Pre-Phase A Report - Lisa - Nasa

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60 Chapter 3 Experiment Description Diodes Diode heaters Crystal heater Crystal Fiber coupler LIGHT Laserhead Supply Unit EOM Photodiode Diode current source Diode temperature controller Crystal temperature controller Frequency stab. feedback servo Power stab. feedback servo POWER RS 422 Spacecraft BUS 10 MHz LiNbO crystal Optics Bench InGaAs diode Figure 3.5 Laser system block diagramm for the identification of the components and interfaces. area of 1 µm×200 µm at unit magnification onto the entrance surface of the crystal, using two identical lenses with plano-convex surfaces to minimize spherical aberration (best form lens shape). A polarizing beamsplitter is inserted between the two lenses to combine the pump light from the two diodes, which are orthogonal in polarization. All of the above mentioned components are glued to a solid fused silica spacer to ensure mechanical stability. Glued to that spacer are three heat sinks, which serve as the mechanical and thermal interface to the radiator plate. There is a heater integrated in each heat sink to control the operating temperature of the diodes and the crystal. The supply unit mainly contains two current sources for the laser diodes, three temperature controllers, two for the diodes and one for the crystal, the mixer and feedback servo for the frequency stabilisation and the feedback circuit for power stabilisation. The supply unit power interface to the S/C power subsystem shall be the only power interface between the laser system and the S/C. The electro-optic modulator (EOM) is a resonant phase modulator. These devices use lithium niobate crystals as the electro-optic medium, where a few volts drive voltage induce a change in the crystal‘s refractive index. The only electrical interface to the EOM is the rf supply. The stabilisation photodiode is a InGaAs diode operated with a few volts reverse voltage in order to reduce its capacitance. That capacitance is part of a LC-circuit that resonantly enhances the rf signal modulated on the the laser beam. The ac-signal from the photodiode is taken as a voltage from the LC-circuit. The dc-signal is obtained by converting the photocurrent into a voltage with a transimpedance operational amplifier. 3-3-1999 9:33 Corrected version 2.08 AC pathl DC pathl
3.1 The interferometer 61 3.1.6 Laser performance Laser frequency noise. The presence of laser frequency noise can lead to an error in the measurement of each arm length. If the arms are equal these errors cancel out but if they are unequal, the comparison of lengths used to search for gravitational waves may be dominated by frequency noise. For an arm of length L the phase difference between the outgoing and returning light of frequency ν is given by: φ = 4πνL . (3.3) c Thus, for slow changes in L and ν, δφ = 4π c (Lδν + νδL) = 4πνL c δν ν δL + , (3.4) L where δφ is a phase fluctuation resulting from either a change δL in arm length or a change δν in frequency of the laser. In fact a fractional change in frequency of δν/ν gives a signal equivalent to a fractional change in length of δL/L. Thus if the difference in two arm lengths is ∆x and the relative frequency stability of the laser is δν/ν the smallest relative displacement which can be measured is given by: δx =∆x δν ν . (3.5) For the 5 ×106 km arms of LISA, a maximum value of ∆x of the order of 105 km is likely. For a relative arm length measurement of 2×10−12 m/ √ Hz, which is needed to achieve the desired overall sensitivity, a laser stability of 6×10−6 Hz/ √ Hz is required. The monolithic structure of the nonplanar Nd:YAG ring laser and the low technical noise of the supply electronics offer a high intrinsic frequency stability of this laser system. In order to reach the desired sensitivity that intrinsic stability has to be even improved and a high precision frequency stabilisation has to be provided. The primary method of stabilisation is to lock the frequency of one laser in the system on to a Fabry-Perot cavity mounted on one of the craft making use of a rf reflection locking scheme known as Pound-Drever-Hall scheme. This stability is then effectively transfered to other lasers in the system by phase locking techniques. With the temperature fluctuations inside each craft limited in the region of 10−3 Hz to approximately 10−6 K/ √ Hz by three stages of thermal insulation, a cavity formed of material of low expansion coefficient such as ULE allows a stability level of approximately 30 Hz/ √ Hz . This level of laser frequency noise is clearly much worse than the required 6×10−6 Hz/ √ Hz and a further correction scheme is required. Such a correction is provided by comparing the mean phase of the light returning in two adjacent arms with the phase of the transmitted light. The phase difference, measured over the time of flight in the two arms, allows an estimate of laser frequency noise to be made. For each arm δφ =(4π/c) L δν (since ν δL ≪ L δν) and thus if the spectral density δφ is measured, the spectral density δν can be estimated. A detailed analysis of this scheme is given in Section 4.3 . Corrected version 2.08 3-3-1999 9:33
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LISA Laser Interferometer Space Ant
