Roma 29.01.09. Sources / Targets / Orbit Target field 60° on the ecliptic Possible sources: Sun,...

Roma 29.01.09

Sources / Targets / Orbit

Target field 60° on the ecliptic Possible sources: Sun, Earth,

Moon, ? Satellite in orbit around L2

Max distance form ecliptic ~0.5 Million Km

Distances of sources▪ Sun <-> Earth 150 Milllion Km▪ Earth <-> Satellite 1.5 Million Km▪ Moon <-> Satellite 1.12 Million Km

Roma, 29.01.09 Matteo Munari- INAF OACatania

Satellite in orbit around L2 Minimal Sources angles from

satellite axis▪ Sun 60° Earth 41.6° Moon 35.9°

Sources / Targets / Orbit

Fiji Islands, 30 Feb 2008 Matteo Munari- INAF OACatania

Lines Of Sight Telescopes field Overlap


Telescope scale ~ 12.5 arcsec/px -> Telescope Field f=24.9° side Configuration Total field side

(2-k)f K= overlapping factor

K=1 -> 1 LOS ->Total field side =f K=0-> 4 LOS ->Total field side =2f

Sources angle variation


Sources angles from telescopes axis will vary with the variation of the overlapping factor k and among the telescopes: some of them will be ‘favored’ by the overlapping mounting, some disfavored ( the telescopes directed toward the source).

We consider the disfavored ones to calculate external baffle; the source angles from the telescope axis will be

α(s,k)=α(s,0)+f/2(k-1)

Where s is the source, f the single telescope field side, k the overlapping factor

One / Two Stage External Baffle


Two kind of baffle One stage baffle: light from the source is scattered at least once by the baffle

and then enters the system. The first lens Of the system ‘sees’ the baffle Two stage baffle: light form the source is scatterd at least twice; first by a

the more external part of baffle (stage two), then by a more internal part (stage one). Stage two is directly illuminated by the source, but is not seen by the first lens of the system; Stage one is seen by the lens, but is not directly illuminated

Both kinf of baffle may be emproved by design of vanes that multiplies the scattering, but in a one stage baffle the edge of the vanes are directly seen by the first lens.

Obviously, a two stage baffle gives better performancesbut is bigger!

One step baffle Two steps baffle

One / Two Stage External Baffle Dimensions


One step baffle Two steps baffle

Two stages baffle dimensions DB=DL (tan(A)+tan(F))^2/(tan(A)-tan(F))^2 LB=2DL tan(A)/(tan(A)-tan(F))^2 LB2=DL / (tan(A)-tan(F)) DB2=DL (tan(A)+tan(F)/(tan(A)-tan(F))

One stage baffle dimensions DB=DL (tan(A)+tan(F)/(tan(A)-tan(F))

LB=DL /(tan(A)-tan(F))

DL = first lens diameter Α = source angle with

telescope axis F= single telescope semi-fov

diagonal angle ( fov side / sqrt(2))

DB= Baffle Max Diameter LB=Baffle Total Lenght LB2=Second Stage Length

From Lee et al., 2000

DL=200mm Scale=12.5arcsec/pixel, f=24.9° Source= Sun


One Step Baffle Two Steps Baffle

K 0 0.5 1

DB mm 363 321 290

LB mm 258 190 141

K 0 0.5 1

DB mm 661 515 419

LB mm 725 497 346

LB2 mm 258 190 141

DL=200mm Scale=12.5arcsec/pixel, f=24.9° Source= Earth



K 0 0.5 1

DB mm 729 524 423

LB mm 834 510 351

K 0 0.5 1

DB mm 2657 1371 894

LB mm 3872 1846 1093

LB2 mm 834 510 351

DL=200mm Scale=12.5arcsec/pixel, f=24.9° Source= Moon



K 0 0.5 1

DB mm 1279 700 511

LB mm 1701 788 490

K 0 0.5 1

DB mm 8181 2451 1306

LB mm 12581 3548 1744

LB2 mm 1701 788 490

DL=200mm Scale=15 arcsec/pixel, f=29.9° Source= Sun



K 0 0.5 1

DB mm 450 368 314

LB mm 324 217 148

K 0 0.5 1

DB mm 1016 678 495

LB mm 1056 618 382

LB2 mm 324 217 148

Single step D=400mm, f=40°

From a message of Levacher about ‘next step thermal analysis’ for the baffle can be allocated a space of 400x400mm

