Prospects for Terrestrial Planet Finder (TPF-C, TPF-I, & TPF-O)

Transcription

1 Prospects for Terrestrial Planet Finder (TPF-C, TPF-I, & TPF-O) Wesley Traub, Stuart Shaklan, and Peter Lawson, The Spirit of Lyot Conference University of California - Berkeley, 4-8 June 2007 Purpose of Talk Exoplanet detection science is maturing rapidly Exoplanet characterization science is in its childhood, and needs data on all nearby planets (not just transits) to begin maturing We are told that science mission funds are scarce Dilemma: how to get data cheaply? We may need to revise our view of desired science: - More Jupiters & zodis? - Fewer Earths? Nevertheless, let us remain prepared for better times, and missions that could give head-turning or world-view changing science

2 Exoplanet Mission Discovery Space Scalable Architecture vs Science Yield Instrument Concept Primary Mirror (m) IWA (λ/d max ) # Earths # Targets # Jupiters # Targets Spectra λλ, R COST OVER $2B Classic-X Array Interferometer 4m B 600m , , µm; R=75 5 Year Mission: 25% detection 25% characterization 50% astrophysics η(earth) = 1 τ(jupiter) = 1 FB-1 Coronagraph with Band Limited Mask FB-1 Coronagraph with Pupil Mapping (PIAA) Emma-X Array (I) 8 x x 3.5 2m B 400m , 85 73, 140 COST RANGE $1B-$2B 70, , , , µm; R= µm; R= µm; R=25 Band Limited Mask or Shaped Pupil (C) , , µm; R= 75 Pupil Mapping (PIAA-C) , , µm; R= 75 Pupil Mapping (PIAA-C) 4 2.5* 48, , µm; R= 75 External Occulter 4 +50m occulter , 64 70, µm; R= 75 COST UNDER $1B Band Limited Mask or Shaped Pupil (C) , , µm; R= 10 Pupil Mapping (PIAA-C) , , µm; R= 10 Pupil Mapping (PIAA-C) * 16, , µm; R= 10 Visible Nuller 1.5 2* 3, , µm; R= 10 * very aggressive IWA assumption Fourier Kelvin Stellar Int. JWST and occulter 2@1m,B~12m 6 m , 80 25, µm; R= µm

3 Summary: the path for exoplanet missions? world-view changing future prospects results head-turning dazzling current prospects nothing cost Community Effort TPF-C TOTAL TECHNOLOGY INVESTMENTS since 2002 ($K) Masks 1,906 ITT 10,360 HCIT 8,766 Princeton 919 UCB 286 Florida 171 UofHA 662 BostonU 564 VN 798 CTM 316 STSci 242 SAO 210 Xintetics 2,146 TOTAL = $30,154K JPL $14,277K Industry $12,507K Universities $3,371K UCB, 286 UNIVERSITY FUNDING ($K) from TPF-C since JUNE 2002 UofHA, 662 STSci, 242 SAO, 210 BostonU, 564 CTM, 316 Princeton, 919 Florida, 171

4 TPF-C HCIT Electric Field Conjugation Results

5 Coronagraphy Primer Image Plane Masks Pupil External Plane Occulter Masks BL8 Vortex Best so far, good aberration rejection, hard to achromatize, low throughput Shearing Nulling Interferometry Easy Broad to band, manufacture, uses standard easy to telescope, achromatize, large simplest floppy structure, design, low limited throughput, mobility large IWA. Pupil Mapping (PIAA) No optics in image plane, most complicated to implement, throughput similar to band-limited mask. Closest to ideal high throughput, small IWA, challenging optics, unknown WFC issues. Shaped Pupil Fabrication 10-9 mask 10-7 mask with 3 lambda/d IWA Smallest features ~ 5 microns. Silicon-on-Insulator wafers. DRIE process. 2-sided etching. Manufactured at JPL Microdevices Laboratory

6 Shaped Pupil HCIT result (monochromatic) Model Validation Monochromatic contrast to < 10-9 Explore variations in contrast with bandwidth Null at 785 nm with 2% bandwidth Measure contrast at 10% bandwidth without changing DM Agreement with model ~ 20% Modeling shows path for improvement Performance limited by systematic mask errors (dispersion) Optimal Lyot stop improves by ~ 2x

