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NASA NTRS2004

Self-Gravity Modeling for LISA

The Laser Interferometer Space Antenna (LISA) mission, a space based gravitational wave detector, uses laser metrology to measure distance fluctuations between proof masses aboard three spacecraft. The total acceleration disturbance to each proof mass is required to be below 3 x 10(exp 15) m/sq square root of Hz. Self-gravity noise due to spacecraft distortion and spacecraft motion is expected to be a significant contributor to the acceleration noise budget. To minimize these effects, the gravitational field at each proof mass must be kept as small, flat, and constant as possible. It is estimated that the static field must be kept below 5 x 10(exp -10) m/sq s with a gradient below 3 x 10(exp -8)/sq s in order to meet the required noise levels. Most likely it will not be possible to directly verify by measurements that the LISA spacecraft meets these requirements; they must be verified by models. The LISA Integrated Modeling team developed a new self-gravity tool that calculates the gravitational forces and moments on the proof masses to aid in the design and verification of the LISA spacecraft. We present here an overview of&e tool and the latest self-gravity results calculated using the current baseline design of LISA. We also present results of a self-gravity analysis of the ST-7 DRS package that will fly on the LISA Pathfinder mission.

Merkowitz, Stephen↗

NASA NTRS2010

LISA Technology Development and Risk Reduction at NASA

The Laser Interferometer Space Antenna (LISA) is a joint ESA-NASA project to design, build and operate a space-based gravitational wave detector based on a laser interferometer. LISA relies on several technologies that are either new to spaceflight or must perform at levels not previously demonstrated in a spaceflight environment. The ESA-led LISA Pathfinder mission is the main effort to demonstrate LISA technology. NASA also supports complementary ground-based technology development and risk reduction activities. This presentation will report the status of NASA work on micronewton thrusters, the telescope, the optical pointing subsystem and mission formulation. More details on some of these topics will be given in posters. Other talks and posters will describe NASA-supported work on the laser subsystem, the phasemeter, and aspects of the interferometry. Two flight-qualified clusters of four colloid micronewton thrusters, each capable of thrust Levels between 5 and 30 microNewton with a resolution less than 0.l microNewton and a thrust noise less than 0.1 microNewton/vHz (0.001 to 4 Hz), have been integrated onto the LISA Pathfinder spacecraft. The complementary ground-based development focuses on lifetime demonstration. Laboratory verification of failure models and accelerated life tests are just getting started. LISA needs a 40 cm diameter, afocal telescope for beam expansion/reduction that maintains an optical pathlength stability of approximately 1 pm/vHz in an extremely stable thermal environment. A mechanical prototype of a silicon carbide primary-secondary structure has been fabricated for stability testing. Two optical assemblies must point at different distant spacecraft with nanoradian accuracy over approximately 1 degree annual variation in the angle between the distant spacecraft. A candidate piezo-inchworm actuator is being tested in a suitable testbed. In addition to technology development, NASA has carried out several studies in support of the mission formulation. The results of systems engineering work on flight software, avionics and reliability will be summarized.

Stebbins, Robin T.↗

NASA NTRS2020

In-flight Testing of the Injection of the LISA Pathfinder Test Mass into a Geodesic

LISA Pathfinder is a technology demonstrator space mission, aimed at testing key technologies for detecting gravitational waves in space. The mission is the precursor of LISA, the first space gravitational waves observatory, whose launch is scheduled for 2034. The LISA Pathfinder scientific payload includes two gravitational reference sensors (GRSs), each one containing a test mass (TM), which is the sensing body of the experiment. A mission critical task is to set each TM into a pure geodesic motion, i.e. guaranteeing an extremely low acceleration noise in the sub-Hertz frequency bandwidth. The grabbing positioning and release mechanism (GPRM), responsible for the injection of the TM into a geodesic trajectory, was widely tested on ground, with the limitations imposed by the 1-g environment. The experiments showed that the mechanism, working in its nominal conditions, is capable of releasing the TM into free-fall fulfilling the very strict constraint imposed on the TM residual velocity, in order to allow its capture on behalf of the electrostatic actuation. However, the first in-flight releases produced unexpected residual velocity components, for both the TMs. Moreover, all the residual velocity components were greater than maximum value set by the requirements. The main suspect is that unexpected contacts took place between the TM and the surroundings bodies. As a consequence, ad hoc manual release procedures had to be adopted for the few following injections performed during the nominal mission. These procedures still resulted in non compliant TM states which were captured only after impacts. However, such procedures seem not practicable for LISA, both for the limited repeatability of the system and for the unmanageable time lag of the telemetry/telecommand signals (about 4400 s). For this reason, at the end of the mission, the GPRM was deeply tested in-flight, performing a large number of releases, according to different strategies. The tests were carried out in order to understand the unexpected dynamics and limit its effects on the final injection. Some risk mitigation maneuvers have been tested aimed at minimizing the vibration of the system at the release and improving the alignment between the mechanism and the TM. However, no overall optimal release strategy to be implemented in LISA could be found, because the two GPRMs behaved differently.

