TPF-I SWG Report - Exoplanet Exploration Program - NASA

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C HAPTER 4 interferometer. How this information is processed determines such fundamental properties as the proper geometry of the spacecraft and the size of the telescopes. It became clear early in the design stage that understanding planetary signal extraction (PSE) would be important in the Pre-Phase A design, if realistic designs were to be considered. There is an extensive literature on signal processing from Earth-bound interferometers, both optical and radio. When <strong>TPF</strong>-I was first proposed, the problem of detecting a signal was already realized as being important. The work of the PSE Working Group was to determine whether these techniques were adequate, and if not, to develop improved methods. In addition, a set of metrics was developed which was independent of signal processing technique that could be used to evaluate different architectures without the computationally expensive process of actually testing each proposed architecture with several different PSE algorithms and many different target solar systems. The basic performance parameter is SNR. In this effort, the signal is the planetary signal, which is the output of the phase-chopped interferometer. Noise comes from two sources (the star itself and extraneous light), and it comes in two ways (simple background and systematic errors). In the studies that we did, we considered only astronomic sources of background (local zodiacal and exozodiacal light), and we did not yet study systematic backgrounds and errors (imperfect maintenance of the null and thermal backgrounds from other spacecraft). The difficulty of the problem is that the SNR is inherently low, limited by finite observing times and the aperture of the telescopes, and that the most interesting signal bands are at the high and low wavelengths, where the sensitivity of the interferometer is lowest. The other fundamental problem is that any interferometer has limited coverage in the u-v plane, so the information obtained from the planetary system is fundamentally incomplete. This is exacerbated by the probability that there are multiple planets in the system, causing confusion in the signal. The combination of low SNR and incomplete information makes identifying a planet and extracting a spectrum a difficult, but not impossible, challenge. These challenges fundamentally drive the mission design. The most basic source of noise is the stellar leakage from the finite suppression of the interferometric null, which is determined by the architecture of the interferometer. For these preliminary studies, we developed a simulation that included the effects of stellar leakage, exozodical dust, and local zodiacal background, and that could simulate the light from arbitrary planetary systems. Systematic effects were not included. This simulation was independently validated by comparison to several other calculations and simulations. Many methods have been proposed for extracting the signal from background by different members of the <strong>TPF</strong>-I collaboration. In the literature, inconsistent assumptions have been made in testing various algorithms, so we decided to have a blind comparison of various algorithms using the JPL standard simulator and a small set of test cases which included solar systems which we thought would be both easy and difficult. A group of scientists from JPL, The University of Arizona, Ball Aerospace, and eventually several other organizations formed a science working group and developed several new algorithms, in addition to a baseline cross-correlation/CLEAN (CC/CLEAN) algorithm. Each of these was tested against simulated planetary systems with a realistic SNR. It was found that the CC/CLEAN algorithm did reasonably well, and improved algorithms were both proposed and implemented. While none of these have yet turned out 88
D ESIGN AND A R C H I T E C T U R E T RADE S TUDIES to be a silver bullet for planet finding, the results are quite encouraging. It should be emphasized that this research is still in an early state. In order to compare architectures without running time-consuming simulations (both generating planetary systems and analyzing them), we developed a set of metrics based on the PSF, which allowed us to calculate comparative planet-finding ability between proposed architectures. These metrics were validated against the CC/CLEAN algorithm and found to be representative of the performance of different spatial configurations and telescope apertures. There is much work left to be done in this area. When this work wound down, the following items were still pending as possible future areas of research: • Identify regular and pathological solar systems – what phase space needs to be tested • Add bumps in the zodiacal background. • Incorporate prior knowledge of exozodiacal spatial covariance into a point process algorithm. This should suppress false positives. • What is the density of background objects • Do spectroscopy. • What is the optimal number of channels • How do you get a quick spectra • How do you obtain reliable spectra • How does variability of planets over observational time scales affect spectroscopy (and detection) • What is the optimal strategy for baseline selection • Investigate changing baselines to increase u-v plane coverage. • How do we set confidence limits for false positives, false negatives • Start incorporating revisit information. • Alternate approaches to cross-correlation for initial maps. • Literature search—written survey of possibilities considered and discarded. • Think of a better algorithm. Still open to new ideas. This work led to two peer-reviewed papers. Draper et al. (2006) laid out the problem, defined important metrics (such as SNR, which is more complex in this problem than it might seem), and tested various solutions. In addition, Velusamy et al. (2005) came up with a new approach at analyzing the signal which seems very promising in initial tests. 89
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JPL Publication 07-1 Terrestrial Pl
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Abstract Over the past two years, t
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Acknowledgements Twenty-two represe
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Table of Contents 1 Introduction...
