Optical Telescope Assembly R&D Phase WBS 2.2

M. Lampton

Space Sciences Laboratory

University of California Berkeley

09 July 2002

Draft OTA10, 5 June 2002

Telescope: Overview

Schedule and WBS OverviewScience Driven RequirementsBaseline CharacteristicsTelescope StatusR&D IssuesR&D GoalsR&D ScheduleR&D ManpowerR&D CostsR&D ManagementSummary

Overall Scheduledraft May 28 2002

Telescope: WBS Overview

2.2.2 TELESCOPE SYSTEMS ENGINEERING2.2.2.1 Develop telescope requirements2.2.2.2 Telescope design and evaluate trades2.2.2.3 Telescope analyses2.2.2.3.1 Optical performance2.2.2.3.2 Stray light2.2.2.4 Telescope I&T planning2.2.3 TELESCOPE SUBSYSTEMS2.2.3.1 Optical subsystems; GSE2.2.3.1.1 Mirrors2.2.3.1.2 Baffles2.2.3.2 Mechanical: structure & GSE2.2.3.2.1 Precision metering structure2.2.3.2.2 Mechanisms: focussers, alignment...2.2.3.2.2.1 Mirror actuators2.2.3.2.2.2 Shutter2.2.3.3 Thermal control2.2.3.4 Electrical2.2.4 TELESCOPE INTEGRATION AND TEST2.2.5 TELESCOPE SOFTWARE (alignment; focussing)2.2.6 TELESCOPE SUPPORTING ACTIVITIES

Telescope: Science Driven Requirements

• Light Gathering Power — must measure SNe 4 magnitudes fainter than 26 magnitude peak

— require SNR of 50:1 at peak brightness

— presence of zodiacal light foreground radiation

— time-on-target limited by revisit rate & number of fields

— spectroscopy demands comparable time-on-target

— requires geometric diameter ~ 2 meters

• Angular resolution— signal to noise ratio is driver

— diffraction limit is an obvious bound

— Airy disk at one micron wavelength is 0.12 arcseconds FWHM

— other blur contributions must be kept well below this limit.

• Field of View— determined by required supernova discovery rate

— volume of space is proportional to field of view

— one degree field of view will deliver the requisite discovery rate

• Wavelength Coverage— 0.35 to 1.7 microns requires all-reflector optical train

Telescope Status: Baseline Configuration

• Prolate ellipsoid concave primary mirror• Hyperbolic convex secondary mirror• Flat folding mirror with central hole• Prolate ellipsoid concave tertiary mirror• Flat focal plane• Delivers < 0.06 arcsecond FWHM geometrical blur over annular field 1.37 sqdeg• Adapts to focal lengths 15 meters through 30 meters; baseline=21.66m• Provides side-mounted detector location for best detector cooling

Baseline OTA Characteristics

• Aperture: 2 meters

• Annular Field of View: ~1 sq deg

• Wavelength Range: 0.35 to 1.7 microns

• Strehl: >90% at 1.0 microns

• WFE: <50 nm RMS

• Focal surface: flat

• EFL: 21.66 meters, f/11

• Stray light: << Zodiacal foreground

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Telescope Status: History

• Wide-field high-resolution telescopes are NOT new—Schmidt cameras (1930 to present)

—Wynne cameras (e.g. FAUST)

—Field-widened cassegrains, Gascoigne (1977-); SDSS

—Paul three-mirror telescopes (1935) and Baker-Paul

—Cook three-mirror anastigmats “TMAs” (1979)

—Williams TMA variants (1979)

—Korsch family of TMAs (1980)

—Angel-Woolf-Epps three-mirror design (1982)

—McGraw three-mirror system (1982)

—Willstrop “Mersenne Schmidt” family (1984)

—Kodak “IKONOS” Earth Resources telescope = TMA

—LANL/Sandia/DoE Multispectral Thermal Imager = TMA

Telescope Status: Downselection

• 1999-2002: TMA Suitability Assessments—off-axis designs attractive but unpackagable; rejected

—four, five, and six-mirror variants explored; rejected

—annular field TMA concept rediscovered & developed

—TMA43 (f/10): satisfactory performance but lacked margins for adjustment

—TMA55 (f/10): improved performance, shorter pri-sec, margins OK

—TMA59 (f/15): same but with longer focal length

—TMA62 (f/11): transverse rear axis with filter wheel

—TMA63 (f/11): transverse rear axis, no filter wheel

Payload Layout 1

Telescope is a three-mirror anastigmat

2.0 meter aperture

1.37 square degree field

Lightweight primary mirror

Low-expansion materials

Optics kept near 290K

Transverse rear axis

Side Gigacam location

passive detector cooling

combines Si & HgCdTe detectors

Spectrometers share Gigacam focal plane

Minimum moving parts in payload

shutter for detector readouts

Payload Layout 2

Telescope: Image Quality Issues

• Image quality drives science SNR, exposure times, ....

