Spacecraft with solar arrays operate throughout the near earth environment and are planned for outer planet missions. An often overlooked test condition for solar arrays that is applicable to these missions is micrometeoroid impacts and possibly electrostatic discharge (ESD) events resulting from these impacts. NASA Marshall Space Flight Center (MSFC) is partnering with Space Systems/Loral, LLC (SSL) to examine the results of simulated micrometeoroid impacts on the electrical performance of an advanced, lightweight flexible solar array design. The test is performed at MSFC's Micro Light Gas Gun Facility with SSL-provided coupons. Multiple impacts were induced at various locations on a powered test coupon under different string voltage (0V-150V) and string current (1.1A - 1.65A) conditions. The setup, checkout, and results from the impact testing are discussed

Gardiner, G.

Hoang, B.

Schneider, T. A.

Vaughn, J. A.

Wong, F.

Wright, K. H.

NASA Technical Reports Server

14th Spacecraft Charging Technology Conference, ESA/ESTEC, Noordwijk, NL, 04-08 APRIL 2016                   1 
 
 
MICROMETEORITE IMPACT TEST OF FLEX SOLAR ARRAY COUPON 
 
K. H. Wright(1), T. A. Schneider(2), J. A. Vaughn(2), B. Hoang(3), F. Wong(3), G. Gardiner(3) 
 
(1)UAH, Jacobs ESSSA Group, 301 Sparkman Drive, Huntsville, AL 35899, USA, Email:Ken.Wright@uah.edu 
(2)NASA/MSFC, Mail Code: EM50, Huntsville, AL 35812, USA, Email:todd.a.schneider@nasa.gov; 
jason.a.vaughn@nasa.gov 
(3) Space Systems/Loral, LLC, 3825 Fabian Way, Palo Alto, CA 94303, USA (email: Bao.Hoang@sslmda.com; 
Frankie.Wong@sslmda.com) 
 
 
Abstract— Spacecraft with solar arrays operate 
throughout the near earth environment and are 
planned for outer planet missions.  An often 
overlooked test condition for solar arrays that is 
applicable to these missions is micrometeoroid 
impacts and possibly electrostatic discharge (ESD) 
events resulting from these impacts. NASA Marshall 
Space Flight Center (MSFC) is partnering with Space 
Systems/Loral, LLC (SSL) to examine the results of 
simulated micrometeoroid impacts on the electrical 
performance of an advanced, lightweight flexible 
solar array design.  The test is performed at MSFC’s 
Micro Light Gas Gun Facility with SSL-provided 
coupons.  Multiple impacts were induced at various 
locations on a powered test coupon under different 
string voltage (0V-150V) and string current (1.1A – 
1.65A) conditions.   The setup, checkout, and results 
from the impact testing are discussed.   
 
