Re-entry Safety Assessment of Rocket Upper Stage

JAXA Supercomputer System Annual Report February 2025-January 2026

Report Number: R25EEK10100

Subject Category: Space Technology

Responsible Representative: Akito Hattori, Director, Space Transportation Technology Directorate, Launch Capability Unit
Contact Information: Masatoshi Kodera(kodera.masatoshi@jaxa.jp)
Members: Masaaki Fukui, Taku Inoue, Masatoshi Kodera, Toshihiko Munakata

Abstract

After a satellite is inserted into orbit, the upper stage of the rocket becomes space debris. Therefore, it is necessary to properly assess the risk that, when it naturally falls and re-enters the atmosphere, it may reach the ground without fully melting.

Currently, JAXA is developing LS-DARC, an ablation analysis tool consisting of multidisciplinary coupled simulations that account for six‑degree‑of‑freedom orbit dynamics, aerodynamics, heat flux, heat conduction, and shape changes due to melting.

To use this tool for ablation assessments in actual launch license applications and in safety design during the early stages of system development, its prediction accuracy is being validated through wind tunnel tests and CFD.

Reference URL

N/A

Reasons and benefits of using JAXA Supercomputer System

To validate LS-DARC, relying solely on wind tunnel test data makes comprehensive verification difficult due to limited test conditions and the small number of measurement points. Therefore, CFD is used to supplement areas where data is unavailable and to gain a more detailed understanding of the phenomena.

Achievements of the Year

To validate the heat flux model of LS-DARC, we conducted a HIEST test using an upper‑stage engine model and obtained heat‑flux data on the nozzle surface. In addition, CFD analysis was performed to understand the detailed flow field around the model and to complement untested conditions. Figure 1 shows the distribution of the average heat flux on the inner wall of the nozzle when the upper-stage engine nozzle is oriented upstream.

Fig.1: Average heat flux distributions on inner nozzle wall

Publications

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Usage of JSS

Computational Information

Process Parallelization Methods: MPI
Thread Parallelization Methods: N/A
Number of Processes: 1920 - 3840
Elapsed Time per Case: 28 Hour(s)

JSS3 Resources Used

Fraction of Usage in Total Resources*1(%): 0.08

Details

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

Computational Resources
System Name	CPU Resources Used (Core x Hours)	Fraction of Usage*2(%)
TOKI-SORA	2057254.40	0.09
TOKI-ST	9.01	0.00
TOKI-GP	0.00	0.00
TOKI-XM	0.00	0.00
TOKI-LM	0.00	0.00
TOKI-TST	0.00	0.00
TOKI-TGP	0.00	0.00
TOKI-TLM	0.00	0.00

File System Resources
File System Name	Storage Assigned (GiB)	Fraction of Usage*2(%)
/home	0.00	0.00
/data and /data2	102400.00	0.67
/ssd	0.00	0.00

Archiver Resources
Archiver Name	Storage Used (TiB)	Fraction of Usage*2(%)
J-SPACE	4.39	0.01

*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

ISV Software Licenses Resources
	ISV Software Licenses Used (Hours)	Fraction of Usage*2(%)
ISV Software Licenses (Total)	106.00	0.07

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