, and structure formation itself. These signals arise from the final stage in the development of a massive black-hole binary emitting strong gravitational radiation that accelerates the system's inspiral toward merger. The strongest part of the signal, at the point of merger, carries much information about the system and provides a probe of extreme gravitational physics. Theoretical predictions for these merger signals rely on supercomputer simulations to solve Einstein's equations. We discuss recent numerical results and their impact on LISA science expectations.

Kelly, Bernard J.↗
NASA NTRS2009

Measuring Massive Black Hole Binaries with LISA

The coalescence of two massive black holes produces gravitational waves (GWs) which can be detected by the space-based detector LISA. By measuring these waves, LISA can determine the various parameters which characterize the source. Measurements of the black hole masses and spins will provide information about the growth of black holes and their host galaxies over time. Measurements of a source's sky position and distance may help astronomers identify an electromagnetic counterpart to the GW event. The counterpart's redshift, combined with the GW-measured luminosity distance, can then be used to measure the Hubble constant and the dark energy parameter $w$. Because the potential science output is so high, it is useful to know in advance how well LISA can measure source parameters for a wide range of binaries. We calculate expected parameter estimation errors using the well-known Fisher matrix method. Our waveform model includes the physics of spin precession, as well as subleading harmonics. When these higher-order effects are not included, strong degeneracies between some parameters cause them to be poorly determined by a GW measurement. When precession and subleading harmonics are properly included, the degeneracies are broken, reducing parameter errors by one to several orders of magnitude.

Lang, Ryan N.↗
NASA NTRS2009

The LISA Pathfinder Mission

LISA Pathfinder (formerly known as SMART-2) is a European Space Agency (ESA) mission designed to pave the way for the joint ESA/NASA Laser Interferometer Space Antenna (LISA) mission by testing in flight the critical technologies required for spaceborne gravitational wave detection: it will put two test masses in a near-perfect gravitational free-fall and control and measure their motion with unprecedented accuracy. LISA Pathfinder is currently in the integration and test phase of the development, and is due to be launched on a dedicated launch vehicle in late 2011, with first results on the performance of the system being available approx 6 months later. This poster will describe the mission in detail, give the current status of the spacecraft development, and highlight the future milestones in the integration and test campaign.

Stebbins, Robin↗
NASA NTRS2009

Mitigation of Laser Frequency Noise for LISA

The Laser Interferometer Space Antenna (LISA) is a proposed detector of gravitational waves in the 0.1 mHz - 0.1 Hz band. LISA will measure gravitational wave strain at the 10(exp -21) level by monitoring the distance between freely-falling test masses s(exp -11) m. These distance measurements will be made using heterodyne interferometry with multiple light sources on moving platforms with changing baselines, all of which cause frequency noise to couple into the displacement measurement. I will describe how LISA interferometry mitigates the effects of laser frequency noise through active suppression and common mode rejection. Recent laboratory developments will also be discussed.

Thorpe, Ira J.↗
NASA NTRS2010

A LISA Interferometry Primer

A key challenge for all gravitational wave detectors in the detection of changes in the fractional difference between pairs of test masses with sufficient precision to measure astrophysical strains with amplitudes on the order of approx.10(exp -21). ln the case of the five million km arms of LISA, this equates to distance measurements on the ten picometer level. LISA interferometry utilizes a decentralized topology, in which each of the sciencecraft houses its own light sources, detectors, and electronics. The measurements made at each of the sciencecraft are then telemetered to ground and combined to extract the strain experienced by the constellation as a whole. I will present an overview of LISA interferometry and highlight some of the key components and technologies that make it possible.

Thorpe, James Ira↗
NASA NTRS2010

Development of Fiber-Based Laser Systems for LISA

We present efforts on fiber-based laser systems for the LISA mission at the NASA Goddard Space Flight Center. A fiber-based system has the advantage of higher robustness against external disturbances and easier implementation of redundancies. For a master oscillator, we are developing a ring fiber laser and evaluating two commercial products, a DBR linear fiber laser and a planar-waveguide external cavity diode laser. They all have comparable performance to a traditional NPRO at LISA band. We are also performing reliability tests of a 2-W Yb fiber amplifier and radiation tests of fiber laser/amplifier components. We describe our progress to date and discuss the path to a working LISA laser system design.

Numata, Kenji↗
NASA NTRS2010

Preliminary LISA Telescope Spacer Design

The Laser Interferometric Space Antenna (LISA) mission observes gravitational waves by measuring the separations between freely floating proof masses located 5 million kilometers apart with an accuracy of approximately 10 picometers. The separations are measured interferometrically. The telescope is an afocal Cassegrain style design with a magnification of 80x. The entrance pupil has a 40 cm diameter and will either be centered on-axis or de-centered off-axis to avoid obscurations. Its two main purposes are to transform the small diameter beam used on the optical bench to a diffraction limited collimated beam to efficiently transfer the metrology laser between spacecraft, and to receive the incoming light from the far spacecraft. It transmits and receives simultaneously. The basic optical design and requirements are well understood for a conventional telescope design for imaging applications, but the LISA design is complicated by the additional requirement that the total optical path through the telescope must remain stable at the picometer level over the measurement band during the mission to meet the measurement accuracy. This poster describes the requirements for the telescope and the preliminary work that has been done to understand the materials and mechanical issues associated with the design of a passive metering structure to support the telescope and to maintain the spacing between the primary and secondary mirrors in the LISA on-orbit environment. This includes the requirements flowdown from the science goals, thermal modeling of the spacecraft and telescope to determine the expected temperature distribution,layout options for the telescope including an on- and off-axis design, and plans for fabrication and testing.

Livas, J.↗