Technology Development for ELTs

Steve StromTerry Herter

Doug Simons

GSMT SWG April 28, 2003

2

Driving Science Themes

The Birth of Galaxies:The Archaeological Record

The physics of young Jupiter's

Characterize Exo-Planets

The Birth of Planetary Systems

The Birth of Galaxies:

Witnessing the Process

Directly

The Birth of Large

Scale Structure

3

And Science Themes Drive Needed Performance…

The physics of young Jupiter's

The Birth of Galaxies:The Archaeological Record

Near-diffraction limited performance over

~ 2 arc-minute fields

Characterize Exo-PlanetsHigh dynamic range

imaging

High sensitivity Mid-IR

spectroscopy

The Birth of Galaxies:

Witnessing the Process

Directly

Enhanced-seeing over ~ 5

arc-minute field

The Birth of Large

Scale Structure

Wide-field, seeing-limited multi-object spectroscopy

The Birth of Planetary Systems

4

Achieving Needed Performance Requires Technology Development

• Multiple ELT programs have identified key technology investments and studies required to achieve desired performance

• Four key areas require investments• For each of the above we summarize

– The need for new or enhanced technology– Potential performance enhancements– Relationship to science enabled– Other investment returns: e.g. reliability;

cost

Telescope Systems

Wind

Site Characterization

Adaptive Optics SystemsInstrumentation

5

Telescope Systems & Key Technologies

CELT Magellan 20GSMTAdaptive Secondary Mirrors

High Performance Durable CoatingsAdvanced Primary Mirror Materials

Active Optics Control Systems

6

Active Optics Control Systems

• Requirement– Control primary segment alignment errors and secondary mirror

misalignments due to gravity, temperature, and windshake

• Need– Inexpensive and reliable sensors and actuators; robust control

• Potential performance enhancements– Essential for telescope concepts with small segments

• Potential science gain– Reduced PSF artifacts; improved Strehls with AO

• Potential cost/reliability gains– Reduced costs/simplified fabrication of small segments

7

Alternate Mirror Technologies

• Requirement– Light weight, readily molded + polished segments of size 1-2m

– SiC?

• Need– Reduce complexity and cost for primary mirror system

• Potential performance enhancements– Higher bandwidth for active control system

• Potential science gain– none

• Potential cost/reliability gains– Major savings in life-cycle costs

8

Alternative Technologies: Adaptive Primary

• Requirement– Smaller segments (~ 0.5 – 1 m)

– Bandwidth to handle wind buffeting

• Need– First element of AO system for GSMT, CELT & LAT designs

• Potential performance enhancements– Higher throughput, lower emissivity

– Larger primary mirror (for given cost)

• Potential science gain– Reduced time to complete all programs

• Potential cost/reliability gains– Major savings in mount costs (lighter weight system)

9

Alternative Technologies: Adaptive Secondaries

• Requirement– ~ 2m deformable mirror with ~2000 actuators and 5-10 micron stroke

• Need– First element of AO systems– For Magellan 20: key to phasing optical elements– For GSMT: wind-buffeting compensation

• Potential performance enhancements– Efficient ground-layer compensation– Low emissivity, high throughput AO feed for mid-IR

• Potential science gain– Wide-field studies of high z galaxies– Imaging and spectroscopic studies of YSOs

10

High Performance, Durable Coatings

• Requirement– High reflectivity from 0.4 - 20 microns

– Retain coating performance for ~10 years

• Need– Minimize time between coatings; mirror handling

• Potential performance enhancements– Higher throughput, lower emissivity

• Potential science gain– Reduced time to complete all programs

• Potential cost/reliability gains– Major savings in life-cycle costs

11

Facility AO Systems

12

Systems & Key Technologies

• Multi-conjugate adaptive optics system– Systems design studies and

performance simulations

– Low cost, ultra-reliable Na lasers (20-50 W power)

– Deformable mirrors with up to 5000 actuators

– Fast readout, low-noise optical and infrared detectors

– Advanced wavefront control algorithms and processors MCAO Model

13

Systems & Key Technologies

• Extreme AO system– Systems design studies and

performance simulations– Deformable mirrors with up

to 10000 (or more) actuators

• Ground-layer adaptive optics system– Systems design studies and

performance simulations– Site studies to identify those

best suited to GLAO– Pathfinder systems to verify

proof of concepts

Natural

Compensated

Pachon Cn2 Profile

V

J

K

GLAO Model

14

Deformable Mirrors

• Requirement– Wavefront correction elements with >>1000 degrees

of freedom; high stroke– Multiple technology paths need exploration (MEMS;

thin face sheet DMs)

