A Large Aperture Deployable Telescope for the Next UV/Optical Telescope (NHST) Mission

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1 A Large Aperture Deployable Telescope for the Next UV/Optical Telescope (NHST) Mission C. F. Lillie Next Large Aperture Optical/UV Telescope Workshop 11 April 2003

2 Science Objectives Continue to obtain the UV-Optical observations begun with HST, with much higher resolution (3-6 milli-arcseconds) and sensitivity (<1 nano-jansky) Galactic star formation Formation and evolution of galaxies and clusters Quasars and black holes Cosmology Connect the high-redshift universe observable with SIRTF and JWST to the low - redshift universe that NHST can study in detail with wide-field imaging and high resolution spectroscopy by: Measuring the density and distribution of baryons and large scale structure Detecting unseen matter in the modern universe Understanding the chemical evolution of the elements Observing the major construction phase of quasars and galaxies Detect and characterize planets around nearby stars 2

3 Design Begins With Top-Level Requirements Parameter Class I Mission Requirement Class II Mission Source Orbit Geosynchronous or L2 Geosynchronous or L2 WP Spectral resolution 1,000 plus 5,000 to 10,000 and 30,000 to 50, 000 a goal of 50,000 to 200,000 1,000 plus 5,000 to 10,000 and 30,000 to 50, 000 a goal of 50,000 to 200,000 Aperture 4.2 meters 8 meters WP Effective Area >2.0 m 2 (10 x HST/COS) >10.0 m 2 WP Spectral Multiplexing 2 integrations at R=30,000 2 integrations at R=30,000 WP Spatial Resolution Wavelength Coverage 30 mas at 500 nm required <10 mas at 115 nm goal nm for spectroscopy nm for imaging ( nm goal) nm for integral field 15 mas at 500 nm <5 mas at 115 nm goal nm for spectroscopy nm for imaging ( nm goal) nm for integral field WP WP, NGST Field of View 13.6 x 17.9 arc minutes 12.3 x 15.8 arc minutes WP Imaging CCD for tracking/acquisition, plus 16K 2 for WF and Hi-res imaging CCD for tracking/acquisition, plus 24K 2 for WF and Hi-res imaging Discovery Efficiency 100 to to 1760 WP Launch Date WP, NGST Mission duration 5 years, 10 year goal 5 years, 10 year goal WP Mission Cost Target $450M WP WP WP WP refers to UVOWG White Paper; NGST refers to requirements derived by Northrop Grumman Space Technology 3

4 Requirements Flowdown Process Refines Requirements Mission Requirements Phenomenology SNR for detection SNR for characterization Target List Stars & planets UV wavelength range VIS wavelength range Galaxies & Clusters, Quasars & IGM Mission duration Max time per target Target Characteristics Contrast ratio Angular size Star-Planet Separation Distribution on sky Background emissions Operational scenario development, performance modeling, and system sizing Data rate Integration time Coronagraph spot size Telescope temperature Slew rate Aperture Spectral resolution Pointing control Field of view Field of regard 4

5 A Single Requirement Can Impact Many Areas Number of Targets Duration of Mission Slew Time Settle Time Average Separation of Targets Flight System Dynamics Slew Rate Telescope Stiffness RWA Size Distribution of Targets Sunshield Stiffness Sky Coverage Size of Habitable Zone Integration Time Readout Rate FPA Read Noise Data Storage Slew Range Types of Stars Target Brightness Angular Size of Planet Orbit Performance of Telescope Data Rate Data Processing Sunshield Dimensions Thermal Control WFE Spot Size Collecting Area Aperture Telescope Deployment Sunshield Deployment Deformable Mirror Coronagraph Performance Number of Mirror Segments Manufacturing Schedule 5

6 Candidate NHST Optical Configuration TMA provides Wide FOV with few surfaces for high throughput Simple on-axis conic prescription avoids costly fabrication, provides generous alignment tolerances Fine Steering Mirror eliminates low frequency motion, provides FOV offsets (dither), and offloads large angles to spacecraft ACS Segmented deformable mirror corrects for higher order uncorrected Wave Front errors Simple, clean interface keeps AI&T and verification costs low Secondary Mirror 6-7 m flat-to-flat FSM/ Segmented DM Primary Mirror with 6 to 36 Replicated Segments and Protected Al Coatings Tertiary Mirror Focal Surface Interface to Instrument Module Telescope LOS Replicated Mirror Reaction Structure ROC Actuator (in center) Tip/Tilt/Piston Actuators Force Actuators at corners Mid-high frequency optical quality manufactured into segments Segments fully tested before OTE assembly System optic performance end-to-end test at operating temperature prior to launch Actuators simplify wave front sensing & control system Tip, tilt, piston, and ROC control Rigid body motion independent of ROC control Rigid body corrections do not induce surface distortions or stress 6

