Session G16: Technology for Space-Based Gravitational-Wave Detectors

Live

The early successes of ground-based gravitational wave astronomy have dramatically illustrated the power and promise of this new technique for understanding our universe. As impressive as they are, these results are only the beginning. Additional discoveries await as ground-based detectors are improved and new facilities provide access to other regions of the gravitational-wave spectrum. The ESA/NASA Laser Interferometer Space Antenna (LISA) will play an important role by making the first observations in the milliHertz band, a regime expected to have a rich set of astrophysical sources. LISA’s mission concept and science case have been developed for several decades and have consistently garnered positive recommendations from review committees. More recently, LISA’s technical readiness has been bolstered by two flight demonstrations: the ESA/NASA LISA Pathfinder (2015-2017) mission and the Laser Ranging Instrument on the US-German GRACE-FO mission (2018-). I will highlight the LISA-relevant results of these two missions and provide an update on progress in the development of LISA itself.   

Live

LISA, the planned space-based gravitational wave observatory to complement the LIGO ground-based gravitational wave network of observatories, will extend the current capabilities to frequencies in the range of 0.1 mHz to 0.1 Hz, and the masses of binary black hole mergers that may be observed from the current \textasciitilde 10 solar mass pairs to \textasciitilde 10 M solar masses. Although the nominal launch date for LISA is in the early 2030's, current planning and technology development for the mission is focused on the much more immediate milestone of mission adoption, currently scheduled for the end of 2022. This gate marks the transition from the Project formulation phase into implementation, with a nominal lifecycle time to launch of \textasciitilde 8.5 years. An optical telescope is required to transmit laser beams between pairs of three widely spaced spacecraft arranged as an equilateral triangle to form a precision heterodyne interferometry metrology system, and must satisfy requirements that include a high degree of dimensional stability and careful pupil-plane imaging to avoid coupling angular jitter to displacement noise. We will describe the application, requirements, design, and current status of the technology development effort on the telescope.   

Live

Paraxial mode decompositions of a beam are a powerful tool to circumvent classical diffraction integrals for the propagation of a light distribution. Hermite Gauss modes provide a complete basis of functions to build any planar light distribution out of, and paraxial propagation of these modes is as simple as updating a modes q-factor. These modes are widely used in the laser community as they are also eigenfunctions of many optical resonators. They can even be used to, for example, accurately model light transmitted from one spacecraft to the next within the constellation of the upcoming Laser Interferometer Space Antenna (LISA) mission, as well as modeling the effects of wavefront aberrations to these beams. We discuss the validity of the paraxial wave approximation in the far field as a function of the diffraction angle or waist size. We go on to discuss the proper propagation matrix through free space between these modes as a correction to the paraxial propagation matrix i.e. the Identity.   

Live

Capacitive inertial reference sensors in space are a necessary technology for earth geodesy and gravitational wave observations past and future. They consist of a test mass (TM) in free fall surrounded by an electrode housing. In the space environment, the TM accrues electric charge that eventually pollutes the science measurement. To minimize electrostatic force noise contributions, it is necessary to maintain a near-neutral TM charge relative to the housing. The TM can be discharged in a contact-free manner, exploiting ultraviolet light via the photoelectric effect to preserve instrument sensitivity. Understanding the physics of UV light-based charge control is critical to the success of LISA, a gravitational wave detector in space to be launched in the early 2030s. The University of Florida's torsion pendulum is a ground-based experimental testbed of the free fall space environment. It is equipped with a LISA-like inertial sensor with a novel UV illumination scheme more robust to variations in photoemissivity and offering either increased redundancy or decreased complexity compared to the sensor on LISA. To test various charge control schemes, experiments using UV LEDs have been performed and match an analytical model developed to describe photon and photoelectron movement.   

Live

We present updated theoretical results for detecting gravitational waves with a levitated nano object optically suspended within a cavity as a complementary instrument to experiments like LIGO. Our experimental proposal is designed to detect gravitational waves in the 10's to 100's of Kilohertz bandwidth on a tabletop scale. The planned experimental setup is detailed and several optimizations to the proposal are outlined. Finally, the proposal is placed within the context of newly analysed predicted sources within such a frequency band.   

On Demand

The LISA observatory, a space based gravitational wave detector, consists of three drag-free spacecraft (SC) flying in an equilateral triangle formation. The SC motion is determined by their inertial reference sensors, which consist of a test mass (TM) in free fall at the level of fm/s$^{\mathrm{2}}$/Hz$^{\mathrm{1/2}}$ in the mHz band, surrounded by an electrode housing (EH). Due to the charge build-up caused largely by cosmic rays, the LISA TMs will need to be discharged to minimize the effect of electrostatic forces on gravitational wave observations. Contactless discharge can be performed using photoemission under illumination by ultraviolet light with a wavelength around 250 nm. One of NASA's technology contributions to this ESA led mission is the development of a Charge Management Device (CMD) responsible for maintaining a neutral TM potential with respect to its EH. The use of ultraviolet LEDs (UV LEDs) as a light source has many advantages over previously used Hg lamps such as the ability to run them in a pulsed mode that can be synchronized with 100 kHz electric fields around the test mass, as well as low size, weight and power consumption. The status of the LISA CMD hardware development will be presented, as well as some of the initial performance and lifetime testing results from the UV LEDs.   

On Demand

Gravitational wave missions like the Laser Interferometer Space Antenna (LISA) and future Earth geodesy missions use reference isolated bodies called test masses (TM) in free-fall within each spacecraft. Their motion is measured by laser interferometer and capacitive sensing systems. These and related technologies are tested within the torsion pendulum, an experimental testbed comprised of four cubic TMs at the ends of two identical orthogonal rods suspended from a 1 meter long, 50-micron diameter tungsten fiber. Each TM represents an inertial sensor in a near free-fall condition in the torsional degree of freedom, close to the required performance for space-based gravitational missions. Capacitive sensors measure the position for two opposite TMs while the other two are end points for the Torsion Pendulum Interferometer (TPI). The TPI is a Mach-Zehnder and homodyne interferometer that measures the differential motion between the TMs with a target sensitivity below 100 pm/sqrt(Hz) in the mHz band. It uses focusing optics to maintain contrast for over a 1 mm range of motion, polarization multiplexing to maximize sensitivity, and two output beams to reject common noise. The performance of the University of Florida torsion pendulum and upgraded interferometer system is presented.