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

C. F. LillieNext Large Aperture Optical/UV Telescope Workshop11 April 2003

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Science ObjectivesContinue 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

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Design Begins With Top-Level RequirementsRequirement

Parameter Class I Mission 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

WP

Aperture 4.2 meters 8 meters WP

Effective Area >2.0 m2 (10 x HST/COS) >10.0 m2 WP

Spectral Multiplexing ≤ 2 integrations at R=30,000 ≤ 2 integrations at R=30,000 WP

Spatial Resolution 30 mas at 500 nm required <10 mas at 115 nm goal

15 mas at 500 nm <5 mas at 115 nm goal

WP, NGST

Wavelength Coverage 115-320 nm for spectroscopy 200-1000 nm for imaging (115-1000 nm goal) 350-1000 nm for integral field

115-320 nm for spectroscopy 200-1000 nm for imaging (115-1000 nm goal) 350-1000 nm for integral field

WP

Field of View 13.6 x 17.9 arc minutes 12.3 x 15.8 arc minutes WP

Imaging CCD for tracking/acquisition, plus 16K2 for WF and Hi-res imaging

CCD for tracking/acquisition, plus 24K2 for WF and Hi-res imaging

WP

Discovery Efficiency ≈ 100 to 480 ≈ 500 to 1760 WP Launch Date 2010 2012 WP, NGST Mission duration 5 years, 10 year goal 5 years, 10 year goal WP Mission Cost Target $450M WP

WP refers to UVOWG White Paper; NGST refers to requirements derived by Northrop Grumman Space Technology

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Requirements Flowdown Process Refines Requirements

Slew rate

Operational scenario development, performance modeling, and system sizing

Field of regard

Telescope temperature

Field of view

Coronagraph spot size

Pointing control

Integration time

Spectral resolution

Data rate

Aperture

Target CharacteristicsContrast ratioAngular size

Star-Planet SeparationDistribution on sky

Target List

Mission Requirements

SNR for detectionSNR for

characterization

Phenomenology

Mission duration

Max time per target

UV wavelength rangeVIS wavelength range

Galaxies & Clusters, Quasars & IGMStars & planets

Background emissions

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A Single Requirement Can Impact Many Areas

Number of Targets Duration of

Mission

Slew Time

Settle Time

AverageSeparation of

TargetsSlew Rate RWA Size

Flight System Dynamics

TelescopeStiffness

Sunshield Stiffness

Distribution of Targets

Target Brightness

Angular Size of Planet Orbit

Types of Stars

Number of Mirror Segments

IntegrationTime

Performance of Telescope

Readout Rate

FPA Read Noise

Data RateData

Processing

Data Storage

Aperture

CollectingArea

Spot Size

Sky Coverage

Slew Range

SunshieldDimensions Thermal

Control

SunshieldDeployment

TelescopeDeployment

Manufacturing Schedule

WFE

Coronagraph Performance

Size of Habitable Zone

Deformable Mirror

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Candidate NHST Optical Configuration

Telescope LOSSecondaryMirror

Primary Mirror with 6 to 36 Replicated Segments and Protected Al Coatings

TertiaryMirror

Focal SurfaceInterface to Instrument Module

FSM/Segmented DM

6-7 m flat-to-flat

Tip/Tilt/Piston Actuators

Reaction Structure

ROC Actuator (in center) • 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 launchActuators 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

TMA provides Wide FOV with few surfaces for high throughputSimple 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 ACSSegmented deformable mirror corrects for higher order uncorrected Wave Front errorsSimple, clean interface keeps AI&T and verification costs low

Replicated Mirror

Force Actuators at corners

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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 mid-spatial 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

0%

10%

20%

30%

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50%

60%

70%

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1 4 7 10 13 16Number of Actuators

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Power

Astigmatism

Trefoil

Moments atMounts

Actuator Quantity Trades: Figure Correct ability vs. Number of Actuators

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Deployable UVO Telescope

• Telescope Baffles omitted for clarity

Solar Array (1 of 2) 4.5 m dia.

Primary Mirror

6-DOF Secondary Mirror

Spacecraft Bus

Inflatable Sunshade

Instrument Module

High Gain Antenna

• 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

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11/24/98

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9.5’ Delta II Fairing

Launch Vehicle Adapter

Inflatable Sunshade

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

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(Very) Large Aperture Telescope Design Concept28-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 >106

– Mirror heated to ~24±0.01° CCoronagraph for planetary detection/characterizationCameras and spectrographs for general imaging/spectroscopy

– 3 x 3 arcmin FOVLaunched with EELV to L2

– Delta IV or Atlas V– Direct or Lunar flyby

~35 x 50-m Multi-layer Sunshield

28-m Primary

6-DOF Secondary

50m3 Science Instrument

Module

Design Easily Scaled to 8 or 12 meter Apertures

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NHST Telescope Technology NeedsLarge, lightweight optics

– 5-10 kg/m2 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 coatingsLarge 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

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Composite Mirror State-of-the-ArtMirror 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/m2

– CMA thin replicated mirrors- Pyrex mold- 15 cm spheres at 0.79 µm RMS and 1.3 kg/m2

- 90 cm sphere at 1.7 kg/m2

- 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

Technology Roadmap 10-9

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Telescope Deployment

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

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High Accuracy Reflector Demonstration

60- 94 GHz reflector developed in1991-92 with 25 micron rms repeatability, 5 kg/m2 areal density

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Multi-Ring Mirror Mirror Deployment

Automatic deployment concept expandable to much larger apertures

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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 segmentso 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 deploymentNo technical “show-stoppers” identified