LISA↗

NASA NTRS2014

Free-Flight Experiments in LISA Pathfinder

The LISA Pathfinder mission will demonstrate the technology of drag-free test masses for use as inertial references in future space-based gravitational wave detectors. To accomplish this, the Pathfinder spacecraft will perform drag-free flight about a test mass while measuring the acceleration of this primary test mass relative to a second reference test mass. Because the reference test mass is contained within the same spacecraft, it is necessary to apply forces on it to maintain its position and attitude relative to the spacecraft. These forces are a potential source of acceleration noise in the LISA Pathfinder system that are not present in the full LISA configuration. While LISA Pathfinder has been designed to meet it's primary mission requirements in the presence of this noise, recent estimates suggest that the on-orbit performance may be limited by this 'suspension noise'. The drift-mode or free-flight experiments provide an opportunity to mitigate this noise source and further characterize the underlying disturbances that are of interest to the designers of LISA-like instruments. This article provides a high-level overview of these experiments and the methods under development to analyze the resulting data.

The technique of drag-free↗

NASA NTRS2009

Black Holes, Gravitational Waves, and LISA

Binary black hole mergers are central to many key science objectives of the Laser Interferometer Space Antenna (LISA). For many systems the strongest part of the signal is only understood by numerical simulations. Gravitational wave emissions are understood by simulations of vacuum General Relativity (GR). I discuss numerical simulation results from the perspective of LISA's needs, with indications of work that remains to be done. Some exciting scientific opportunities associated with LISA observations would be greatly enhanced if prompt electromagnetic signature could be associated. I discuss simulations to explore this possibility. Numerical simulations are important now for clarifying LISA's science potential and planning the mission. We also consider how numerical simulations might be applied at the time of LISA's operation.

Baker, John↗

NASA NTRS2013

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(exp−1/2) 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,

carbide↗

NASA NTRS2016

Sub-Femto-g Free Fall for Space-Based Gravitational Wave Observatories: LISA Pathfinder Results

We report the first results of the LISA Pathfinder in-flight experiment. The results demonstrate that two free-falling reference test masses, such as those needed for a space-based gravitational wave observatory like LISA, can be put in free fall with a relative acceleration noise with a square root of the power spectral density of 5.2 +/- 0.1 fm s(exp -2)/square root of Hz, or (0.54 +/- 0.01) x 10(exp -15) g/square root of Hz, with g the standard gravity, for frequencies between 0.7 and 20 mHz. This value is lower than the LISA Pathfinder requirement by more than a factor 5 and within a factor 1.25 of the requirement for the LISA mission, and is compatible with Brownian noise from viscous damping due to the residual gas surrounding the test masses. Above 60 mHz the acceleration noise is dominated by interferometer displacement readout noise at a level of (34.8 +/- 0.3) fm square root of Hz, about 2 orders of magnitude better than requirements. At f less than or equal to 0.5 mHz we observe a low-frequency tail that stays below 12 fm s(exp -2)/square root of Hz down to 0.1 mHz. This performance would allow for a space-based gravitational wave observatory with a sensitivity close to what was originally foreseen for LISA.

space science↗

NASA NTRS2017

The Lightweight Integrated Solar Array and anTenna (LISA-T) Big Power for Small Spacecraft

