TPF-I SWG Report - Exoplanet Exploration Program - NASA

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A PPENDIX C Figure C-4. FAST Flight and simulation clusters (left) and schematic (right). The FAST configuration is representative of one that would be used in a flight project to test and debug the real-time flight code before proceeding to full flight-system testing. Essentially an extension of a singlespacecraft flight software testbed to formations, FAST can evaluate end-to-end performance, functionality, and long-term robustness of precision formations. The next section presents the FAST hardware in detail. Then, the functional architecture of FAST is discussed, including HYDRA and its distributed timing architecture. Next, the software executive and the FACS currently used in FAST are reviewed. Finally, two-spacecraft distributed interferometer and tworobot FCT simulation results are given. FAST Functional Architecture The functional architecture of FAST is shown in Fig. C-4. The five spacecraft computers are shown, each hosting a software executive and formation software. The formation software on each spacecraft computer is referred to as a Formation and Attitude Control System (FACS), described previously. The simulation computers have models for sensors, actuators, spacecraft dynamics, environmental forces, and communication. Standard single-spacecraft actuators, sensors, and uplink/downlink models are included. For formations, additional models for inter-spacecraft communication (ISC) and relative sensing are 184
F ORMATION F LYING A L G O R I T H M D E V E L O P M E N T required. Relative sensing and ISC are the unique hardware models that couple individual spacecraft simulations. This coupling differentiates a formation simulator from a constellation simulator. As the number of spacecraft in a formation increases, the overhead required to manage communication and synchronization between distributed simulation components grows rapidly. A scalable, flexible, and easily extensible architecture is needed to automate communication and manage connections between distributed applications. HYDRA automates the connection of distributed simulation elements using a publish– subscribe, client-server paradigm. As each client application is started, it provides the HYDRA server with a list of offered and desired services. The HYDRA server commands two clients to form a connection when they have advertised compatible services. Adding a simulated spacecraft to the formation only requires starting up another spacecraft client. HYDRA allows the user to override default behaviors at several layers. While HYDRA is similar to other distributed architectures (such as CORBA and HLA), it was specifically designed for the needs of high-speed, distributed simulation. In HYDRA, client applications communicate through connectors that abstract message passing over a variety of protocols and infrastructure, including Scalable Coherent Interface (SCI) and transmission control protocol/internet protocol (TCP/IP). Each spacecraft simulation in FAST is a HYDRA client. A sixth simulation computer functions as the HYDRA server. All clients register with the server over the Ethernet local-area network (LAN). The majority of inter-process communication in is handled by HYDRA, including: 1. ISC traffic over the SCI connection, ii) 2. Uplink, downlink, time coordination, and relative sensor traffic over Ethernet, and 3. Inter-process traffic within a computer. Simulation computer-to-spacecraft computer traffic over the fiber-optic reflective memory cards is controlled via an interface specification. Each simulation computer simulates the dynamics for only its associated spacecraft. The spacecraft dynamics are integrated using the Dynamics Algorithms for Real-Time Simulation (DARTS) software package (Jain and Rodriguez 1992). DARTS is a multi-platform software library written in C and is based on spatial operator algebra. It provides efficient numerical algorithms for both rigid-body and flexible-body dynamics. Spacecraft mass and inertia properties are input to DARTS using a Tool Command Language (TCL) script. A lightweight interface to DARTS provides external actuator and sensor models access to force and torque inputs and state outputs. A numerical integrator is used to propagate the system state based on accelerations computed by DARTS. FAST currently provides either a fixed-step, fourth-order Runge- Kutta integrator or the variable-step CVODE integrator (Cohen and Hindmarch 1996). The fixed step integrator provides real-time, deterministic performance while the variable step integrator provides higher accuracy. A critical function of HYDRA is the synchronization of the separate spacecraft simulations for relative sensing (Sohl et al. 2005). Specifically, relative sensing requires synchronization of the dynamics integrators running on separate computers to provide consistent state information at a given time. A second crucial function coupled to state synchronization is the simulation of local spacecraft clocks (SCLKs). Spacecraft clocks are used to time-tag measurements and initiate digital control cycles. As spacecraft clocks will have different offsets and drifts, control cycles on spacecraft will start at different true times and will move with respect to one another. In addition, ISC will have jitter and dropouts. These characteristics must be accurately simulated to evaluate formation robustness. 185
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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
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C HAPTER 2 Reach, W. T., Franz, B.
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C HAPTER 3 3.1.1 Darwin/TPF-I Prope
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C HAPTER 3 clouds or an OB associat
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C HAPTER 3 Figure 3-3. Three possib
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C HAPTER 3 the circumstellar disk,
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C HAPTER 3 Figure 3-6. (Left panel)
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C HAPTER 3 Continuum interferometry
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C HAPTER 3 Figure 3-9: Simulated im
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C HAPTER 3 3.3 Conclusions Darwin/T
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C HAPTER 3 Nguyen, H. T., Kallivaya
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D ESIGN AND A R C H I T E C T U R E
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C HAPTER 5 Heavy launch vehicle. Th
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C HAPTER 5 5.3.2 Combiner Spacecraf
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C HAPTER 5 5.3.5 Beam Transfer betw
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C HAPTER 5 Figure 5-8. Control sche
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C HAPTER 5 Figure 5-9. First sectio
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C HAPTER 5 Figure 5-9 shows the fir
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C HAPTER 5 5.4.4 Shear Metrology Sh
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C HAPTER 5 Figure 5-15. TPF-I Fligh
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C HAPTER 5 secondary mirror along t
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C HAPTER 5 a) c) b) d) IWA = 43 mas
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C HAPTER 5 planets found. Figure 5-
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C HAPTER 5 30 25 5 M earth 3 M eart
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C HAPTER 5 5.8.4 Angular Resolution
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C HAPTER 5 Table 5-3. Angular Resol
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C HAPTER 5 The optimization works b
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T E C H N O L O G Y R OADMAP FOR TP
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Page 208 and 209: A PPENDIX E Appendix E TPF-I Review
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