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National Aeronautics and Space Administration 



Micrometeoroid and Orbital 
Debris (MMOD) Risk Overview 


Eric Christiansen 
NASA Johnson Space Center 
July 2014 


National Aeronautics and Space Administration 

Agenda 

• Background on micrometeoroid and orbital debris (MMOD) environment 

• MMOD shielding overview 

• ISS MMOD risk issues 

- Radiators 

- Solar arrays 

- Solar array masts 

- EVA Handrails 

- Hardware behind bumpers or covers 

- Return vehicle thermal protection systems (TPS) 



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MMOD Environment Models 

• Orbital Debris provided by JSC & is the predominate threat in low Earth 
orbit 

- ORDEM 3.0 is latest model (released December 2013) 

- Man-made objects in orbit about Earth impacting up to 16 km/s 

• average 9-1 0 km/s for ISS orbit 

- High-density debris (steel) is major issue 

- http://orbitaldebris.jsc.nasa.gov/ 

• Meteoroid model provided by MSFC 

- MEM-R2 is latest release 

- http://www.nasa.gov/offices/meo/home/index.html 

- Natural particles in orbit about sun 

• Mg-silicates, Ni-Fe, others 

- Meteoroid environment (MEM): 11-72 km/s 

• Average 22-23 km/s 



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Spatial Density [km 3 ] 


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MMOD Environment Models 



• Meteoroids consist of background sporadic flux (static), and streams from 
meteor showers (variable) 

- Occasionally, showers can turn into storms 

• Orbital Debris is dynamic, changing as function of the rate of on-orbit 
explosions & collisions, launch rate and atmospheric drag/solar activity 


400km altitude 


Time Evolution of >1 cm ORDEM 3.0 Debris at 400 km Altitude 

5.0E-08 
4.5E-08 
4.0E-08 
3.5E-08 
3.0E-08 
2.5E-08 
2.0E-08 
1.5E-08 
1.0E-08 
5.0E-09 
0.0E+00 

1995 2000 2005 2010 2015 2020 2025 2030 2035 

Year 

Note, Spatial Density is proportional to impact risk 



6.0E-07 


5.0E-07 


4.0E-07 


c 3.0E-07 

o 

Q 


CL 


705km altitude 

Time Evolution of >1 cm ORDEM 3.0 Debris at 705 km Altitude 

t * ^ H- • Average Future Collisions 

2009 Iridium-Cosmos Collision & 


2.0E-07 


Explosions near this 
Altitude in 2006 2007 


1.0E-O7 



0.0E+00 


1995 


2000 


2005 


Non-Collision Sources 


2010 2015 2020 2025 2030 2035 

Year 


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1960 



Cataloged objects >10 cm diameter 





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1970 




Cataloged objects >10 cm diameter 


6 




A 


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1980 



Cataloged objects >10 cm diameter 


7 





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Cataloged objects >10 cm diameter 




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2000 




Cataloged objects >10 cm diameter 




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2010 



Cataloged objects >10 cm diameter 





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Effects of Micrometeoroid and 
Orbital Debris (MMOD) Impacts 



• Even small MMOD impacts can cause a lot of damage 

- Hypervelocity MMOD impacts represent a substantial threat to spacecraft 

- Rule of thumb: at 7km/s, aluminum sphere can penetrate completely through an 
aluminum plate 4x the sphere’s diameter 


Damage from a 1.3cm diameter sphere 
at 7km/s 



Comparison of size of projectile to 
size of impact crater 



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Monolithic versus Stuffed Whipple Shield 
Weight Comparison of Equal-Performance Shielding 


Aluminum “Monolith ” Shield 
29.1 pounds per square foot 


Scale: 1” = 1” 


aluminum sphere 

(debris simulant) 


(spacecraft exterior) 


V^^y'dian 

1 


Stuffed Whipple Shield 
4.5 pounds per square foot 

r~\ o, 

y ydiam 

x 


aluminum sphere 

(debris simulant) 


. 5 ” 

1 diameter 


5 ” 
diameter 


(spacecraft exterior ) 


Impact Velocity 

(7 km/s) 


2.00” aluminum 



equal 
performance 


84% 

weight 

reduction 


C 


(spacecraft interior ) 


These shields can stop a 0.5” diameter aluminum debris 
projectile impacting at 7km/s, but the Stuffed Whipple 
shield weighs 84% less (94% if rear wall is excluded) 
and costs much less to launch to orbit 


Impact Velocity 

(7 km/s) 


0.08” aluminum 




(vacuum) 


thermal insulation 


(vacuum) 


6 layers Nextel® AF-62 


6 layers Kevlar® Style 710 
(or KM2-705) 


(vacuum) 


0.188” aluminum 


(spacecraft interior) 


4.50 







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ISS shielding overview 

• Several hundred MMOD shields protect ISS, differing by materials, standoff 
distance, and capability 

• Heavier shields on front & sides (where we expect most MMOD impacts), 
less capable shielding on aft, nadir and visiting vehicles 




Russian 


r> 


velocity 

direction 


Earth 


JAXA 


colors represent different MMOD shield configurations 


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Issues: MMOD Damage to ISS Radiators 





MMOD impact damages observed to ISS radiator panels during Russian EVA 
(June 2013) 



ISS036e011356 




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MMOD Damage to ISS Radiators 





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MMOD Damage to ISS Radiators (US) 

