Development of Space Environment
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Nagatsuma et al. Earth, Planets and Space (2021) 73:26 https://doi.org/10.1186/s40623-021-01355-x FULL PAPER Open Access Development of space environment customized risk estimation for satellites (SECURES) Tsutomu Nagatsuma1* , Aoi Nakamizo2 , Yasubumi Kubota2 , Masao Nakamura3 , Kiyokazu Koga4 , Yoshizumi Miyoshi5 and Haruhisa Matsumoto4 Abstract Plasma variations in the geospace environment driven by solar wind–magnetosphere interactions are one of the major causes of satellite anomaly. To mitigate the efect of satellite anomaly, the risk of space weather disturbances predicted by space weather forecasting needs to be known in advance. However, the risk of satellite anomaly owing to space weather disturbances is not the same for all satellites, because the risk depends not only on the space envi‑ ronment itself but also on the design and materials of individual satellites. From the viewpoint of satellite operators, it is difcult to apply a general alert level of the space environment to the risk of individual satellites. To provide tailored space weather information, we have developed SECURES (Space Environment Customized Risk Estimation for Satel‑ lites) by combining models of the space environment and those of spacecraft charging. In SECURES, we focus on the risk of spacecraft charging (surface/internal) for geosynchronous satellites. For the risk estimation of surface charging, we have combined the global magnetosphere magnetohydrodynamics (MHD) model with the satellite surface charg‑ ing models. For the risk estimation of internal charging, we have combined the radiation belt models with the satellite internal charging models. We have developed prototype products for both types of charging/electrostatic discharge (ESD). The development of SECURES and our achievements are introduced in this paper. Keywords: Space weather forecasting, Geospace, Satellite anomaly, Satellite charging, Customized risk estimation Introduction malfunctions. Terefore, satellites are designed and Te space around Earth (geospace) has been used by developed with measures to prevent anomalies due to many types of satellite for various purposes, such as tel- geospace disturbances during operation and in the satel- ecommunications, broadcasting, Earth observation, lite’s orbit. and positioning. Te plasma and electromagnetic envi- A space weather forecast provides the current status ronments in geospace change signifcantly owing to and future condition of the geospace environment on the geospace disturbances, such as substorms and storms basis of observation and modeling. If there is a possibil- caused by solar wind–magnetosphere interactions. Tey ity of spacecraft anomalies due to the space environment, can also be afected by high-energy particles, known as the following three utilizations of space weather forecasts solar energetic particle (SEP) events. Te geospace dis- are necessary to improve the stability and safety of satel- turbances cause various satellite anomalies, such as lite operation. charging/discharging and central processing unit (CPU) Firstly, when a satellite anomaly occurs, triage deter- mination should be the frst action. Te satellite operator *Correspondence: [email protected] needs to identify the cause of the anomaly (misoperation, 1 National Institute of Information and Communications Technology, manufacturing problem, or space environment) to decide 2‑1‑3 Katahira, Aoba‑ku, Sendai, Miyagi 980‑0812, Japan the next action for mitigating the efect of the anomaly. Full list of author information is available at the end of the article © The Author(s) 2021. 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Earth, Planets and Space (2021) 73:26 Page 2 of 14 For this purpose, it is necessary to understand the current since there are few observations between the Sun–Earth condition (nowcast) of the space environment around line, the current status of forecasting lead time is about the satellite to determine whether the malfunction/fail- 1 h ahead when using data from the solar wind observa- ure is caused by the space environment or other factors tion at the L1 point of the Sun–Earth system. Prediction (O’Brien et al. 2013). with longer lead times is much less accurate. Secondly, if there is a high possibility that the satellite Finally, as will be described later, the risk of satellite anomaly is caused by the space environment, postanaly- anomaly due to the geospace environment also varies sis of data will be performed to clarify the relationship depending on the materials and structure used for the between geospace disturbances and the satellite anomaly. satellite itself. In other words, it is difcult for satellite It is necessary to take future measures and to improve the operators to judge the risk of individual satellites from satellite itself on the basis of the outcome of the posta- only the space weather forecasts. Terefore, to achieve nalysis of data analysis. the safety and stability of satellite operation, it is neces- Tirdly, in the case of conducting critical operations, sary to understand not only the status of the geospace such as attitude control and/or rewriting onboard pro- environment but also the risks of individual satellites. grams, where mistakes and errors can seriously afect the On the basis of this background, we have been develop- satellite, the satellite operator should refer to the space ing a charging risk estimation scheme for satellite opera- weather forecast and make a Go/NoGo decision for tors, called SECURES (Space Environment Customized critical operations in order to reduce the risk of satellite Risk Estimation for Satellites), under PSTEP (Project anomaly. In addition, if the risk of satellite anomaly due for Solar–Terrestrial Environment Prediction) (Nagat- to space weather disturbance can be predicted, the stabil- suma 2017). In this paper, we will introduce the outline ity and continuity of satellite operation can be improved of SECURES, the surface charging module, and the inter- by taking measures, such as increasing the number of nal charging module, and summarize and discuss our staf in charge of operation and preparing backup plans. achievements. It is possible to realize rapid recovery in the event of a satellite anomaly. Outline of SECURES However, the specifc utilization of space weather Electrostatic discharge (ESD) due to space weather dis- forecasts in the current satellite operation is still in the turbances is one of the major causes of satellite anoma- development stage for the following reasons. First, there lies (e.g., Ferguson et al. 2015). More than half of the are many unsolved problems regarding the relationship satellite anomalies are caused by ESD (Koons et al. between space weather disturbances and satellite anom- 1999). Tere are two types of charging mechanism that alies. Since the operating satellite is in space, the status will cause ESD, namely, surface charging and internal of the satellite cannot be directly confrmed, making it charging. Surface charging occurs on the surface of the difcult to directly investigate the cause of any failure. satellite structure and is caused by exposure to plasma In addition, it is difcult for satellite manufacturers and of several tens to several hundred keV. An electric satellite operators to disclose detailed information about potential is formed on the surface of the satellite by the satellite anomalies to the public. To overcome these infow of ions and electrons from the plasma environ- problems, the United Nations Committee on the Peace- ment around the satellite and the emission of photo- ful Uses of Outer Space (UN/COPUOS) has called for the electrons because of sunlight. Internal charging occurs sharing of information about satellite design standards, inside the satellite structure. Electrons with energies space weather observations and models implemented in higher than several hundred keV penetrate the wall of each country, satellite anomalies, and eforts to mitigate the satellite structure as well as the interior, leading to the efects of satellite anomalies (UN/COPUOS 2019). the charging and discharging of cables and equipment Another issue is the accuracy and lead time of space inside the satellite. Owing to plasma variations in geo- weather forecasts. Te space environment signifcantly space, the electric potential on the surface and inside changes in space and time depending on the solar wind– of the satellite may change, resulting in electrical dis- magnetosphere interactions. Terefore, the condition of charges that lead to malfunctions and failures. Charg- the surrounding space environment may be considerably ing and discharging conditions difer depending on the diferent depending on the position of the satellite,