7 Pupil Mapping (PIAA) Schematic Courtesy of Olivier Guyon After speckle subtraction using a 32 x 32 DM

8 Coronagraph Summary Direct Imaging of Terrestrial Planets: 6 years of Lessons Learned Community has established science requirements Mission studies: observational completeness Detailed engineering studies and analysis Preliminary instrument concepts including astrophysics camera Technology Status State of the art is 10-9 contrast in 2% bandwidth at 4 λ/d (about the 4 th Airy ring) Shaped pupil masks are close behind, 6e-9 in 10% bandwidth. Demonstrated stability in the laboratory for detecting Earths. Other approaches including external occulters are at Bottom Line For <$1B NASA, 1.5 m coronagraph could detect and characterize a few (<6) Earths, but significant R&D required Already have the technology for a large sample of cold Jupiters. A phased approach a small coronagraph later joined in orbit by a large occulter may make the most sense. A Case Study Band-limited 8 th -order Mask Excellent aberration rejection. Modest throughput. 1 st pupil 1 st image bright star 8 m x 3.5 m aperture Places planets in foothills of Mt. Everest. Large throughput, high resolution reduces contribution of exo-zodi. Mission Modeling Tools Which stars to look at, how long, how deep. mask 2 nd pupil Lyot stop 2 nd image bright planet Results Detailed engineering studies show we meet thermal, vibration, and pointing requirements. No show-stoppers. Detects 41 Earths, 390 Jupiters (η=1)

9 Completeness Results Type IWA (! /D max ) Primary Mirror # Earths # Targets # Jupiters # Targets BL8 4 8 m x 3.5 m PIAA BL8/SP m PIAA m SoA: 460 1e-7580 Ext. Occ. JWST SoA: 71 1e-9 78 Known SoA: 1e-7 RV: 7 Known SoA: RV: 1e-710 BL8/SP m PIAA m PIAA m A Phased Approach Fly small coronagraph Characterize Jupiters & disks with existing technology. Could find a few Earths. Discovery-class missions Follow with an occulter Can observe the systems most likely to harbor Earths. Allows time to develop external occulter technologies. Telescope angular resolution comparable to JWST (80 mas). TPF-O Approach: use proven technology for bright planets, then new technology for Earth-like planets.

10 Useful coronagraph throughput Deformable Mirrors

11 Coronagraph Stability Demonstration Trauger & Traub, Nature 2007 Small Scale TPF-C Attributes Telescope does not deploy. Simple thermal shroud deployment Standard solar panel and solar sail deployments Simplified observational scenario Line-of-site dither for image subtraction Circular aperture means no need for multiple rolls about line of sight Requirements For terrestrial planets, much tighter stability requirements than FB-1 Lower throughput and smaller aperture, so integration times grow. Stiffer Telescope Greatly reduce gravity sag relative to FB1 Stiffer structure relative to FB1 to reduce beam walk and aberrations End-to-end testing looks feasible No major new facilities Easily fits in low-cost launch vehicles.

12 TPF-I Planet Characterization in Mid-IR Science requirements Architecture trade studies Starlight suppression Null depth & bandwidth Null stability Formation flying Formation control Formation sensing Propulsion systems Cryogenic systems Active components Cryogenic structures Passive cooling Cryocoolers Integrated Modeling Modeling uncertainty factors Model validation and testbeds

13 Ongoing Work TPF Manager Dan Coulter TPF-I Systems Manager Peter Lawson TPF-I Architecture Oliver Lay, Project Architect Stefan Martin, Design Team Lead TPF-I Science Charles Beichman, Project Scientist Stephen Unwin, Deputy Project Scientist Ground-based software validation Formation Control Testbed Daniel Scharf (PI) SPHERES Guest Scientist Program (MIT) Fred Hadaegh (PI) Software validation at the ISS Mid-IR Spatial Filters Alexander Ksendzov (PI) Achromatic Nulling Testbed Robert Gappinger (PI) Adaptive Nuller Testbed Robert Peters (PI) Planet Detection Testbed Stefan Martin (PI) Broadband Nulling 1 x 10-5 null 25% BW System Testbed Technology for Mid-Infrared Nulling

14 Broadband Nulling: Achromatic Nulling Testbed null, & 25% bandwidth null, with & 20% bandwidth (left) null, & laser source average null with 20% bandwidth Goal is 1.0x10-5 average null depth at 25% bandwidth centered at 10 micron. Only the Adaptive Nuller has achieved comparable results Broadband Nulling: Adaptive Nuller In April 2007 demonstrated control to 0.2% and 5 nm, 8-12 microns Null depths of over a 32% bandwidth demonstrated Percent Intensity Difference (RMS) Intensity Stability Run 1 RMS Phase (nm) 5.0 Phase Stability Run Time (Hours) Time (Hours)

15 Sensor Data Sensor Data Actuator Cmd. Actuator Cmd. System Testbed: Planet Detection Testbed Formation Algorithm & Simulation Testbed (FAST) Formation Control Testbed Formation Control Testbed (FCT) Leader Spacecraft Formation and Attitude Control System (FACS) Formation State Estimator Formation Path Planner Formation Controller Control Mapper Formation Mode Commander Inter-spacecraft Communication (ISC) - Wireless Follower(s) Spacecraft Formation State Estimator S/C Path Planner Formation Controller Control Mapper Spacecraft Mode Commander Distributed Realtime Simulation Architecture Formation Flying Control Architecture Ground Testbed Performance Simulation Achieved Formation Control of FCT Robots with FF S/W Controlling the two robots using the wireless Inter-Spacecraft Communication (ISC), Timing, and Synchronization functions Formation Software to Robots H/W I&T Integrated FF Inter-Spacecraft Communication (ISC) software (new capability) Integrated Inter-S/C Clock Timing and Synchronization software (new capability)

