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NASA NTRS2010

LISA Telescope Spacer Design Issues

The LISA mission observes gravitational waves by measuring the separations between freely floating proof masses located 5 million kilometers apart with an accuracy of - 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. We describe the mechanical 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. Plans for fabrication and testing will be outlined.

Livas, Jeff↗

NASA NTRS2011

LISA: Opening New Horizons

The Laser Interferometer Space Antenna (LISA) is a space-borne observatory that will open the low frequency (approx.0.1-100 mHz) gravitational wave window on the universe. LISA will observe a rich variety of gravitational wave sources, including mergers of massive black holes, captures of stellar black holes by massive black holes in the centers of galaxies, and compact Galactic binaries. These sources are generally long-lived, providing unprecedented opportunities for multi-messenger astronomy in the transient sky. This talk will present an overview of these scientific arenas, highlighting how LISA will enable stunning discoveries in origins, understanding the cosmic order, and the frontiers of knowledge.

Centrella, Joan M.↗

NASA NTRS2014

LISA Pathfinder and eLISA news

Two important gatherings of the space-based gravitational-wave detector community were held in Zurich, Switzerland this past March. The first was a meeting of the Science Working Team for LISA Pathfinder (LPF), a dedicated technology demonstrator mission for a future LISA-like gravitational wave observatory. LPF is entering an extremely exciting phase with launch less than 15 months away. All flight components for both the European science payload, known as the LISA Technology Package (LTP), and the NASA science payload, known as the Space Technology 7 Disturbance Reduction System (ST7-DRS), have been delivered and are undergoing integration. The final flight component for the spacecraft bus, a cold-gas thruster based on the successful GAIA design, will be delivered later this year. Current focus is on completing integration of the science payload (see Figures 1 and 2) and preparation for operations and data analysis. After a launch in Summer 2015, LPF will take approximately 90 days to reach its operational orbit around the Earth-Sun Lagrange point (L1), where it will begin science operations. After 90 days of LTP operations followed by 90 days of DRS operations, LPF will have completed its prime mission of paving the way for a space-based observatory of gravitational waves in the milliHertz band. Immediately following the meeting of the LPF team, the eLISA consortium held its third progress meeting. The consortium (www.elisascience.org) is the organizing body of the European space-based gravitational-wave community, and it was responsible for the "The Gravitational Universe" whitepaper that resulted in the November 2013 election of a gravitational-wave science theme for ESA's Cosmic Visions L3 opportunity. In preparation for an L3 mission concept call, which is expected later this decade, and for launch in the mid 2030s, the eLISA consortium members are coordinating technology development and mission study activities which will build on the LPF results. The final mission concept is expected to include some international (non-European) contributions, and NASA has expressed an interest in participating in this ground-breaking mission. The US research community supports such a collaboration, or any other mission scenario that achieves the high-priority science of a space-based gravitational-wave observatory at the earliest possible date.

pathfinder↗

NASA NTRS2015

Advancements of the Lightweight Integrated Solar Array and Transceiver (LISA-T) Small Spacecraft System

This paper describes recent advancements of the Lightweight Integrated Solar Array and Transceiver (LISA-T) currently being developed at NASA's Marshall Space Flight Center. The LISA-T array comprises a launch stowed, orbit deployed structure on which thin-film photovoltaic (PV) and antenna devices are embedded. The system provides significant electrical power generation at low weights, high stowage efficiency, and without the need for solar tracking. Leveraging high-volume terrestrial-market PVs also gives the potential for lower array costs. LISA-T is addressing the power starvation epidemic currently seen by many small-scale satellites while also enabling the application of deployable antenna arrays. Herein, an overview of the system and its applications are presented alongside sub-system development progress and environmental testing plans/initial results.

Russell, Tiffany↗

NASA NTRS2015

Advancements of the Lightweight Integrated Solar Array and Transceiver (LISA-T) Small Spacecraft System

Lockett, Tiffany Russell↗

NASA NTRS2016

The Lightweight Integrated Solar Array and Transceiver (LISA-T): Second Generation Advancements and the Future of SmallSat Power Generation

This paper describes the second generation advancements of the Lightweight Integrated Solar Array and Transceiver (LISA-T) currently being developed at NASA's Marshall Space Flight Center. LISA-T is a launch stowed, orbit deployed array on which thin-film photovoltaic and antenna elements are embedded. Inherently, small satellites are limited in surface area, volume, and mass allocation; driving competition between power, communications, and GN&C (guidance navigation and control) subsystems. This restricts payload capability and limits the value of these low-cost satellites. 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. 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. In both cases, power generation ranges from tens of watts to several hundred with an expected specific power >250W/kg and a stowed power density >200kW/m(sub 3). 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.