Assuming Max Db=400mm FoV (Diag)=40° Dl=200mm

We can have Lb~250 (corresponding to max 50° offaxis,enough for Sun with K=0.5)


SS400mm ABSORBING R0%



SS400mm REFLECTING R5%

IN :7.5E-1WOUT :3.3E-2WR=0.044

SS400mm LAMBERTIAN R5%


IN :5.0E-1WOUT :1.1E-3WR=2.2E-3

IN :7.5E-1WOUT :2.9E-3WR=3.9E-3

SS400mm REFLECTING R5%


IN :5E-1WOUT :6E-3WR=1.2E-2

SS400MM LAMBERTIAN R5%


IN :5E-1WOUT :1.6E-3W R=3.2E-3

IN :7.5E-1WOUT :7.5E-5W R=1.0E-4

SS400mm with vanes

Vanes are used so to ensure that the entrance of the system cannot see part of the baffle directly illuminated by the offaxis source

Geometrically designed for specular reflection

For our baffle 8 vanes


SS400MM Vanes Reflective R5%


IN :5E-1WOUT :3.8E-6WR=7.6E-6

SS400MM Vanes 100% Lambertian R5%


IN :5E-1WOUT :1.8E-5WR=3.6E-5

SS400MM On Axis Vanes 100% Lambertian R5%


IN :7.5E-1WOUT :4.7E-5WR=6.3E-5

SS400MM Vanes 50% Lambertian R5%


IN :5E-1WOUT :1.0E-5WR=2.0E-5

Weights

Element Weight(g)

Tube 1705

Front 60

Edge1 85

Edge2 120

Edge3 164

Edge4 221

Edge5 288

Edge6 363

Edge7 439

Back 509

TOTAL 3954

CILINDER 2374

CONE 1280


Alluminium (2.7 g/cm3)2mm thickness

Issuses/Future work

Total assembly of TOUs/satellite Reciprocal Straylight System Sunshield Different baffles for different groups

Sources Other sources Impact on duty cycle

Materials Paints Baffling system (thermal issues) Specular / Scattering Weight

Internal Baffling / StrayLight Mechanics Ghosts Requisites (evaluation method)


NOTES

Fiji Islands, 30 Feb 2008 Mago Merlino - INAF OACamelot

What is the role of the sun shield of the satellite? Does it makes an external baffle, for objects ‘lower’ than the sun on the telescope horizon useless?

Aumenting the scale of the telescope will bring at last some source in the fov (is the scale is 20 arcsec/px, for K<~0.6 the Moon could enter in the fov, the Earth for K<~0.35)

Other Sources may be present (brilliant objects near the target field, the satellite itself or reciprocal straylight from the telescopes).

The calculation here performed refers to the worst case: groupes of telescopes pointing in a more favorable LOS can have a smaller baffle

Should be checked how often sources are near the telescopes axis and how this affect the satellite duty cycle

Internal baffling system will not impact in telescopes disposition and should have not a great impact on the mass budget

NOTES


The termal baffle and the optical baffle will obviously be the same object. A maximum diameter of 400 mm (as proposed by Levacher for the next step thermal study) means also a trade off between minimun ‘baffled angle’ overlapping factor and baffling system performances (one or two steps). 400mm could mean K=0, Sun baffled with a single step system K=1, Sun baffled with a double step system K=1, Earth baffled with a single step system

Preliminary masses


Calculated as cilinders of aluminium of 2 mm thickness Vanes are not considered (and consequent growth of

dimensions of tube…) -> so this is an Optimistic Estimate!

One Step Baffle [g]

K 0 0.5 1

Sun 1580 1033 690

Earth 10283 4156 2506

Moon 36856 9339 4235

Second Steps Baffle [g]

K 0 0.5 1

Sun 8109 4331 2451

Earth 174441 42892 16540

Moon 1.75 E6 147463 38582

Roma 29.01.09. Sources / Targets / Orbit Target field 60° on the ecliptic Possible sources: Sun,...

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Transcript of Roma 29.01.09. Sources / Targets / Orbit Target field 60° on the ecliptic Possible sources: Sun,...