the shuttle\'s nozzle joint persists as focus of debate over safety
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Just as engineers carefully studied the space shuttle booster rocket launched in Utah a week ago, the debate about one element of the rocket redesign continues, and some engineers think it will actually bring as much as possible
The debate is not focused on the joints that failed in the Challenger accident --
The \"Shell to Shell\" joint connecting the rocket\'s huge fuel housing section.
Instead, it focuses on another key seam at the tail of the rocket, where the nozzle is.
On the shuttle flight before January
28,1986, accident, clumsy shape \"nozzle-to-
Case combination is home to some of the most serious cases.
Flight erosion of safety seals.
The retrofit nozzle joint is one of the trickiest problems facing Morton tiokor, which cannot be seen from the outside of the rocket.
Manufacturer of booster.
Thiokol adopts a new design with the approval of Allan J, including an additional O-ring, 100 bolts to hold the joint together and other changes
A Thiokol engineer who warned against launching a challenger, MacDonald.
But the new design was severely criticized by Roger Boisjoly, a former Thiokol engineer, who also opposed the bad behavior.
He called the new design \"absolutely, incredibly bad\" and said space agency officials should adopt a completely different technology from the oil drilling industry.
The opinions of both of them have great interests:
Macdonald is now in charge of Thiokol\'s redesign team.
After the disaster, Boisjoly angrily resigned from the company and filed a lawsuit against it on the grounds of fraud and slander.
The disagreement over trying to replace design engineers was the subject of an informal discussion last week by rocket experts gathered in the desert of Utah to watch the first test --
Improved rocket launch
And most experts concluded that,
They say the McDonald\'s team at Thiokol may work.
Boisjoly pointed out the real weakness.
Even the independent National Research Council panel, which oversees the redesign, has questions about Thiokol\'s choice: under its supervision, the company issued a subcontract to Vetco Gray Inc.
Houston design and test Alternative high nozzle joints
Temperature metal alloy seals for primary rubber O-rings in Thiokol design.
A member of the group said last week that the ad \"if we start from scratch and have enough time, the metal seal could be a way . \" He insisted on anonymity.
\"In fact, the metal seal is the first backup plan if we have a problem.
\"But under the pressure of the launch, the two segments are sometimes separated by an inch, and the heat begins to erode the rubber O-ring.
If the rings were completely burned, there was little doubt that the shuttle would be destroyed.
To prevent the problem from recurring, the engineers redesigned the insulation around the joint, just like around the box --to-
Case joint, using \"j-
Any hot air should be prevented from being sealed close to the O-ring.
A third O-ring was added as a \"Wiper seal\" to prevent contaminants from entering the joint during assembly.
Most importantly, 100 bolts were added around the joint at right angles to the existing bolts to ensure that the two metal segmnets were not separated under stress.
They weakened the layoffs.
Boisjoly\'s criticism focused on the new radial bolts.
In the redesign, the bolts are placed between the main O-ring in the joint and the secondary O-ring providing spare, with the aim of preventing the flow of hot air.
\"They have weakened the redundancy of the secondary seal in 100 places,\" Mr.
Boisjoly said in a recent interview.
In other words, each bolt provides a potential leakage path for any hot gas injection that makes it around the main O-ring.
The bolt itself has a rubber seal like a washer under the head of the bolt, but Sir
Boisjoly said there is no guarantee that the bolts will be firmly fixed on the seat.
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\"It\'s like tightening the bolts on the wheels of the car,\" he said . \".
\"You make one side and then go to the bolt opposite and tighten it,\" he said . \".
However, when all 100 bolts in the nozzle joint are connected together, Mr.
Boisjoly said that the joint itself may be deformed, creating great pressure throughout the whole part.
If the bolt is \"locked\" because the thread of the bolt or hole is broken, it may not be obvious. Mr.
Boisjoly also believes that it is almost impossible to test the seal after assembly.
\"Murphy\'s Law is waiting for them,\" he insisted . \".
\"If they\'re right, then they\'re heroes, and I\'m a tramp. And that\'s O. K.
If I am right, there may be more people dying.
We are, he said.
McDonald\'s responded that metalto-
The metal seal formed by the bolt itself has been tested and proved to be effective, providing additional protection even if there is no Viton rubber seal around the bolt head.
\"We believe it will be successful and testing can prove it to be effective,\" he said . \".
\"But we\'re just as worried as Roger is, so we\'re testing alternatives.
\"The ad-leading alternative is the design of Gray co Gray in Houston.
The design of the Vetco eliminates the radial bolts and the main rubber O-ring.
In the O-ring position is a nickel
It\'s kind of like the alloy \"u-shaped seal\" of clothes \".
The open part faces the source of gas pressure.
So if the joint is opened, the leg of the seal should be opened with it.
The hot air experience of the impact seal forced it to be more firmly in place.
The rubber O-ring will be used as a backup or auxiliary seal under the Vetco design.
\"The metal seal was the rig we used, and it exploded about six or 8 feet away,\" said Frank.
Adamek, product engineering manager, Vetco.
The seal is \"very durable\" and can withstand a much larger temperature range than the fluorine rubber used for O-rings, he said.
In pipes, U-shaped seals are used at temperatures of minus 450 degrees and up to 2,000 degrees.
However, metal seals may be damaged during assembly.
\"Our experience has shown that this is a solid seal,\" he said . \"Adamek.
\"But if you drop a fully loaded motor on it, I think it may lose its integrity.
Later this year, Thiokol plans to take a short test shot at the Vetco seals.
The members of the National Research Committee\'s supervisory team said they believed
Boisjoly\'s concerns about the Thiokol design and its bolts may be exaggerated, as bolts like this have proven successful elsewhere in the shuttle.
Nevertheless, they acknowledge that the bolts may bend and deform the joints, and that the bolt holes may weaken the overall steel structure.
A member of the group said that\'s why we did the test.
\"Of course,\" he added, \"the booster was also extensively tested before the space shuttle accident.
See what happened.
\"A version of this article appears on page C00003, the national edition of September 8, 1987, with the title: the nozzle joint of the shutt sub has always been the focus of debate on safety.