Pre-Phase A Report - Lisa - Nasa

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4 Executive Summary wave signal). The sum will give information on laser frequency fluctuations. Each spacecraft contains two optical assemblies. The two assemblies on one spacecraft are each pointing towards an identical assembly on each of the other two spacecraft to form a Michelson interferometer. A 1 W infrared laser beam is transmitted to the corresponding remote spacecraft via a 30-cm aperture f/1 Cassegrain telescope. The same telescope is used to focus the very weak beam (a few pW) coming from the distant spacecraft and to direct the light to a sensitive photodetector where it is superimposed with a fraction of the original local light. At the heart of each assembly is a vacuum enclosure containing a free-flying polished platinum-gold cube, 4 cm in size, referred to as the proof mass, which serves as an optical reference (“mirror”) for the light beams. A passing gravitational wave will change the length of the optical path between the proof masses of one arm of the interferometer relative to the other arm. The distance fluctuations are measured to sub-˚Angstrom precision which, when combined with the large separation between the spacecraft, allows LISA to detect gravitational-wave strains down to a level of order ∆ℓ/ℓ =10−23 in one year of observation, with a signal-to-noise ratio of 5 . The spacecraft mainly serve to shield the proof masses from the adverse effects due to the solar radiation pressure, and the spacecraft position does not directly enter into the measurement. It is nevertheless necessary to keep all spacecraft moderately accurately (10−8 m/ √ Hz in the measurement band) centered on their respective proof masses to reduce spurious local noise forces. This is achieved by a “drag-free” control system, consisting of an accelerometer (or inertial sensor) and a system of electrical thrusters. Capacitive sensing in three dimensions is used to measure the displacements of the proof masses relative to the spacecraft. These position signals are used in a feedback loop to command micro-Newton ion-emitting proportional thrusters to enable the spacecraft to follow its proof masses precisely. The thrusters are also used to control the attitude of the spacecraft relative to the incoming optical wavefronts, using signals derived from quadrant photodiodes. As the three-spacecraft constellation orbits the Sun in the course of one year, the observed gravitational waves are Doppler-shifted by the orbital motion. For periodic waves with sufficient signal-to-noise ratio, this allows the direction of the source to be determined (to arc minute or degree precision, depending on source strength). Each of the three LISA spacecraft has a launch mass of about 400 kg (plus margin) including the payload, ion drive, all propellants and the spacecraft adapter. The ion drives are used for the transfer from the Earth orbit to the final position in interplanetary orbit. All three spacecraft can be launched by a single Delta II 7925H. Each spacecraft carries a 30 cm steerable antenna used for transmitting the science and engineering data, stored on board for two days, at a rate of 7 kB/s in the Ka-band to the 34-m network of the DSN. Nominal mission lifetime is two years. LISA is envisaged as a NASA/ESA collaborative project, with NASA providing the launch vehicle, the Ka-band telecommunications system on board the spacecraft, mission and science operations and about 50 % of the payload, ESA providing the three spacecraft including the ion drives, and European institutes, funded nationally, providing the other 50 % of the payload. The collaborative NASA/ESA LISA mission is aimed at a launch in the 2008 – 2010 time frame. 3-3-1999 9:33 Corrected version 2.08
Mission Summary 5 LISA Mission Summary Objectives: Detection of low-frequency (10 ,4 to 1 Hz) gravitational radiation with a strain sensitivity of4 10 ,21 p = Hz at 1 mHz. Abundant sources are galactic binaries (neutron stars, white dwarfs, etc.); extra-galactic targets are supermassive black hole binaries (SMBH-SMBH and BH-SMBH), SMBH formation, and cosmic background gravitational waves. Payload: Laser interferometry with six electrostatically controlled drag-free reference mirrors housed in three spacecraft; arm lengths 5 10 6 km. Each spacecraft has two lasers (plus two spare) which operate in a phaselocked transponder scheme. Diode-pumped Nd:YAG lasers: wavelength 1.064 m, outputppower 1 W, Fabry-Perot reference cavity for frequency-stability of10Hz= Hz. Quadrant photodiode detectors with interferometer fringe resolution, corresponding to 4 10 ,5 p = Hz. 30 cm diameter f/1 Cassegrain telescope (transmit/receive), =10 outgoing wavefront quality. Drag-free proof mass (mirror): 40 mm cube, Au-Pt alloy of extremely low magnetic susceptibility (< 10 ,6 ); Ti-housing at vacuum < 10 ,6 