Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!zaphod.mps.ohio-state.edu!van-bc!rsoft!mindlink!a752
From: a752@mindlink.UUCP (Bruce Dunn)
Newsgroups: sci.space
Subject: The Ariane V36 failure
Message-ID: <3795@mindlink.UUCP>
Date: 12 Nov 90 01:43:42 GMT
Organization: MIND LINK! - British Columbia, Canada
Lines: 81

> lvron@earth.lerc.nasa.gov writes:
> 
> [commenting on a report that a piece of cloth in a water-line to an engine
> caused the Ariane V36 failure on February 22]
> 
> I've never been part of a failure investigation (thankfully ;-)) since I
> joined NASA, so I don't know much about the procedure.  I hope someone can
> offer insight on the following questions:
> 
> (1) the failure was due to a piece of cloth.  How could this have been
>     isolated after the failure?
> (2) what is the mechanism by which a piece of cloth was able to cause the
>     failure?  By that I mean
>     - was the cloth of sufficient size/porosity to totally restrict water
>       flow?  or did it have to be?
>     - how is a piece of cloth able to be in the water line anyway?
>     - what is the sequence of events leading to the failure, given the
>       presence of the cloth?
> (3) how can Arianespace ensure no repeat of this mechanism/sequence of
>     events?
> 


     The following information, abbreviated from 3 issues of Spaceflight, may
be of interest.

May, 1990:
     The Ariane V36 Inquiry Board has presented its findings.  They identify a
blocked water line as the cause of the accident.  The launcher exploded shortly
after its launch on February 22. ...  The loss of the mission was due to the
decrease in thrust of one of the four Viking V motors on the first stage.  The
drop in thrust occurred 6.2 seconds after motor ignition.  It was due to an
almost total obstruction of the water feeding circuit of Viking motor D.  The
engine itself is not at fault.  The obstruction occurred upstream of the motor
before the water pump.  The precise cause of the obstruction is either a
foreign object in the pipe or a failure of the main water valve.      [The
article goes on to talk about how debris from the exploded launcher fell at the
shoreline and just off-shore of the launch site.]       A search of mangrove
swamps in zone 2 located some 350 different objects from the first, second and
third stages.  In particular, this search located external tubing of engine D
as well as water tank elements.  The first stage propulsion bay along with the
four Viking motors was found.  Despite extremely difficult conditions, the
suspect elements of the water circuit were recoverd shortly before this issue
of Spaceflight went to press.

June, 1990:
     The loss of Ariane V36 was caused by a small piece of cloth that blocked
the water supply to one of the vehicle's first stage engines.  ...  The rag was
probably left in the pipe when the tubing was dismantled and readjusted during
first stage integration before transfer to French Guiana.  Arianespace Chairman
Frederic c'Allest said the cause of the failure was "not only shocking but hard
to accept."

September, 1990:
     The investigation into the loss of V36 revealed that a first stage engine
lost thrust because a small piece of cloth blocked a water pipe.  In an
unconnected incident a small fire broke out in one of the strap-on liquid
boosters due to a fuel leak. From flight V37, the water line and the N2O4 feed
line of each engine will be examined.  The inspection will take place at
Kourou, using a fibroscope type video camera with integrated light source. ...
Additional leak checks were made on the first stage and strap-on fuel lines to
ensure that there was no repeat of the fire on the previous mission.  Also, new
thermal protection inside the propulsion bays of the first stage will protect
electrical systems in the event of a fire.

Spaceflight is an excellent journal received by members of the British
Interplanetary Society. Address: 27/29 South Lambeth Road, London, SW8 1SZ,
England.

     My understanding is that as the engine lost thrust, the remaining engines
gimbeled to correct for the thrust imbalance.  When the running engines reached
the end of their gimbel limits the vehicle could no longer be kept on course,
and in effect started to skid sideways through the air.  Breakup due to
aerodynamic forces followed shortly.  What I have not been able to find out is
why Viking engines need a water supply.  This is presumably for cooling,
however I have never heard of an engine that used anything other than its own
propellants as a cooling source.  Can someone familiar with the Viking engine
explain the function of the water, and what happens when its supply is
interrupted.
--
Bruce Dunn   Vancouver, Canada    a752@mindlink.UUCP