Ryotaro Sakamoto, Japan Air Self Defense Force; Nobuhiro Sakamoto, Japan Air Self Defense Force
Keywords: Japan Air Self Defense Force, SSA operational system
Abstract:
Outer space is an essential region nowadays, which supports any activities on the globe including economic and scientific issues. On the other hand, the increasing population of space objects, either active or defunct satellites, or more generally, space debris, requires us to consider emerging risks toward conventional space activities. For the continuous stable use of outer space in the future, Space Situational Awareness (SSA) becomes more and more important for all over the world.
To cope with the emerging risks, the Government of Japan plans to construct the new SSA system in Japan based on the National Space policy. Along with the policy, Japan Air Self Defense Force (JASDF) of the Japan Ministry of Defense (JMOD) has been constructing the new SSA system toward the commencement of the operation from 2024. The JASDF plans to confirm the major functions of the system collaboratively with Japan Aerospace Exploration Agency (JAXA), which has led the development of space capability in Japan for a long time including SSA, and related manufacturing companies and the U.S. partners.
The new SSA system is composed of an operational system and related sensors. The construction of the operational system will be finished in 2022 before the installation of the related sensors in 2024. Generally, when a new equipment is introduced to a current system, to confirm each function of the equipment itself and the connectivity to the current system is significant to ensure the adequate operation. The Electronic Development and Test Group (EDTG), which is responsible for the confirmation and evaluation of ground -based electronic equipment, is going to lead the confirmation of the operational system in 2022. Subsequent to this, the test including the related sensors will be conducted.
Commonly, SSA operational system has orbital analysis capability as a core function, even if there are multiple purposes for operation, such as maneuver detection, re-entry analysis, conjunction assessment, and so on. The new SSA system of JASDF has the similar capability of orbital analysis, which should be confirmed appropriately. However, the operators of each satellite basically do not make their satellites operational information to the general SSA community. Therefore, other operators need to calculate the operational information such as orbital maneuver using public database such as the United States Strategic Commands two-line element (TLE) catalog. The data base is not updated in real-time, so the TLEs orbital information would have uncertainty. In addition, even if the new SSA system has a high performance calculator, the processed results using the data of open source would be inaccurate. Therefore, to clarify the accuracy of the TLEs, statistical studies have been conducted not only maneuver detection, but also re-entry analysis.
In the actual mission, re-entry analysis was a crucial event of Hayabusa2. Hayabusa2 and its capsule were on the re-entry trajectory to Earth as of December 2020. Because of the insufficient orbital data of space objects, and their events in the Geosynchronous Earth Orbit such as perturbation and maneuver, the density of collision probability gets smaller. But this is not because of the low collision probability, rather, because of the low accuracy of orbital data of space objects. To recover this gap, a vast number of collision probabilities of the trajectory were calculated by hand in the case of Hayabusa2. Besides, conjunction assessments are conducted through two steps. One is propagation form TLE, another is to obtain more reliable orbital information from Combined Space Operation Center (CSpOC).
The long term goal is to estimate orbital trajectories by the new SSA system as precisely as possible. Before that, the performance of the operational system will be confirmed. The goal of this paper is to present beneficial information for operational decision making under uncertainty of orbital estimation and errors. As already known, the accuracy of orbital estimation depends on the number of sensors. Then, its accuracy is improved with the accumulation of actual radar plots and calculation using statistical methods. However, to smoothly move forward the new SSA system to operational phase in JASDF, the cause of the orbital errors of the system from the reference trajectory (on-board GPS data) should be understood. The new SSA system is cooperatively constructed by multiple Japanese companies, and our challenge is to integrate each companies technology in matured way. Furthermore, international assets will be connected with our system. These efforts would contribute to strengthen the international cooperation on SSA with the U.S and other friendly nations, and to ensure the stable use of outer space in the future.
Date of Conference: September 14-17, 2021
Track: SSA/SDA