1. INTRODUCTION 
Space Systems/Loral, LLC (SSL) first reported charging 
induced electrostatic discharge of a solar array that 
resulted in loss power in 1997 [1].  Since then, SSL has 
implemented a series of design solutions that have 
mitigated such failure recurrence [1].  Ground tests have 
further demonstrated design robustness from ESD events 
[2, 3].  However, other possible failure mechanisms such 
as micrometeoroid impact, although rare in Earth 
geosynchronous orbit, can be a possible cause of solar 
array string loss.  SSL is developing and qualifying an 
advanced flexible solar array for commercial spacecraft 
and possibly future NASA missions [4].  The flexible 
solar array technology is based on the Deployable Space 
System’s (DSS) Roll-Out Solar Array (ROSA) [5].  
Unlike common rigid panel solar array technologies 
which typically have a composite rigid panel as the 
substrate, the ROSA substrate consists of a 2-mil thick 
Kapton layer and an ~0.4 mm thick fiberglass mesh.  The 
key advantage of the ROSA technology is its low mass 
and low stowage volume.  With estimated orbital debris 
velocities ranging from 0 to 16 km/s and micrometeoroid 
velocities ranging from 11 km/s to 72km/s in Earth orbits 
[6], a typical low-mass space solar array would be 
penetrated easily by an impact event.  Notable impact 
damages of such light-weight solar arrays were observed 
and reported from the International Space Station [7]. 
Although an impact would cause local mechanical 
damage to a solar array, SSL and NASA MSFC are 
evaluating the extent of the impact to this low-mass 
ROSA design.  Furthermore, an ESD event caused by 
plasma generation from the impact is also a possibility 
[8].    
2. TEST ARTICLES 
Two (2) test coupons were built for micrometeoroid 
impact evaluation testing.  The solar cell used for these 
coupons was SolAero ZTJ with area = 59.7cm2.  The 
coverglass was Qioptiq CMG that is 100-μm thick with a 
single-layer of MgF2 anti-reflective coating.   Each solar 
cell assembly (SCA) has a discrete silicon bypass diode. 
Fig. 1 presents the test coupon configuration.  There are 3 
solar array strings, each with 2 cells in series.  As shown 
in Fig. 1, the strings are configured with 1-mm and 15-
mm gaps between strings.  The 1-mm gap represents the 
nominal gap between segments of cells within a string. 
The larger 15-mm gap represents the nominal gap 
between strings.  The solar cell assemblies were bonded 
to a 50 micron thick Kapton sheet with room temperature 
vulcanizing (RTV) adhesive CV10-2568 from Nusil 
Technologies.  There is no adhesive grout between the 
gaps of the solar cells.  The photovoltaic blanket module 
was spot-bonded to a fiberglass mesh with RTV 
adhesive.  The fiberglass mesh was tensioned to the 
flight-like condition.  Prior to the micrometeoroid impact 
tests, these coupons were subjected to thermal bake-out 
at +125°C and 25 thermal vacuum cycles from +106°C 
to -198°C.  
The two test coupons were designated as Test Coupon A 
and Test Coupon B. Test Coupon A is used for ESD 
evaluation during the micrometeoroid impacts.  Test 
Coupon A was under electrically biased conditions 
during the impact testing.  Test Coupon B will be used 
for micrometeoroid impact testing followed by thermal 
cycling exposure.  The utility of Test Coupon B is to 
evaluate for damage propagation from thermal cycling 
after impact events.  In this paper, only testing with 
Coupon A is reported.  
https://ntrs.nasa.gov/search.jsp?R=20160005691 2019-08-31T03:29:20+00:00Z
14th Spacecraft Charging Technology Conference, ESA/ESTEC, Noordwijk, NL, 04-08 APRIL 2016                   2 
 
 
 
 
 
 
 
 
Figure 1. Micrometeoroid Test Coupon Configuration.       
a. front view and b. back view 
3. TEST FACILITY 
Testing was conducted at the Micro Light Gas Gun 
(MLGG) facility at MSFC.  Figures 2-5 show the various 
components of the MLGG facility.  The force from a 
blank 22-caliber shell is captured by a piston which 
impacts a helium pressurized chamber.  The pressure 
pulse accelerates a 1.76 mm diameter Nylon projectile to 
velocities > 5 km/s.  The particle velocity is determined 
from timing signals from a diode at the beginning of the 
drift tube and a diode in the target chamber.   
 
 
 
 
 
 
 
 
 
Figure 2. Side View of the Micro Light Gas Gun at the 
NASA MSFC Impact Test Facility 
 
 
 
 
 
 
Figure 3.  Close-up view of firing line. 
 
 
 
 
 
 
 
Figure 4.  Side view of target chamber showing pumping 
system. 
 
 
 
 
 
 
 
 
Figure 5. Target chamber layout.  A mounting fixture 
allows adjustment of coupon for precise targeting.  A 
laser mounted at the beginning of the drift tube aids in 
coupon alignment. 
The challenges for impact testing include precise coupon 
alignment to control impact location; pressure 
management during the impact process; and 
measurement of the true transient electrical response 
during impact on the powered coupon. To address these 
challenges, a throughout checkout of the test facility was 
performed prior to testing with Coupon A.  Several test 
shots were executed to validate the projectile velocity 
and impact location accuracy.  A target was attached to a 
mounting plate that contains both vertical and horizontal 
positioning capability. To moderate the pressure increase 
in the target chamber after pellet firing, a baffle plate 
with a 3.8 cm diameter tube was installed in the upstream 
opening in the target chamber.  Based upon several 
practice firings, the target chamber base pressure briefly 
increased from ~8e-6 Torr to ~1e-3 Torr.   
A proxy coupon was constructed of copper plates that 
reproduced the three string morphology.  This proved 
essential for checkout of the coupon electrical test circuit 
discussed in Section 4.  
  
a. b.
 
