The Chandra Proposers’ Observatory Guide Prepared by: Chandra X-ray Center Chandra Project Science, MSFC Chandra IPI Teams Version 15.0 December 2012 2 Contents What’s New for Cycle 15? xv 1 Mission Overview 1 1.1 Program Organization . 1 1.2 Unique Capabilities . 1 1.3 Observatory Overview . 2 1.4 Pointing Control and Aspect Determination (PCAD) . 3 1.5 HRMA . 3 1.6 Science Instrument Module (SIM) . 3 1.6.1 Aimpoints . 4 1.7 Ground System . 4 1.8 Orbit . 4 1.9 Particle Detector . 5 1.10 ACIS . 5 1.11 HRC . 6 1.12 HETG . 6 1.13 LETG . 6 1.14 Effective Area Comparisons . 7 1.15 Allocation of observing time . 7 1.16 How to get information and help . 7 2 Spacecraft, Telescope, Operations, & Mission Planning 11 2.1 Introduction . 11 2.2 Spacecraft . 11 2.3 Telescope System . 13 2.4 Science Instrument Module (SIM) . 14 2.4.1 SIM Motions . 15 2.5 Electron Proton Helium Instrument (EPHIN) . 15 2.6 Operations . 16 2.6.1 Launch and On-orbit Verification . 16 2.6.2 The Ground System . 16 2.6.3 Commanding . 17 i ii CONTENTS 2.6.4 Telemetry . 17 2.6.5 SI Science Data . 18 2.6.6 Event Timing and the Spacecraft Clock . 18 2.7 Mission Planning . 18 2.7.1 The Long-Term Schedule . 18 2.7.2 Selecting Candidates for Short-Term Scheduling . 19 2.7.3 The Short Term Scheduling Process . 20 3 Offset Pointing, Visibility, and other Constraints 21 3.1 Introduction . 21 3.2 Offset Pointing . 21 3.3 Visibility . 21 3.3.1 Radiation Belt Passages . 21 3.3.2 Avoidances . 24 3.3.3 Pitch Angle Constraints . 24 3.4 Other Constraints and Considerations . 27 3.4.1 Instrument Constraints and Considerations . 27 3.4.2 User-Imposed Constraints . 28 4 High Resolution Mirror Assembly (HRMA) 29 4.1 Introduction . 29 4.1.1 Description and Physical Configuration . 29 4.1.2 Sub-assembly Calibration . 31 4.1.3 Operating Environment . 31 4.1.4 Heritage . 31 4.2 Calibration and Performance . 31 4.2.1 Calibration and Model . 31 4.2.2 HRMA Effective Area . 32 4.2.3 Point-Spread-Function and Encircled Energy Fraction . 34 4.3 Ghost Images . 43 4.4 Effects of Aspect and Instrument Uncertainties . 49 4.5 References . 54 5 Pointing Control and Aspect Determination System 57 5.1 Introduction . 57 5.2 Physical configuration . 57 5.2.1 ACA . 58 5.2.2 Fiducial lights and Fiducial Transfer System . 59 5.2.3 IRU . 60 5.2.4 Momentum control – RWA and MUPS . 60 5.3 Operating principles . 61 5.4 Performance . 61 5.4.1 Post-Facto and On-Orbit Aspect Determination . 61 CONTENTS iii 5.4.2 On-Board Acquisition and Tracking . 64 5.5 Heritage . 65 5.6 Calibration . 65 5.6.1 Pre-launch calibration . 65 5.6.2 Orbital activation and checkout calibration . 65 5.6.3 On-orbit calibrations . 66 5.7 Operations . 68 5.7.1 PCAD modes . 68 5.7.2 Operational constraints . 68 5.7.3 Output data . 70 5.8 Performing an Observation . 70 5.8.1 Star acquisition . 70 5.8.2 Science pointing scenarios . 70 5.8.3 PCAD capabilities (advanced) . 72 5.9 Ground Processing . 73 5.9.1 Data products . 73 5.9.2 Star catalog . 73 6 ACIS: Advanced CCD Imaging Spectrometer 75 6.1 Introduction & Layout . 75 6.2 Basic Principles . 78 6.3 Optical Blocking Filter & Optical Contamination . 80 6.4 Calibration . 80 6.5 Quantum Efficiency and Effective Area . 81 6.5.1 Molecular Contamination of the OBFs . 86 6.6 Spatial Resolution & Encircled Energy . 87 6.7 Energy Resolution . 87 6.7.1 Correcting the Energy Resolution of the CCDs . 88 6.8 Hot Pixels and Columns . 89 6.9 Cosmic Ray Afterglows . 89 6.10 Aimpoints . 89 6.11 Dither . 93 6.11.1 Gaps Between the CCDs . 93 6.12 Operating Modes . 95 6.12.1 Timed Exposure (TE) Mode . 95 6.12.2 Alternating Exposures . 97 6.12.3 Continuous Clocking (CC) Mode . 98 6.13 Bias Maps . 99 6.14 Event Grades and Telemetry Formats . 99 6.14.1 Event Grades . 99 6.14.2 Telemetry Formats . 101 6.15 Pileup . 102 iv CONTENTS 6.15.1 Other Consequences of Pileup . 104 6.15.2 Pileup Estimation . 106 6.15.3 Reducing Pileup . 107 6.16 On-Orbit Background . 109 6.16.1 The Non-X-ray Background . 109 6.16.2 The Total Background . 112 6.16.3 Background Variability.