• Need– Enable high order correction and high Strehls over

desired FOV

• Potential enhancements– Significant improvement in delivered Strehl compared

to current DMs – Extension of AO performance to shorter wavelength

• Potential science gains– Improved photometric accuracy; higher fidelity

imaging of high contrast scenes

• Potential cost/reliability gains– Must reduce costs of conventional DM approaches

(~$1.5K/actuator)

Xinetics, ~12” clear aperture

MEMS(~ 1 cm)

15

Sodium Lasers

• Requirement– ~50 W Na lasers with good beam quality– Low-cost, robust commercialized product (solid-state; fiber

options); multiple vendors– Good wall plug efficiency and small footprint

• Need– Provide all-sky coverage for SCAO systems– Provide multiple beacons to enable wavefront

reconstruction for MCAO systems

• Potential enhancements– Strehl ~ 0.7 images at K-band over several arc-minute FOV

• Potential science gains– Enable accurate photometry in crowded fields– Extend AO performance to shorter wavelengths

• Potential cost/reliability gains– Increased reliability and reduced cost through investment in

2 or more product lines

Prototype Fiber Laser

16

Wavefront Sensors

• Requirement– 512x512 optical CCD with (1-3 e- readout noise); kHz readout rate– Larger arrays with 3-5 e- read noise for LGS wavefront sensing– 128x128 near-IR detector (~5 e- readout noise); kHz readout rate

• Need– Fast, well-sampled wavefront sensing– Fast tip-tilt correction in optically-obscured fields

• Potential enhancements– Improved delivered Strehl– Supports extension of AO performance to shorter wavelength

• Potential science gains– Improved image quality for all programs

• Potential cost/reliability gains– TE-cooled NIR AO sensors avoid complex cryo-environments

17

Wavefront Control Algorithms and Processors

• Requirement– Process ~30-50K WFS measurements to drive ~10K actuators at ~1KHz

• Need– Advanced, computationally efficient reconstruction algorithms– Implementations on parallel processors with low latency

• Potential enhancements– Enables MCAO– Supports extension of ExAO performance to shorter wavelength

• Potential science gains– Improved image quality for all programs

18

Site Evaluation

Remote sensing

Wind

CFD Simulations Weather stations Turbulence MASS

19

Key Requirement

• Uniform evaluation information + data for multiple sites– Cloud cover– Precipitable water vapor– Long-term weather patterns– Wind flow and turbulence modeling– in situ measurements of temperature; wind– Ground-layer and upper atmospheric turbulence measurements– Seismicity and geotechnical characteristics– Light pollution; demographic and ownership issues

20

Need for Investment

• Site choice is a key element in overall system performance– AO performance– Atmospheric transmission – Structure, enclosure and controls systems implications

• Delivered science is intimately linked with site characteristics• At this stage a range of sites should be evaluated

– Wide range of prime science cases among ELT groups– Final selection requires life-cycle cost vs science value trade

• Program must begin immediately– Site selection is on the critical path for CELT/GSMT

• A minimum 2-year base is desirable

– Mag20 favoring Las Campanas though still interested in comparing that site’s quality vs. alternatives before committing

21

First Steps - Remote Sensing Survey of Cloud Cover and PWV

• Survey uses meteorological satellite images

• Long time baseline

• Well-defined methodology provides:– Photometric, spectroscopic, unsuitable

conditions based on cloud cover– Precipitable water vapor above the sites

• Dispassionate comparison thus possible

• Areas studied:– Northern Chile – SW USA-Mexico– Mauna Kea – Chile comparison

• Finish August 2003

Various Sites Studied Thus Far

22

First Steps - Computational Fluid Dynamics

• Characterize wind flow to allow pre-selection of sites– Wind intensity

– Turbulence characteristics

– Down-wind wakes

• NIO has recruited CFD modeling expert -- Konstantinos Vogiatzis

• Characterization of Chilean sites well underway

• Analysis of other sites planned for 2nd Qtr 2003

Wind

Las Campanas Peak 2

500 m

Turbulent Kinetic Energy

23

First Steps - Weather Station on Honar

24

Measuring Turbulence Layers with MASS

25

Combining MASS + DIMM Results

Free atmosphere seeing steady at ~ 0.25” for 4 nights

26

GSMT Site Evaluation: Status

• NIO collaborating with Carnegie, CELT, Cornell, ESO, UH, UNAM; to test:– Las Campanas– Chajnantor– One or two additional Chilean Sites– Mauna Kea ELT site– San Pedro de Martir

