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
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A
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1980
Cataloged objects >10 cm diameter
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Cataloged objects >10 cm diameter
National Aeronautics and Space Administration
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
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