1 / 17

GBI TMA CONCEPTS Rev B

GBI TMA CONCEPTS Rev B. M. Sholl 26 July 2007. Previous Work (UM and M. Lampton). Much good work has been done on RCC RC requires transmissive Corrector for wide-field applications (see Lampton presentations) Key advantages of RCC: Simple mechanical design (tube)

clancy
Download Presentation

GBI TMA CONCEPTS Rev B

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. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. GBI TMA CONCEPTSRev B M. Sholl 26 July 2007

  2. Previous Work (UM and M. Lampton) • Much good work has been done on RCC • RC requires transmissive Corrector for wide-field applications (see Lampton presentations) • Key advantages of RCC: • Simple mechanical design (tube) • Loose tolerances (thermal stability) • Major design tradeoffs between chromatic aberration, image sharpness and field distortion • Mapping imagers tend to be TMAs (Ikonos, Quickbird, Worldview, Nextview, Topsat, ROCSAT II, HiRISE)

  3. TMA: Three Mirror Anastigmat • Dietrich Korsch, 1972, proposed a class of telescopes with three curved mirrors • Anastigmatic Three Mirror Telescopes, Applied Optics, vol. 16, No. 8, August 1977 • Wide FOV, easy stray light baffling, zero chromatic aberrations • Advanced at time for LST (aspheric mirrors, electronic focal planes could not take advantage of FOV) • Aspheric mirror manufacturing now routine (Tinsley, Reosc, Kodak/ITT, Goodrich, SESO) with numerically controlled polishing machines • Large arrays and TDI may utilize large FOV • Real TMAs optimize for small blur across field, and strictly speaking are not anastigmatic

  4. TMA classes • On-axis (axisymmetric PM) • Annular field • Full field • See Lampton/Sholl, 2007 SPIE 6687 #23

  5. Annular Field TMAs • On-axis (axisymmetric PM) • Annular field • Blind spot in center of focal plane • Large FOV • Front end (PM/SM) can be optically slow (easier tolerances) • High distortion (~1-2%), bad for cartesian TDI • Adopted for step and stare 2-D focal plane array on SNAP • Example: Hirise, Pleiades (only uses eccentric slice, ref. Fappani et al SPIE 6687 #24 2007)

  6. HiRISE: Annular Field TMAGallagher et. Al., SPIE 5874, 2005

  7. Full Field TMA • On-axis (axisymmetric PM) • No blind spot • Large FOV • Very low distortion (~0.01-0.02%), good for TDI • Often used with only one half of FP, and incomplete (non-circular) mirror sections on aft end to prevent vignetting

  8. On-axis designs have central obscuration, which degrades MTF

  9. Off-axis, full-field • No obscuration in FOV or pupil plane • Improved MTF • MTI, Worldview, TOPSAT • Space inefficient (requires optics to side of PM) • PM is “cookie cut” from larger mirror • PM/SM spacing must be relatively long to keep geometric aberrations low • Not easy to package in Pegasus fairing

  10. Off-axis telescopes • Topsat • MTI

  11. Pegasus Fairing

  12. Full-field off-axis

  13. Pleiades • Will not fit in Pegasus fairing • High distortion (pincushion) • Requires CCDs at various angles to accommodate distortion • Pranyies et al SPIE 5570 P.568, 2004

  14. Full-Field Tertiary-Pickoff(FFTP, recommended GBI baseline) • 9km swath • 480km • 7m focal length

  15. FFTP Optical Prescription 6 surfaces FFTP _1.OPT Diam diam X Z pitch mir? Curv Aspher note ---------:---.------------:--------------:------:----.---------:---.-------:-------:-----:------- 0 : 0.0 : 0 : mir : -0.756230778: -0.9502878: 0.66 : 0.19: PM 0 : -0.484000 : 0 : mir : -1.883182489: -3.4676032: 0.25 : : SM 0 : 0.66 : 0 : mir : -1.147305396: -0.4417273: : : TM 0 : 0.045 : -20 : mir : 0 : : : : EM -0.25 : 0.36 : -65 : mir : 0 : : : : FM 0.25 : 0.368483933357: 90 : film : 0 : : : : FP : : : : : : : :

  16. FFTP Performance • Residual phase error: • 18nm RMS • 0.78um geometric blur • Sensitivity: • 46mn RMS @ ±1um SM/PM despace • Touchy! Diffraction limited OPD at 0.633um is 45nm RMS • 2um @ ±1um SM/PM despace • Desire: slow front end • Packaging difficulty: extraction mirror close to PM

  17. Conclusions • Annular Field (AF) configurations • High distortion (unacceptable for TDI) • FFTP configuration • Sensitive to mechanical misalignment • Packaging of extraction mirror difficult due to close proximity to PM • Low distortion • Easily delivers requisite 1.1º FOV • Fully illuminates circular focal plane (S. Harris FP) • Telecentric focus greatly simplifies bandpass filters • TBD • Packaging work with Paul Turin • Slow down front end? • Detailed vignetting analysis

More Related