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GoBears Telescope Ideas

GoBears Telescope Ideas. M. Lampton UCB Space Sciences Lab 15 March 2007. Overview of Telescopes. Telephoto ratio = effective focal length / telescope package length; EFL is constrained by pixel size / angular resolution Telescope package length is constrained by spacecraft envelope.

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GoBears Telescope Ideas

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  1. GoBears Telescope Ideas M. Lampton UCB Space Sciences Lab 15 March 2007

  2. Overview of Telescopes Telephoto ratio = effective focal length / telescope package length; EFL is constrained by pixel size / angular resolution Telescope package length is constrained by spacecraft envelope. M. Lampton, UCB SSL Mar2007

  3. Zurbuchen et al 2007 Ritchey-Chretien cassegrain with refractive corrector/flattener M. Lampton, UCB SSL Mar2007

  4. But.... • Lenses are not usually first choice in space environment; radiation damage can degrade transparency • Field correction is marginal if 2.3 degree field full-width is sought *and* if diffraction limited images are required • Better is to adopt a telescope design whose theoretical performance allows significant margins --- so that the in-process degradations still allow full on-orbit performance M. Lampton, UCB SSL Mar2007

  5. However.... • Ritchey-Chretien + corrector may well be cheapest alternative! Important! Two mirrors, five lenses, one barrel. • Ritchey-Chretien + corrector may well be quickest alternative! Also important! • Ritchey-Chretien + corrector may well be the least fussy! Tolerant of misalignments, easiest focussing. • It may well prove best to deliver some telescope that is quick & cheap rather than something that is the best optically! M. Lampton, UCB SSL Mar2007

  6. What is usual: mountaintops? • Wide field mountaintop observatories have all gone to Ritchey-Chretien + corrector configuration • Sloan Digital Sky Survey: 2.3 deg field, five wavebands vis-NIR, flat field • Not diffraction limited! • Seeing limited, ~ one arcsecond. OK when viewing upward through atmosphere M. Lampton, UCB SSL Mar2007

  7. What is usual: space? • Hubble is a Ritchey-Chretien • no corrector • not widefield: narrow field observatory • strongly curved focal surface • strong astigmatism M. Lampton, UCB SSL Mar2007

  8. What is usual: spaceborne remote sensing? • Three-mirror anastigmats are the rule • “anastigmat” = no spherical, no coma, no astig, no curvature • Three powered (curved) mirrors + one flat mirror • no lenses, hence no chromatic aberration • since no chroma, can align/focus with a laser at one wavelength and be *certain* optimum at other wavelengths • waveband filters can however complicate this! • Easily diffraction limited throughout visible and NIR • Widely adopted for contemporary space astronomy: • narrow field telescopes e.g. JWST • wide field telescopes e.g. SNAP M. Lampton, UCB SSL Mar2007

  9. Example: Korsch 1972 style TMALampton & Sholl SPIE 2007 Fig 1 • 60 cm aperture • EFL=3.33m, f/5.55 • 5 mirrors, no lenses • Baffling not shown • requires SM fez • requires outer tube • requires inner tube • 50% central obscur • Delivers 2 micron rms geometrical over 2.2 degree field diam • Flat field • No spherical, astig, chroma, coma, .... 6 surfaces GoBears3.OPT MLL Mar 2007 EFL=3.33m f/5.55 X Z pitch mir? Curv Aspher Diam dia ------:---.-------:------:------:----.-------:---.-----:------:-----:--- 0 : 0 : 0 : mir : -1.1294872? -0.95053? 0.62 : 0.2 : 0 : -0.33 : 0 : mir : -2.7749497? -4.20359? 0.28 : : 0 : 0.40 : 0 : mir : -1.5772654? -0.43998? 0.36 : : 0 : -0.03 : -20 : mir : 0 : : 0.19 : 0.05: -0.22: 0.2321858? -65 : mir : 0 : : 0.15 : : 0.22: 0.2321858e 90 : film : 0 : : 0.15 : : : : : : : : : : M. Lampton, UCB SSL Mar2007

  10. Resolution: MTF, PSF, EE M. Lampton, UCB SSL Mar2007

  11. Resolution Spreadsheet OPTICAL CONSTANTS Optical Aperture = 0.6 meters Focal Length = 3.33 meters f/number or "speed" = 5.55 VIEWING SITUATION Orbit Altitude = 460 km Orbit Speed = Desired Ground resol = 1.2 m Angular resolution = 2.61 microrad or angular resolution = 0.52 arc sec Required Linear resol = 8.69 microns Detector Pixel size= 8.8 microns RMS effect of pixels = 2.5 microns RMS blur silicon diffusion= 1.0 microns RMS blur attitude control = 0.0 microns RMS blur aberrations = 3.0 microns Total RMS Gauss= 4.0 microns Total FWHM Gauss= 9.6 microns BLUR SUM OF SQUARES INCLUDING DIFFRACTION Live linked to above data set Gaussians Bessel diffraction Total wavel FWHM FWHM FWHM microns microns microns w/diffract 0.30 9.6 1.7 9.7 microns 0.40 9.6 2.2 9.8 microns 0.50 9.6 2.8 10.0 microns 0.60 9.6 3.3 10.1 microns 0.70 9.6 3.9 10.3 microns 0.80 9.6 4.4 10.5 microns 0.90 9.6 5.0 10.8 microns 1.00 9.6 5.6 11.1 microns M. Lampton, UCB SSL Mar2007

  12. Signal/Noise Spreadsheet In work..... M. Lampton, UCB SSL Mar2007

  13. Conclusions so farRitchey-Chretien+Corrector versus TMA M. Lampton, UCB SSL Mar2007

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