Astrometric Telescope Facility isolation and pointing study

The Astrometric Telescope Facility (ATF), an optical telescope designed to detect extrasolar planetary systems, is scheduled to be a major user of the Space Station's Payload Pointing System (PPS). However, because the ATF has such a stringent pointing stability specification and requires + or - 180 deg roll about its line of sight, mechanisms to enhance the basic PPS capability are required. The ATF pointing performance achievable by the addition of a magnetic isolation and pointing system (MIPS) between the PPS upper gimbal and the ATF, and separately, by the addition of a passive isolation system between the Space Station and the PPS base was investigated. The candidate MIPS can meet the ATF requirements in the presence of a 0.01 g disturbance. It fits within the available annular region between the PPS and the ATF while meeting power and weight limitations and providing the required roll motion, payload data and power services. By contrast, the passive base isolator system must have an unrealistically low isolation bandwidth on all axes to meet ATF pointing requirements and does not provide roll about the line of sight

Dose, exposure time, and resolution in Serial X-ray Crystallography

The resolution of X-ray diffraction microscopy is limited by the maximum dose that can be delivered prior to sample damage. In the proposed Serial Crystallography method, the damage problem is addressed by distributing the total dose over many identical hydrated macromolecules running continuously in a single-file train across a continuous X-ray beam, and resolution is then limited only by the available molecular and X-ray fluxes and molecular alignment. Orientation of the diffracting molecules is achieved by laser alignment. We evaluate the incident X-ray fluence (energy/area) required to obtain a given resolution from (1) an analytical model, giving the count rate at the maximum scattering angle for a model protein, (2) explicit simulation of diffraction patterns for a GroEL-GroES protein complex, and (3) the frequency cut off of the transfer function following iterative solution of the phase problem, and reconstruction of an electron density map in the projection approximation. These calculations include counting shot noise and multiple starts of the phasing algorithm. The results indicate counting time and the number of proteins needed within the beam at any instant for a given resolution and X-ray flux. We confirm an inverse fourth power dependence of exposure time on resolution, with important implications for all coherent X-ray imaging. We find that multiple single-file protein beams will be needed for sub-nanometer resolution on current third generation synchrotrons, but not on fourth generation designs, where reconstruction of secondary protein structure at a resolution of 0.7 nm should be possible with short exposures.Comment: 19 pages, 7 figures, 1 tabl

Phasemeter core for intersatellite laser heterodyne interferometry: modelling, simulations and experiments

Inter satellite laser interferometry is a central component of future space-borne gravity instruments like LISA, eLISA, NGO and future geodesy missions. The inherently small laser wavelength allows to measure distance variations with extremely high precision by interfering a reference beam with a measurement beam. The readout of such interferometers is often based on tracking phasemeters, able to measure the phase of an incoming beatnote with high precision over a wide range of frequencies. The implementation of such phasemeters is based on all digital phase-locked loops, hosted in FPGAs. Here we present a precise model of an all digital phase locked loop that allows to design such a readout algorithm and we support our analysis by numerical performance measurements and experiments with analog signals.Comment: 17 pages, 6 figures, accepted for publication in CQ

Towards the Design of Gravitational-Wave Detectors for Probing Neutron-Star Physics

The gravitational waveform of merging binary neutron stars encodes information about extreme states of matter. Probing these gravitational emissions requires the gravitational-wave detectors to have high sensitivity above 1 kHz. Fortunately for current advanced detectors, there is a sizeable gap between the quantum-limited sensitivity and the classical noise at high frequencies. Here we propose a detector design that closes such a gap by reducing the high-frequency quantum noise with an active optomechanical filter, frequency-dependent squeezing, and high optical power. The resulting noise level from 1 kHz to 4 kHz approaches the current facility limit and is a factor of 20 to 30 below the design of existing advanced detectors. This will allow for precision measurements of (i) the post-merger signal of the binary neutron star, (ii) late-time inspiral, merger, and ringdown of low-mass black hole-neutron star systems, and possible detection of (iii) high-frequency modes during supernovae explosions. This design tries to maximize the science return of current facilities by achieving a sensitive frequency band that is complementary to the longer-baseline third-generation detectors: the10 km Einstein Telescope, and 40 km Cosmic Explorer. We have highlighted the main technical challenges towards realizing the design, which requires dedicated research programs. If demonstrated in current facilities, the techniques can be transferred to new facilities with longer baselines.Comment: 14 pages, 15 figures, published versio