# Presentation: 177364

## AMSD Test Plan

- H. Philip Stahl, Ph.D.
- NASA MSFC
- James Hadaway
- University of Alabama in Huntsville

## AMSD Deliverable Requirements

- Each AMSD contractor shall deliver to NASA MSFC a complete mirror system (including any unique hardware) capable of demonstrating compliance with all AMSD requirements, a data package, models and traceability report.
- Key AMSD Requirements to be Verified:
- Prescription
- Figure Error
- Stiffness
-  Data package shall include:
- complete drawing package
- measured and analytical data including exact dimensions (size, mass, etc)
- mass breakdown and areal density calculation
- surface error data as a function of spatial frequency (PSD, PV and RMS)
- simulation data showing mirror surface error under random loads
- fundamental modal test data and survivability data

## Slide 3

## Areal Density

- Areal density will be calculated from physical dimension and total mass measurements.
- If the mirror does not include position actuators, their mass values as supplied by the vendor will be added to the total mass measurement.
- Areal density will be calculated over the mirror’s entire physical aperture.

## AMSD Prescription

**R**

**c**

**“****Full Parabola”**

**x= 2**

**/R**

**c**

**OFF AXIS SEGMENT**

** **

**2 m**

**D**

## Radius of Curvature

- Absolute ROC shall be 10 m _+_ 1mm.
- All residual surface figure errors resulting from active control to achieve desired ROC must be included in the overall wavefront error.
-  Actuator stroke and resolution must be demonstrated such that when incorporated into the mirror system they achieve a 0.00004m/d^2 ROC matching over the ROC tolerance band.
- The contractor is also required to test for ROC change over the operating temperature range of the AMSD.
- Active Control, if required, can be implemented to correct the ROC at each temperature range extreme after change in ROC data is acquired.

## Total Surface Error Requirement

- Total surface error is measured over a clear aperture which is 15 mm from the physical edge.
- Active control is allowed to obtain required surface figure.
- Total Surface Error is defined to include:
- _Component_				_Spatial Frequency_
- low-spatial frequency (figure) 		1 to 0.2 meter  (Z4 to Z36)
- mid-spatial frequency (ripple), 		200 to 1 millimeter
- high-spatial frequency (micro-roughness)	1000 to 1 micrometer
- Generate a composite average two-dimensional (2-D) power spectral density (PSD) of the mirror surface error where no point deviates from its local, nominal average by more than 10X.

## Total Surface Error

- MSFC will use at least two instruments to measure total surface error from 1.0 meter to 1.0 micrometer spatial periods.
- Phase-measuring interferometers will measure from 1.0 m to 3-6 mm.
- Interferometer Sampling		Pixel Size	Spatial Period
- 1.2 m diameter / 400 pixels 	3 mm		6 mm
- 1.2 m diameter / 800 pixels 	1.5 mm		3 mm
- For below 1.0 mm periods, change magnification and test sub-apertures.
- If necessary, measure AMSD or a surface replication with profilometer:
- Long Trace Profilometer
- Baurer Profilometer
- Nanosurf Profilometer
- Interference microscope profilers will measure to 1 micrometer.

## Stiffness

- Modal analysis and testing is required to define the first 5 structural modes that impact the optical surface.
- Modal testing will be accomplished via two methods
- Accelerometer - measure mirror response when exposed to random noise and/or sine sweep inputs.
- Stroboscope Interferometer – measure mirror surface shape as a function of sine frequency input at both ambient and cryogenic temperature.

## AMSD Verification

- At MSFC, each mirror will be tested at
- Ambient temperature to verify compliance with base contract requirements
- Cryogenic temperatures to characterized cryogenic performance and/or suitability for cryo-null figuring.
- Any parameter which can not be directly measured or calculated will be modeled.
- From the drawings, NASA will create independent NASTRAN & Thermal models to predict ambient & cryogenic performance, including modal response.
- NASA and Vendor Models will be validated with measured data.

## AMSD Handling

- MSFC has extensive experience in testing high-value flight hardware:
- Chandra, SXI, etc.
- and performing cryogenic optical tests
- 3 SBMD tests,
- 2 NMSD tests and
- several Space Act tests
- AMSD will be handled to maximize:
- safety,
- functionality and
- cleanliness
- AMSD will be tested according to detailed written approved test plans.

## AMSD Test Schedule

- It is NASA MSFC’s desire to adhere to the following:
- Take delivery of all three mirrors		April 02
- Ambient / Cryogenic Mirror Testing		May to Aug 02
- AMSD Test Data Review			Sept 02
- Each AMSD Mirror will be tested as follows:
- In-Coming Inspection
- Visual Inspection
- Physical Measurement – Dimensions and Mass
- Ambient Optical Test
- Prescription & Figure
- Radius of Curvature Matching
- Cryogenic Optical Test
- Prescription & Figure
- Radius Change vs Temperature & Radius Matching

## Optical Test

- Prescription Certification requires accurate measure of:
- Mirror Conjugate Positions – Radius & Conic Constant
- Optical Vertex Location – Figure Error vs Alignment Aberration
- Measure AMSD Prescription
- Define Optical Axis – Vertex and Center of Curvature
- Accomplished via Physical Alignment of AMSD to Test Palette
- Center of Curvature defined by Test Palette
- Vertex defined by AMSD Fiducials
- Measure Conjugate Locations
- Center of Curvature defined by Test Palette
- Conjugate Error defined by Residual Spherical Aberration
- Measure Radius of Curvature – Leica
- Measure Total Wavefront Error
- Alignment Aberration & Gravity Sag Limit Low Frequency Accuracy

## Top View

## AMSD Optical Testing

- Coordinate System Defined by Interferometer Test Palette
- Interferometer Camera defines XY
- CGH defines Optical Axis and Center of Curvature
- XY Calibration
- Calibrated camera scale factors using standard machine vision techniques – known object
- Interferometer has fixed magnification and focus
- Calibrate CGH Distortion – use Camera Calibration
- Z-Axis Calibration
- Align CGH to Interferometer Camera
- X,Y, z via Fiducials
- Align CGH to Interferometer Test Wavefront
- Z, x, y via Annular Reflective Zone
- Final result is fully aligned/calibrated Test Palette

## Potential AMSD Fiducials

## Slide 17

## AMSD Optical Testing

- Align AMSD to Test Palette Wavefront / Coordinate System
- Set Off-Axis Distance (X,Y, z)
- Coarse Align – via Fiducials to Interferometer Camera
- Fine Align – Aberration Ratio as a function of Displacements
- Align to Center of Curvature
- Adjust AMSD x, y via Tilt Fringes
- Correct or Subtract Gravity Sag
- Gravity Off-Load, Active Mirror
- Rotation Test, Model
- Adjust for Paraxial Focus
- Measure Radius of Curvature
- Change Focus as required
- Repeat as required

## Alignment Degrees of Freedom

## Null Lens

- Null Lens Prescription
- 10th order polynomial
- Distortion Calibration
- Alignment to Interferometer
- Phase with Bias		Phase w/o Bias			Bias

## Slide 21