• MMOD impact damages observed to ISS radiator panels (Aug. 2013) 


% ■ 

it 



ISS036e037365 



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P4 photovoltaic radiator 

• Initial indication found on 6/30/2014 




Measurement of P4-PVR Radiator Damage 

“2A” Side of Panel 3 






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ISS Solar Array Damage 



MMOD 

caused disconnected 
bypass diode, leading 
to cell overheat 
damage 



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ISS Solar Array Mast 



Deployable structural booms or masts used to support ISS solar arrays 



ISS022E067792 



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MMOD Damage to ISS Solar Array Masts 


• Elements of the solar array masts have been damaged from MMOD impacts 





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Hypervelocity impact tests 



Mast elements have been hypervelocity impact tested and structurally tested 
to assess residual strength for ISS life extension 







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Handrail and EVA tool MMOD damage 


Many craters noted to ISS handrails and EVA tools 
Sharp crater lips have lead to cuts on EVA gloves 
EVA terminated early on STS-118 due to glove cuts 

Modifications to EVA suit and ISS EVA procedures necessary to reduce cut 
glove risk from MMOD damage 




Crater on D-handle tool 
5mm diameter 

Repaired on-orbit during STS- 123 


Tear in EVA glove 
(STS-118 EVA#3) 




Crater on ISS pump module handrail 
1.85mm diameter x 0.8mm deep 
Returned STS- 135 




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Ku-band antenna 



An MMOD Strike was seen on the ISS Ku Antenna Gimbal Gear Cover. 
The image was captured during Mission ULF2 / STS-126. 

Interior damage? 





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Thermal protection systems (TPS) for 
crew return vehicles 

MMOD risk to thermal protection system (TPS) of ISS crew return vehicles 
(Soyuz, Commercial vehicles) is high 

- Concern is TPS damage that can lead to loss-of-vehicle during reentry 

- Issue can be mitigated by inspection and repair or safe-haven (not Program baseline) 

| 0KXSl^i®pi8l§§ 

Soyuz vehicle 


Orbital Module 


Descent Module 


backshell 


heatshield 


niiirument- Service Modu e 


1 0.0 m 


'■ 


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BACKUP CHARTS 


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ISS016E009184 


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STS-120 Solar Array Wing (SAW) EVA repair 
was caused by MMOD impact damage 




During STS-120 two solar array wings were removed from Z1 truss and relocated to P6 location. During re- 
deployment, the 4B solar array wing was torn in two places, due to a snagged guide wire. The guide wire was 
removed and “cuff-links” added to stabilize the array. 


S120E008247 


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Scanning Electron Microscope EDXA 
Evaluation of retrieved guide wire 



7 of 21 wires in the guide wire cable were broken, causing the guide wire to hang -up in a solar array grommet. 
3 of the 7 cut wires exhibited evidence of extensive melt at broken ends, indicative of MMOD impact. 











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MMOD Damage to ISS 



• MMOD impact damages observed to radiator panel during EVA-20 (Nov. 2012) 



ISS033e017859 


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Observed Spacecraft MMOD Impacts 

Shuttle Windows 




STS 132 Window 6 .« 

Crater diameter 0. 13 mm 
Smallest photographed 
impact 


iT 

* rt i / .r & . * V* > U 


' 

* / V i. M 




STS 126 Window 6 

Crater diameter: 1 1 .2 mm 
Largest photographed impact 


STS 130 Window 1 

fc Ck V Crater diameter: 3.97 r 

/ 5®' i» u %>:4 


j'i / ' 1 *v 4 vl*/ 

' 

'• V. Mir 

Mil/' 


/ 'i *x * % * W:4 

8HF 

*• . /,:• ,V’\ 


4 mm 


STS 123 Window 1 A 

Crater diameter: 3.10 mm! 


STS 128 Window 1 

Crater diameter: 3.05 mm 


STS 122 Window 8 

Crater diameter: 2.60 mm 


NASA Johnson Space Center 
Hvpervelocity Impact Technology Group 


STS 130 Window 4 

Crater diameter: 0.46 mm 


Space Shuttle Window Damage Comparison 
http://ares.jsc.nasa.gov/ares/hvit/index.cfin 


Montage by Lakshmi Nathan 
July 2011 


Sampling of Shuttle Window MMOD Impact Craters 

(all displayed on same dimensional scale) 


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MMOD Risk Assessment Process 

• Process used to identify MMOD risk drivers, evaluate risk mitigation 
options & optimization, verify compliance with protection requirements 




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ISS Service Module Shielding 



Service Module (SM) identified as high 
penetration risk using Bumper risk analysis 

- large cone region 

- forward sides of small diameter cylinder 

Shields designed and tested, EVA installed 

- 23 augmentation shields for the cone region 

- 5 augmentation shields for the cylinder region 

28 shields reduced SM MMOD risk by 30% 



High-risk (red) 
Low-risk (blue) 


SM “conformal" 
augmentation shield 

O 


ImmAl . — 

Corrugated 0.5mm A1 * 


3mm Fiberglass panel 
Russian “Kevlar” fabric (6) 


MLI Thermal Blanket p= 
0. 5/1 0/0.5mm graphite-epoxy LL-I 
honeycomb 
2mm A1 pressure shell 


m e 8 


3r 



EVA Installation 


23 “conformal” panels on cone region 


5 panels on small diameter cylinder 




/ M S 


k! 

/ y / 


f 

I / X *"■ 


■ I