NASA is developing a space power system using lightweight, flexible photovoltaic devices originally developed for use here on Earth to provide low cost power for spacecraft. The Lightweight Integrated Solar Array and anTenna (LISA-T) is a launch stowed, orbit deployed array on which thin-film photovoltaic and antenna elements are embedded. The LISA-T system is deployable, building upon NASA's expertise in developing thin-film deployable solar sails such the one being developed for the Near Earth Asteroid Scout project which will fly in 2018. One of the biggest challenges for the NEA Scout, and most other spacecraft, is power. There simply isn't enough of it available, thus limiting the range of operation of the spacecraft from the Sun (due to the small surface area available for using solar cells), the range of operation from the Earth (low available power with inherently small antenna sizes tightly constrain the bandwidth for communication), and the science (you can only power so many instruments with limited power). The LISA-T has the potential to mitigate each of these limitations, especially for small spacecraft. Inherently, small satellites are limited in surface area, volume, and mass allocation; driving competition between their need for power and robust communications with the requirements of the science or engineering payload they are developed to fly. LISA-T is addressing this issue, deploying large-area arrays from a reduced volume and mass envelope - greatly enhancing power generation and communications capabilities of small spacecraft and CubeSats. The problem is that these CubeSats can usually only generate between 7W and 50W of power. The power that can be generated by the LISA-T ranges from tens of watts to several hundred watts, at a much higher mass and stowage efficiency. A matrix of options are in development, including planar (pointed) and omnidirectional (non-pointed) arrays. The former is seeking the highest performance possible while the latter is seeking GN&C simplicity. Options for leveraging both high performance, 'typical cost' triple junction thin-film solar cells as well as moderate performance, low cost cells are being developed. Alongside, UHF (ultrahigh frequency), S-band, and X-band antennas are being integrated into the array to move their space claim away from the spacecraft and open the door for more capable multi-element antenna designs such as those needed for spherical coverage and electronically steered phase arrays.

Space Exploration↗

NASA NTRS2017

The Lightweight Integrated Solar Array and anTenna (LISA-T) - Big Power for Small Spacecraft

NASA is developing a space power system using lightweight, flexible photovoltaic devices originally developed for use here on Earth to provide low cost power for spacecraft. The Lightweight Integrated Solar Array and anTenna (LISA-T) is a launch-stowed, orbit-deployed array on which thin-film photovoltaic and antenna elements are embedded. The LISA-T system is deployable, building upon NASA's expertise in developing thin-film deployable solar sails such the one being developed for the Near Earth Asteroid Scout project which will fly in 2018. One of the biggest challenges for the NEA Scout, and most other spacecraft, is power. There simply isn't enough of it available, thus limiting the range of operation of the spacecraft from the Sun (due to the small surface area available for using solar cells), the range of operation from the Earth (low available power with inherently small antenna sizes tightly constrain the bandwidth for communication), and the science (you can only power so many instruments with limited power). The LISA-T has the potential to mitigate each of these limitations. Inherently, small satellites are limited in surface area, volume, and mass allocation; driving competition between their need for power and robust communications with the requirements of the science or engineering payload they are developed to fly. LISA-T is addressing this issue, deploying large-area arrays from a reduced volume and mass envelope - greatly enhancing power generation and communications capabilities of small spacecraft and CubeSats. The problem is that these CubeSats can usually only generate between 7 watts and 50 watts of power. The power that can be generated by the LISA-T ranges from tens of watts to several hundred watts. A matrix of options are in development, including planar (pointed) and omnidirectional (non-pointed) arrays. The former is seeking the highest performance possible while the latter is seeking GN&C (Guidance, Navigation and Control) simplicity. In both cases, power generation ranges from tens of watts to several hundred with an expected specific power greater than 250 watts per kilogram and a stowed power density greater than 200 kilowatts per cubic meter. Options for leveraging both high performance, 'typical cost' triple junction thin-film solar cells as well as moderate performance, low cost cells are being developed. Alongside, both UHF (ultra high frequency) and S-band antennas are being integrated into the array to move their space claim away from the spacecraft and open the door for omnidirectional communications and electronically steered phase arrays.

Johnson, Les↗

NASA NTRS2023

Prototype Global Analysis of LISA Data with Multiple Source Types

The novel data analysis challenges posed by the Laser Interferometer Space Antenna (LISA) arise from the overwhelmingly large number of astrophysical sources in the measurement band and the density with which they are found in the data. Robust detection and characterization of the numerous gravitational wave sources in LISA data can not be done sequentially, but rather through a simultaneous global fit of a data model containing the full suite of astrophysical and instrumental features present in the data. While previous analyses have focused on individual source types in isolation, here we present the first demonstration of a LISA global fit analysis containing combined astrophysical populations. The prototype pipeline uses a blocked Metropolis Hastings algorithm to alternatingly fit to a population of ultra compact galactic binaries, known “verification binaries” already identified by electromagnetic observations, a population of massive black hole mergers, and an instrument noise model. The Global LISA Analysis Software Suite (GLASS) is assembled from independently developed samplers for the different model components. The modular design enables flexibility to future development by defining standard interfaces for adding new, or updating additional, components to the global fit without being overly prescriptive for how those modules must be internally designed. The GLASS pipeline is demonstrated on data simulated for the LISA Data Challenge 2b. Results of the analysis and a road-map for continued development are described in detail.