 
Drift Tube 
Target Chamber 
Diode for start pulse 
Particle loading 
assembly 
Trigger 
 
Trigger 
Gun tube pressurization line 
 
 Capacitor Box  
Coupon 
Mount  
Proxy 
Coupon  
Blow-off Plate (West)  Blow-off Plate (East)  
Baffle 
Plate 
Diode for 
stop pulse  
14th Spacecraft Charging Technology Conference, ESA/ESTEC, Noordwijk, NL, 04-08 APRIL 2016                   3 
 
 
4. TEST PARAMETERS 
Prior to the impact tests, Coupon A was thoroughly 
inspected and photo documented. Electrical test included 
dark I-V measurements of the cells and the bypass 
diodes.  The NASA MSFC Large Area Pulse Solar 
Simulator (LAPSS) was used to measure the I-V 
performance of each 2-cell string. 
4.1 Test Coupon A 
Test Coupon A was designated for micrometeoroid 
impact test while the coupon is under electrical bias.   
Figs. 6 and 7 show the planned pellet impact locations.    
 
 
Figure 6. Coupon A Front Impact Locations 
 
 
Figure 7. Coupon A Rear Impact Location 
As shown in Figs. 6 and 7, the projectile target locations 
on the Coupon A were at the solar cell edges and at the 
solar cell center. The targeting of the cell edges was to 
determine if plasma generation from the impact could 
result in sustained arcing between substrings of cells.  
Table 1 presents the impaction location and the 
electrically biased conditions of the substrings. 
Table 1. Electrical Test Parameters for Coupon A 
Coupon A 
Test 
Shot 
Impact 
Side 
SAS  
Volt./Cur. 
String 
A 
String 
B 
String 
C 
1 Front 100V/1.1A High Low NP 
2 Front 15V/1.1A NP Low High 
3 Front 22.5V/1.65A NP Low High 
4 Front 150V/1.65A High Low NP 
5 Back 150V/1.65A High Low NP 
High = Solar Array Simulator (SAS) voltage 
Low = SAS Return 
NP= Not Powered 
   
Test shots nos. 1 and 5 were targeted at the edges of the 
solar cells with 15 mm gap from adjacent cells. This 
represented design gap between strings where the 
maximum voltage differential can be at 100 V. The larger 
voltage and current values in shots no. 4 and 5 represent 
a test margin factor of 1.5.  Test shot nos. 2 and 3 were 
also targeted at the edges of the solar cells where the gap 
between these cells is 1 mm.  This gap represented the 
nominal gap between cells within a string.  Note that 
none of the gaps were filled with RTV adhesive grout.  
The higher voltage and current in test shot no. 3 represent 
a test margin factor of 1.5.   These test margins were 
applied to demonstrate the design robustness to any ESD 
events caused by resulting plasma plumes during the 
micrometeoroid impact [8].  Test shot no. 4 was targeted 
at the center of a solar cell. Visual inspection and photo-
documentation was scheduled after each impact shot.  At 
the end of the 5 shots, I-V measurement using LAPSS 
are to be repeated for each 2-cell string on the both 
coupons. 
Fig. 8 shows the electrical schematic of the test circuit 
used during impact testing of Coupon A.  This test 
schematic is based on ISO-11221.  The key difference of 
this schematic from that of previous ESD testing [2, 3] is 
that the ROSA coupon has no substrate.  Only the strings 
are electrically biased by the Solar Array Simulator 
(SAS). The electrical currents and differential voltage 
between the strings are controlled by a network of bypass 
resistors and voltage clamp (Vclamp), respectively.  
These components control the proper biased voltage 
across the solar cells as well as the differential voltages 
between strings under test.  A network of capacitance in 
the test circuit simulated the capacitance of the missing 
cells in the strings since only 4 cells were under test 
during each shot.  An arc interruption circuit is used to 
open the High Voltage (HV) relay after 3 milli-sec to 
14th Spacecraft Charging Technology Conference, ESA/ESTEC, Noordwijk, NL, 04-08 APRIL 2016                   4 
 
 
limit the duration of any sustained arc. Three 
oscilloscopes were used to capture the current and 
voltage probe data.    
 
 
 
 
 
 
 
 
 
 
 
Figure 8. Electrical Schematic of Coupon A during 
Micrometeoroid Impact Test 
 
A special circuit (noted as RLC circuit in Fig. 8) is 
employed to shape a primary arc pulse.  The generic 
attributes of the pulse were modeled after consideration 
of an early ROSA array application.  Fig. 9 shows the 
primary arc pulse obtained with the proxy coupon test. 
Vbias was set to -650 V for all impact tests.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 9. Primary Arc pulse used in the ESD testing.  
Nominal peak at ~25 A for ~ 100 µsecs.  Total charge 
contained in the pulse is ~ 1.3mC. 
Prior to the first impact test, a gas only shot (no 
projectile) was performed in order to check-out the ESD 
circuit response and optimize oscilloscope settings for 
data capture.  The gas only shot also served to verify that 
a temporary sustained arc would not be initiated just due 
to background pressure increase.    
 
