Charging mitigation on solar cell by using semi conductive coating for Horyu IV and MicroDragon satellites
Nguyen Tien Su
14350942
Department of Applied Science for Integrated System Engineering
Laboratory of Spacecraft Environment Interaction Engineering
1. Research background and purpose
Spacecraft charging is the buildup of
spacecraft surface potential and in the spacecraftinterior. Dícharges resulting from spacecraft
charging induce many kinds of effects, such as
structure damage, degradation or failure ofspacecraft components and operation anomalies
due to damage of electronic devices. A majorityof satellite failure has been reported is caused bycharging and discharging phenomena, especiallyon solar array, which is one of the mostimportant systems on every satellite. A charging
mitigation method on solar array using semiconductive Antimony Tin oxide (ATO) coating
is being developed in Laboratory of Spacecraft
Environment
INteraction
Engineering(LaSEINE). The purpose of this research is tostudy the effectiveness of ATO coating in
mitigating charging-discharging phenomena on
solar cells.

beam. After a certain of time, surface potential ofcoupon is measured with non-contact highvoltage probe.
Once the effectiveness of ATO coating isconfirmed by charging mitigation capability,
discharge experiment is conducted. In thisexperiment, solar cell coupon is biased at -5kV
and irradiated under the same electron beam
condition in charging mitigation experiment.
After applying a coating on solar cell surface,power generation of solar cell is the mostimportant factor that needs to be considered.
Therefore, it needs to be measured before andafter applying coating. The effect of coating topower loss of solar cell could be estimated bycomparing these two results.
Thermal cycling test also needs to be
conducted to investigate thermal variation effectto ATO coating performance.
3. Experiment results

2. Experiment method
By applying an ATO coating on entire solar
cell surface, it will connect cover glass of solar
cell to the satellite’s ground. The coating layer
allows charge to conduct to satellite’s chassis
and mitigate local surface charging on solar celland keep it at a safe level, there will be no
significant potential difference between coverglass surface and satellite’s ground. Therefore
discharges will not occur.
To evaluate performance of ATO coating, it isnecessary to conduct four kinds of experiments.
First is charging mitigation experiments. thecoated solar cell coupon is connected to theground and irradiated under high-energy electron

Figure 1 Surface potential of coated solar
cell and cover glass.

Figure 1 shows surface potential of acoated solar cell coupon and a non-coated coverglass under electron beam at 10keV in charging
mitigation experiment. From the color scale, it isclear that cover glass surface is highly chargedup to -6kV while coated solar cell coupon ishardly charged.
During the discharge experiment, there wereseveral discharge points observed on non-coatedsolar cell while no discharge occurred on coatedsolar cell. The number of discharge observed inexperiment is shown in table 1. The effectivenessof ATO coating could be verified.
Table 1 Number of discharges

Power generation of solar cell coupon withand without coating are shown in the Figure 2.
By comparing the two results, power generationof the coupon after coating is decreased about
2.4% at peak power point. This is significant
improvement in comparison with the result ofprevious research, which was 35.5% [1].
Figure 2 I –V characteristic of solar cellwith and without coating.

Thermal cycle test is also conducted andno affect after 50 thermal cycles could be foundin charging mitigation capability of ATO coating.
After doing necessary experiments on
ground, a coating solar cell coupon is attached on
Horyu IV satellite. Discharge experiments on
solar cell coupons were conducted to evaluate
charging mitigation capability of ATO coating in
Low Earth Orbit. A camera was used to detectthe discharge position if it occurred. Experimentresults show that the coating is not fully effective
to prevent discharges on solar cell. Several
discharges were observed and images ofdischarge points were captured. Reason ofdischarges occurred is the coating might not wellcover the edges of solar cell, when it is exposedto space environment, they become very weak
points against discharges.
Two other triple junction solar cells areprepared and will be mounted on MicroDragonsatellite after doing same experiments with solarcell coupon on Horyu IV satellite. One I-V
measuring circuit is designed in order to measure
power generation of both coated and non-coatedsolar cell. Measured data shall be used tocalculate power loss of coated solar cell when it
is operating in space.
4. Summary
This charging mitigation method using
ATO coating is intended to implement on
Geosynchronous Orbit (GEO) satellite. However,
it is difficult for a student research to have achance to attach solar cell coupon on a GEO
satellite. On ground experiment results showed ahigh capability of ATO coating in charging
mitigation but Horyu IV’s on orbit experimentresults show that this ATO coating could notprevent discharge on solar cell. Therefore, tomake the coating works in LEO environment, weneed to conduct more experiments to find abetter coating condition to mitigate chargingdischarging phenomena on solar cell while
keeping its power generation.
Reference[1] A. Takahashi, R. Muraguchi, M. Iwata,and M. Cho, “Charging and Arcing Test on
Semiconductive Coated Solar Coupon Panel”,
IEEE Transactions on plasma science, Vol. 43.