• Many factors contribute to science image quality— diffraction: size of aperture, secondary baffle, struts, ...

— aberrations: theoretical imaging performance over field

— manufacturing errors in mirrors

— misalignments & misfocussing of optical elements

— dirt, contamination, or nonuniformity in mirror coating

— guiding errors

— spacecraft jitter

— detector issues

• Work has begun on a comprehensive budget— ongoing simulation team efforts

— Bernstein’s “Advanced Exposure Time Calculator” PASP

— telescope studies feed into the simulations

Telescope Status: Ray Trace

TMA62/TMA63 configuration

Airy-disk zero at one micron wavelength

26 microns diam=0.244arcsec

Telescope Status: Pupil Obscuration Trades

Three 4cm ThickRadial Vanes

Six 2cm thickTangential Vanes

Ø2m

Ø45cm

3X 4cm

Ø45cm

Ø2m6X 2cm

Ø2m

Radial VanesFour 4cm Thick

Ø45cm

3X 4cmØ2m

Ø45cm

Tangential VanesEight 2cm thick

6X 2cm

Telescope Status: Stray Light Trades

• Guiding principle: keep total stray light FAR BELOW natural Zodi

• R.O.M. assessment gives...

— Natural Zodi (G.Aldering) = 1 photon/pixel/sec/micron

— Starlight+Zodi scattered off primary mirror = 0.002

— Starlight+Zodi scattered off support spider < 0.001

— Sunlight scattered off forward outer baffle edge = 2E-5

— Earthlight scattered off forward outer baffle inner surface = 0.02

— Total stray = 0.02 photon/pixel/sec/micron

• Long outer baffle is clearly preferred

— limit is launch fairing and S/C size

• ASAP software in place

• ASAP training 2001; further training in 2003

• Preliminary telescope ASAP models being built

• ASAP illumination environment models being built

• Our intension is to track hardware & ops changes as they occur, allowing a “system engineering management” of stray light.

Telescope Technology Roadmap

• Existing technologies are suitable for SNAP Optical Telescope Assembly• New materials, processes, test & evaluation methods are unnecessary• Mirror materials

— Corning ULE glass: extensive NRO flight history; lightweight

— Schott Zerodur glass/ceramic composite: lower cost, widely used in ground based astronomical telescopes; huge industrial base

— Astrium/Boostec SiC-100: newcomer; unproven in space optics; higher CTE; adoped for Herschel/FIRST in infrared

• Metering structure materials— M55J carbon fiber + cyanate ester resin; epoxy adhesive bonds

— full report in Pankow presentation

• Mirror finishing technology— conventional grind/polish/figure using abrasives

— ion-beam figuring available from two vendors

• Mirror surface metrology— same as other space telescopes, e.g. cassegrains

— standard interferometer setups will do the job for SNAP

— no unusual accuracy drivers have been encountered

Telescope Status: Mirror Materials Trade

• Corning ULE ultra-low expansion glass— face sheets bonded to honeycomb core

— achieves 85-90% lightweight; anticipate 250kg primary

— extensive manufacturing & test history

— meets our performance requirements

— attractive for its high natural resonance frequencies, low sag

— eases mass margin for entire mission

• Schott Zerodur glass/ceramic material— solid blank, weight relieved by milling backside

— achieves 70-80% lightweight; anticipate 350kg primary

— extensive manufacturing & test history

— meets our performance requirements

• Study contract is in place

Telescope Trade Studies Summary

• Trade Studies worked during Pre-R&D Phase

— Optical configuration: >>TMA

— Warm optics vs cold optics: >>warm

— FIDO integrated sensor array vs separated: >>integrated

• Trade Studies continuing through R&D Phase

— Mirror materials: ULE vs Zerodur vs others

— Exact aperture: cost & schedule vs aperture

— Strehl ratio: cost vs performance

— Focal length: is 21.66m the right value?

— Pupil obscuration issues

• secondary mirror baffle

• strut configuration

— Mirror thickness, rib design, stiffness, mass....

— Protoflight vs Prototype + Flight metering structures

— Detailed test & acceptance sequence

• gravity unloading scheme

• full aperture vs partial aperture

• during thermal-vacuum testing?

Telescope: Overall Risk Assessment

• Mirror fab/test risks

—Far less demanding than HST: we are NIR not NUV

—yet -- need comprehensive test plan.

• Mechanical structural risks

—comprehensive test plan: static, dynamic, etc

• Thermal and mechanical disturbance issues

—“Easy” thermal environment: HEO has few eclipses

• Schedule risks: OTA is a long lead item!

• Error budget: fixturing, optical test equipment, etc

—Do we need a full-aperture reference test flat?

