Gubarev, Mikhail V.

NASA Technical Reports Server

Overview of full-shell 
approach
Optics for X-ray Surveyor workshop, March 2016
https://ntrs.nasa.gov/search.jsp?R=20160004220 2019-08-31T03:35:54+00:00Z
Outline
• Error Allocation
• Process flow
• Replication
• Direct Fabrication
• Pros and Cons
• Zeeko experiments
• Post-fabrication correction
• Mounting and Alignment
Requirement 1 0.5
Margin 0.66 0.20
Pointing jitter 0.28 0.14
Vibrational Effects 0.13 0.07
Defocus error 0.01 0.007
Launch shifts 0.13 0.07
Thermal effects 0.15 0.075
Gravity release 0.1 0.05
Epoxy effects 0.13 0.07
Shell-to-shell misalignment 0.24 0.12
Installation errors 0.24 0.12
Reflector pair 0.70 0.38
Surface slope error 0.18 0.10
Error Allocation
Process flow
Replication
Mandrel fabrication Electrolytic plating Shell Separation
Post replication 
correction
Direct Fabrication
Substrate fabrication Plating
Figuring, 
Superpolishing
Post fabrication 
correction
Replication
Direct fabrication
One mandrel for multiple shells (if multiple 
modules)
Nickel – higher density
Replication process – need for stress
Low density
Chandra-like resolution is doable
If metal - Taylor the alloy to match CTE, 
the telescope structure can be done 
from the same material – simplifying 
thermal design, less epoxy
Simplified alignment, especially if the shell has monolithic structure
Relatively stiff – less complicated support structure, less obscuration, less weight for 
support
Less susceptible to residual stresses (if any) in coating based corrections
Relatively thick, 1-3 mm
Limit on diameter ~ 2 meters
Replication
Pros and Cons
Pros:
Cons:
Direct Fabrication
Technique is pioneered by the Astronomical Observatory of Brera, Italy
Coarse and Fine Grinding Figuring Super-polishing
X-ray test at PANTER : 17.8” HPD
contribution
- low-frequency errors 6˝
- mid-frequency errors 13˝ 
- out-of-roundness error 5.3˝ 
- the optical axis tilt between segments 8.9˝
Ion Figuring
Potential
Direct Fabrication
Diamond turning Figuring Super-polishing Differential Deposition
Whiffle tree station with an 
aluminum shell supported at 12 
points.
A metrology fixture to 
support the mirror shell 
during the skip test.
Coating stress and magnetic materials 
Melville P. Ulmer (Northwestern 
University)
Differential Deposition
Kiranmayee Kilaru (USRA, MSFC)
David Windt (Reflective X-ray Optics, 
LLC) 
Ion Figuring (Brera Obervatory, Italy)
Direct Fabrication Post-
fabrication Correction methods
Material Density 
(g/cm3)
CTE
(10-6 / K-1)
Elastic Modulus
GPa
Yield Strength
MPa
Fused Silica 2.2 0.5 72 48*
Beryllium 1.8 12 318 240
BeAL-162MET 2.1 24 69 276
AlSi 2.8 13.9 193 314
Duralcan F3S.30S
AlSi+SiC(30% by vol)
2.8 14.6 120 210
Mechanical Properties of Potential Mirror Substrate Materials
*Maximal achievable value. The ‘working’ value is typically much less and depends on the surface/subsurface condition.
Ideally, the mirror shell has low 
density, low coefficient of expansion 
(CTE), high modulus of elasticity and 
high yield strength. It should also be 
a material that is not too difficult to 
figure and polish. 
- Be + NiP (CATS-ISS telescope)
- BeAl +NiP
- AlSi + NiP
Direct Fabrication
Additional Benefits of metal substrate: 
Less joints – less epoxy error
Thermal design could be simplified
Zeeko machine
- The machine utilizes a “bonnet” 
technique in which an inflated rubber 
hemispherical diaphragm supports the 
polishing medium. 
- there are different “bonnet” sizes (20 
mm, 40 mm and 80 mm radii of 
curvature) 
- This computer-controlled deterministic 
polishing processes leads to a high 
convergence rate. 
before after
Figure error (St. Dev.) 500 nm 10.7 nm
Slope error (> 2 cm) cm(RMS) 6.32 arcsec 0.30 arcsec
Low frequency (> 7 cm) slope error (RMS)   2.66 arcsec 0.09 arcsec
Mid frequency (2-7 cm) slope error (RMS) 5.73 arcsec 0.29 arcsec
Alignment
Shell can be supported from one end 
The use of the clips (FOXSI – 2007) 
minimizes the distortions due to epoxy 
shrinking
There is a “sweet spot” the influence 
on the angular resolution performance 
is minimal
Strings approach – XMM
Equalizing the  strings tension in 
azimuthal direction
CDA or UV
Conclusions
• To meet the stringent angular resolution requirements for the X-Ray 
Surveyor Mission all the error contributors should be addressed;
• Full shell approach could be viable option for inner mirrors of the X-ray 
Surveyor;
• Direct fabrication technique has  potential to meet the angular resolution 
requirements;
• Post-fabrication and post-assembly figure correction provides an additional 
venue to meet the requirements.


Overview Of Full-Shell Approach

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