Carr, John A.↗

NASA NTRS2017

Drag-Free Performance of the ST7 Disturbance Reduction System Flight Experiment on the LISA Pathfinder

The Space Technology-7 Disturbance Reduction System (DRS) is an experiment package aboard the European Space Agency (ESA) LISA Pathfinder spacecraft. LISA Pathfinder launched from Kourou, French Guiana on December 3, 2015. The DRS is tasked to validate two specific technologies: colloidal micro-Newton thrusters (CMNT) to provide low-noise control capability of the spacecraft, and drag-free controlflight. This validation is performed using highly sensitive drag-free sensors, which are provided by the LISA Technology Package of the European Space Agency. The Disturbance Reduction System is required to maintain the spacecrafts position with respect to a free-floating test mass to better than 10nm/(square root of Hz), along its sensitive axis (axis in optical metrology). It also has a goal of limiting the residual accelerations of any of the two test masses to below 30 x 10(exp -14) (1 + ([f/3 mHz](exp 2))) m/sq s/(square root of Hz), over the frequency range of 1 to 30 mHz.This paper briefly describes the design and the expected on-orbit performance of the control system for the two modes wherein the drag-free performance requirements are verified. The on-orbit performance of these modes are then compared to the requirements, as well as to the expected performance, and discussed.

Attitude Control↗

NASA NTRS2017

Drag-Free Performance of the ST7 Disturbance Reduction System Flight Experiment on the LISA Pathfinder

The Space Technology-7 Disturbance Reduction System (DRS) is an experiment package aboard the European Space Agency (ESA) LISA Pathfinder spacecraft. LISA Pathfinder launched from Kourou, French Guiana on December 3, 2015. The DRS is tasked to validate two specific technologies: colloidal micro-Newton thrusters (CMNT) to provide low-noise control capability of the spacecraft, and drag-free control flight. This validation is performed using highly sensitive drag-free sensors, which are provided by the LISA Technology Package of the European Space Agency. The Disturbance Reduction System is required to maintain the spacecrafts position with respect to a free-floating test mass to better than 10nmHz, along its sensitive axis (axis in optical metrology). It also has a goal of limiting the residual accelerations of any of the two test masses to below 30 (1 + [f3 mHz]) fmsHz, over the frequency range of 1 to 30 mHz.This paper briefly describes the design and the expected on-orbit performance of the control system for the two modes wherein the drag-free performance requirements are verified. The on-orbit performance of these modes are then compared to the requirements, as well as to the expected performance, and discussed.

Attitude Control↗

NASA NTRS2018

Possible LISA Technology Applications for Other Missions

The Laser Interferometer Space Antenna (LISA) has been selected as the third large class mission launch opportunity of the Cosmic Visions Program by the European Space Agency (ESA). LISA science will explore a rich spectrum of astrophysical gravitational-wave sources expected at frequencies between 0.0001 and 0.1 Hz and complement the work of other observatories and missions, both space and ground-based, electromagnetic and non-electromagnetic. Similarly, LISA technology may find applications for other missions. This paper will describe the capabilities of some of the key technologies and discuss possible contributions to other missions.

Livas, Jeffrey↗

NASA NTRS2018

Gravitational Wave Sources as Timing References for LISA Data

In the megahertz gravitational-wave band, galactic ultra-compact binaries (UCBs) are continuous sources emitting at near-constant frequency. The signals from many of these galactic binaries will be sufficiently strong to be detectable by the Laser Interferometer Space Antenna (LISA) after approximately Omicron (1 week) of observing. In addition to their astrophysical value, these UCBs can be used to monitor the data quality of the observatory. This paper demonstrates the capabilities of galactic UCBs to be used as calibration sources for LISA by demanding signal coherence between adjacent week-long data segments separated by a gap in time of a priori unknown duration. A parameter for the gap duration is added to the UCB waveform model and used in a Markov-chain Monte Carlo algorithm simultaneously fitting for the astrophysical source parameters. Results from measurements of several UCBs are combined to produce a joint posterior on the gap duration. The measurement accuracy's dependence on how much is known about the UCBs through prior observing, and seasonal variations due to the LISA orbital motion, is quantified. The duration of data gaps in a two-week segment of data can be constrained to within approximately 0.2 s using Omicron (10) UCBs after one month of observing. The timing accuracy from UCBs improves to approximately or less than o.1 s after 1 year of mission operations. These results are robust to within a factor of approximately 2 when taking into account seasonal variations.

Gravitation Wave Sources↗

NASA NTRS2019

Space Based Gravitational Wave Astronomy Beyond LISA

The Laser Interferometer Space Antenna (LISA) will open three decades of gravitational wave(GW) spectrum between 0.1 and 100 mHz, the mHz band [1]. This band is expected to be the richest part of the GW spectrum, in types of sources, numbers of sources, signal-to-noise ratios and discovery potential. When LISA opens the low-frequency window of the gravitational wave spectrum,around 2034, the surge of gravitational-wave astronomy will strongly compel a subsequent mission to further explore the frequency bands of the GW spectrum that can only be accessed from space. The 2020's is the time to start developing technology and studying mission concepts for a large-scale mission to be launched in the 2040's. The mission concept would then be proposed to Astro2030. Only space-based missions can access the GW spectrum between 108 and 1 Hz because of the Earth's seismic noise. This white paper surveys the science in this band and mission concepts that could accomplish that science. The proposed small scale activity is a technology development program that would support a range of concepts and a mission concept study to choose a specific mission concept for Astro2030. In this white paper, we will refer to a generic GW mission beyond LISA as bLISA.

