Pre-Phase A Report - Lisa - Nasa

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166 Chapter 8 Technology Demonstration in Space 8.3.4 Drag-free control Verification of the performance of the drag-free control system is a key element of the ELITE mission concept. Since the spacecraft contains two inertial sensors (as with the new LISA baseline), it cannot be manoeuvred to centre each proof mass within its housing electrodes. Instead, there will be a single location (the “drag-free null”) within the spacecraft where the acceleration is minimised by the drag-free control system. Forces will have to be applied on the proof masses to compensate for any force gradients relative to this drag-free null. ELITE will test various control strategies. For example, perhaps the simplest approach is to have the spacecraft translation controlled to centre, in all three components, on one of the two proof masses (i.e. locating the drag-free null at the centre of one proof mass). The attitude of the spacecraft could then be controlled using the information from the other proof mass. The other proof mass will need to have forces applied to it to follow the primary proof mass. These forces would be applied electrostatically by means of its sensing electrodes. The magnitude of the applied force in each component would be comparable to the expected forces on the primary proof mass, i.e. corresponding to an acceleration of order 10 −10 ms −2 . A key objective for ELITE will be to demonstrate that these forces can be applied in such a way that the noise introduced within the measurement band is acceptable. Also, the orientation of each proof mass needs to be controlled to match the orientation of its housing at the nanoradian level. 8.4 ELITE Satellite design The ELITE system will consist primarily of institute-provided payload elements (e.g. inertial sensors, thrusters, lasers/optical package, flight computer, etc.). The spacecraft, which comprises the structure, power, communication etc. subsystems will be ‘built around the payload’ using commercially-available off-the-shelf components as far as possible. In order to minimise costs, the satellite will be single-string (in terms of failure modes) with limited functional redundancy and graceful degradation of all items. 8.4.1 Power subsystem For the six-month duration, the GEO orbit can be chosen to be free of eclipses. Then the nominal continuous power requirement is ≈ 150 W, including ≈ 25 W for battery charging (for safe-mode). 8.4.2 Command and Data Handling A main central processor unit (CPU, e.g. RAD 6000) will be responsible for all command & data handling, and computation of control laws. A smaller backup processor will be used for initial set-up and safe-modes. Command and data I/F between the processors and all sensors and actuators will be via a 1553 bus with maximum throughput of 100 kbps. RS 422 serial communication may also be an option for some payload items [TBD]. Control of the 1553 bus can be software-switched between the processors. The main CPU will 3-3-1999 9:33 Corrected version 2.08
8.4 ELITE Satellite design 167 incorporate its own warm reset/reboot capability. The backup processor will provide a cold boot capability for the main CPU. Both the main and back-up processors will have anomaly detection and safing functions. 8.4.3 Telemetry and mission operations For the GEO-type orbit, the nominal operations can be performed via a single groundstation, essentially in real-time. NORAD and on-board GPS [TBD for GEO] (to ≈ 100 m) will provide sufficiently accurate orbit determination so ground-based tracking/ranging will not be required. Telemetry will be packetised according to CCSDS standards and managed by either the main or backup processor [TBD]. Standard S-band telemetry rates are: 2 Mbps S-band downlink (11 m ground-station), 1 kbps uplink. If a 1 m portable station is used, the available downlink rate is reduced by an order of magnitude (i.e. to 1.4 kbps) which is, nevertheless, sufficient for ELITE (see Table 8.1). For the GEO orbit, an on-board solidstate storage capability would not be required. 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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1.1 Theory of gravitational radiati
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1.2 Low-frequency sources of gravit
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Chapter 2 Different Ways of Detecti
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2.2 Ground-based detectors 39 2.2 G
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2.2 Ground-based detectors 41 Count
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2.4 Spacecraft tracking 43 2.4 Spac
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2.7 Heliocentric versus geocentric
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2.8 The LISA concept 47 telescopes
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2.8 The LISA concept 49 Figure 2.6
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2.8 The LISA concept 51 seem rather
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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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Page 141 and 142: 5.7 Thermal analysis 127 the Y-shap
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Page 175 and 176: Chapter 8 Technology Demonstration
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Page 191 and 192: 10.3 Schedule 177 The ESA Project M
Page 193 and 194: References [1] C.W. Misner, K.S. Th
Page 195 and 196: References 181 [35] C. Cutler, T.A.
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Page 201 and 202: List of Acronyms - and other abbrev
Page 203 and 204: List of Acronyms 189 LHC Large Hadr
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