Failure Knowledge Database / 100 Selected Cases

Failed Launching of H-ⅡA Rocket #6
Nov. 29th, 2003, Pacific Ocean, Off Tanegashima Island, Kagoshima
KOBAYASHI, Hideo (Yokohama National University)
TERADA, Hiroyuki (Japan Aerospace Technology Foundation)(Summary)
H-ⅡA Rocke t #6 was la unched from Tanegashima Sp ace Center of NASDA at 13:33 on Nov. 29th,
2003. About 105 se conds a fter t he l ift-off, t he sig nal f or se paration of t he tw o so lid roc ket boosters w as
sent from the on board computer. However, the solid rocket booster on the right was not separated. Without
the separation, the rocke t was not able to gain the height and velocity necessary for launc hing the payload
to the scheduled orbit, so the signal for self-destruction was sent from the ground control center at 13:43:53.
As a result, the rocket and payload were lost in the Pacific Ocean.
The Technical Investigation Committee of the Space Development Commission of Japan conducted theinvestigation into the cause of the accident.
The direct cause of the incomplete separation of the forward brace connecting the solid booster to mainrocket was the malfunction of the separation system, which was due to the leak of fuel gas from the nozzleof the solid rock booster into the aft adapter. The cause of the leak of fuel gas was found to be the thickness
reduction by local erosion of the nozzle insulator that was made of carbon fiber reinforced plastic (CFRP).
1. Component
Solid Rocket Booster
2. Event
The sequence of the SRB separation is shown in Fig.4. The SRB on the left hand side failed to separate
because the forward brace connecting the fuselage and the SRB was not cut.
Figure 3 shows the structure of the nozzle. Thermal protection is to be achieved by the liner aft B2 withthe abrasion behavior of the carbonized layer.
The sequence of events leading to the failure is believed to have occurred as follows. (See Figure 5)○Because of the difference in the m aterials used for the nozzle throat and the liner aft, a st ep emerged
along the front edge of the liner aft B2 on the inner side of the SRB-A nozzle during combusting.

○ This step caused a disturbance in the flow of the combustion gas, the heating rate became higher, and athickness reduction was induced downstream of the flow.
○ Somewhere i n t his ar ea of reduc tion in t hickness, relatively de ep gro oves w ere form ed b y thedeterioration of the binding properties of the carbonized layer.
○ As the grooves grew, the inter-laminate pressure and delamination increased, causing the exfoliationof the CFRP laminates. As a result of this phenomenon, local erosion was accelerated.
1

Failure Knowledge Database / 100 Selected Cases○As a result of the increase of local erosion of the liner-aft B2, the combustion gas reached holder B,
resulting the melting of the holder, which led finally to the leakage of the hot gas into the aft adapter.

○ The combustion gas leaked into the aft adapter, heated the cable that carried the electric signals for theseparation device causing the cable to fail so that the separation signal of SRB was not transmitted.
3. Course
During the development of the SRB-A, the following combustion tests were carried out.
･ Ground combustion test (EM): Heat resistant property test of FRP･ Ground combustion test (PM): Assurance test of design and manufacturing process･ Ground combustion test (QM): Reliability assurance and evaluation of the manufacturing process
Results of the QM tests:
In August 1999, si gnificant er osion w as o bserved at the aft li ner B d ue t o the exfoliation of CFRP
induced by the d elamination t hat occurred as a resu lt of t he th ermal reso lution o f th e phenolic resin . In
order to minimize this erosion, a design change was made from a separate to a monocock structure, and thethickness and the material were also changed.
In June 2000, an incident occurred where the throat inset dropped into the motor case at the final stageof combustion. In order to avoid this from occurring in the future, a design change was made on the shapeof the throat insert and the liner aft B2.
In October 2000, significant erosion was found to have occurred in a local area of the liner aft B2 due tothe induced vortices. Additional experiments were performed, but the true mechanism of the local erosion
was not discovered. In order to c ounter the effects of the erosion, the wall thickness was increas ed and aCFRP outer panel was added.
4. Cause
Factors accelerating the local erosion were examined.
Due to the uneven thickness reduction of the insulator, the delamination and exfoliation of CFRP tends
to take place locally. The formation of a carbonized layer also accelerates these phenomena, resulting in theformation of deep grooves.
The higher c ombustion pr essure of SRB-A co mpared with c onventional SRB may also be a factor
contributing to the acceleration of the above-mentioned phenomena.
As the lo cal e rosion a t t he CFRP n ozzle structure is t he st ochastic phenomenon t hat is rel ated to t hemicroscopic mechanism, the l ocation and the depth of the er osion cannot be calculated in a deterministicmanner. Furthermore, it was pointed out that the present design tools cannot prevent deep erosion that leads
to the development of an open hole from occurring. It is difficult to predict the site where the local erosion
occurs. However, once the erosion occurs, it will continue to grow at that site.
This phenomenon of local erosion occurred and continued until an open hole in the left SRB-A of H-ⅡA #6 for the first time2