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LISA Laser Interferometer Space Ant
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Foreword The first mission concept
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The result of the Team-X study was
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Contents Foreword iii Executive Sum
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Contents ix 4.2.3 Acceleration nois
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Contents xi 9 Science and Mission O
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Executive Summary 1 Executive Summa
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Executive Summary 3 Complementarity
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Mission Summary 5 LISA Mission Summ
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Chapter 1 Scientific Objectives By
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Page 53 and 54: 2.2 Ground-based detectors 39 2.2 G
Page 55 and 56: 2.2 Ground-based detectors 41 Count
Page 57 and 58: 2.4 Spacecraft tracking 43 2.4 Spac
Page 59 and 60: 2.7 Heliocentric versus geocentric
Page 61 and 62: 2.8 The LISA concept 47 telescopes
Page 63 and 64: 2.8 The LISA concept 49 Figure 2.6
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Page 67 and 68: Chapter 3 Experiment Description 3.
Page 69 and 70: 3.1 The interferometer 55 Fiber to
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Page 81 and 82: 3.2 The inertial sensor 67 design (
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4.4 Data analysis 111 with the phas
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4.4 Data analysis 113 density Sn(f)
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4.4 Data analysis 115 box (in stera
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4.4 Data analysis 117 LISA’s dist
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Chapter 5 Payload Design 5.1 Payloa
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5.2 Payload structural components 1
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5.2 Payload structural components 1
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5.4 Mass estimates 125 5.4 Mass est
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5.7 Thermal analysis 127 the Y-shap
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5.8 Telescope assembly 129 surface
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5.9 Payload processor and data inte
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5.9 Payload processor and data inte
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Chapter 6 Mission Analysis 6.1 Orbi
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6.3 Injection into final orbits 137
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6.4 Orbit configuration stability 1
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6.5 Orbit determination and trackin
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Chapter 7 Spacecraft Design 7.1 Sys
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7.1 System configuration 145 2220 m
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7.1 System configuration 147 7.1.4
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7.2 Spacecraft subsystem design 149
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7.3 Micronewton ion thrusters 151 b
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7.3 Micronewton ion thrusters 153 F
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7.3 Micronewton ion thrusters 155 (
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7.3 Micronewton ion thrusters 157 F
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7.4 Mass and power budgets 159 The
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Chapter 8 Technology Demonstration
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8.1 ELITE - European LISA Technolog
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8.3 ELITE Technologies 165 8.2.2 Co
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8.4 ELITE Satellite design 167 inco
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Chapter 9 Science and Mission Opera
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9.2 Mission operations 171 9.2 Miss
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9.3 Operating modes 173 Power savin
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Chapter 10 International Collaborat
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10.3 Schedule 177 The ESA Project M
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References [1] C.W. Misner, K.S. Th
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References 181 [35] C. Cutler, T.A.
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References 183 [77] J.E. Faller and
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References 185 [104] E. Grun, H.A.
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List of Acronyms - and other abbrev
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List of Acronyms 189 LHC Large Hadr
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Rear cover figure : This Report has
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Pre-Phase A Report - Lisa - Nasa

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