**3. Measurement algorithm**

As the onboard camera used for this experiment was originally designed to monitor the de‐ ployment of a folded solar array paddle, its field of view is thus as wide as 90 [deg] (Fig. 5), while the camera's number of pixels is limited to SXGA (1280 X 1024 pixels). The size of the markers is also limited to 50 [mm] X 26 [mm], while distance from the camera to the target markers is as far as 6 [m]. These constraints mean that one pixel of the camera is equivalent to 7 [mm] at the target marker's position. Therefore, a technique for processing sub-pixel level image data is required to identify deformation of the solar array paddle.

Since solar energy from the Sun is the primary energy provided on the satellite and its solar array paddle, deformation of the solar array paddle should occur so that its structure on the Sun side is extended and causes bending of the solar panels toward the rear side of the solar array paddle. Previous results have indicated that the solar array paddle will bend toward its solar cell side, however. When the initial results of these measurements were recorded,

Vibration of Satellite Solar Array Paddle Caused by Thermal Shock When a Satellite Goes Through the Eclipse

http://dx.doi.org/10.5772/52626

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Fig. 6 shows a sudden offset in the motion of the solar array paddle. When the solar array paddle is straight, the value of displacement may indicate -12 or -11 [mm] in Fig.6. Although we attempted to identify cause of this offset, we could not imagine a proper mechanism that would produce such a direction. We therefore assumed that the previous image data proc‐ essing contained unidentified data processing errors, and consequently modified the algo‐ rithm that identifies the target markers. The earlier version of the algorithm used to identify locations of the target markers assumed such highly illuminated areas as those of the target markers. This algorithm works well when the markers are brightly illuminated. When the target markers are weakly illuminated, however, we found that this algorithm produces

Fig. 7 and Fig. 8 illustrate the difference described above. Fig. 7 is based on the previous al‐ gorithm. The areas enclosed by a yellow line are pixels that are brighter than the threshold level and thus can be assumed to be the target markers as based on sub-pixel level image

**Figure 7.** Target markers estimated by the previous algorithm under weak illumination. The areas of target markers

Fig. 7 shows that the sizes of the estimated target markers are smaller than the actual target markers. We therefore modified the algorithm used to estimate the area of a target marker so that the size of the predicted target marker is similar to that calculated from the actual

data processing. The red cross indicates the center position of the marker.

assumed by the previous algorithm are smaller than the actual target marker size.

Case 0 Case-1

we were unable to identify the source of the errors.

**5. Revised results**

some data processing errors.

**Figure 5.** Constraints on image data processing

## **4. Previous results**

The initial results of these measurements were reported in another paper in this series (Oda et al., 2011). Fig. 6 shows typical results. It shows an offset of a few millimeters appeared when solar array paddle illuminated by the Sun and when in an eclipse. However, these re‐ sults pose certain difficulties in explaining the phenomena, as the tendency of the solar array paddle to bend does not agree with the observation results and conventional research.

**Figure 6.** Motion of the solar array paddle's tip position as estimated from onboard camera images

Since solar energy from the Sun is the primary energy provided on the satellite and its solar array paddle, deformation of the solar array paddle should occur so that its structure on the Sun side is extended and causes bending of the solar panels toward the rear side of the solar array paddle. Previous results have indicated that the solar array paddle will bend toward its solar cell side, however. When the initial results of these measurements were recorded, we were unable to identify the source of the errors.
