Space environment that causes satellite anomalies and negative effects to the human activities both in space and on the ground is referred to as space weather. In order to avoid such risks, it is important to gather information on space weather, to make space weather forecasts and to consider best practices for mitigating the risks. In this review paper, we identify risks from space weather and demonstrate current procedures such as observations of space weather phenomena, development of models and forecast tools and engineering approaches to mitigate space weather effects. Important point will be an international collaboration. We introduce a new activity by the United Nations, which aims to safeguard space activities by the extended collaboration of the space weather activities in the world.

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In JAXA, the Space Debris Coordinating Board is coordinating a Research and Development (R&D) Plan in activities related to accelerating debris, involving controlling the budget, reviewing the results, and supporting international activities. The author, as secretariat of the board, drafted a Strategic Plan for debris-related R&D and other mission support activities in 2008, and has maintained it ever since. The basic concept of the Strategic Plan is firstly to ensure mission success, including retaining functions to engage in minimum disposal actions, secondly to preserve the orbital environment by limiting the generation of debris, thirdly to ensure ground safety from re-entering objects, and finally to remedy the orbital environment by removing large objects and preventing the chain reaction of orbital collision. The Strategic Plan and more detailed tactics were induced, based on the risk assessment in orbital activities. A contingency planning approach was also applied to determine crucial preventive measures and threat detection. The author applied the same approach to propose a work procedure to the Working Group for the Long-Term Sustainability of Outer Space Activities assembled in the UNCOPUOS. Also reflecting this approach, the author proposed and is now leading efforts to develop the Spacecraft Design and Operation Manual to show comprehensive measures for spacecraft engineers in JAXA and ISO.

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This paper briefly introduces efforts made at Kyushu University in the area of orbital debris modeling and applications. The orbital debris modeling, which describes debris generation and orbit propagation, enables us to build orbital debris evolutionary models as essential tools to predict the future orbital debris population, and as applications to discuss what and how to do for orbital debris mitigation and remediation. The orbital debris modeling also enables us to devise an effective search strategy applicable for breakup fragments in the geostationary region using ground-based optical sensors, and to evaluate the effectiveness of space-based measurements of objects not tracked from the ground, both to contribute to space situational awareness. Ultimately, this paper includes atmospheric density modeling necessary for orbital decay and re-entry analyses, and space tether modeling to assess risks of using electrodynamic tethers for removing hazardous objects from the low Earth orbit region.

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Although a large spacecraft such as the International Space Station and other artificial satellites arelaunched in the earth orbit thanks to the remarkable progress in the space development, their collisions with orbital debris are an increasing concern. To examine the impact protection performance of spacecraft against orbital debris, hypervelocity impact experiments using a two-stage light gas gun and so on are necessary. There has been an active facility cross calibration program between space agencies, where tests were performed using identical targets and test conditions for each pair of tests, to assure that the results were comparable. Six distinct facility cross calibration testing campaigns have been performed between NASA and gun ranges in Germany, Russia, Japan, France, China and Canada. The test conditions for individual campaigns were negotiated at different times, so the target configuration varied between different campaigns. Projectiles with a diameter of 1 mm were used to simulate orbital debris impacting a target at velocity of 5 km/s. Copper witness plates were used as witness plates to catch the secondary debris, namely ejecta, generated due to hypervelocity impacts. The size distributions of diameter of craters made by ejecta were measured on the witness plates, and they are compared one another among a solar array coupon, CFRP honeycomb and Aluminum honeycomb in this study.

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