Failure Knowledge Database / 100 Selected Cases

5. Immediate Action
Japan Aerospace Exploration Agency (JAXA) conducted a gene ral re-examination of the H-ⅡA rocket
development systems. In this ex amination, which covered the basic designing of t he system as well as thecountermeasures adopted t owards the direct ca uses of th e fai lures, to p pr iority w as plac ed on theimprovement of system reliability.
By estab lishing the Re-e xamination S pecialist Bo ard on the H- ⅡA rocket , t he Space Deve lopment
Commission watched and discussed the re-examination conducted by JAXA.
6. Countermeasure
The fundamental policies of the design changes of SRB-A were as follows.
･ Develop a re vised version of SRB-A that m inimizes local erosion, at the cost of tentatively reducing
the launching payload capability of the rocket.
･ In order to regain the launching capability, try to develop a new type of SRB-A with high reliability byestablishing sound measures to suppress the occurrence of local erosion.
The following is the draft of design changes of the revised version of the SRB-A nozzle.
○ Re-examination of combustion pattern
A combustion pattern having lower combustion pressure and longer combustion period was adopted.
○ Re-examination of nozzle geometry
A bell-type nozzle with a higher angle at the nozzle mouth was adopted to more effectively prevent thedelamination that accelerates the local erosion.
○ Extension of throat insert width
The thickness redu ction of the li ner-aft made of CFR P w as fo und t o b e a lleviated by extending t hethroat insert in the downstream direction of the exhaust gas flow.
○ Re-examination of the thickness of the liner-aft
A new design criterion was adopted to establish the reliability of nozzle. In accordance to this criterion,
the thickness of the liner-aft was increased.
○ Improvement of manufacturing and inspection
Enforcement of spe cification m anagement for

the raw

material and pro ducts of CFRP

wasimplemented.
Inspections for flaw detection of the CFRP and 3-D C/C components were also enforced.
The l iner-aft thic kness w as incre ased by usin g a d ouble-liner structure f ormed fro m tw o CFRP
components that are bonded together. In this context, non-destructive inspections had to be c arried out forevery process of manufacturing.
Moreover, design changes were proposed to assure system redundancy in w iring of ignition cables andothers. Spe cifically, the i gnition cable fo r SRB separ ation a nd ot her wire cab les were ins talled by tworoutes - the, main tunnel and a sub tunnel - in order to mitigate the risk of malfunction.

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Failure Knowledge Database / 100 Selected Cases

7. Knowledge(1) The importance of taking an honest attitude towards recognizing what was happenedAt the moment when the local erosion was observed during the QM3 ground test, the engineers shouldhave honestly acce pted the facts e ven if thos e fac ts did not agree with t heir pas t experi ence, because
unknown phenomena are o ften encountered in development of new systems.

The engineers should haveexamined the difference between the observed phenomenon and ordinary erosion in order to elucidate themechanisms g enerating the local erosion. Consultation with o utside specialists might have been effective
for finding a solution to the local erosion caused by unknown phenomena.
(2) The importance of taking an earnest attitude towards pursuit of all of possibilities
At the moment when the delamination occurred during the QM3 ground test, the engineers should havetaken the attitude that the delamination of CFRP must be prevented from occurring in the heating test.

In

particular, th ey sho uld have d etermined t he co nditions of d elamination occurrence a nd the m aterial
characteristics under those conditions.
8. Sequel
The local erosion might recur as the number of launches and tests are increased, if the phenomenon wasin fact a probabilistic event and had occurred at the right side of the SRB-A just by chance. To check thispossible and to obtain technical data on the local erosion, a combustion test using the same conical nozzle
as the #6 rocket engine was conducted on the ground on July 7th, 2004. Using ultrasonic sensor, the tested
nozzle was discovered to have developed a hole.
The sp ecific results of th e test w ere: t he n ozzle fra ctured a t t he hol e t hat de veloped through t hethickness reduction by local erosion, and combustion gas started to leak about 50 seconds after the ignitionof the e ngine.

Because of the sensor hole for the t est, the liner-aft B2 fracture d earlier than i n the actual

case. However, this ground test proved that the hypothesis of the accident cause was correct: local erosion
readily occurs with high probability.
After this experiment, the Re-examination Specialist Board on the H- ⅡA rocket issued the re port on
September 2nd, 2 004. D esign c hanges of the rev ised v ersion of SRB-A w ere made i n acc ordance t o t herecommendations in the report.
The insulation an d therm al prot ection c haracteristics of the revised no zzle were evaluated i n threeground tests as follows:･ The maximum and av erage values of t he thickness reduction of the revised liner-aft showed similarvalues in all ground combustion tests, and the reductions were almost a half those of the conventional
nozzle. The thickness reduction values also showed good characteristics of reproducibility.
･ In the new bell type nozzle, the angle between the laminated and the heated face was greater than thedesignated value, and hence no delamination was observed.
On February 26th, 2005, 15 months after the accident, H-ⅡA rocket #7 was launched successfully fromTanegashima Space Center.