• Status of “First Steps”:– Erasmus remote sensing studies (cloud cover; water vapor) nearly complete

• MK / US / Chile comparison to finish in August– CFD modeling of sites: good progress on first three sites – Weather stations deployed on several mountains– Multi-Aperture Scintillation Sensor (MASS):

• Performance verified by SCIDAR comparison• Manufacturing instruments for all sites

27

Site Evaluation: Needed Investment

• MASS and DIMM purchase and deployment• Weather station purchase and deployment• Common data analysis tools• Manpower to install and operate site evaluation stations• Manpower to compile and distribute common database• All of this proposed new investment builds upon

previously described “First Steps”

28

Instrumentation

29

Representative Science Instruments

• Multi-Object Multi-Fiber Spectrograph– Requires VPH gratings ~1 m in size

• Mosaic of diffraction gratings is possible fallback but this still requires tech-dev

– Photometric stability of ~60 m long fiber assemblies on moving telescope

– Mass production of fiber/lens coupling optics with high throughput

– Fiber-to-fiber coupler to simplify removal from telescope

30

• Million Element Integral Field Spectrograph– Large format cylindrical lenslet

arrays need to be developed– Mass production of individual

spectrograph components - atypical for astronomical instruments

– Complex high accuracy/capacity mechanism design replicated many times throughput instrument

• Major cost factor

Representative Science Instruments

31

• Deployable Integral Field Spectrograph– Mass produced IFU

technology– Cryogenic robotic arms

need development– Large format infrared

arrays in significant numbers (~30)

• Need to get cost per pixel down…

Representative Science Instruments

32

• Mid-IR High Dispersion Spectrograph– Large format mid-IR buttable

detectors– Advanced gratings

• Immersed Si?– Large cryogenic mechanisms

and high capacity cooling system

Representative Science Instruments

33

• MCAO Imager– Large cryogenic optics for full

field imaging

• ~500 mm CaF2 lenses

– Need ~1 Gpixel focal plane to sample full MCAO field

• ~50 4x4k detectors• Drives need to reduce

cost per pixel through tech-dev

Representative Science Instruments

34

Design Concept Studies

• Additional investment in design concepts is critical – Engage university and private sector groups– Encourage innovative designs– Key step to resolving uncertainties in performance, cost, and science trades– Used to develop firm cost estimates before proceeding to build instruments

• Given enormous costs of these instruments, this is an important risk reduction strategy

• Parallel funding of technology development and instrument design studies– Need to fund detector development soon, independent of instrument design

studies, since this is a long-lead effort with “dividends” applicable to most ELT instrumentation

– Some tech-dev best handled through design studies

35

Common Technology Needs

Adaptive Secondary

Durable Coatings

Alternate Segment (SiC)

AO system studies & simulations

Deformable Mirrors

Na Lasers

Detectors for Wavefront Sensors

Site Evaluation

Large format near-IR detectors

Large format mid-IR detectors ?

Image multiplexers ?

VPH; immersed Si gratings ? ?

Fiber Positioner ?

Large Mosaic Grating

Advanced Optical Nulling Technology

Instrument Concept studies

Mag 20 GSMT CELT LAT

36

Conclusions

• Investment in key technologies critical to all ELT programs• Large overlap in technology developments needed by all

ELT programs• The GSMT SWG should strongly endorse the following

recommendation from the decadal survey:

“The committee recommends that technology development for GSMT begin

immediately and that construction start within the decade.” Astronomy and Astrophysics Survey Committee

38

System Design Studies & Simulations

• Requirement– Modeling/Simulation tools that enable evaluation of AO system performance– Evaluation of alternative approaches to wavefront sensing; reconstruction

• Need– Design optimized AO systems tailored to science requirements– Guide system-wide trade studies (e.g. controls; instrument design)

• Potential enhancements– Improved wavefront correction

• Potential science gains– Improved sensitivity for all science programs

• Potential cost/reliability gains– Exploration of multiple design efforts prior to costly prototyping programs