Epsilon S Development Updates Thread

[ZachS09]

I thought the M-35 rocket motor from Epsilon-2 was supposed to be the second stage for Epsilon-S.

[Galactic Penguin SST]

I thought the M-35 rocket motor from Epsilon-2 was supposed to be the second stage for Epsilon-S.

The original (till ~2020) plan was to continue to use it (it was, in turn, an upgrade from the original one that flew on the 1st Epsilon, and before that as M-V's 3rd stage), perhaps with a new propellant mix, but somewhere in between the 2nd stage got a stretch.

[FutureSpaceTourist]

twitter.com/cnspaceflight/status/1680767115463364609

JAXA released a report on the Epsilon-S motor explosion:
🔵 Damages caused to the vacuum engine test building
🔵 chamber pressure deviated from designed value 20 seconds after ignition & was 7.5MPa at the moment of explosion, still below the allowed maximum of 8.0MPa
📸 JapanNews

https://twitter.com/cnspaceflight/status/1680772775701786624

🔵 also below the pressure limit of 10MPa achieved in past tests
🔵 The nozzle drive was normal until the explosion
🔵 Root cause under investigation

https://www.jaxa.jp/press/2023/07/20230717-1_j.html

[HVM]

https://www.jaxa.jp/press/2023/07/20230717-1_j.html
Automated translation of the report:

Ground Combustion Test of Epsilon S Rocket’s Second Stage Motor (Second Report)
July 17, 2023

Japan Aerospace Exploration Agency

We sincerely apologize for causing a lot of trouble to the local residents, the local community, and all other parties involved in the explosion and fire accident that occurred during the combustion test conducted on July 14.
We would like to inform you of the extent of the damage and the progress of the investigation that we have confirmed as of July 16th.

<Confirmation status of damage>
The confirmed status so far is as follows. If we find out any information that should be announced in the future, we will inform you again.
■ Human damage: No reported damage
■ Third party property damage: No reported damage
■ Damage to JAXA’s equipment: Damage to the vacuum combustion test building and its internal equipment, damage to nearby buildings on the test site (window glass, doors, etc.)

<Cause investigation status>
■Confirmation status: ・About 20 seconds after the motor was ignited, the combustion pressure started to deviate from the expected pressure. The motor exploded when the combustion pressure reached about 7.5 MPa, about 57 seconds after ignition. (Note that the combustion pressure was lower than the maximum operating pressure (8.0 MPa) and the pressure test pressure (10.0 MPa).) It was also confirmed that the nozzle drive functioned normally until the explosion. ・Most of the second stage motor debris was scattered both inside and outside the vacuum combustion test building. For safety reasons, some of the debris outside the vacuum combustion test building has been retrieved.
■ Estimated cause: Still being investigated
■ We are conducting a detailed data analysis, verifying images and other evidence, and checking the inspection records of the motor used in the test.

This concludes our report.

[Asteroza]

Sounds like grain failure leading to burn through, as the abnormal pressure rise indicates more burning (increased surface area, which could be caused by solid propellant grain failing), but since it blew before max pressure you're likely left with a burn through in the casing from abnormal/asymmetric propellant burning causing early case failure (or the other possibility is an actual case strength problem but that would be a different/worse outcome).

[tul]

JAXA Identifies Cause of Explosion during Rocket Engine Test

https://japannews.yomiuri.co.jp/science-nature/science/20231213-155452/

[Steven Pietrobon]

JAXA Identifies Cause of Explosion during Rocket Engine Test

https://japannews.yomiuri.co.jp/science-nature/science/20231213-155452/

The relevant bit.

"The Japan Aerospace Exploration Agency (JAXA) said Tuesday it has concluded that an explosion during a ground combustion test of an engine for the new Epsilon S solid-fuel rocket in July was caused by the melting and scattering of a metal part from the ignition device inside the engine."

[catdlr]

Has it been over 400 days....  bump


Epsilon S rocket second stage motor ground re-firing test overview

Streamed Live on November 24, 20924,
We will broadcast an online briefing on the retest of the Epsilon S rocket second-stage motor (E-21), which exploded during a combustion test at the Noshiro Rocket Test Site in Akita Prefecture on July 14, 2023. Become a member of this channel to access the benefits:

[TheKutKu]

The re-try of the static test firing of Epsilon-S’ 2nd stage (E-21-2TVC) after the July 2023 explosion was attempted on November 26 08h30 JST (Nov 25 23h30 UTC) on a test bench at Tanegashima.

Sadly, it suffered a catastrophic failure after 46 seconds
https://twitter.com/nvslive/status/1861191807457206715

The Epsilon S rocket second stage motor re-fire test on the ground appears to have failed...

Replay of test
https://www.youtube.com/live/VTs-MDI1f9g
Link to the moment of failure
https://www.youtube.com/clip/UgkxwcsNAHnQcz4Mv-WF7TgAzWnKOPMOI1dN
Another view of the test

[catdlr]

edited version of the long live stream

[catdlr]

Link for the management briefing.

Briefing on the status of the Epsilon S rocket second-stage motor re-fire test (enclosed interview)

Scheduled for Nov 25, 2024
At approximately 8:30:46 on January 26th, an explosion occurred during a combustion test of the Epsilon S rocket's second-stage motor E-21-2TVC at the Tanegashima Space Center.

[HVM]

Only way to receive this news:
https://twitter.com/clearusui/status/1861193811202048363

[catdlr]

Only way to receive this news:
https://x.com/clearusui/status/1861193811202048363

Yes, the emojis say it all.  Nonetheless, here is the translated version, Tissue anyone?

[Blackstar]

https://gizmodo.com/japans-epsilon-s-rocket-test-ends-in-fiery-explosion-marking-another-big-setback-2000530138

[Galactic Penguin SST]

JAXA currently has a press briefing on this 2nd stage test firing failure redux:
https://www.youtube.com/live/-EMOR_sotZ8

From what I can make out, it seems the SRM's chamber pressure went exceeding the predicted value again after about 20 seconds, just like in the July 2023 test failure, until the case was breached. (blue = July 2023 test; orange = November 2024 test; black = predicted value)

[Steven Pietrobon]

The expected maximum pressure was about 6.8 MPa, but the cases failed at 7.3 MPa (2023) and 7.0 MPa (2024), only 7% and 3% above the expected maximum! Whatever caused the increased burn rate also resulted in a much weakened case.

[Fuji]

Retrieved ignition device was not abnormally melting.
Combustion gas leak was seen before explosion at this time.
So, they can possibly cause of failure estimate misunderstanding, I guess.

[StraumliBlight]

Development Status of the Flagship Launch Vehicle [Sep 29]

2.2.2 Review Status
◼ We are considering replacing the E-21 second-stage motor with the M-35a (reducing the aircraft's overall length by approximately 0.4 m).
◼ The M-35a reflects measures to address the depletion of propellant and insulation materials. There is no impact on motor performance. There are changes from the M-35, and we are considering conducting M-35a ground combustion tests to verify that the same factors as the E-21 combustion anomaly are not inherent in the M-35a.

Minutes of the 99th Space Development and Utilization Subcommittee & Handouts [Sep 29]

Regarding the Epsilon rocket, it is expected that a considerable amount of time will be required to address the explosion that occurred during a combustion test last November. Therefore, we are considering measures to minimize the gap and transition to operational status as quickly as possible, from the perspective of responding to necessary missions and sustainably maintaining our technological foundation.