Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session K16: LISA Instrument PhysicsLive
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Sponsoring Units: DGRAV Chair: Paul Fulda, Univ. of Florida |
Sunday, April 18, 2021 1:30PM - 1:42PM Live |
K16.00001: Charge Management Numerical Modeling and Experimental Demonstrations for the LISA Gravitational Reference Sensor Samantha Parry Kenyon, John Siu, Anthony Dávila Álvarez, Stephen Apple, Taiwo Olatunde, Timothy Sumner, Guido Mueller, Peter Wass, John W. Conklin Capacitive inertial reference sensors in space are a necessary technology for earth geodesy and gravitational wave observations. 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. Numerical and analytical modeling of charge movement within the LISA Gravitational Reference Sensor (GRS) is being done to validate if advanced charge control methods remain below the allotted charge-induced force noise budget. In addition, experiments on the University of Florida torsion pendulum are being done to validate the model. Results will include the charge control simulation work, experimental results that match the simulation, and drawing conclusions on the most robust schemes for LISA. [Preview Abstract] |
Sunday, April 18, 2021 1:42PM - 1:54PM Live |
K16.00002: A UV LED-Based Charge Management System for the LISA Gravitational Reference Sensor Myles Clark, Ben Letson, Samantha Parry-Kenyon, Taiwo Olatunde, Simon Barke, Guido Mueller, Tim Sumner, Peter Wass, Mark Storm, John Conklin The LISA Gravitational Wave (GW) observatory consists of three drag-free Spacecraft (SC) flying in an equilateral triangle formation separated by 2.5 Gm in orbit around the Sun. Motion in each SC is determined by onboard Gravitational Reference Sensors (GRS) consisting of a Test Mass (TM) in free-fall surrounded by an Electrode Housing (EH) fixed to the SC. The GRS isolates the test mass from disturbances at the level of fm/s2/rtHz in the mHz band along the 2.5 Gm arm lengths. Due to charge build-up caused primarily by solar radiation and cosmic rays, stray electrostatic forces will begin to affect the GRS sensitivity and if left unchecked would interrupt GW observations. It is the job of the Charge Management System (CMS) to monitor and mitigate this charge build-up with minimal interruption. To achieve this, the CMS utilises the photoelectric effect to move charges between the gold-coated surfaces of the TM and EH using UV LEDs emitting around 250 nm. To maximise the flexibility of the CMS several modes of operation are being developed. Some are for discharging quickly while violating the sensitivity requirements for GW observation, while others discharge slowly without violation to extend observation windows. CMS operation in these different modes and the performance requirements they impose will be discussed in the presentation. [Preview Abstract] |
Sunday, April 18, 2021 1:54PM - 2:06PM Live |
K16.00003: Hardware Development and Environmental Test Results for the TRL 5 LISA Charge Management Device Ben Letson, Samantha Parry Kenyon, Myles Clark, Taiwo Olatunde, Simon Barke, Guido Mueller, Peter Wass, Mark Storm, John W. Conklin 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 team at the University of Florida has recently developed a breadboard CMD to demonstrate technology readiness level 5. Validation of the unit will include over 1600 hours of thermal vacuum testing as well as shock and vibration testing of the full system. CMD environmental test results as well as the performance of the UV LEDs will be presented. [Preview Abstract] |
Sunday, April 18, 2021 2:06PM - 2:18PM Live |
K16.00004: The LISA Telescope Test Structure Alignment Analysis for Dimensional Stability Testing Ada Uminska, Jose Sanjuan, Soham Kulkarni, Joseph Gleason, Paul Fulda, Guido Mueller The LISA telescope is a critical part of the LISA instrument and has to meet pm/$\surd $Hz length stability requirements within the LISA band and \textmu m length stability over the ten-year lifetime of the mission. Our group is developing ground support equipment (GSE) to verify that the telescope meets these requirements. The GSE consists of a telescope test structure (TTS) which allows to integrate the telescope into an optical cavity. In this talk we report on the optical design (length, mirror radii of curvature) and the resulting internal and external alignment tolerances and requirements as well as the robustness against dynamic (in-band) misalignments. [Preview Abstract] |
