A tale of Ghosts (and Baffles and Straylight)

A foreword…

Myth: 3 sec memory

Reality: 3 years are passed

I’m not a goldfish, but…

Requirements

From PLATO-CAMTO-TS-90-LESIA Dimension ed energy of Ghosts

▪ Extended and pointlike Absent: requirements on scattered

straylight▪ Once there was a requirement: 20ph/pxl/s, but

has been excluded (or forgot…), or my copy of the doc…

▪ Reduce to a PST/rejection requirement? Requirements on transmission (to limit

‘blue’ light) Requirements on cleanliness levels (not

justified)

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

Once Upon A Time (2011)

Point like Ghosts

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 flat window

Using Rlenses=1%, Rccd=1-QE Deltam~6

0 1 2 3 4 5 6 70

0.00050.001

0.00150.002

0.00250.003

0.00350.004

Ghost fraction

ghost fraction

deg

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).

2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 0.657375 39081546 20552834 6407781 25466577 13250603 39658990 20817512 12916445 8033711 13978216 35533.91 7923.599 1.405447

2 38505771 15442910 106155 25568149 13249169 39652789 20949539 12915525 205152.6 13976081 35512.38 7921.934 1.371451

3 76796589 79232838 14446536 59813598 1215345 25317.94 57636682 62170387 61005065 3761422 26468089 30286981

4 3006966 48918990 32755067 63360528 53172592 29875450 32918026 47295199 9341820 5802954 4374436

5 72886831 49892259 67672385 661567.9 45715989 5908082 47119158 4115350 3342162 2808424

6 70424141 66368402 9302555 76840087 78190442 88617179 1372559 14400762 16567682

7 84530609 8266808 31107833 55770994 14129048 21798990 926485 4311070

8 2209413 66079763 27970837 63268229 5985306 18247946 19956264

9 82569393 59280938 93889903 8298264 10933807 9554658

10 79196730 2672098 1232973 3784643 9592194

11 2327847 4491655 3135173 3910651

12 9734777 19178788 16979918

13 24315.9 159146.8

14 38899.98Column Min 0.657375 38505771 15442910 106155 14446536 13249169 1215345 25317.94 12915525 205152.6 2327847 35512.38 7921.934 38899.98

Once Upon A Time (2011)

Stellar Model

Up to m Nstars Up to m Nstars Up to m Nstars Up to m Nstars0 0 7 808 15 1.73E+06 22 1.36E+081 1 8 2311 16 4.41E+06 23 1.79E+082 4 9 6640 17 1.02E+07 24 2.28E+083 12 10 14338 18 2.11E+07 25 2.85E+084 34 11 33519 19 3.87E+07 26 3.49E+085 98 12 84452 20 6.40E+07 27 4.22E+086 282 13 228308 21 9.74E+07 28 5.05E+08

14 635252 29 6.00E+08

0 5 10 15 20 25 30 351.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

mag

Star

s bp

er s

quar

ed d

eg

Based on • Allen (1973) m<10• Bahcall&Soneira m>10

Spectrum: G0

Number of stars in Plato TOU field up to the m mag

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

Once Upon A Time (2011)

Extended Ghosts

Mag StarExtended

GhostsPoint-like

ghosts

Average due to extended

ghosts Variance

0 0 0 0 0.00E+00 0.00E+00

1 1.69E+09 1.43E+06 0 1.76E-02 9.80E-02

2 2.02E+09 1.83E+06 0 2.25E-02 5.36E-02

3 2.14E+09 2.04E+06 113901 2.51E-02 2.44E-02

4 2.02E+09 2.52E+06 2.75E+06 3.09E-02 1.17E-02

5 2.42E+09 2.73E+06 2.06E+06 3.36E-02 5.71E-03

6 2.79E+09 3.04E+06 1.79E+06 3.74E-02 3.34E-03

7 3.06E+09 3.32E+06 1.59E+06 4.08E-02 1.57E-03

8 3.55E+09 3.80E+06 1.79E+06 4.67E-02 1.15E-03

9 3.96E+09 4.10E+06 1.77E+06 5.05E-02 7.30E-04

10 2.92E+09 3.07E+06 1.52E+06 3.78E-02 3.83E-04

11 2.82E+09 3.01E+06 1.52E+06 3.70E-02 3.47E-04

12 3.02E+09 3.21E+06 1.66E+06 3.94E-02 3.70E-04

13 3.39E+09 3.58E+06 1.74E+06 4.40E-02 4.37E-04

14 3.81E+09 4.03E+06 1.99E+06 4.96E-02 5.50E-04

TOTAL 3.96E+10 4.17E+07 2.03E+07 5.13E-01  

Brightes features are present from the beginningAdding higher mags adds an offsetEvolution of extended ghosts with mag

Once Upon A Time (2011)

StrayLight

0 10 20 30 40 50 60 70 80 901

10

20A d500 only ghost6 lenses 6 lenses 'old'

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

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

Type Cut Angle Rotation angle

H N exemplars

1 37.03 9.05 117 82 24.3 14.23 157 (92)? 83 24.3 -14.23 157 (92)? 84 37.03 -9.05 117 85 30 0 100 2

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

Future WorkRequirements (from system?)Model

Migration to ASAP Optical design Mechanical design Coatings

Sources Check calculations ph/s/pxl Earth /Moon

Satellite / Mutual scattering