16 MIT SPHERES at ISS JPL is participating in the SPHERES Guest Scientist Program to allow testing of TPF-I formation flying algorithms at the ISS Nominally 8 opportunities for testing over two years Prof. David Miller (MIT) MIT completed a three-spheres formation maneuver during testing at ISS in March 2007 Summary TPF-I Technology Goals Demonstrate 10-5 broadband mid-ir nulling Demonstrate fault-tolerant algorithm for formation flying in a ground-based lab and at the ISS Highlights Formation Flying Testbed now operational Laser nulling exceeding 10-6 Broadband nulling now within a factor of two of flight requirement: Adaptive Nuller Testbed demonstrates (5 nm phase and 0.2% intensity compensation) Adaptive Nuller Testbed achieves a null with a 32% bandwidth Current performance would add only 5% to the integration time needed to detect Earth at 15 pc TPF-I & Darwin now very well aligned Both projects working with the same design Performance estimates closely agree Old co-planar geometry Emma geometry reduces complexity & increases sky coverage Formation Control Testbed Precision performance milestone upcoming in mid-2007 Adaptive Nuller New Emma geometry Simulated earth extracted at contrast ratio Planet Detection Testbed Record broadband mid-ir nulls: % BW

17 State of the Art in Broadband Nulling Wavelengths: Mid-Infrared 6 20 µm Contrast: Earth-Sun ~ µm Biomarkers: O 3, CO 2, CH 4, H 2 O TPF-I Key Features Technique: Nulling Interferometry Implementation: Formation Flying Selsis

18 Emma Three Telescope Nuller TPF-I Darwin Linear DCB Bow-Tie X-Array Planar TTN Stretched X-Array Emma TTN Emma X-Array TPF-Darwin Combiner moved 1.2 km out of plane Collectors are spherical mirrors (f = 1.2 km) Simplified collectors; no deployables This design by Alcatel Classic design Collector: old vs new Emma design Five layer sunshade Deployed stray light baffles Deployed secondary mirror and shroud 4-m diameter telescope aperture Cold Sunshade Deployment Booms (4 pl.) Fixed 4 layer sunshade 3-m diameter mirror 15.3 m Deployed payload cryo radiators Fixed radiators 4.5 m diameter

19 Collector spacecraft 3 m spherical mirror Passively cooled Readily scaled to smaller apertures No deployables Combiner spacecraft: old vs new Classic design Emma design Cryogenic nulling beam combiner Five layer sunshade Cold sunshade deployment booms Fixed 4 layer sunshade Cryogenic nulling beam combiner 15.3 m Deployed payload cryo radiators Fixed payload cryo radiators

20 Beam combiner spacecraft Mass and volume 3 m design = 6900 kg (w 30% reserve) Mass saving of 30% over previous design Compatible with medium lift LV Delta IV M+ Ariane 5 ECA Scaling to smaller diameters 3.0 m 6900 kg 2.0 m 4800 kg 1.5 m 4100 kg 1.0 m 3700 kg Inspired by Alcatel design

21 Performance: Inner Working Angle 120 x 20 m array 400 x 67 m array IWA = 25 mas IWA = 7 mas Single Visit Completeness > 90% 300 Performance: detectable Earths m diameter # Earths m diameter m diameter Mission time / weeks From Sarah Hunyadi s completeness code Assumes 1 Earth per star Good agreement with European analysis

22 Spectroscopic characterization m diameter 120 # planets characterized m diameter 1.5 m diameter yr 2 yr Available time for characterization / days SNR = 5 in µm ozone channel η earth = 1 TPF-O

23 Occulters Planet Target Star Occulter Telescope Telescope big enough to collect enough light from planet Occulter big enough to block star Want low transmission on axis and high transmission off axis Telescope far enough back to have a properly small IWA No outer working angle: View entire system at once New Worlds Observer

24 Fly the Telescope into the Shadow Binary Shape

25 Performance a=b=12.5m n=6 F=50,000km End

26 Summary We are exploring several approaches to TPF-C including 4 classes of internal coronagraphs, and external occulters. For internal coronagraphs, only Guyon s PIAA approaches the theoretical limit and may potentially enable Exo-Earth detection with a 1.5 m aperture. If this approach is successfully developed, it can find up to ~ 5 Earth-like planets (for η Earth = 1) and requires an ultra-stable 1.5 m aperture telescope. Phased approach may yield the best overall science return, and be affordable over time.