Gravitational Waves↗

NASA NTRSDate not supplied

Independent Reliability Assessment of the NASA GSFC Laser Transmitter for the LISA Program

The Laser Interferometer Space Antenna (LISA) is a partnership between the European Space Agency (ESA) and NASA to build a Gravitational Wave (GW) observatory. The observatory, which consists of a three-spacecraft constellation with a nominal separation of 2.5 million km between each spacecraft, provides a tool for scientists to directly detect gravitational waves generated from various astronomical phenomena in a waveband that is not accessible from Earth. NASA is developing laser transmitters as one of the potential US contributions to LISA. The NASA laser design leverages lessons learned from previous flight missions and included the latest technologies in photonics packaging and reliability engineering to ensure a laser lifetime of >16 years covering integration and test through a possible extended mission phase. As part of the laser development process, NASA’s Goddard Space Flight Center (GSFC) requested support from the NASA Engineering and Safety Center (NESC) to independently assess the Technology Readiness Level (TRL) of the LISA Laser System (LS). The independent assessment included the following tasks: (a) assess the design for weaknesses and suggest improvements to mitigate risks, (b) assess the laser reliability plan for weaknesses and suggest improvements to mitigate risks and improve effectiveness, and (c) assess the current redundancy plan on laser subsystems for weaknesses and suggest improvements to mitigate risks and improve effectiveness. The NESC team comprised of a team of subject matter experts (SMEs) and performed a 12-month review of every aspect of the laser design. We present the assessment findings and the current development progress of the LISA laser to meet the mission requirements with a delivery of a form, fit, and functional TRL6 laser to the LSIA mission by late 2023.

LISA↗

NASA NTRS2004

Microthrust Propulsion of the LISA Mission

We present the most recent propulsion requirements for the Laser Interferometer Space Antenna (LISA) Mission and describe potential microth ruster technology that can meet these requirements. LISA consists of three spacecraft in heliocentric orbits, forming a triangle with 5x l 0 (exp 6) km sides that are the arms of three Michelson-type interferometers. Reflective proof masses provide the reference surfaces at the end of the interferometer arms as part of the Gravitational Referenc e Sensor (GRS) designed to detect gravitational waves. The microthrus t propulsion system will be part of the Disturbance Reduction System (DRS), which is responsible for maintaining each spacecraft position w ithin approximately 10 nm around the proof masses. To provide the nec essary sensitivity, the GRS must not experience spurious acceleration s >15 (exp -10) m/ s(exp 2) in the 0.1 mHz to 1 Hz bandwidth, requiring precision formation flying and drag-free operation of the LISA spa cecraft. This leads to the following microthruster performance requir ements: a thrust range of 2-30 Micro N, a thrust resolution < 0.1 Mic ro N, and thrust noise <0.1 Hz(exp -1/2) over the LISA measurement bandwidth. The microthruster must provide this performance for 5 years c ontinuously, contain 10 years worth of propellant, and not disrupt th e science measurements. Potential microthruster technologies include Colloid, Field Emission Electric Propulsion (FEEP), and precision cold gas microthrusters. Each of these technologies is described in detai l with focus on the NASA microthruster development of the Busek Collo id Micro-Newton Thruster (CMNT).

Field Emission Electric Propulsion (FEEP)↗

NASA NTRSDate not supplied

Independent Reliability Assessment and Progress Review of the NASA GSFC Laser Transmitter for the LISA Program

NASA Goddard Space Flight Center (GSFC) has been actively developing the laser transmitter for the Laser Interferometer Space Antenna (LISA) program since the late 2017. In 2021 we delivered a prototype laser transmitter to the LISA program for performance evaluation as well as performed an independent technology assessment on the laser design supported by the NASA Engineering and Safety Center (NESC). We continued to further develop the LISA laser with a goal of advancing the technology readiness level (TRL) of the laser to 6 by the end of 2023. In this paper, we report on the progress we made on the laser development for the LISA program as well as the technology assessment findings by the NESC.

