IEEE - Aerospace and Electronic Systems - May 2021 - 55

Bai et al.

Figure 6.
Flowchart of the solar cell replacement.

The above process is a normal one-time solar cell
replacement, which will cause 1 to 2 bends to the interconnector. This bending will not cause damage to the fatigue
resistance of the interconnector. Subsequently, if the adjacent cell is to be replaced due to the occurrence of fragmentation into many pieces, the removal of the NQ-704
silicone rubber coated on the back of the replaced cell is
more difficult than the conventional two-component film
adhesive and will cause the interconnector to be bent
many times. Therefore, the multiple replacements of the
adjacent solar cell will increase the number of bending of
the interconnector. The bending part is the stress relief
loop of the interconnector as shown in Figure 7. As silver
is a face-centered cubic crystal with 12 slip systems, the
silver material in the bending zone will enter plastic deformation under the action of mechanical stress and cause a
certain degree of microstructure multisystem slip when
the bending angle is large. As the number of bending
increases, the multisystem slip and cross-slip of the microstructure will further intensify. When it intensifies to a certain extent, the entanglement of these slip dislocations
causes the crystal grains to elongate and break and microcracks are generated in local areas of the silver matrix.

experiments shown quantitatively in [27, Table 2-1], it
can be seen that silver has the worst resistance capacity to
AO erosion and its AO reaction efficiency is more than
4 Â 10-24 cm3/atom.
The erosion of silver by AO is divided into two
stages: during the initial oxidation process, a layer of
Ag2O film is formed on the surface of the silver; the
second stage of the oxidation process is the formation
of AgO on the top of the oxide film. When the thickness of the oxide film increases, a great growth stress
will be generated in the oxide film, leading to wrinkling, cracking, and peeling of the oxide film. Under
the action of OA, uneven corrosion pits will be formed
on the silver surface, which will easily cause stress
concentration and result in a reduction in the thickness
of the silver body.
We can obtain the AO reaction efficiency, that is, the
erosion yield, which is 10.5 Â 10-24 cm3/atom, and
the average front AO flux of 7.39 Â 1011 atoms/cm2Ás or
the front AO fluence of 3.496 Â 1019 atoms/cm2 for
1.5 years from the ESA's SPace ENVironment Information System (SPENVIS) website [28] with the orbital
parameters of the TTS-5. The front erosion depth for silver
surface can be calculated to be 3.67 Â 10-4 cm, that is,
3.67 mm for a year and a half.

FRACTURE AND OPEN-CIRCUIT MECHANISM OF THE
INTERCONNECTOR
After the silver interconnectors are eroded by AO, the
surface evolves into uneven corrosion pits to form
stress concentration areas and the interconnector
strength decreases. Under the action of the alternating
stress of the space environment temperature, these
weak areas (high-concentration stress areas) are the first
to initiate fatigue microcracks. These microcracks
steadily grow under the action of temperature stress
and other external stresses, and finally cause fatigue
fracture and open-circuit of the silver interconnector.
The schematic diagram of microcrack growth under
alternating temperature stress and other external
stresses is shown in Figure 8.

EROSION MECHANISM OF AO ON THE
INTERCONNECTOR
As we all know, in the LEO 200 to 700 km away from the
Earth's surface, AO is the most abundant residual gas particle, accounting for more than 90% of neutral gas [26].
From the summary of data obtained from space flight
MAY 2021

Figure 7.
Schematic diagram of stress relief loop being bent.

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