# Presentation: 407870

## Optical Telescope AssemblyWBS 2.2

**M. Lampton**
**     ****Space Sciences Laboratory**
**University of California Berkeley**
**09  July 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 Scheduledraft May 28 2002

## Telescope:  WBS Overview

**2.2.1        TELESCOPE MANAGEMENT**
**2.2.1.1      Telescope Management**
**2.2.1.2      Resource Management**
**2.2.1.3      Schedule Management**
**2.2.1.4      Configuration Management**
**2.2.1.5      Reviews**
**2.2.1.6      Travel**
**2.2.1.7      Contracts**
**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**
**2.2.6        TELESCOPE SUPPORTING ACTIVITIES**

## Telescope: Science Driven Requirements

**Light Gathering Power **
**must measure SNe 4 magnitudes  fainter than 26 magnitude  peak**
**want SNR of  30:1 at peak brightness, aggregate exposure fit**
**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**
**all blur contributions must be budgeted**
**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

**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: Milestones Accomplished

**1999**
**comparisons of alternative wide field telescope configurations**
**found off-axis designs attractive but unpackageable; rejected**
**explored, discarded coaxial TMTs (Willstrop etc): unworkable thermally**
**annular-field TMA concept rediscovered, developed **
**2000**
**TMA43 (f/10): longitudinal rear axis, separate NIR/VIS;  filter wheel**
**began mechanical, structural studies w/ subcontractor**
**explored vignetting (marginal), stray light (marginal)**
**2001**
**US DoE R&D Review**
**efforts to achieve shorter optical package for stiffness, stray light: TMA55/56**
**explored longer focal lengths for potentially higher sampling: TMA59 (f/15)**
**design validated at NASA/GSFC Instrument Systems Analysis Laboratory**
**image quality;  stray light;  metering structure; actuators**
**2002**
**FIDO detector package, single focal plane, transverse rear axis**
**TMA62 (f/11): transverse rear axis with filter wheel**
**TMA63 (f/11): transverse rear axis, no filter wheel**
**major efforts in materials, metering structure,  thermal,  launch loads....**
**detailed mirror analysis & trades with subcontractor**

## Payload Layout   1

**Payload Layout   1**

- Main Baffle Assembly

- Door Assembly

- Solar Array, ‘Sun side’

- Secondary Mirror
- Hexapod
- Bonnet

- Secondary Metering structure

- Primary Mirror

- Optical Bench

- Instrument Metering Structure

- Tertiary Mirror

- Fold-Flat Mirror

- Spacecraft

- Shutter

- Instrument Bay

- Instrument Radiator

- Solar Array, ‘Dark side’

- Hi Gain Antenna

- Solid-state recorders

- ACS
- CD & H
- Comm
- Power
- Data

- CCD detectorsNIR detectorsSpectrographFocal Plane guiders
- Cryo/Particle shield

## Payload Layout  2

- 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
- Few  moving parts in payload
- two-blade shutter for Gigacam
- focussers/adjusters at secondary & tertiary

## Payload Layout  3

## 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**
**constancy of the PSF is important to the weak lensing science**
**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

## 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**
**science driver: *stable* figure to guarantee constant focus and PSF**
**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**
**Metering structure materials**
**science driver:  *stable* structure for constant focus and PSF**
**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**

## Telescope  Status: Mirror Materials Trade

**Corning ULE ultra-low expansion glass**
**extremely low CTE: 20-50 parts per billion per dec C**
**face sheets bonded to honeycomb core**
**achieves 85-90% lightweight; anticipate 200kg 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**
**extremely low CTE:  20-50 parts per billion per deg C**
**solid blank, weight relieved by milling backside**
**achieves 70-85% lightweight; anticipate 250kg primary**
**extensive manufacturing & test history**
**meets our performance requirements**

## 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**
**Exact aperture: cost & schedule vs aperture**
**Wavefront error: cost vs  performance**
**focal length: is 21.66m the best choice?**
**pupil obsuration, diffraction, stray light...**
**Primary mirror thickness, stiffness, mass trade**
**resonance freqs, sag under 1G testing, ...**
**Protoflight vs Prototype + Flight metering structures**
**Vendor-dependent issues**
**mirror material: ULE? Zerodur?**
**test: gravity unloading scheme**
**test:  full aperture vs partial aperture**

## 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**
**optical image quality**
**stability of focus, point spread function, ...**
**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**
**Focusing/Alignment Tolerance Analysis**
**Focusing/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 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/integration 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**

## OTA R&D Schedule

## OTA: R&D Schedule

## Deliverables WBS 2.2 Telescope

## 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 acceptance 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**