Baker, John↗

NASA NTRS2019

Multi-axis Heterodyne Interferometry at MHz Frequencies: a Short-Arm Measurement Demonstration for LISA with Off-The-Shelf Hardware

We report the design, construction, and operation of a multi-axis heterodyne interferometry (MAHI) system operating at MHz heterodyne frequencies, which provides a testbed for technologies to be used in the Laser Interferometer Space Antenna (LISA) space-based gravitational wave mission. The system was calibrated for measurement of the piston, pitch, and yaw of a three-axis piezo-actuated mirror, giving measured calibration values that closely match those predicted by a simulation based on Gaussian beam tracing. The piston sensitivity of the MAHI system in the LISA band was measured to be below 10pmHz 1/2 10pmHz1/2 for frequencies above 4 mHz and below 1pmHz 1/2 1pmHz1/2 for frequencies above 35 mHz. The sensitivity is limited above 2 Hz by the mechanical vibrations of the apparatus and below 1 mHz by dimensional changes caused by temperature fluctuations. Evidence points towards scattered light as the limiting noise source at intermediate frequencies. The angular sensitivity of the MAHI system was measured to be close to or below 10nradHz 1/2 10nradHz1/2 for frequencies above 4 mHz and below 1nradHz 1/2 1nradHz1/2 for frequencies above 100 mHz. Noise budgets for both length and angle were determined, indicating the areas in which improvements must be made in order to reach increased sensitivity. The current operating sensitivity already provides a useful testbed for LISA technologies and a potential blueprint for future ground segment equipment.

Fulda, P.↗

NASA NTRSDate not supplied

Independent Reliability Assessment of the Laser Transmitter for the ESA-NASA Laser Interferometer Space Antenna (LISA) Program

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 presentation will focus on 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 LISA mission by late 2023.

Laser Interferometry↗

NASA NTRSDate not supplied

Advancement of the Laser System for the LISA Mission

NASA Goddard Space Flight Center (GSFC) is developing the Laser System (LS) for the Laser Interferometer Space Antenna (LISA) mission, led by the European Space Agency (ESA) with a launch date of 2035. In this talk, we will present the roadmap in advancing the LISA Laser System to meet the LISA mission requirements.

Anthony W. Yu↗

NASA NTRS2006

Engineering the LISA Project: Systems Engineering Challenges

The Laser Interferometer Space Antenna (LISA) is a joint NASA/ESA mission to detect and measure gravitational waves with periods from 1 s to 10000 s. The systems engineering challenges of developing a giant interferometer, 5 million kilometers on a side, an: numerous. Some of the key challenges are presented in this paper. The organizational challenges imposed by sharing the engineering function between three centers (ESA ESTEC, NASA GSFC, and JPL) across nine time zones are addressed. The issues and approaches to allocation of the acceleration noise and measurement sensitivity budget terms across a traditionally decomposed system are discussed. Additionally, using LISA to detect gravitational waves for the first time presents significant data analysis challenges, many of which drive the project system design. The approach to understanding the implications of science data analysis on the system is also addressed.

systems engineering↗

NASA NTRS2006

Overview of the LISA Phasemeter

The LISA phasemeter is required to measure the phase of an electrical signal with an error less than 3 (micro)cycles/pHz over times scales from 1 to 1000 seconds. This phase sensitivity must be achieved in the presence of laser phase fluctuations 108 times larger than the target sensitivity. Other challenging aspects of the measurement are that the heterodyne frequency varies from 2 to 20 MHz and the signal contains multiple frequency tones that must be measured. The phasemeter architecture uses high-speed analog to digital conversion followed by a digital phase locked loop. An overview of the phasemeter architecture is presented along with results for the breadboard LISA Phasemeter demonstrating that critical requirements are met.

offset phase locks↗

NASA NTRS2002

LISA phase measurement technique

The LISA mission will form the equivalent of a Michelson interferometric beat signal from the 1064nm laser beams traversing the inter-spacecraft arms. The design gravitational wave sensitivity requires measurement of round trip path differences for each detector to be about 10 pddHz over a frequency range from 10^10-4 to 10^-1 Hz. Thus LISA'S phasemeter must measure the beat signal phase to 10^-5 cycle/square root of Hz at 1mHz. Doppler shifts between spacecraft in their orbits are expected to range from 1 to 15 MHz. Phase measurement using the digital phase-locked loop approach incorporated in a modified TurboRogue GPS receiver has been investigated in this study. It is found that only resolution in the range of 10^-4 to 10^-3 cycle/square root of Hz at 1 mHz is achievable with this hardware. Abrupt fluctuations in the phase measurement at the millicycle level are responsible for the limitation.

phasemeter↗

NASA NTRS1996

Getting Astrophysical Information from LISA Data

The gravitational wave signals from a large number of astrophysical sources will be present in the LISA data. Information about as many sources as possible must be estimated from time series of strain measurements...Here we describe a candidate process for disentangling the gravitational wave signals and estimating the relevant astrophysical parameters from one year of LISA data. Nearly all of the sources will be identified by searching with templates based on source parameters and directions.

LISA↗