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PostPosted: Wed Jul 13, 2005 11:49 pm 
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I watched the post-scrub briefing on the NASA channel today, and the reason for canceling was fairly simple.

There are four sensors in the hydrogen section of the external tank. They're connected to a control box that operates indicators and is connected into the computer that controls the main engines.

When two of the four sensors stop sending a "wet" signal and start sending a "dry" signal, the computer stops the main engines. This is MECO or Main Engine Cut Off, shortly after which the external tank is discarded.

In that control box is a circuit card which is used in a test mode to simulate a "dry" signal from all four sensors when the tank is full.

Two of the indicators did not switch to empty, therefore they could not confirm that the rest of the control box was operating properly and had to scrub the launch.

Sounds like an ordinary random failure, right? Not quite!

The exact same control box design has been used on all Shuttle flights since the first one. At some point the boxes began to have problems passing bench tests and the intermittent fault was traced to "suspect transistors" on the simulation circuit card.

NASA replaced those transistors on every one of those boxes they have in inventory, EXCEPT FOR THE ONE CURRENTLY INSTALLED IN DISCOVERY!

It's not that they would've had to remove it from Discovery, replace the transistors then reinstall it. That specific box was removed from Endeavour, bench tested, then installed in Discovery during its refit.

NASA did not have an explanation for why that box did not get the transistors replaced even though all the others did, no matter what. They said the box in Discovery had passed the bench tests.

But why when they were replacing all the "suspect transistors" to make certain they were all good, would they not do the replacement on only ONE of the boxes?

I'd like to know how much those transistors cost, how much money NASA saved, because it looks like that little bit of penny pinching wasted over $600,000 on labor and other costs associated with filling up then emptying the external tank.

Yup, definately a government run project!

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"I am a machine. I am a weapon of war. I am a destroyer of life in the service of life, the sword and shield of my human creators." Bolo Invincibilus, Mark XXIII, Model B (Experimental) 0075-NKE "Nike".


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PostPosted: Thu Jul 14, 2005 12:11 am 
Somebody overlooked something. Shit happens.

And if you want to discuss the relative merits of a government-run or commercially-run space program, Donkeys & elephants is over thataway.


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PostPosted: Thu Jul 14, 2005 12:41 pm 
This article says that it was replaced on the discovery's module, but they didn't know for sure if the transistors were the problem or not. Hurrah for several news sources saying different things.


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PostPosted: Thu Jul 14, 2005 10:38 pm 
Unless of course it was.... a CONSPIRACY! 0X

Muhuhahahahahaha!


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PostPosted: Sat Jul 16, 2005 2:27 am 
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"Tests in the early days of the shuttle program indicated that such a condition could result in "serious, uncontained damage" to the propulsion system, Hale said."

In other words, the turbopumps, which burn hydrogen and oxygen in a gas turbine to spin fast enough to feed LH2 and LOX to the main engines, might go *BLAM*.

"Problems with the fuel-tank sensor system have bedeviled NASA for months: They first popped up while testing a different fuel tank back in April, but engineers could not reproduce the glitch or track down its source. Instead, they replaced components of the system with approved spares."

Right, the "approved spare" was the complete sensor control box from Endeavour. The only one of those boxes to not have the transistors on the simulation circuit card replaced. Why go to the effort to remove the box from another shuttle when they had other spares on a shelf? Or could it be that the entire "inventory" amounts to exactly three, all installed on the shuttles? The NASA guys in the briefing never said how many of the boxes they have. :P

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Fandemonium!
August 1st, 2nd, 3rd, 2014

"I am a machine. I am a weapon of war. I am a destroyer of life in the service of life, the sword and shield of my human creators." Bolo Invincibilus, Mark XXIII, Model B (Experimental) 0075-NKE "Nike".


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PostPosted: Sat Jul 16, 2005 5:47 pm 
All the spares are probably the ones already installed on shuttles.

While having an entire shuttle's worth of spare parts on hand might be a good idea, someone, somewhere, would complain about the wasted money and spare parts would either have to be sold back or built into a working shuttle. This is the way both large businesses and governments work.


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PostPosted: Sun Jul 17, 2005 2:29 am 
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Enterprise has been scavenged several times for spare parts, as well as for some bits like landing gear that went into building Endeavour to replace Challenger.

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Fandemonium!
August 1st, 2nd, 3rd, 2014

"I am a machine. I am a weapon of war. I am a destroyer of life in the service of life, the sword and shield of my human creators." Bolo Invincibilus, Mark XXIII, Model B (Experimental) 0075-NKE "Nike".


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PostPosted: Sun Jul 17, 2005 2:58 pm 
I wonder if some day the Smithsonian will try to refit Enterprise to flying condition. I know it was never intended for that, but it seems like the kind of thing they would do.


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PostPosted: Mon Jul 18, 2005 1:26 am 
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The Enterprise will never be fitted out for use. It was actually the second shuttle to begin construction, Columbia was started first.

Enterprise was used for several glide tests, launched from the back of the 747 shuttle transport aircraft, first with the tailcone then without. It was never fitted with real engines, just ballast to simulate their weight.

After the approach and landing tests were complete, it was subjected to an extensive series of vibration tests, so it has the equivalent of several launches worth of stress on the airframe.

Enterprise is also heavier than Columbia, so even if it could be completely refit for flight, it couldn't carry as much payload as Columbia, which was the heaviest of the operational shuttles.

Many parts have been scavenged from Enterprise over the years for the others, and some major components were taken to build Endeavour.

Enterprise was recently given a cosmetic restoration and put back on display at the Air and Space Museuem.

Even if the money was available to embark on a crash program to totally dismantle and rebuild Enterprise, including a bunch of updates to make it lighter, it wouldn't be worthwhile because the shuttles will be retired in 2010 after the International Space Station assembly is completed.

IIRC, that was looked at as a possibility after the loss of Challenger, but it was deemed easier and cheaper to build Endeavour using mostly new parts and a some of the "low mileage" bits from Enterprise that weren't possibly compromised in strength by the vibration tests.

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Fandemonium!
August 1st, 2nd, 3rd, 2014

"I am a machine. I am a weapon of war. I am a destroyer of life in the service of life, the sword and shield of my human creators." Bolo Invincibilus, Mark XXIII, Model B (Experimental) 0075-NKE "Nike".


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PostPosted: Mon Jul 18, 2005 3:23 pm 
Oh I know it would never be launched. It's something of a tradition for the Air and Space museum to try and keep as much of their collection in flyable condition as is feasable. Maybe they'll do it once the shuttles are retired and they can get the parts.


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PostPosted: Wed Aug 17, 2005 8:52 pm 
Personaly I think they should just turn the space program over to Burt Rutan


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PostPosted: Thu Aug 18, 2005 12:27 am 
Grumpy_Penguin wrote:
Personaly I think they should just turn the space program over to Burt Rutan


Wait till Burt Rutan gets into orbit, then do that. :)


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PostPosted: Thu Aug 18, 2005 11:26 pm 
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Wait till Burt Rutan gets into orbit, then do that. Smile

Ya got ten bucks (or does ) that says he won't ?


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