shaklan MSC Summer School 04

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Information about shaklan MSC Summer School 04

Published on January 21, 2008

Author: Quintino


The Terrestrial Planet Finder Coronagraph:  The Terrestrial Planet Finder Coronagraph Stuart Shaklan TPF Coronagraph Architect Jet Propulsion Laboratory, California Institute of Technology July 23, 2004 Overview:  Overview History Science Requirements Trade Studies How aggressive to make the coronagraph? Baseline Mission Design Telescope Thermal Control System Coronagraph Instrument Technology Development …and into the future… A Brief History of the Project:  A Brief History of the Project 2000-2002: Industry/University teams conducted feasibility study Concluded that with suitable technology investment starting now, a mission to detect terrestrial planets around nearby stars could be launched by the middle of the next decade (2010–2020). Summary report available at: In mid-2002, JPL set up Interferometer and Coronagraph pre-project teams Working toward a mission selection in 2006 Science Working Group chartered in October 2002 Spring 2004: NASA decided to fly a visible coronagraph first, followed by an IR interferometer. We are now working toward ‘Phase A’ project status. JPL is the project lead. Goddard will build the telescope. Ball Aerospace 2000-2002 Pre-Phase A Final Architecture Review Concept: Shaped pupil coronagraph Off-axis unobscured system 4x10m elliptical off-axis monolithic primary mirror High density deformable mirror for wave front correction l= 0.5-1.7 µm 1 AU orbit (L2 or Earth-trailing) TPF Science Requirements:  TPF Science Requirements The minimum TPF must be able to detect planets with half the area of the Earth, and the Earth’s geometric albedo or the equivalent equilibrium effective temperature, searching the entire HZ of the 35 core-group stars with 90% completeness per star. HZ = Habitable Zone = 0.7 – 1.5 AU scaling as sqrt(luminosity) Flux ratios must be measured in 3 broad wavelength bands, to 10% accuracy, for at least 50% of the detected terrestrial planets. The spectrum must be measured for at least 50% of the detected terrestrial planets to give the equivalent widths of O2, H2O, and O3 in the visible or H2O, and O3 in the infrared to an accuracy of 20%; we desire to detect CO2 and CH4 as well. Distances, IHZ of 50 best targets:  Distances, IHZ of 50 best targets These are the 50 nearby stars that offer the best ‘completeness’ after 9 observations over 3 years. Aperture Size:  Aperture Size Telescope Architecture Trades:  Telescope Architecture Trades Baseline Mission Parameter Summary:  Baseline Mission Parameter Summary Aperture: 6x3.5 m off-axis Cassegrain IWA: 3 lambda/D DM: 96 x 96 actuators Bandpass: 500-600 nm (detection), 500-800+ nm (spectroscopy) Mask: 1-D linear 1-sinc^2 mask (others work as well) SNR = 4 per observation (photon-statistics limited) Solar Zodi: V=22.7 per sq. arcsec. Exo Zodi: 2x brighter than Solar Zodi (and double pass for 4x total ) Total integration time: 1 year for detection (not including overhead) Total program length: 3 years for detection 50 targets 9 visits per target over 3 years Each visit requires 3 Line-of-sight roll positions (two 60 degree steps) Photometric sensitivity: delta magnitude = 25 Slide9:  2nd Order Dependence Focus, Coma, Spherical 4th Order Dependence Tilt, Astigmatism, Trefoil Other occulters exhibit different dependencies (e.g.) Visible Nuller 4th order focus sensitivity Sensitivity to Low Order Aberrations Radial Cosine (s = 4 l/D) Evaluated at 3 l/D Calculated using Fourier Plane mathematics and small wave front perturbations in a pupil plane. Zernike C-matrix These calculations form the Zernike Sensitivity coefficients appear in worksheets: