Добірка наукової літератури з теми "LISA space mission"

Laser Interferometer Space Antenna (LISA) Pathfinder (formerly known as SMART-2) is a European Space Agency mission designed to pave the way for the joint ESA/NASA LISA mission by testing in flight the critical technologies required for space borne gravitational wave detection; it will put two test masses in a near-perfect gravitational free-fall and control and measure their motion with unprecedented accuracy. This is achieved through technology comprising inertial sensors, high precision laser metrology, drag-free control and an ultra precise micro-Newton propulsion system. LISA Pathfinder (LPF) essentially mimics one arm of space-borne gravitational wave detectors by shrinking the million kilometer scale armlengths down to a few tens of centimeters, giving up the sensitivity to gravitational waves, but keeping the measurement technology. The scientific objective of the LPF mission consists then of the first in-flight test of low frequency gravitational wave detection metrology.

The LISA space mission requires laser frequency pre-stabilization of the 1064[Formula: see text]nm laser sources. While cavity-based systems are the current baseline, laser frequencies stabilized to a hyperfine transition in molecular iodine near 532[Formula: see text]nm are a possible alternative. Several setups with respect to space applications were developed, putting special emphasis on compactness and mechanical and thermal stability of the optical setup. Vibration testing and thermal cycling were performed. These setups show frequency noise below 20[Formula: see text]Hz/[Formula: see text] for frequencies between 4[Formula: see text]mHz and 1[Formula: see text]Hz with an absolute frequency reproducibility better than 1[Formula: see text]kHz. They fulfil the LISA requirements and offer an absolute laser frequency simplifying the initial spacecraft acquisition procedure. We present the current status of iodine-based frequency references and their applicability in space missions, especially within the LISA mission.

The existence of gravitational waves is the most prominent of Einstein's predictions that has not yet been directly verified. The space projects LISA and (partially) ASTROD share their goal and principle of operation with the ground-based interferometers currently under construction: the detection and measurement of gravitational waves by laser interferometry. Ground and space detection differ in their frequency ranges, and thus the detectable sources. Towards low frequencies, ground-based detection is limited by seismic noise, and yet more fundamentally by 'gravity gradient noise', thus covering the range from a few Hz to a few kHz. On five sites worldwide, detectors of armlengths from 0.3 to 4 km are nearing completion. they will progressively be put in operation in the years 2002 and 2003. Future enhanced versions are being planned, with scientific data not expected until 2008, i.e. near the launch of the space project LISA. It is only in space that detection of signals below, say, 1 Hz is possible, opening a wide window to a different class of interesting sources of gravitational waves. The project LISA consists of three spacecraft in heliocentric orbits, forming a triangle of 5 million km sides. A technology demonstrator, designed to test vital LISA technologies, is to be launched, aboard a SMART-2 mission, in 2006. The proposed mission ASTROD will, among other goals, also aim at detecting gravitational waves, at even lower frequencies than LISA. Its later start will allow it to benefit from the expertise gained with LISA.

AbstractThe three Laser Interferometer Space Antenna (LISA) spacecraft are going to be placed in a triangular formation in an Earth-trailing or Earth-leading orbit. They will be launched together on a single rocket and transferred to that science orbit using Solar Electric Propulsion. Since the transfer Δv depends on the chosen science orbit, both transfer and science orbit have been optimised together. For a thrust level of 90 mN, an allocation of 1092 m/s per spacecraft is sufficient for an all-year launch in 2034. For every launch month a dedicated science orbit is designed with a corner angle variation of 60° ± 1.0° and an arm length rate of maximum 10 m/s. Moreover, a detailed navigation analysis of the science orbit insertion and the impact on insertion errors on the constellation stability has been conducted. The analysis shows that Range/Doppler measurements together with a series of correction manoeuvres at the beginning of the science orbit phase can reduce insertion dispersions to a level where corner angle variations remain at about 60° ± 1.1° at 99% C.L. However, the situation can become significantly worse if the self-gravity accelerations acting during the science orbit phase are not sufficiently characterised prior to science orbit insertion.