Sunday, April 18, 2021 2:18PM - 2:30PM Live |
K16.00005: Using Allvar to Create Near-Zero CTE Structures Suitable for Space Missions Daniel George, Soham Kulkarni, Ada Uminska, Joseph Gleason, Josep Sanjuan, Paul Fulda, Guido Mueller, Jeremy McAllister, James Monroe, Ilya Gavrilyuk ALLVAR Alloys are Titanium-based metals which have the unique property of a negative coefficient of thermal expansion (CTE). They enable the construction of non-magnetic compact support structures with near zero CTE by matching it with positive CTE materials such as regular Titanium. These structures will find many applications in space telescope missions for significantly reducing the wavefront error caused by differential thermal expansion. Our group is characterizing a test structure in which two 25 cm Zerodur® blanks are separated by three low CTE bipods made from Ti-6Al-4V and ALLVAR Alloy-30. If properly matched, these bipods should separate the Zerodur® blanks with pm/√Hz stability. If successful, this work might help qualify these negative CTE alloys as a spacer material for use in the optical path of interferometric gravitational wave observatories such as LISA. [Preview Abstract] |
Sunday, April 18, 2021 2:30PM - 2:42PM Live |
K16.00006: Picometer dimensional stability testing of the LISA telescope at the University of Florida Jose Sanjuan, Ada Uminska, Soham Kulkarni, Joseph Gleason, Paul Fulda, Guido Mueller The European Space Agency (ESA) future space-based gravitational wave detector LISA, with a scheduled launch in 2034, consists of three spacecraft (SC) forming a triangle of 2.5 Gm on a side in a heliocentric orbit 20$^{\rm o}$ behind the Earth. Laser links between the SC enable laser interferometry to measure relative displacements at the picometer level. The measurement sensitivity is ultimately limited by the number of photons exchanged between the SC, which is maximized using telescopes that serve as afocal beam expanders and reducers. The telescopes, one of NASA's contributions to the mission, are part of the science interferometer and as such, they need to be dimensionally stable at the 1 pm/$\sqrt{\rm Hz}$ level in the milli-Hertz band, which is particularly challenging given the properties of the telescopes: one-meter long with a 300 mm primary mirror and a magnification of 134. The LISA telescope engineering model dimensional stability will be tested at the University of Florida throughout 2022/23 and will conclude the efforts to reach technology readiness level (TRL) 6. In this presentation, we will give an overview of the measurement challenges and the efforts being made at the University of Florida to carry out the telescope dimensional testing. [Preview Abstract] |
Sunday, April 18, 2021 2:42PM - 2:54PM Live |
K16.00007: Torsion Pendulum for Testing of Space Gravity Mission Technology Anthony Dávila Álvarez, John Siu, Derek Klein, Stephen Apple, Samantha Parry Kenyon, José Sanjuán, Timothy Sumner, Guido Mueller, Peter Wass, John Conklin Space based gravity science instruments measure the motion of isolated reference bodies, called test masses (TM), to detect gravitational field changes. A Gravitational Reference Sensor (GRS) uses two methods to capture this movement, a laser interferometer, and a capacitive sensor system. The University of Florida torsion pendulum is used to test and improve the performance of this technology. It is comprised of four cubic TMs at the ends of identical orthogonal rods, connected to a central piece suspended from a 1 m long, 50 um 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. Their charge is measured and controlled by an UV LED system that is connected to light injection ports in the GRS housing. Capacitive sensors measure the position for two opposite TMs while the other two are end points for a Mach-Zehnder and homodyne interferometer (IFO) that measures their differential motion. The IFO uses polarization multiplexing to maximize its range of sensitivity, and two output beams to reject common noise. The torsion pendulum, GRS and IFO are described along with their components and performance. [Preview Abstract] |
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