Optical Telescope Assembly R&D Phase WBS 2.2

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 Overview • Science Driven Requirements • Baseline Characteristics • Telescope Status • R&D Issues • R&D Goals • R&D Schedule • R&D Manpower • R&D Costs • R&D Management • Summary

Overall Scheduledraft May 28 2002

Telescope: WBS Overview 2.2.2 TELESCOPE SYSTEMS ENGINEERING 2.2.2.1 Develop telescope requirements 2.2.2.2 Telescope design and evaluate trades 2.2.2.3 Telescope analyses 2.2.2.3.1 Optical performance 2.2.2.3.2 Stray light 2.2.2.4 Telescope I&T planning 2.2.3 TELESCOPE SUBSYSTEMS 2.2.3.1 Optical subsystems; GSE 2.2.3.1.1 Mirrors 2.2.3.1.2 Baffles 2.2.3.2 Mechanical: structure & GSE 2.2.3.2.1 Precision metering structure 2.2.3.2.2 Mechanisms: focussers, alignment... 2.2.3.2.2.1 Mirror actuators 2.2.3.2.2.2 Shutter 2.2.3.3 Thermal control 2.2.3.4 Electrical 2.2.4 TELESCOPE INTEGRATION AND TEST 2.2.5 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

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 TraceTMA62/TMA63 configuration Airy-disk zero at one micron wavelength 26 microns diam=0.244arcsec

Telescope Status: Pupil Obscuration Trades

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 FY04 FTE FTE --------------------------------------------------------------------------------- M.Lampton, SSL Team Lead 0.75 0.80 D.Pankow, SSL Mech/Therm Lead 0.40 0.40 M.Sholl, SSL Optics Lead 0.70 0.70 R.Pratt, SSL Mech Design 0.3 0.30 H.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 FY04 FTE FTE --------------------------------------------------------------------------------- Krim Consulting 0.25 0.5 Boeing-SVS -0- 0.25 Corning -0- 0.25 Breault 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

Optical Telescope Assembly R&D Phase WBS 2.2