ABSTRACT A strong indication is presented that the space-based gravitational antennas, in particular the Laser Interferometer Space Antenna (LISA) concept introduced in 2017 in response to the ESA call for L3 mission concepts, are going to be sensitive to a strong background signal interfering with the prospected signal of gravitational waves. The false signal is due to variations in the electron number density of the solar wind, causing variations in the refractive index of plasma flowing through interplanetary space. As countermeasures, two solutions are proposed. The first solution is to deploy enough solar wind detectors to the LISA mission to allow for reliable knowledge of the solar wind background. The second solution is to equip the LISA interferometer with a second laser beam with a distinct wavelength to allow cancelling of the background solar wind signal from the interferometric data.

Abstract Gravitational waves are a prediction of Einstein’s general relativity theory. In autumn 2017, the Laser Interferometer Gravitational-Wave Observatory (LIGO; https://www.ligo.caltech.edu/) experiment reported the first detection of gravitational waves in addition to electromagnetic radiation from the collision of two neutron stars. This marks the first time that a cosmic event has been viewed in both gravitational waves and light and opens the door to a new type of astronomical observatory based on gravitational waves. The gravitational wave spectrum covers a broad span of frequencies and requires both space- and ground-based observatories to cover the full range. Space-based gravitational wave observatories, such as the proposed Laser Interferometer Space Antenna (LISA), operate at frequencies between 0.1 mHz and 1 Hz and complement the frequency range of 30–1000 Hz accessible by ground-based gravitational wave observatories, such as LIGO. A rich array of high-energy astrophysical sources is expected in the LISA measurement band. LISA was selected in 2017 as the third large mission of the Cosmic Vision program of the European Space Agency. The National Aeronautics and Space Administration will collaborate on both the scientific and technical aspects of this mission. This paper addresses the design of the optical telescope as an essential component of LISA’s long-distance interferometric measurement system.