 
5. TEST RESULTS 
Fig. 10 shows the cumulative impact location map for all 
impacts. Due to some uncertainty in targeting precision 
(pellet strikes the coupon within a semi-circle of radius 6 
mm from laser spot), impact #2 was repeated to strike the 
intended string.  The first execution of shot 2 conditions 
is labeled 2A while the second execution of shot 2 
conditions is labeled 2B.  
The size of the impact hole for the pellet striking the cell 
front-side is ~ 4 mm.  This is applicable for impacts 1, 
2A, 2B, 3, and 4.  For impact 5, the pellet strikes the cell 
back-side first and in this case a rectangular-like section 
is torn away.  
It is also observed that a halo of residue exists about the 
impact hole.  This residue halo was observed in the gas-
only shot that was executed before impact 1 on Coupon 
A.  The residue halo may result from debris from the 
burst disk that holds the pellet in place before firing.     
 
 
 
 
   
 
 
 
 
Figure 10. Impact location map for Coupon A as viewed 
from the front side. Nominal impact hole size is ~ 4 mm.   
In Figs. 11-13, current and voltage probe data is 
presented for impact 2B on String C.  Circuit conditions 
for this shot were 15 V between string C and string B 
(1mm gap) with the SAS set to 1.1 A.  No current 
activity on the strings beyond the duration of the primary 
arc was observed.  In Fig. 14, the path of the primary arc 
current within the circuit is illustrated.  
 
 
CP6 
CP2 
CP7 
CP5 
CP4 
CP1 
Vclamp 
Vbias 
 
HV Relay 
B
yp
as
s 
C
ir
cu
it 
S
A
S
 
R
LC
 C
ir
cu
it 
A 
O 
V 
 
 
Chamber Wall 
14th Spacecraft Charging Technology Conference, ESA/ESTEC, Noordwijk, NL, 04-08 APRIL 2016                   5 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 11. Current and voltage probe data for impact 2B.  CP1 shows SAS current flow and is stopped by the arc 
interruption circuit at ~ 3 milli-sec. The charge contained in the primary arc is calculated via two methods and is noted 
on the Vbias and CP4 panels.  A small difference in primary arc amplitude and duration is noted between the proxy 
coupon with copper plates and Coupon A.    
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 12. Current probe data for each string during impact 2B.  CP6 and CP2 corresponds to String C plus and 
minus, respectively.  CP7 and CP5 corresponds to String B plus and minus, respectively.   
 
 
 
14th Spacecraft Charging Technology Conference, ESA/ESTEC, Noordwijk, NL, 04-08 APRIL 2016                   6 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 13. Blow-off plate data during impact 2B. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 14. Diagram of paths for primary arc current during impact 2B.
 
 
14th Spacecraft Charging Technology Conference, ESA/ESTEC, Noordwijk, NL, 04-08 APRIL 2016                   7 
 
 
 
6. SUMMARY  
NASA MSFC has performed micrometeoroid impact 
tests of SSL-provided advanced low-mass flexible solar 
array coupons.  The tests were performed in the Micro-
Light Gas Gun facility at MSFC.  Analysis of the ESD 
circuit probe data and as well as analysis of coupon 
functional test data is ongoing.  The impact testing is part 
of a large risk-reduction campaign that will lead to a final 
ROSA flight design [10].  Although no permanent 
sustained arcs (PSAs) were observed from the impacts 
presented in this paper, further impact testing may be 
needed to clarify the results and to demonstrate the 
flexible array design robustness. Post-impact inspection 
showed that damage from the impacts was local and that 
no array structural breakdown was observed. The 
insulation resistance measurement that was performed 
after each impact shows the same value as the 
Beginning-of-Life value; namely, resistance > 50 GΩ at 
250V between all string combinations.  
7. ACKNOWLEDGEMENTS 
The authors would like to thank the DSS ROSA design 
team, the SSL flexible solar array design team and the 
SolAero SPM design team for their contributions to this 
paper.    
 
8. REFERENCES 
[1]  Hoeber, C., Katz, I., & Snyder, D. (1998). Solar Array 
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[3] Wright, K. H., Schneider, T. A., Vaughn, J. A., 
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[4]  Hoang, B., & Spence, B. (2015). SSL Flexible Solar 
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Micrometeorite Impact Test of Flex Solar Array Coupon

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