A tale of Ghosts (and Baffles and Straylight)

1. A tale of Ghosts (and Baffles and Straylight)

2. A foreword… • Myth: 3 sec memory • Reality: 3 years are passed • I’m not a goldfish, but…

3. Requirements • From PLATO-CAMTO-TS-90-LESIA • Dimension ed energy of Ghosts • Extended and pointlike • Absent: requirements on scatteredstraylight • Once therewas a requirement: 20ph/pxl/s, buthasbeenexcluded (or forgot…), or my copy of the doc… • Reduce to a PST/rejectionrequirement? • Requirements on transmission (to limit ‘blue’ light) • Requirements on cleanlinesslevels (notjustified)

4. Once Upon A Time (2011) Normal TOU Reference Model • It is the model of reference ZEMAX • Based on a slightly old design (some radii of curvature) • Structure is semiconceptual (tube & diaphgrams) 90% absorbing, 10% lambertian scattering • All lenses and window (front face included) have 1% AR coating • 20A microroughness and CL500 dust on window • The CCD has a 1-QE reflectivity • Fed by a 240mm diam circular collimated source of 4W (1W on the entrance pupil), moved along the diagonal of FoV • Wavelength weighted to reproduce energy of a G0

5. Once Upon A Time (2011) Point likeGhosts • TOU-OPT28: Should a ghost image be focused on the detector, its relative intensity shall be less than 0.2% (TBC) of the flux of the star which creates the ghost. • Due to the presence the flatwindow • Using Rlenses=1%, Rccd=1-QE Deltam~6

6. Once Upon A Time (2011) Extended Ghost • TOU-OPT27: The surface of ghost light beams at the detector surface shall be greater than 3000 pixels (TBC).

7. Once Upon A Time (2011) Stellar Model • Based on • Allen (1973) m<10 • Bahcall&Soneira m>10 • Spectrum: G0 Number of stars in Plato TOU field up to the m mag

8. Once Upon A Time (2011) Extended Ghosts • Build a Ghost Simulator form several (105) zemax files and IDL routines. • Used in two ways • Single source: to extract data of ghosts: positions, radius and percentage of rays entering the pupil that can form the ghost • Multi source: using the previous stellar model, to simulate an entire field

9. Once Upon A Time (2011) Extended Ghosts Brightes features are present from the beginning Adding higher mags adds an offset Evolution of extended ghosts with mag

10. Once Upon A Time (2011) StrayLight Inside FoV is 2-2.5% (was 1% without CCD reflection) Outside FoV is similar to old 6 lenses or better because the tube is larger and exactly the same of that of ‘6 lenses’ Stars + Zodiacal light

11. Once Upon A Time (2011)Baffles • 3 ‘families’ and 5 models • 1-4,2-3 (N), 5(F) • Composed by two part • interface ring: • identical for all models, • is the interface with the TOU tube • ‘hosts’ the window • Cone: • different cut angle and height according to family • Different orientations according to model

12. Once Upon A Time (2011)Baffles • Not for “direct” stray light from astronomical objects (they are too small) • Thermal? • On a ‘prudence basis’ to ‘fight’ TOU mutual scattering and satellite (sunshield) scattering • At the moment we don’t have any simulation to support that • Simulations are difficult because • We need information about all the system (disposition of TOUs, materials, sunshield…) • The system is big but the single TOU pupil is small: raytracing may have poor statistic

13. Future Work • Requirements (from system?) • Model • Migration to ASAP • Optical design • Mechanical design • Coatings • Sources • Check calculations ph/s/pxl • Earth /Moon • Satellite / Mutual scattering