LISA (Laser Interferometer Space Antenna) est un interféromètre spatial dédié à la détection des ondes gravitationnelles dans la gamme de fréquence [20 µHz-1 Hz], actuellement en développement (phase B). Ce projet international géré par l'ESA sera composé d'une constellation de trois satellites en formation triangulaire, chacun d'entre eux émettant deux faisceaux laser vers les deux autres satellites. Il y a donc au total 6 liens laser, et 6 unités, appelées MOSA (Moving Optical Sub-Assembly) chargées d'émettre et de recevoir les faisceaux, et de réaliser la mesure des variations de distance inter-satellites. Chaque MOSA contient trois interféromètres hétérodynes, et comme dans tout dispositif optique la lumière parasite peut compromettre l'exactitude, la résolution ou encore la dynamique des mesures.Il est donc nécessaire d'élaborer une instrumentation (appelé le SL-OGSE, Stray Light-Optical Ground Support Equipment) pouvant détecter et identifier les contributions de lumière parasite cohérente interférant avec les faisceaux nominaux du dispositif. Il devra répondre notamment à deux exigences : déterminer le chemin optique de la lumière parasite avec une résolution meilleure que 2 mm, donnant une précision de 1 mm sur la position du composant défectueux, et atteindre un plancher de mesure en amplitude optique fractionnaire de 1,1.10-6 (ou 2,2.10-6 en amplitude fractionnaire électrique) dans la gamme de chemins optiques à couvrir.La méthode qui a été retenue est l'interférométrie à dérive de fréquence (FMCW, Frequency Modulated Continuous Wave) en injectant un laser à balayage de fréquence dans le système sous test. Les signaux optiques et électriques sortants sont capturés pendant le balayage de fréquence optique, et toute modulation de ces signaux sera attribuée à l'existence d'une amplitude de lumière parasite, qui interfère avec l'amplitude de lumière nominale. La différence de chemin optique (DCO) entre la lumière parasite et le faisceau nominal est déduite de la fréquence de ces franges d'interférence. C'est en exploitant la valeur de la DCO qu'on peut identifier le trajet suivi par la lumière parasite, et remonter au composant fautif.La thèse vise donc à développer un prototype de cette instrumentation comprenant essentiellement une diode laser balayable sur 2 nm (pour atteindre la résolution désirée en DCO), une boucle d'asservissement en phase du laser, une mesure précise de la rampe en fréquence, un calibrateur temps réel de la rampe et un système d’acquisition et de traitement de données.Ce prototype, testé d'abord sur un montage simplifié où nous contrôlons la présence de lumière parasite puis sur un système complexe proche du MOSA, aura permis entre autres de vérifier que la méthode fonctionne pour la détection de tout type de lumière parasite, qu'elle soit de type faisceau parasite ou de type lumière diffusée. La résolution permet d'enregistrer séparément les réflexions sur la face avant et arrière d'une lame de verre de 1 mm d'épaisseur et d'atteindre un plancher de détection meilleur que 10-6 en amplitude optique fractionnaire (10-12 en puissance optique fractionnaire) dans une gamme de valeurs de DCO allant de 15 mm à plus de 10 m, qui couvre les trajets typiques de la lumière parasite dans le MOSA. Le prototype a finalement été utilisé pour mesurer la lumière parasite dans un démonstrateur interférométrique dont la complexité est voisine de la complexité d'un MOSA. Ce test a notamment permis d'identifier certaines perturbations, telles que la modification, du fait du balayage en fréquence, de la polarisation du faisceau injecté, ou les imperfections du balayage en fréquence, qui affectent les signaux optiques enregistrés. Des stratégies sont proposées afin de réduire ces perturbations, ou encore d'en tenir compte au moment du traitement des signaux enregistrés
LISA (Laser Interferometer Space Antenna) is a space interferometer dedicated to the detection of gravitational waves in the frequency range [20 µHz-1 Hz], currently under development (phase B). This international project, managed by ESA, will comprise a constellation of three satellites in a triangular formation, each emitting two laser beams towards the other two. There are therefore a total of 6 laser links, and 6 units, called MOSA (Moving Optical Sub-Assembly) responsible for transmitting and receiving the beams, and for measuring inter-satellite distance variations. Each MOSA contains three heterodyne interferometers, and as with any optical device, stray light can compromise measurement accuracy, resolution and dynamics. It is therefore necessary to develop an instrumentation (called the SL-OGSE, Stray Light-Optical Ground Support Equipment) capable of detecting and identifying the contributions of coherent stray light interfering with the device's nominal beams. It will have to meet two requirements in particular: determine the optical path length of the stray light with a resolution better than 2 mm, giving an accuracy of 1 mm on the position of the faulty component, and achieve a measurement floor in fractional optical amplitude of 1,1.10-6 (or 2,2.10-6 in electrical fractional amplitude) in the range of optical paths to be covered.The chosen method is frequency-drift interferometry (FMCW, Frequency Modulated Continuous Wave) by injecting a frequency-swept laser beam into the system under test. The outgoing optical and electrical signals are captured during the optical frequency sweep, and any modulation of these signals will be attributed to the existence of a stray light amplitude, which interferes with the nominal light amplitude. The optical path difference (OPD) between stray and nominal light is deduced from the frequency of these interference fringes. It is by exploiting the OPD value that we can identify the path followed by the stray light, and trace it back to the offending component.The aim of this thesis is to develop a prototype of this instrumentation, comprising a laser diode that can be scanned over 2 nm (to achieve the desired OPD resolution), a laser phase-locked loop, a precise frequency ramp measurement, a real-time ramp calibrator and a data acquisition and processing system.This prototype, tested first on a simplified set-up where we control the presence of stray light, then on a complex system close to the MOSA, has enabled various verifications. The method works for the detection of any type of stray light (stray beam or scattered light type), effectively resolving the contributions from the two sides of a 1mm glass plate and achieving a detection floor below 10-6 in fractional optical amplitude (below 10-12 in fractionnal optical power) in a range of OPD values from 15 mm to over 10 m, covering typical stray light paths in the MOSA. The prototype was finally used to measure stray light in an interferometric demonstrator whose complexity is close to that of a MOSA. This test enabled us to identify certain disturbances, such as changes in the polarization of the injected beam due to the frequency scanning, or imperfections in the frequency scanning, which affect the optical signals recorded. Strategies are proposed to reduce these disturbances, or to take them into account when processing the recorded signals