Rsinc28ar, lcos4ar, rcos4ar…. Green and Shaklan, SPIE 2003 Shaped Pupil Aberration Sensitivity:  Shaped Pupil Aberration Sensitivity Green and Shaklan, SPIE 2004 Coronagraph Forms:  Coronagraph Forms TPF Architecture Coronagraph Description:  TPF Architecture Coronagraph Description TPF-Coronagraph Payload M1 M3 M2 Collimator Mirror Polarizer, WFS&C, Coronagraph, Spectrometer Configuration Schematic:  Configuration Schematic Science Payload Telescope Coronagraph System Instruments Spacecraft System Slide14:  Sy Amplitude & Phase Wavefront Correcting Deformable Mirrors Fast Steering Mirror Polarizing Beam Splitter Dispersing Prism Insertable Pickoff Mirror Planet Detection Spectrometer Fine Guidance Camera Pupil Mask Occulting Mask Lyot Stop Focussing Mirror Redundant Instrument S Pol P Pol -100°C -100°C 6DOF Hexapod Acquisition Camera Coronagraph Detectors Primary Mirror Secondary Mirror Fold Mirror Laser Metrology Telescope Metrology Coronagraph Optics Acquisition Camera Deformable Mirror Control Detector Control Instrument Computer Thermal Control Power Optical Actuator Control • • • • • • • • • • • • Corner Cube 0°C Coronagraph Thermal Radiators Coronagraph Electronics Sun Shade Power Conditioning Power Distribution Batteries Pyro Power N2H4 N2H4 P P P Fill Drain Propulsion Solar Sail Solar Arrays Drain Filter Pressure Transducers 20 lbf Thrusters Branch A Branch B Attitude Control Actuators Propulsion Driver Electronics Spacecraft Computer Spacecraft Loads Transponder Amplifier (50W) 3dB Coupler HGA LGA Transmit LGA Receive HGA LGA Transmit LGA Receive +X/-X Hi/Lo Hi/Lo +X Panel -X Panel Telecom 3 Axis Gyros Analog Sun Sensors Attitude Control Sensors Dynamic/Thermal Isolation Key Launch Support Structure LV Adapter Launch Vehicle Spacecraft Optical Path Electrical Interface RF Path Propellant Line 1 axis actuator 2 axis actuator Thermal Path Patch Antenna Visco-elastically Damped booms Thermal Control System Block Diagram Star Tracker Systems Summary:  Systems Summary Mission Overview 2014 Launch Date Earth Drift-Away orbit (ala SIRTF) 0.1AU/yr average earth separation rate No cruise phase to operating orbit Delta-IVH launch vehicle with 5m x 19m fairing 10,000 kg lift capacity to C3 of 0.4 5 year primary mission duration with consumables for 10 years 6 month post-launch checkout and calibration Planet search phase spans 3 years X-Band communications to 34m DSN Continuous link capability & Hi Rate science downlink concurrent with data collection Capability to downlink 3 days of stored data (~2Gb per day) in 1 8hr pass Systems Overview Power: 3,000W solar array Propulsion: 100kg Hydrazine in Blow-Down Mode No ∆V required Provide safe sun point and some momentum management (solar sail is prime) Attitude Control: 3 axis stabilized Star-trackers, gyros, sun sensors, plus instrument provided Acquisition Camera 6 Reaction Wheels (Ithaco E Wheels) Solar Sail with 1 axis articulation for balancing solar pressure torques Telecommunications: 256 kbps science downlink X-Band transponder 50W amplifier 2 30dB HGAs with 2 axis articulation Thermal Control: V-Groove sun shade Minimum Mission Configuration:  Minimum Mission Configuration X Z Secondary Mirror Primary Mirror Back end coronagraph optics 10m 6m Z Y Tertiary mirror surface Optical Bench 10m 3.5m Slide17:  Deployed secondary tower V-groove deployment boom Spacecraft equipment support panel Deployed HGA Primary mirror thermal enclosure (coronagraph sensor and spectrograph inside) Deployed solar array Primary mirror (6m x 3.5m) Cross section of deployed V-groove layers Telescope and Secondary Mirror Assemblies Secondary Mirror Secondary Bracket Acquisition Camera Thermal Enclosure Actuated hexapod Thruster cluster (2 pl) Spacecraft equipment support panel Reaction wheels (6) Spacecraft bus