JAXA Supercomputer System Annual Report February 2025-January 2026

Report Number: R25EDG20155

Subject Category: Research and Development

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• Responsible Representative: Kaname Kawatsu, Research and Development Directorate Research Unit III
• Contact Information: Keiichiro Fujimoto, Research and Development Directorate Research Unit III(fujimoto.keiichiro@jaxa.jp)
• Members: Keiichiro Fujimoto, Takayuki Ito, Shohta Inagawa, Akari Murata, Shinjiro Tsuji, Naoto Tsubaki

Abstract

Reentry safety evaluation of rocket upper stages and spacecraft (risk assessment of surviving debris) is an important topic for ensuring the sustainability of space development. It is also essential to establish integrated system design and model-based design and development methods that can deal with complex systems such as innovative future space transportation systems. This project addresses the common issue of these two important themes, 'development of efficient integrated simulation technology for system behavior,' and conducts research and development of methods that can efficiently perform large-scale analyses on JSS using the reentry melting analysis code LS-DARC and the launch and reentry integrated analysis tool LS-LUCA for new transportation systems such as next-generation flagship launch vehicles and for safety design in human space transportation.

Reference URL

N/A

Reasons and benefits of using JAXA Supercomputer System

- The system can be used quickly by JAXA employees without complicated and time-consuming procedures.

- Since JSS is a JAXA internal system, it can be connected within the same JAXA intranet, and there is little risk of information leakage.

- The system can securely handle sensitive information, such as highly confidential rocket upper stage and spacecraft design information, in a closed environment within JAXA.

- Immediate support for system usage is available.

Achievements of the Year

During this fiscal year, numerical accuracy and computational efficiency of reentry safety analyses were improved by introducing an equivalent‑thickness thermal model as a reduced‑order alternative to full 3D conduction, and by refining the heat‑flux prediction model of LS‑DARC through comparison with high‑enthalpy wind‑tunnel experiments of an upper‑stage rocket engine. These enhancements increased the fidelity of heating predictions under complex flow phenomena, such as shock–shock interactions and internal recirculating flows, and enabled efficient execution of large‑scale parametric and probabilistic analyses on the JSS supercomputer. For human space transportation, a multi‑body dynamics model and aerodynamic database for cluster‑parachute systems were developed and integrated into LS‑LUCA, enabling feasibility assessments of launch abort system (LAS) trajectories and descent behavior of large crewed spacecraft. Using a three‑component aerodynamic model derived from NASA wind‑tunnel data together with probabilistic evaluations via Latin Hypercube Sampling, the analysis successfully captured oscillatory motion during the transient phase, steady‑state parachute alignment, landing dispersion characteristics, and attitude stabilization requirements, all of which are essential for early‑phase safety design. These accomplishments collectively strengthened (1) the credibility of LS‑DARC for destructive reentry analysis, (2) the capability of LS‑LUCA for human‑spaceflight system feasibility evaluation, and (3) the computational workflow for large‑scale uncertainty‑driven simulations, contributing to enhanced system‑level safety assessment and conceptual design of next‑generation launch and reentry vehicles.

Fig.1: Heat-flux distribution obtained from HIEST tests of a 3D-printed model of the LE-5B upper-stage engine and the corresponding LS-DARC prediction

Fig.2: Cluster-parachute model of a crewed spacecraft and its probabilistic behavior and landing-dispersion evaluation

Publications

- Peer-reviewed papers

1) Fujimoto, K., Kawatsu, K., Amakawa, H., Multi-physics Simulation Code LS-LUCA for Innovative Space Transportation System Design, IEEE Aerospace Conference, 2026.

2) Fujimoto, K., Tsuji, S., Kamiya, T., Yatsuyanagi, S., Development and Validation Status of High-Fidelity Re-entry Analysis Tool LS-DARC, IEEE Aerospace Conference, 2026.

- Oral Presentations

1) Fujimoto, K., Kawatsu, K., Amakawa, H., Development of Quantitative Crew Safety Analysis Model for Launch Abort System of Human Space Flight – 3rd Report, 69th Space Science and Technology Conference, 2025.

Usage of JSS

Computational Information

• Process Parallelization Methods: MPI
• Thread Parallelization Methods: OpenMP
• Number of Processes: 1 - 216
• Elapsed Time per Case: 16 Hour(s)

JSS3 Resources Used

Fraction of Usage in Total Resources*1(%): 0.04

Details

Please refer to System Configuration of JSS3 for the system configuration and major specifications of JSS3.

*1: Fraction of Usage in Total Resources: Weighted average of three resource types (Computing, File System, and Archiver).

*2: Fraction of Usage：Percentage of usage relative to each resource used in one year.

ISV Software Licenses Used

*2: Fraction of Usage：Percentage of usage relative to each resource used in one year.

JAXA Supercomputer System Annual Report February 2025-January 2026