The European Space Agency (ESA) has plans to build a space-based gravitational wave detector known as LISA. The recent LISA Pathfinder mission has demonstrated that the technology required for LISA will be sufficiently sensitive to detect gravitational waves. LISA will detect events that are invisible to LIGO and other Earth-based gravitational wave detectors. These include the mergers of distant supermassive black holes.

“Legal Frameworks for Historic Preservation” provides an overview of the various federal and international laws and guidelines for historic preservation of culture, and explains how preservation of space heritage sites like those noted in the book can fit into that system. Particular attention is paid to the World Heritage List, the United Nations, the National Register of Historic Places, and the National Historic Landmark programs, in terms of the criteria for inclusion in them. The authors make the case for the overarching significance of space heritage sites within this context by referring to their integrity and elaborating on the Man in Space Theme Study.

Abstract Missions are the lifeblood of planetary science. Unfortunately, planetary missions are expensive and because they are expensive only a few nations or agencies have independent planetary exploration programs. At the time of this writing the list was restricted to four: the United States, Russia, Japan, and the European Space Agency. To lay out a rational, step-by-step program for the exploration of Mars is not difficult, but the likelihood of such a plan being followed is small. Because the missions are expensive, their approval requires support of a much broader constituency than the small planetary science community. Planetary missions may serve a variety of purposes in addition to advancing scientific knowledge. They may be used to demonstrate to the rest of the world a nation’s technical virtuosity and the superiority of its economic system. They have been used to promote technological innovation and to preserve specialized technical capabilities. They may foster international cooperation and cement economic alliances. They stimulate interest in science and technology among a nation’s youth. They must also have public appeal, for it is the public who pays for them. This multiplicity of objectives often leads to frustration in planning, for not only do the different goals pull the exploration strategies in different directions, but the weight given to the different goals is constantly shifting with the political climate.

Abstract This chapter centers on a Dimensions in Testimony interview with the Holocaust survivor Eva Schloss, the posthumous stepsister of Anne Frank. We begin by exploring the dynamics of the extended question-and-answer format, before discussing three different written accounts that Schloss gave of her Holocaust experiences at different times in her life. We discuss the influence of Schloss’s book for young adults, The Promise (2006), while noting that the project’s aim of making Holocaust testimony available to future generations of young people means that Schloss censors out some of the most disturbing, traumatic, and taboo aspects of her childhood Holocaust experiences, including incidents of sexual abuse. If certain aspects of the Dimensions in Testimony methodology tend to keep the interviews free from what Lawrence Langer terms “anguished memory,” we note that their extended duration equally means that the orderliness of what Charlotte Delbo calls “common memory” is often fractured by moments of raw emotion. Finally, this chapter argues that the USC Shoah Foundation’s institutional mission means that survivors such as Schloss are incited to extract uplifting messages from their life histories. In its humanism and optimism, Dimensions in Testimony reflects the ongoing legacy of a film such as Schindler’s List. Yet we close by asking whether the occlusion of some of the most traumatic physical and psychological experiences risks making the spaces of virtual Holocaust memory overly sanitized, arguing that future projects must creatively acknowledge the silent accounts of the victims whom Primo Levi termed “the drowned.”