Dynamic isolation (3 pl) Propulsion tank (2 pl) Deployed v-groove platform Slide18:  Laser Truss for TPF Coronagraph Fiber Optics (2) Beam Launcher Corner cube Power, signal Six metrology beams form an optical truss with ~0.3 nm resolution. In addition to the identified components, a stabilized NPRO laser (wavelength=1.3 um), a heterodyne frequency modulation system, and fiber distribution system are used. The laser and modulation system feed the beam launchers from a remote location on the s/c. Corner cubes must be attached around the perimeter of the optics so as not to obscure the beam. They are required to maintain sub-nm piston (normal to optical surfaces) stability during observations. For short design, we get ~ factor of 2 more precision with 1.6x more precise metrology. Metrology System Configuration:  Metrology System Configuration Corner Cube with vertex removed Beam Launchers Isothermal Cavity Slide20:  Stowed Mechanical Configuration Stowed Configuration in Delta IV-H (19.8m gov’t standard) 5.08m (OD) 4.57m (ID) 12.192m 16.484m Top View 19.814m 1.448m dia Launch support cylinder – closed on both ends to control contamination on primary mirror Deployment:  Deployment Thermal Control Concept - Cocoon:  Thermal Control Concept - Cocoon Cocoon Advantages: Fully blocks sun light, earth or moon shine from telescope baffle at near 90º angle Isolates baffle by keeping heat from sun in outer layers Deploys in same direction as telescope baffle V-Groove Radiator Cocoon: Sunshine heats one side of radiator – outer v-groove shield heats & emits IR light Shiny surfaces reflect IR light outward into space Slide23:  Telescope Steady-State Temperature for Two 20 deg Dither Cases (80 to 100 & 170 to 190) Temperature (C) Distribution for all Sun Angles (variations<mC) Delta Temperature (C) for Dither from 80 to 100 deg Delta Temperature (C) for Dither from 170 to 190 deg 19.0C -142C -0.035C 0.041C 0.0014C -0.0032C Minimum Mission Thermal Modeling Thermal Modeling Continued:  Thermal Modeling Continued Dynamic Results 2 stage passive isolation:  Dynamic Results 2 stage passive isolation Rigid Optics Wavefront Error Design meets requirements passively Flexible Primary Wavefront Error Mode 8 exceedance can be avoided by running wheels above 4hz Top 14 Contrast Contibutors:  Top 14 Contrast Contibutors Major contrast contributor in the Error Budget. The numbers shown do not include reserve factors. 0.09 mas 1-sigma per axis 0.8 mas 1-sigma per axis dL = 217 pm 1-sigma df/f =2.95e-11 1 sigma Z4=2.28 pm 3-sigma Z12=0.3 pm 3-sigma Z4=1.4 pm 3-sigma Z8=0.57 pm 3-sigma Z4 Z8 Z12 Integral Field Unit:  Integral Field Unit Detector Lenslet Array Collimator Optics Grating Camera Optics Focal Plane Pupil Plane AO Focus Cold Pupil Filters R. I. Collimating Singlet R.I. Camera Singlet Reimaging Optics Lenslet Spectrograph Slide from J. Larkin, presented at TPF-C Technical Interchange Meeting, June 9, 2004 Additional Instrument accomodations:  Additional Instrument accomodations Telescope Coronagraph Telescope Field Stop 400nm to 950nm 0.95um to 1.7um Dichroic Splitter Slide29:  Ecltel170: 2.5arcmin FFOV, 4 mirror “Best Fit” Conclusion:  Conclusion Working toward a 2014 launch date. ‘Phase A’ start hoped for in January 2007 Current Trades Telescope size: 6 – 8 m Sun-shade form and deployment Active or passive vibration isolation Cassegrain or Gregorian Telescope Technology issues Polarization: coating design and uniformity to eliminate cross-polarization Mask leakage: mask design with acceptable phase and amplitude errors Modeling: do our models have the right physics to characterize stability at picometer levels? Active Wave Front Sensing: can we actively stabilize speckles while we observe?

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