# Presentation: 483431

## Technology Days at MSFC 

- Technology Days at MSFC
- Auburn Micrometeoroid Experiments
- May 9-10, 2001

**Steve Best**
- Space Power Institute
- Auburn University
- 334-844-5939
- bestste@auburn.edu

**Chuck Perrygo**
- NGST Systems Engineering
- Swales Aerospace / GSFC
- 301-286-7193
- charles.perrygo@gsfc.nasa.gov

## Presentation Outline

**Why micrometeoroid testing is important to NGST**
**Description of Auburn test facility & testing performed for NGST**
**Analysis of test results**

**Chuck Perrygo**

**Steve Best**

**Chuck Perrygo**

## Why micrometeoroid testing is important to NGST

## Understanding the threat posed by the meteoroid environment

**Understanding the threat posed by the meteoroid environment**

**	****Knowledge of meteoroid impact effects**
**+****	****Knowledge of the meteoroid environment**
**=****	****Knowledge of degradation due to meteoroid environment**

**On-going subject of study since early days of space age**

**Studied for Apollo, space station, & comet missions, but focus has been on shielding against large particles**

**At a minimum, need to quantify worst-case degradation effects for NGST**

## NGST particularly vulnerable to meteoroid environment

**NGST particularly vulnerable to meteoroid environment**

**NASA sunshield concept consists of a few thin film layers - each layer provides significant isolation**

**NGST has an “open” telescope configuration - no telescope tube as on HST or SIRTF to shield against meteoroids**

*NASA Yardstick concept*

## Micrometeoroid impact damage effects

**Micrometeoroid impact damage effects**

_**Sunshield**_
- Key concern: Local gross failure of inner film layer
- Debris from a single impact on outer layer generating many holes in inner layers
- Cratering of outer layers degrading thermal-optical properties

_**Mirrors**_
- Mirrors will be glass or beryllium
- Glass is a particular concern as it is both brittle and exhibits low tensile strength
- Brittle  crack propagation not stopped by material yielding
- Low tensile strength  spalls easily
- Behavior at cryo?
- Contamination from impact debris (mirrors & sunshield)

***This is a qualitative assessment - need to quantify***

## Impact effects models

**Local gross failure scaling  ~**

**Front surface impact effects:**

**Inner-layer damage effects - No model**

***Test data required for all***

## Transition-region test results

**Al 1100 target & soda-lime glass projectiles @ 6 km/s **

**Projectile size**

## The meteoroid environment at L2Meteoroid flux

**Total fluxes in 10 years:  Mass ~0.2 mg/m****2****;  Area ~2 mm****2****/m****2**
**Knowledge of environment:  Particle flux ~3X;  Mass flux ~5X**

## The meteoroid environment at L2Particle directionality

## Testing at AU

**No test facility comes close to providing mass & velocity of space environment**
**Auburn HIF capabilities closest to highest-probability particle mass/velocity range**
**Auburn HIF has large target chamber to accommodate test fixture**
**NASA WSTF light-gas guns were dedicated to space station testing**
**Electrostatic accelerators located in Europe**

## Description of Auburn test facility & testing performed for NGST

## Auburn University Hypervelocity Impact Facility

_**Facility  Summary**_
**Velocity ~12 km/sec**
**Particle size - 40-120 μm dia.**
**Soda lime glass**
**Olivine**
**Aluminum oxide**
**Number of particles/shot**
**40-70**
**Equivalent to 3-7 yrs on orbit**
**Electrical discharge firing**
**Extensive diagnostics**
**Particle velocity  and size**
** ****X-Y impact coordinates and dimensions**

## Auburn Univ. Hypervelocity Facility Schematic

## Hypervelocity Impact Facility

**Gun chamber**
**Isolated from target chamber**
**40 kV capacitor discharge (~50 μsec)**
**Skimmer cone particle selection**
**Flight tube**
**Long flight distance (~5 meters)**
**Separates particles from plasma**
**Metalforming shutter**

## ‘HyperShutter’   Open  View 

**Have installed new metalforming shutter**
**Time delay**
**Firing controlled by another capacitor**
**Eliminates slow moving projectiles**
**Can control selection of low velocity cutoff, e.g.:**
**< 5 km/sec**
**< 7 km/sec**
**< 9 km/sec**

