Periscope Configuration

1
Periscope Configuration
Detector
Periscope Module
2
Mirror Parameters
Reflecting surface
TBD

• Active area is 30cm long x 2, 10 or 30cm wide.
• Surface figure requirement l/400 rms (at 633nm)
  --Mounted
• Mirror mass must be minimized
• Geometry TBD

3
Mirror Module Coordinate System
Mirror Control X linear Roll
about LOS Pitch
LOS
Fixed Mirrors
Module Control Yaw Pitch Roll about LOS
To Detector
4
Mirror Geometry and Figure

• Mirror geometry must
• Meet the surface figure requirement
• 1g release
• Operating temperature range
• Thermal gradient
• Mount distortions
• Have minimum mass
• Accommodate mount and mechanisms
• Survive launch and environment extremes

5
First Order Wavefront Error Budget
Error Budget for ?/400 RMS Mirror Mount All
values given in RMS wavefront error ? 6328Å
Thermal gradient .0011
Jitter .0006
Mirror blank surface figure .0013
Mount interface surface finish .0003
Stability .0013
Assembly (neglected)
Surface distortion due to gravity .0004
Motion due to gravity (neglected)
Manufacturing .0013
Alignment .0013
Test .0013
Reflective coating .0009
Bolt preload .0002
Adhesive strain .0002
Bulk temp (5C) .0005
1g sag .0004
Total RMS error .0025
6
Initial Geometries considered

• Rectangular, held from back
• Various lightweighting patterns/pockets cut from
  back
• Single Arch
• Various thicknesses
• Double arch over length on backside
• Lightweighting pockets in back of main rib

7
First Order FEM results of different geometries
for 1m long mirror
8
Attempted Wavefront Analysis
9
Wavefront analysis

• Wavefront analysis not adequate Zernike
  polynomials do not fit to long rectangular
  optical surface
• Consider using LeGendre polynomials?
• Good for cylindrical optic fits (used Chandra
  mirror analysis)
• Orthogonal polynomials?
• Ref. Integrated Optomechanical Analysis
• Doyle, Genberg, Michels, p.61

10
Optical Tolerances

• Goal Good fringe clarity at the focal plane
• Maintain phase information as it passes through
  each channel of the interferometer simultaneously
• Analytical Analysis
• Limit OPD lt l/10
• Raytrace Analysis
• Limit relative Strehl ratio gt 80

11
Mirror Separation within a periscope
h2
h1
12
Analytical vs. RaytraceMirror Position Tolerances
where l 20Å, g 2, m 83cm, and L 400km
13
MAXIM Pathfinder Parameters

• Baseline 2 m
• Focal Length 200 km
• Mirror length 30 cm
• Graze angle 2
• l 10Å

14
MAXIM Pathfinder Position Tolerancesl1nm,
F200km, D2m, m30cm, g2deg, dh1mm
15
Full MAXIM Parameters

• Baseline 1km
• Focal Length 20,000 km
• Mirror length 30 cm
• Graze angle 1
• l 10Å

16
X-direction Sensitivity
F
X
D
Z
y
Allowable Mirror Motion 1.7nm
Allowable Periscope Motion 4mm
17
Y-direction Sensitivity
X
ZLOS
Y
Allowable Mirror Motion 0.3mm
Allowable Periscope Motion 0.5mm
18
Z-direction Sensitivity
F
D
y
Allowable Mirror Motion 94.7nm
Allowable Periscope Motion 0.32m
19
X-rotation yaw Sensitivity
msin(g)
m
Allowable Periscope Motion 7.8 arcmin
20
Y-rotation pitch Sensitivity
F
y
D
Allowable Mirror Motion 2.3 marcsec
21
Z-rotation roll Sensitivity
LOS
X
ZLOS
Roll
Y
Allowable Mirror Motion 0.13 arcsec
To Detector
22
MAXIM Position Tolerances l1nm, F20,000km,
D1km, m30cm, g1deg, dh1mm
23
ISAL Raytrace Position Tolerances l1nm,
F200km, D4m, m30cm, g1deg, dh1mm
24
Move one mirror pair wrt other mirror pair
-d
d
Pathlength is self-correcting
25
Move one mirror in Z-direction
d
dcos2q
2q
-d
dsinq
26
Trade Studies

• Three grating sizes
• 2cm, 10cm, and 30cm wide x 30 cm long
• Optimize graze angle vs. mass
• Lower graze angle can loosen some tolerances
• Lower graze angle will reduce throughput or
  increase mass