Considerations on the lists of the top 50 debris removal targets

Remediation measures, such as Active Debris Removal (ADR) has been studied in order to preserve the space environment. Large derelict objects in crowded orbits are considered ADR targets because they are the source of numerous small debris in case of fragmentation. The target for removal must be chosen carefully because cost is the major issue in realizing ADR, and it is necessary to remediate the orbital environment as efficiently as possible. Last year, Dr. McKnight et al. presented the top 50 debris removal targets by combining each of the top 50 lists compiled by eleven international teams. This paper discusses the considerations involved in selecting debris removal targets. This study first considered the top 50 objects, to be removed according to each index, and then evaluated the consequences of the removal using Near-Earth Orbit Debris Environment Evolutionary Model (NEODEEM), a debris evolutionary model developed by Kyushu University and JAXA. Differences in debris removal targets were studied for long-term stability or short-term safety. This paper discusses why some indices are effective in the short or long term in terms of the orbital distribution of selected targets and the effects of removal in each altitude band. It also discusses the differences between removing 50 objects and removing one object each year, and the effects of removal timing and so on. It found that integrating different indices is effective, and that the removal target must be determined according to the situation. It is more important to remove as much debris as possible as early as possible rather than focusing on an object's ranking in a list.