Independent Reliability Assessment↗

NASA NTRS1998

LISA Mission Concept Study, Laser Interferometer Space Antenna for the Detection and Observation of Gravitational Waves

This document presents the results of a design feasibility study for LISA (Laser Interferometer Space Antenna). The goal of LISA is to detect and study low-frequency astrophysical gravitational radiation from strongly relativistic regions. Astrophysical sources potentially visible to LISA include extra-galactic massive black hole binaries at cosmological distances, binary systems composed of a compact star and a massive black hole, galactic neutron star-black hole binaries, and background radiation from the Big Bang. The LISA mission will comprise three spacecraft located five million kilometers apart forming an equilateral triangle in an Earth-trailing orbit. Fluctuations in separation between shielded test masses located within each spacecraft will be determined by optical interferometry which determines the phase shift of laser light transmitted between the test masses.

Folkner, W. M.↗

NASA NTRS2005

Impact of LISA's Low Frequency Sensitivity on Observations of Massive Black Hole Mergers

LISA will be able to detect gravitational waves from inspiralling massive black hole (MBH) binaries out to redshifts z > 10. If the binary masses and luminosity distances can be extracted from the Laser Interferometer Space Antenna (LISA) data stream, this information can be used to reveal the merger history of MBH binaries and their host galaxies in the evolving universe. Since this parameter extraction generally requires that LISA observe the inspiral for a significant fraction of its yearly orbit, carrying out this program requires adequate sensitivity at low frequencies, f < 10(exp -4) Hz. Using several candidate low frequency sensitivities, we examine LISA's potential for characterizing MBH binary coalescences at redshifts z > 1.

Baker, J.↗

NASA NTRS2005

Laser frequency stabilization for LISA

The requirement on laser frequency noise in the Laser Interferometer Space Antenna (LISA) depends on the velocity and our knowledge of the position of each spacecraft of the interferometer. Currently it is assumed that the lasers must have a pre-stabilized frequency stability of 30Hz/square root of Hz over LISA'S most sensitive frequency band (3 mHz - 30 mHz). The intrinsic frequency stability of even the most stable com- mercial lasers is several orders of magnitude above this level. Therefore it is necessary to stabilize the laser frequency to an ultra-stable frequency reference which meets the LISA requirements. The baseline frequency reference for the LISA lasers are high finesse optical cavities based on ULE spacers. We measured the stability of two ULE spacer cavities with respect to each other. Our current best results show a noise floor at, or below, 30 Hz/square root of Hz above 3 mHz. In this report we describe the experimental layout of the entire experiment and discuss the limiting noise sources.

Mueller, Guido↗

NASA NTRS2005

Simulating Gravitational Radiation from Binary Black Holes Mergers as LISA Sources

A viewgraph presentation on the simulation of gravitational waves from Binary Massive Black Holes with LISA observations is shown. The topics include: 1) Massive Black Holes (MBHs); 2) MBH Binaries; 3) Gravitational Wavws from MBH Binaries; 4) Observing with LISA; 5) How LISA sees MBH binary mergers; 6) MBH binary inspirals to LISA; 7) Numerical Relativity Simulations; 8) Numerical Relativity Challenges; 9) Recent Successes; 10) Goddard Team; 11) Binary Black Hole Simulations at Goddard; 12) Goddard Recent Advances; 13) Baker, et al.:GSFC; 13) Starting Farther Out; 14) Comparing Initial Separation; 15) Now with AMR; and 16) Conclusion.

Baker, John↗

NASA NTRS2008

Current LISA Spacecraft Design

The Laser Interferometer Space Antenna (LISA) mission, a space based gravitational wave detector, uses laser metrology to measure distance fluctuations between proof masses aboard three spacecraft. LISA is unique from a mission design perspective in that three spacecraft and their associated operations form one distributed science instrument, unlike more conventional missions where an instrument is a component of an individual spacecraft. The design of the LiSA spacecraft is also tightly coupled to the design and requirements of the scientific payload; for this reason it is often referred to as a "sciencecraft." A detailed discussion will be presented that describes the current spacecraft design and mission architecture needed to meet the LISA science requirements.

Merkowitz, Stephen↗