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4.8.3 Post-Nulling Calibration.....
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6.4.5 Double Fourier Interferometry
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I NTRODUCTION 1 Introduction Over 2
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I NTRODUCTION et al. 2004), and res
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I NTRODUCTION Standard Interferomet
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I NTRODUCTION 1.4 References Angel,
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C HAPTER 2 0.7 to 1.5 AU scaled by
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C HAPTER 2 Table 2-2. Illustrative
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C HAPTER 2 Classical interferometry
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C HAPTER 2 trivial in the absence o
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C HAPTER 2 Figure 2-3. Simulated mi
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C HAPTER 2 would be in atmospheres
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C HAPTER 2 Figure 2-6. The mid-infr
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C HAPTER 2 Lines of constant stella
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C HAPTER 2 presence of zodiacal clo
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C HAPTER 2 S EZ 2π ∫ θ max ∫
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C HAPTER 2 Figure 2-11. Observation
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C HAPTER 2 Figure 2-12. Models of t
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C HAPTER 2 Beichman, C. A., Fridlun
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C HAPTER 2 2.7.4 Suitable Targets E
Page 52 and 53: C HAPTER 2 Reach, W. T., Franz, B.
Page 54 and 55: C HAPTER 3 3.1.1 Darwin/TPF-I Prope
Page 56 and 57: C HAPTER 3 clouds or an OB associat
Page 58 and 59: C HAPTER 3 Figure 3-3. Three possib
Page 60 and 61: C HAPTER 3 the circumstellar disk,
Page 62 and 63: C HAPTER 3 Figure 3-6. (Left panel)
Page 64 and 65: C HAPTER 3 Continuum interferometry
Page 66 and 67: C HAPTER 3 Figure 3-9: Simulated im
Page 68 and 69: C HAPTER 3 3.3 Conclusions Darwin/T
Page 70 and 71: C HAPTER 3 Nguyen, H. T., Kallivaya
Page 73 and 74: D ESIGN AND A R C H I T E C T U R E
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Page 114 and 115: C HAPTER 5 Heavy launch vehicle. Th
Page 116 and 117: C HAPTER 5 5.3.2 Combiner Spacecraf
Page 118 and 119: C HAPTER 5 5.3.5 Beam Transfer betw
Page 120 and 121: C HAPTER 5 Figure 5-8. Control sche
Page 122 and 123: C HAPTER 5 Figure 5-9. First sectio
Page 124 and 125: C HAPTER 5 Figure 5-9 shows the fir
Page 126 and 127: C HAPTER 5 5.4.4 Shear Metrology Sh
Page 128 and 129: C HAPTER 5 Figure 5-15. TPF-I Fligh
Page 130 and 131: C HAPTER 5 secondary mirror along t
Page 132 and 133: C HAPTER 5 a) c) b) d) IWA = 43 mas
Page 134 and 135: C HAPTER 5 planets found. Figure 5-
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Page 138 and 139: C HAPTER 5 5.8.4 Angular Resolution
Page 140 and 141: C HAPTER 5 Table 5-3. Angular Resol
Page 142 and 143: C HAPTER 5 The optimization works b
Page 145 and 146: T E C H N O L O G Y R OADMAP FOR TP
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T E C H N O L O G Y R OADMAP FOR TP
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F UTURE D EVELOPMENTS 7 Preparatory
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F UTURE D EVELOPMENTS • To comple
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F UTURE D EVELOPMENTS Table 7-1. Pr
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D ISCUSSION AND C ONCLUSION 8 Discu
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Appendices 167
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T E C H N O L O G Y A DVISORY C O M
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F L I G H T S YSTEM C ONFIGURATION
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F L I G H T S YSTEM C ONFIGURATION
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A PPENDIX C 2. Identical FACS fligh
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A PPENDIX C 2. Recall that the coef
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A PPENDIX C Once the formation has
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A PPENDIX C Figure C-3. Example of
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A PPENDIX C Figure C-4. FAST Flight
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A PPENDIX C The “true” time of
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A PPENDIX C References Cohen, S., a
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A PPENDIX D DC DCB DM DM DOCS DOD D
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A PPENDIX D NaCl NAR NASA NASTRAN N
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A PPENDIX E Appendix E TPF-I Review
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A PPENDIX F Alice Quillen, Universi
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A PPENDIX F Figure 3-1 - Original f
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TPF-I SWG Report - Exoplanet Exploration Program - NASA

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