roma 29.01.09. sources / targets / orbit target field 60° on the ecliptic possible sources: sun,...
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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
Roma, 29.01.09 Matteo Munari- INAF OACatania
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
Roma, 29.01.09 Matteo Munari- INAF OACatania
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
Roma, 29.01.09 Matteo Munari- INAF OACatania
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
Roma, 29.01.09 Matteo Munari- INAF OACatania
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
Roma, 29.01.09 Matteo Munari- INAF OACatania
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
Roma, 29.01.09 Matteo Munari- INAF OACatania
One Step Baffle Two Steps Baffle
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
Roma, 29.01.09 Matteo Munari- INAF OACatania
One Step Baffle Two Steps Baffle
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
Roma, 29.01.09 Matteo Munari- INAF OACatania
One Step Baffle Two Steps Baffle
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)
Roma, 29.01.09 Matteo Munari- INAF OACatania
SS400mm ABSORBING R0%
Roma, 29.01.09 Matteo Munari- INAF OACatania
Roma, 29.01.09 Matteo Munari- INAF OACatania
SS400mm REFLECTING R5%
IN :7.5E-1WOUT :3.3E-2WR=0.044
SS400mm LAMBERTIAN R5%
Roma, 29.01.09 Matteo Munari- INAF OACatania
IN :5.0E-1WOUT :1.1E-3WR=2.2E-3
IN :7.5E-1WOUT :2.9E-3WR=3.9E-3
SS400mm REFLECTING R5%
Roma, 29.01.09 Matteo Munari- INAF OACatania
IN :5E-1WOUT :6E-3WR=1.2E-2
SS400MM LAMBERTIAN R5%
Roma, 29.01.09 Matteo Munari- INAF OACatania
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
Roma, 29.01.09 Matteo Munari- INAF OACatania
SS400MM Vanes Reflective R5%
Roma, 29.01.09 Matteo Munari- INAF OACatania
IN :5E-1WOUT :3.8E-6WR=7.6E-6
SS400MM Vanes 100% Lambertian R5%
Roma, 29.01.09 Matteo Munari- INAF OACatania
IN :5E-1WOUT :1.8E-5WR=3.6E-5
SS400MM On Axis Vanes 100% Lambertian R5%
Roma, 29.01.09 Matteo Munari- INAF OACatania
IN :7.5E-1WOUT :4.7E-5WR=6.3E-5
SS400MM Vanes 50% Lambertian R5%
Roma, 29.01.09 Matteo Munari- INAF OACatania
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
Roma, 29.01.09 Matteo Munari- INAF OACatania
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)
Roma, 29.01.09 Matteo Munari- INAF OACatania
Roma, 29.01.09 Matteo Munari- INAF OACatania
Roma, 29.01.09 Matteo Munari- INAF OACatania
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
Fiji Islands, 30 Feb 2008 Mago Merlino - INAF OACamelot
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
Fiji Islands, 30 Feb 2008 Mago Merlino - INAF OACamelot
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