telescope optical performance breakout session
Download
Skip this Video
Download Presentation
Telescope Optical Performance Breakout Session

Loading in 2 Seconds...

play fullscreen
1 / 35

Telescope Optical Performance Breakout Session - PowerPoint PPT Presentation


  • 112 Views
  • Uploaded on

Telescope Optical Performance Breakout Session. M.Lampton UCBerkeley Space Sciences Lab 10 July 2002. Optical Performance: Overview. Review Image quality Diffracted Starlight Stray (scattered) Light Acquisition Plan Materials, manufacturing etc will be discussed in Pankow’s talk.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Telescope Optical Performance Breakout Session' - job


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
telescope optical performance breakout session

Telescope Optical PerformanceBreakout Session

M.Lampton

UCBerkeley Space Sciences Lab

10 July 2002

optical performance overview
Optical Performance: Overview
  • Review
  • Image quality
  • Diffracted Starlight
  • Stray (scattered) Light
  • Acquisition Plan
  • Materials, manufacturing etc will be discussed in Pankow’s talk
review
Review
  • 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
image quality 1 tma62 tma63 configuration
Image Quality 1TMA62/TMA63 configuration

Airy-disk zero at one micron wavelength

26 microns diam=0.244arcsec

image quality 2 continued
Image Quality 2 continued
  • Although the range of radii in use within the focal plane is the nominal design range 129 to 283mm, the extremes are poorly populated with pixels
image quality 3
Image Quality 3
  • Science SNR drives Strehl ratio
    • Imperfections in delivered wavefront cause central PSF intensity to be less than ideal diffraction-limited PSF
    • This ratio is the “Strehl Ratio”
  • Systems Engineer manages WFE budget
    • geometrical aberrations
    • manufacturing figure errors & cost
    • alignment errors in 1-g environment
    • gravity release in mirrors & structure
    • launch induced shifts & distortions
    • on-orbit thermal distortion
    • ageing & creep of metering structure
    • how many on-orbit adjustments?
  • Primary mirror dominates WFE budget because it is the most expensive to figure.
  • Non-optical factors:
    • Attitude control system stability
    • Transparency & optical depth in silicon

Marechal’s equation relates WFE and Strehl

image quality 4
Image Quality 4
  • For diffraction-limited optics, rmsWFE or Strehl @0.633um is usually the governing procurement specification
  • SNAP exposure-time-critical science is at wavelengths > 0.63um
  • Science team needs to be aware of cost/schedule/quality trades
image quality 6
Image Quality 6
  • Example: overall telescope 43 nm RMS WFE
    • gives Strehl= 0.93 at 1000 nm
    • gives Strehl=0.90 at 830 nm
    • gives Strehl=0.83 at 633 nm
  • Example: overall telescope 50 nm RMS WFE
    • gives Strehl=0.91 at 1000 nm
    • gives Strehl=0.87 at 830 nm
    • gives Strehl=0.77 at 633 nm
  • WFE to be budgeted among pri, sec, flat, and tertiary mirrors
    • detailed breakdown to be determined
  • How sensitive are cost & schedule to our WFE specification?
  • Encircled Energy specification needs to be defined
    • central obstruction 40% radius, 16% area
    • with this obstruction alone, EE=50% at 0.088arcsec diam @633nm or EE=80% at 0.23arcsec diam @633nm
    • Budget lower EE for aberrations, spider, figuring, thermal, gravity..
image quality 7
Image Quality 7
  • Strehl vs Aperture Trade
    • Strehl (image quality) costs time & money
    • Aperture (image quantity) costs time & money
    • Central obscuration trades off with stray light
    • NIR (not visible) is where SNR demands the most observing time
    • Is 77% Strehl and 2.0 meters aperture the right mix?
  • Encircled Energy Specification
    • High spatial frequency figure errors lose photons
    • Low spatial frequency figure errors broaden the encircled energy
    • Steeper EE curves demand absence of LSF amplitudes
    • Is 70% EE at 0.1 arcsecond the right target?
  • Quantitative answers require modelling
  • Our sim team can deal with image quality trades
  • We expect to resolve these issues during R&D phase
slide20

Circular 2meter aperture

0.7 meter central obscuration

slide21

Circular 2m aperture

Three radial legs, 50mm x 1 meter

slide22

Circular 2m aperture

central 0.7m obscuration

Three legs, 50mm x 1meter

diffracted starlight 11
Diffracted Starlight 11
  • Extensive work with sim team
  • Modelling PSF for SNR, exposure times...
  • Modelling wings of diffraction pattern
  • Algorithms for photometry in presence of diffraction
  • Determination of effective SNR
  • Inputs from our known sky, down to V=19 (SDSS)
  • How well can these effect be modelled?
stray light 1
Stray Light 1
  • 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
  • ISAL conclusion: “manageable”
  • Long outer baffle is clearly preferred
    • limit is launch fairing and S/C size
  • ASAP software in place
  • ASAP training begun
  • Preliminary telescope ASAP models being built
  • ASAP illumination environment models not yet started
  • Our intension is to track hardware & ops changes as they occur, allowing a “system engineering management” of stray light.
optical performance throughput
Optical Performance: Throughput
  • Protected silver
    • provides highest NIR reflectance currently available
    • durability is an issue: 3 years at sea level prior to launch
    • this is our baseline
    • new developments at LLNL: Thomas & Wolfe process
  • Protected aluminum
    • highly durable coating
    • slight reflectance notch at 0.8 microns wavelength
    • after four reflections, amounts to 30-40% loss at 0.8 um
    • prefer to retain high reflectance at 0.8 microns
    • not our first choice
telescope acquisition plan
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
test plans
Test Plans
  • Individual Mirror Testing
  • Assembly into metering structure
  • Assembled optical testing
    • interferometric
    • reflex testing against reference flat
  • Integration with focal plane assembly
  • End-to-end testing
    • in air at room temperature
    • in vacuum or dry N2 with cold focal plane
    • reflex testing against reference flat
telescope summary
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
ad