• Contamination control: materials & test plan

• Stray light control: management & test plan

Telescope: Main R&D Issues

• Critical path: telescope is a long lead item.

—how big is our slack?

• Need to begin development of the OTA requirements document for potential bidders

—Need to refine performance specifications

—Need to understand & communicate tolerances

—Need to prepare draft Interface Control Documents

• optical

• thermal

• mechanical

• electrical

—Need to assess risks and take steps to minimize them

—Need to perform trade studies (outlined above)

Telescope: R&D Phase Deliverables

• Telescope Requirements Specification Document— include manufacturing tolerance; alignment specifications

• Subcontractors’ Final Reports

• Metering Structure Concept Trades

• Telescope Mirror Materials Trade Study

• OTA Thermal Model and Results Summary

• Focussing/Alignment Tolerance Analysis

• Focussing/Alignment Mechanism Trade Study

• Front Aperture Door: Trade Study

• Integration Flow and Test Plan

• Preliminary Stray Light Analysis

• Shutter Mechanism Reliability & Failure Modes Study

• Telescope acquisition plan: schedule/milestones, cost.

Telescope Acquisition Plan

• Potential Vendors Identified

— Ball Aerospace Systems Division (Boulder)

— Boeing-SVS (Albuquerque/Boulder)

— Brashear LP (Pittsburgh)

— Composite Optics Inc (San Diego)

— Corning Glass Works (Corning NY)

— Eastman Kodak (Rochester)

— Goodrich (Danbury)

— Lockheed-Martin Missiles & Space Co (Sunnyvale)

— SAGEM/REOSC (Paris)

• These vendors have been briefed on SNAP mission

• Each has responded to our Request for Information

• Identify a route (materials, fabrication, test, integration, test)

— Milestones with appropriate incentives

— Visibility into contractor(s) activities

Telescope: R&D Schedule

• Zero-order Design Report 1 Aug 2003• Draft Requirements Review 1 Aug 2003• Long Lead Procurement Budget Request 1 Oct 2003• Systems Engineering Management Plan 1 Feb 2004• Performance Assurance Implementation Draft 1 Feb 2004• Risk Management Plan 1 Feb 2004• OTA Study RFP 1 Feb 2004• OTA Study Contract in place 1 Apr 2004• Preliminary Project Execution Plan 1 May 2004• Preliminary Hazards Analysis 1 May 2004• Systems Requirements Review 1 May 2004• Conceptual Design Report 1 Aug 2004

Telescope: R&D Phase Manpower

U.C.B. SSL Personnel -- Telescope FY03 FY04FTE FTE

---------------------------------------------------------------------------------M.Lampton, SSL Team Lead 0.75 0.80D.Pankow, SSL Mech/Therm Lead 0.40 0.40M.Sholl, SSL Optics Lead 0.70 0.70R.Pratt, SSL Mech Design 0.3 0.30H.Heetderks, SSL Systems (SE) (SE)

In addition -- we make use of varying amounts of support from LBNL engineering personnel.

Telescope: R&D Phase Contracts

Contracts -- Telescope FY03 FY04FTE FTE

---------------------------------------------------------------------------------Krim Consulting 0.25 0.5Boeing-SVS -0- 0.25Corning -0- 0.25Breault Research Organization -0- 0.1

Telescope: R&D Phase Management

• Management objective: biddable Requirements Document that reflects all science requirements and trades

• Experienced team has been assembled

• Have begun dialogs with prospective vendors

• Have begun examining potential fab/test flows

• No need for high-risk “advanced” materials or processes

• Emphasize proven manufacturing & test techniques

• We plan on selection of contractor(s) with sufficient experience to bring successful delivery cost & schedule

• This contractor mix defines the overall acquisition plan

Telescope: CDR Preparations Plan

• Fully complete and document all trade studies

• Supplement these with industry commentary

• Use system-engineering “budgets” to identify optimum allocation of tolerances & resources

• Identify materials and fabrication alternatives taking into account schedule risk and overall cost

• Detail the acquisition plan and milestones

• Prepare acceptance test plan, including flight qual tests:— Structural stability, thermal, stiffness, normal modes, creep

— Alignment and focussing plan

— Thermal vacuum and optical stability

— Stray light

— Gravity unloading plan

— Full-aperture and limited-aperture test opportunities

— Facilities needed, facilities available

Telescope: Summary

• Pre-R&D

— converted science drivers into telescope requirements

— reviewed existing optical telescope concepts

— developed annular-field TMA configuration

— preliminary materials assessment

— begun to explore vendor capabilities

— started a budget for image quality

• R&D Phase

— engineering trade studies and “budgets”

— manufacturing process risk assessments

— test plans and associated cost/risk trades

• facilities; equipment

— prepare the acquisition plan

— performance specifications & tolerance analysis

— create draft ICDs

— develop preliminary cost & schedule ranges