7 Hex-Mirror Actuator Sensitivity Study Defines NHST Needs Actuator density study shows seven force actuators are ample for correcting low order deformations: RoC, astigmatism, trefoil Using Global Influence Functions to control midspatial frequencies from 0.5 to ~ 10 cycles/diameter Residual is corrected by DM with 200 actuators/diameter Coronagraph requires correction of spatial frequencies in the band from ~0.8 to 98 cycles/diameter Figure Correction (percent rms) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Actuator Quantity Trades: Figure Correct ability vs. Number of Actuators Power Astigmatism Trefoil Moments at Mounts Number of Actuators 7

8 Deployable UVO Telescope Segmented UV-Optical Telescope 7-hex, 4.5-m, primary mirror 6 DOF secondary mirror HARD deployment approach Spacecraft bus design derived from SSTI and T300 spacecraft Inflatable sunshade for stray light rejection Launch with Delta III to L2 lissajous orbit X-band communication with 0.6 m S/C antenna and 11m ground antenna 2 Kbps uplink, 1 Mbps return Inflatable Sunshade Solar Array (1 of 2) 4.5 m dia. Primary Mirror High Gain Antenna Spacecraft Bus Telescope Baffles omitted for clarity 6-DOF Secondary Mirror Instrument Module 8

9 Stowed Configuration SUVO shown in 9.5 diameter Delta II fairing 1.86 m diameter payload stack also compatible with 8 and 10 diameter fairings Large performance margin with candidate launch vehicles and orbits 600 x 10,000 km elliptical orbit with Delta 7920 Driftaway or L2 orbit with Delta III or Atlas III 9.5 Delta II Fairing Inflatable Sunshade Launch Vehicle Adapter 11/24/98 9 9

10 (Very) Large Aperture Telescope Design Concept 28-meter filled aperture telescope Three-mirror anastigmat 36 segments, 4-meter flat-flat Composite replica optics Protected Al mirror coatings Multi-layer sunshade Solar radiation reduced by >10 6 Mirror heated to ~24±0.01 C Coronagraph for planetary detection/characterization Cameras and spectrographs for general imaging/spectroscopy 3 x 3 arcmin FOV Launched with EELV to L2 Delta IV or Atlas V Direct or Lunar flyby 6-DOF Secondary 28-m Primary Design Easily Scaled to 8 or 12 meter Apertures 50m 3 Science Instrument Module ~35 x 50-m Multi-layer Sunshield 10

11 NHST Telescope Technology Needs Large, lightweight optics 5-10 kg/m 2 areal density 0.5 mm diffraction limited (0.2 mm goal) Surface roughness < 10 Angstroms (3 Angstroms goal) Mid-spatial frequency errors < 1 nm RMS Lightweight, compact, nanometer resolution actuators Low-cost mirror fabrication Thin replicated mirrors Composite design Mandrel production Large segment production High reflectivity mirror coatings Large deformable mirrors 1-2 millimeter pitch Could be segmented, with tip/tilt piston stage for individual modules Precision deployable structure testbeds Secondary support structures Multi-ring primary mirrors 11

12 Composite Mirror State-of-the-Art Mirror segments produced using replication techniques COI 2-m FIRST demonstrator - Cervit mold polished by University of Arizona 0.25 µm surface accuracy; 100 Angstroms smoothness - Production from 2/99-8/99 - Good wavefront performance 2.32 µm RMS After removing 1st 36 Zernickes, 1.00 µm RMS at room temperature 1.21 µm RMS at 200K vs. 0.2 µm RMS at 30K requirement - Design extrapolated to 3.5 m diameter at 11.4 kg/m 2 CMA thin replicated mirrors - Pyrex mold - 15 cm spheres at 0.79 µm RMS and 1.3 kg/m 2-90 cm sphere at 1.7 kg/m 2 - Surface roughness <10 Angstroms has been demonstrated. - Mid-spatial frequency errors <3 nm RMS has been demonstrated. Composite mirror technology is on track to meet NHST requirements 12 Technology Roadmap 10-9

13 Telescope Deployment Highly mass and volume efficient concept developed for JWST, applicable to NHST 13

14 High Accuracy Reflector Demonstration GHz reflector developed in with 25 micron rms repeatability, 5 kg/m 2 areal density 14

15 Multi-Ring Mirror Mirror Deployment Automatic deployment concept expandable to much larger apertures 15

16 Summary Segmented telescope design concepts developed for aperture sizes from 4 to 28 meters Wide range of options for system trades and analyses Single ring preferred for cononography Enabling technologies at Technology Readiness Level 4-5, could be ready for 2012 launch Replica optics technology demonstrated by CMA for smaller segments o Could provide large cost and schedule reductions Modular deformable mirrors now being developed by Xinetics Primary mirror deployment approach demonstrated, mechanisms developed Deployable telescope testbed needed to for system level demonstration, including secondary mirror deployment No technical show-stoppers identified 16