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Failure Knowledge Database / 100 Selected Cases

9. On the Side(1) The objective of H-ⅡA rocket #6
The objective of H-ⅡA rocket #6 was to launch the Intelligence Satellite #2 into its designated orbit.
The Int elligence Sate llite #1 was succ essfully la unched on March 2 8th, 2 003 by H- ⅡA rocket #5. T heobjective of these satellites was to c ollect data necessary for assuring the sec urity of Japan. Because of thenature of t heir specifi c mission, th e la unching w as n ot ope ned to the pu blic. B ecause of i ts m ission, theself-destruct signal was sent quickly. However, the mission of the Intelligence Satellite can not be achievedby only a single satellite, and so the security of our country can not be assured until the successful launch ofH-ⅡA rocket #7.
(2) H- ⅡA rocket engine and Solid Rocket Booster
H-ⅡA is a tw o stage r ocket ha ving the capacity to la unch a fo ur-ton p ayload i nto orb it. The rocket
consists of first and second stage engines and sub-rockets (a solid rocket booster and a solid sub-booster).
･ The first stage engine (LE-7) is a large-scale LOx/LH2 engine with two combustion cycles.
･ The second stage engine (LE-5) is also a LOx/LH2 engine･ The solid rocket booster (SRB-A) is a large-scale engine with a poly-butadiene related propellant.
H-ⅡA rocket is equipped with two SRB-A.
･ The solid sub-booster (SSB) is an engine with a poly-butadiene related propellant. H-ⅡA rocket isequipped with either two or four SSB depending on its mission.
(3) Erosion/Corrosion
On August 9th, 2004, steam eruption from a pipe of an atomic power plant occurred at Mihama, Fukui
Prefecture. The cause of the burst was a local reduction of the pipe thickness due to erosion and corrosion.
This phenomenon was the same as t hat of CFRP in the case of the launching failure of H-ⅡA r ocket#6. The local erosion of CFRP occurred through the combination of chemical corrosion by the combustion
gas and mechanical erosion.
Therefore, it can be concluded that local thickness reduction occurs both in metallic materials and CFRPby erosion and corrosion. The prediction of the thickness reduction rate is not easy, and a poorly predicted
thickness reduction can be the cause of leakage.
10. Information Source(1) On the I nvestigation of Fai lure of H -ⅡA #6 Rocket Launching and the Countermeasures for Fut ure,
Space Development Commission of Japan (June 9th, 2004).
(2) Report of Specialist Board on Revision of H-ⅡA Rocket, Investigation Group on Revision of H-ⅡA
Rocket, Investigation Board of Space Development Commission of Japan(September 2nd, 2004).
11. Primary Scenario
01. Unknown Cause

5Failure Knowledge Database / 100 Selected Cases

02. Occurrence of Unknown Phenomenon
03. Insufficient Analysis or Research
04. Insufficient Prior Research
05. Usage
06. Operation/Use
07. Rocket launching
08. Bad Event
09. Thermo-Fluid Event
10. Combustion gas
11. Failure
12. Abrasion
13. Erosion
14. Secondary Damage
15. External Damage
16. Leaks
17. Fires
18. Malfunction
19. Poor Hardware20.Mmalfunction of control system
21. Fail of SRB separation
22. Failure
23. Large-Scale Damage
24. Crashes
25. Fail of rocket launching
26. Loss to Organization
27. Social Loss
28. Damage to Society
29. Social Systems Failure
30. Damage to social security

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Failure Knowledge Database / 100 Selected Cases

Solid Propellant
Temp. Sensor
Explosive Ware Unit
for Separation of Fore-brace
Electric Actuator, Thermal Battery
Controller, Wiring unit
NozzleAft Adapter

Fig. 1 H-ⅡA Rocket and SRB-A.

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Failure Knowledge Database / 100 Selected Cases

Fore - guide System tunnel
3.5m

Nose cone

Fore-brace
Fore - adapter

Seen from top

Core rocket
Motorcase

15.2m

Thrust strut

Connecting structure

Aft-brace

Aft-adapte

Aft – guideActuator

Separation motor

Thermal curtain

NozzleLE-7 long nozzle
LE-7 short nozzle

Seem from bottom
Fig. 2

Structure of SRB-A.

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Failure Knowledge Database / 100 Selected Cases②Fore – bracecut-off③Thrust strut cut-off②Aft‐bracecut - off

①Ignition separation motor

Ignition separation motor/
Brace cut-off

SRB - A separation complete【Thrust strut cut-off】
Event Time lag(sec.)

Ignition separation motor-0.1

Fore/Aft Brace cut-off

0Thrust strut cut-off

1.4

Fig. 4 Separation Concept of SRB-A.

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Failure Knowledge Database / 100 Selected Cases①Circumferentially uniform recessive abrasion②Local recessive abrasion

A

燃焼ガス
CombusiongasA

Liner-aft B2(CFRP)

AA

Combusiongas
燃焼ガス

Throat insert(C/C composite)

Section AA

It is possible the local grooves with various widths may appear

Section A④Acceleration of local erosion by flow-in of combustion gas③Acceleration of local by exfoliation of CFRP
A

Combusion
gas
燃焼ガス

AAA

燃焼ガス
Combusion
gas

Section AASection AA

Fig. 5

Acceleration Process of Local Erosion.

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