## HyperShutter’   Closed  View

**Have installed new “magneforming” shutter**
**Time delay**
**Firing controlled by another capacitor**
**Eliminates slow moving projectiles**
**Can control selection of low velocity cutoff, e.g.:**
**< 5 km/sec**
**< 7 km/sec**
**< 9 km/sec**

## ‘HyperShutter’  Crushed  Cylinder

## Target Chamber Preparation

**Target chamber**
**Large - up to 1 meter dia**
**In-situ plasma source (LEO simul’n)**
**Streak camera**
**X, Y and t coordinates**
**Photomultiplier tube**
**Time of arrival at target**
**The target is attached to a  rotatable mount to simulate micrometeorite impacts from different directions.**

## Impact  Site  Location  Diagnostics

## Streak / Impact Site  Analysis  Software

## Post-Shot Analysis

**The target is brought into a scanning room and placed under a video-microscope on a computer controlled 3-axis scanning table where each impact site is identified.**
**Each site is compared to a photographic record  generated by a high-speed streak camera and velocity assignments are made for each impact site. **

## NGST Sunshield Target Design

** ****Experimental test configuration. Layer 1 is front layer and is 25 μm (1 mil) thick with VDA on backside only (orange side faces gun). All other film layers are 12.7 μm (0.5 mil) thick with VDA on both sides. The maximum number of film layers  per shot that can be accommodated in the target chamber varies with layer-to-layer spacing S.**** **

## Example of debris field caused by particle

**This single particle caused a debris field which produced nearly 70 penetrations (>5********m dia.) of the second layer,  52 in the third layer, and none in the fourth layer.**

**Penetration of 1****st**** layer by a 5 km/s  particle 80 ********m diameter**

**Second Layer Debris Field Pattern**

## Analysis Difficulties & Solutions Applied...

**The video microscope image capture apparatus being used was not an efficient means of collecting so many images...**
**Solution:  Purchased new video hardware.**
**The debris field’s overall cross-section area was much larger than the field of view of our microscope at a magnification sufficient to resolve the physical measurements...**
**Temporary Solution:  Microscope scanning table was stepped across field so multiple images of overall debris field could be collected.**
**We needed to assemble the mosaic of images into one clean high resolution image...**
**Temporary Solution: Located and learned use of ‘image-stitching’ software.**
**We quickly realized that we were not equipped to handle the detailed measurement and analysis of thousands of penetrations...**
**Solution:  Software (SigmaScan Pro) to aid in the semi-automated analysis of images.**
**Standard, repeatable image processing techniques were tested.**
**Calibration and testing of software-generated data against manual measurements. **
**Training of lab personnel to use new hardware, techniques, and software.**

## Example of data spreadsheet collected...

## Example of data and statistical measurements

**Note that the analysis of each site includes nominal Major/Minor Length,  Feret Diameter, and Area.  Also, statistics are calculated on these 67 sites...**

## ‘Mirror’ Glass Micrometeoroid Test Analysis...

**Micrometeoroid impact effects on mirror glass samples is currently underway... **

## ‘Mirror’ Glass Micrometeoroid Testing...

## Analysis of test results

## Test Data AnalysisInner-layer gross-failure analysis

**No inner-layer gross-failure occurred - can only predict minimum failure limit**

## Test Data AnalysisImpact-generated holes

**~2 m****2****/g X 0.2 mg/m****2**** = 0.04% hole area**

## Test Data AnalysisEffect of velocity on debris generation

**	****Expect higher velocities to caused more vaporization of particle and corresponding reduced debris particulate damage to inner layers**

## Test Data AnalysisTransition-region data

**Test Data Analysis****Transition-region data**

**Transition-region impacts appear well behaved**

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**1**

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**4**

**5**

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**1**

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**5**

**Ratio of Particle Diameter (D****part****) to Layer Thickness (T)**

**(D****hole**** - D****part****)/T**

**(D****crater**** - D****part****)/T**

## Future testing plans

_**Sunshield**_
**Complete inspection of sunshield test samples**
**Calculate/estimate worst-case degradation effects on sunshield**
**Future testing needs depend upon final analysis of current test data & selected NGST architecture. Possible actions include:**
**Test film samples after exposure to UV/E****-****/p****+**** environment**
**Test coatings to look at potential for delamination**
**Oblique angle impacts**
**Thick target to obtain data on cratering energy**
_**Mirrors**_
**?**