LIGO vacuum system study

A laser interferometer gravitational wave observatory (LIGO) is being developed with sensitivities which will have a high probability of detecting gravitational waves from astrophysical sources. A major component of LIGO is a total of 16 km of 1.2 m (48 inch) diameter tube at a pressure of less than 10 to the minus 8th power torr. It will be of 304L stainless steel procured directly from the steel mills with the initial hydrogen content specially reduced. Projections of the outgassing rates of hydrogen and of water vapor as a function of time are given and the uncertainties discussed. Based on these, a preliminary analysis of the vacuum system is presented

Possible Space-Based Gravitational-Wave Observatory Mission Concept

The existence of gravitational waves was established by the discovery of the Binary Pulsar PSR 1913+16 by Hulse and Taylor in 1974, for which they were awarded the 1983 Nobel Prize. However, it is the exploitation of these gravitational waves for the extraction of the astrophysical parameters of the sources that will open the first new astronomical window since the development of gamma ray telescopes in the 1970's and enable a new era of discovery and understanding of the Universe. Direct detection is expected in at least two frequency bands from the ground before the end of the decade with Advanced LIGO and Pulsar Timing Arrays. However, many of the most exciting sources will be continuously observable in the band from 0.1-100 mHz, accessible only from space due to seismic noise and gravity gradients in that band that disturb ground-based observatories. This poster will discuss a possible mission concept, Space-based Gravitational-wave Observatory (SGO-Mid) developed from the original Laser Interferometer Space Antenna (LISA) reference mission but updated to reduce risk and cost

LISA Telescope Challenges

The LISA Mission proposal was selected by ESA's Science Program Committee (SPC) for the L3 Cosmic Visions launch opportunity, and is currently in a Phase A mission formulation study. An essential component of the instrument is a set of optical telescopes that make precision displacement measurements between pairs of proof masses that are flying drag-free in three separate satellites. We discuss the key requirements on the telescope, the current design, and discuss progress toward solving some of the key challenges for realizing the telescope designs

Time Domain Simulations of Arm Locking in LISA

Arm locking is a technique that has been proposed for reducing laser frequency fluctuations in the Laser Interferometer Space Antenna (LISA), a gravitational-wave observatory sensitive in the milliHertz frequency band. Arm locking takes advantage of the geometric stability of the triangular constellation of three spacecraft that comprise LISA to provide a frequency reference with a stability in the LISA measurement band that exceeds that available from a standard reference such as an optical cavity or molecular absorption line. We have implemented a time-domain simulation of arm locking including the expected limiting noise sources (shot noise, clock noise, spacecraft jitter noise, and residual laser frequency noise). The effect of imperfect a priori knowledge of the LISA heterodyne frequencies and the associated 'pulling' of an arm locked laser is included. We find that our implementation meets requirements both on the noise and dynamic range of the laser frequency.Comment: Revised to address reviewer comments. Accepted by Phys. Rev.

LISA data analysis I: Doppler demodulation

The orbital motion of the Laser Interferometer Space Antenna (LISA) produces amplitude, phase and frequency modulation of a gravitational wave signal. The modulations have the effect of spreading a monochromatic gravitational wave signal across a range of frequencies. The modulations encode useful information about the source location and orientation, but they also have the deleterious affect of spreading a signal across a wide bandwidth, thereby reducing the strength of the signal relative to the instrument noise. We describe a simple method for removing the dominant, Doppler, component of the signal modulation. The demodulation reassembles the power from a monochromatic source into a narrow spike, and provides a quick way to determine the sky locations and frequencies of the brightest gravitational wave sources.Comment: 5 pages, 7 figures. References and new comments adde

Silicon Carbide Telescope Investigations for the LISA Mission

Space-based gravitational wave (GW) detectors are conceived to detect GWs in the low frequency range (mili-Hertz) by measuring the distance between free-falling proof masses in spacecraft (SC) separated by 5 Gm. The reference in the last decade has been the joint ESA-NASA mission LISA. One of the key elements of LISA is the telescope since it simultaneously gathers the light coming from the far SC (approximately or equal to 100 pW) and expands, collimates and sends the outgoing beam (2 W) to the far SC. Demanding requirements have been imposed on the telescope structure: the dimensional stability of the telescope must be approximately or equal to 1pm Hz(exp1/2) at 3 mHz and the distance between the primary and the secondary mirrors must change by less than 2.5 micrometer over the mission lifetime to prevent defocussing. In addition the telescope structure must be light, strong and stiff. For this reason a potential on-axis telescope structure for LISA consisting of a silicon carbide (SiC) quadpod structure has been designed, constructed and tested. The coefficient of thermal expansion (CTE) in the LISA expected temperature range has been measured with a 1% accuracy which allows us to predict the shrinkage/expansion of the telescope due to temperature changes, and pico-meter dimensional stability has been measured at room temperature and at the expected operating temperature for the LISA telescope (around -6[deg]C). This work is supported by NASA Grants NNX10AJ38G and NX11AO26G