Pa; six-degree-of-freedom capacitive sensing. Orbit: Each spacecraft orbits the Sun at 1AU. The inclinations are such that their relative orbits de ne a circle with radius 3 10 6 km and a period of 1year. The plane of the circle is inclined 60 with respect to the ecliptic. On this circle, the spacecraft are distributed at three vertices, de ning an equilateral triangle with a side length of 5 10 6 km (interferometer baseline). Launcher: Delta II 7925 H, 9.5 ft fairing. This constellation is located at 1 AU from the Sun, 20 behind the Earth. Each pair of spacecraft has its own jettisonable propulsion module to providea V of 1300 m/s using solar-electric propulsion. Spacecraft: 3-axis stabilized drag-free spacecraft (three). mass: 203 kg, each spacecraft in orbit. propulsion module: 132 kg, for each spacecraft. propellant: 27 kg, for each spacecraft. total launch mass: 1407 kg power: 151 W, each spacecraft in orbit. dimension: diameter: 1.8 m, height: 0.48 m, each spacecraft. Drag-free performance: 10 ,15 m=s 2 (rms) in the band 10 ,4 to 10 ,1 Hz achieved with 6 4 Cesium FEEP thrusters. Pointing performance: few nrad/ p Hz in the band 10 ,4 to 10 ,1 Hz. Payload, mass: 70 kg, each spacecraft. power: 72 W, each spacecraft. Telemetry: 375 bps per spacecraft for about 5 hours. Ground stations: Villafranca (Spain), Perth (Australia). Mission Lifetime: 2years (nominal); 10 years (extended). Corrected version 2.08 3-3-1999 9:33
Page 1 and 2: LISA Laser Interferometer Space Ant
Page 3 and 4: LISA Laser Interferometer Space Ant
Page 5 and 6: Foreword The first mission concept
Page 7 and 8: The result of the Team-X study was
Page 9 and 10: Contents Foreword iii Executive Sum
Page 11 and 12: Contents ix 4.2.3 Acceleration nois
Page 13 and 14: Contents xi 9 Science and Mission O
Page 15 and 16: Executive Summary 1 Executive Summa
Page 17: Executive Summary 3 Complementarity
Page 21 and 22: Chapter 1 Scientific Objectives By
Page 23 and 24: 1.1 Theory of gravitational radiati
Page 33 and 34: 1.2 Low-frequency sources of gravit
Page 51 and 52: Chapter 2 Different Ways of Detecti
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
Page 65 and 66: 2.8 The LISA concept 51 seem rather
Page 67 and 68: Chapter 3 Experiment Description 3.
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3.1 The interferometer 55 Fiber to
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3.1 The interferometer 57 3.1.4 Sys
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3.1 The interferometer 59 Figure 3.
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3.1 The interferometer 61 3.1.6 Las
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3.1 The interferometer 63 signal sh
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3.1 The interferometer 65 for a sin
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3.2 The inertial sensor 67 design (
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3.2 The inertial sensor 69 and the
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3.2 The inertial sensor 71 Figure 3
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3.2 The inertial sensor 73 sufficie
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3.3 Drag-free/attitude control syst
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3.3 Drag-free/attitude control syst
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Chapter 4 Measurement Sensitivity 4
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4.1 Sensitivity 81 averaged transfe
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4.2 Noises and error sources 83 The
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4.2 Noises and error sources 85 Tab
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4.2 Noises and error sources 87 cod
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4.2 Noises and error sources 89 cha
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4.2 Noises and error sources 91 fre
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4.2 Noises and error sources 93 ele
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4.2 Noises and error sources 95 is
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4.2 Noises and error sources 97 and
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4.2 Noises and error sources 99 Eq.
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4.3 Signal extraction 101 here that
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4.3 Signal extraction 103 phase loc
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4.4 Data analysis 105 • LISA obse
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4.4 Data analysis 107 for ground-ba
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4.4 Data analysis 109 that are defi
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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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