## 5 Conclusions  
ALE-1, the technology demonstration satellite for artificial shooting star generation, successfully conducted an orbital descent maneuver from an initial orbit of about 500 km down to about 400 km with the help of an SDOM system. ALE-1 also succeeded at remaining in the target orbit for a longer period to conduct its mission by separating the DOM. In addition, ALE-1 also succeeded at obtaining camera images of several different configurations of the SDOM during the orbital operation. The SDOM, however, experienced mechanical troubles in space, and the drag sail resulted in a drag flag; nevertheless, the orbit of the ALE-1 was able to be lowered as planned, although it took longer than expected, indicating that the drag flag shape has an effective de-orbiting performance. Consequently, a comprehensive investigation was  
Figure 8: Comparison between the flight data and orbit propagation simulations. conducted on the de-orbiting capabilities of the drag flag by comparing orbital propagation simulation results and the flight data of the satellite altitude over the past three years of operation. A combination of parameters \(C_{\rm D}A\) was used to evaluate the de-orbiting performance of the SDOM, which can be regarded as the mean values of the drag coefficient multiplied by the cross-sectional area. In this way, the mean de-orbiting performance could be evaluated without an explicit analysis on the drag coefficient, which can be affected by the shape of the fluttering drag flag in the rarefied atmosphere in the orbit. Through the investigation, the following points can be found:  
* The \(C_{\rm D}A\) of the drag flag increased as the orbital altitude decreased;
* The \(C_{\rm D}A\) of the drag flag was estimated to be ranging from 3.0 to 4.0, which corresponds to about 22 to 29% of the \(C_{\rm D}A\) of the fully deployed DOM and 39 to 51% of the \(C_{\rm D}A\) of a tumbling satellite with the deployed DOM;
* Drag flags can be effective de-orbit devices and can provide breakthroughs for future PMD devices to solve space debris problems. The exact behaviors of the drag flag and drag sail attached to satellites are subject to further investigations; the above findings, however, indicate that materials in different shapes than sails, such as threads, tapes, and mantles, may have similar de-orbiting performances and can be utilized for future PMD devices to solve space debris problems. In addition, de-orbiting devices based on these various shapes can have possibilities to be implemented more mechanically efficiently, resulting in more lightweight and small solutions. It is therefore also possible that significantly larger and higher performance de-orbiting devices can be developed with reduced mass and envelope. From the satellite system design point of view, the developed de-orbiting device SDOM system has several superior benefits compared with the traditional methods of de-orbiting using thruster systems. Firstly, SDOM's only 4 kg of mass is favorable for micro-satellites with a mass of approximately 100 kg or less. Secondly, it does not contain hazardous materials such as propellant and can be handled very safely on the ground, during the launch, and even possibly inside manned spacecraft. Finally, it does not necessitate active attitude control or power consumption during the de-orbiting as demonstrated in this study; hence, it can ensure that the satellite can de-orbit, even if the satellite is no longer operational after the activation of the device, which is of great benefit as a de-orbiting device. The authors sincerely hope that this research's results can contribute to the enhancement of future peaceful space utilization. Conceptualization, K.T. and T.K. ([PERSON]); methodology, K.T. ; software, K.T. ; validation, T.S., Y.S., S.F., and T.K. ([PERSON]); investigation, H.I. and T.K. ([PERSON]); resources, Y.S. and T.K. ([PERSON]); writing--original draft preparation, K.T. ; writing--review and editing, T.K. ([PERSON]); visualization, K.T. ; supervision, T.K.