Space Shuttle Launch Pad 39A with Challenger STS-6 (1:144) - Page 172

**Algebraist** · #**1711** 07-01-2018, 08:55 AM

As always Manfred, great research and fantastic photos and explanations.

Regards

Kevin

**spacerunner** · #**1712** 07-01-2018, 09:10 AM

Thanks Kevin,

I want to sort this out somehow, because that interests me, and then I hope finding a solution for this pattern.

**spacerunner** · #**1713** 07-05-2018, 05:09 PM

Hello everybody,

BTW, some friends in the Raumcon forum did mean that this flat wavy ring structure was just an optical effect, but this was a three-dimensional effect, as Craig Capdepon has confirmed.

"The SOFI (spray on foam insulation) was applied with automatic spray gun sets on vertical moving rails I think in 3 locations 120 deg. apart around the tank. The tank would rotate and the guns traveled down the rail to apply the desired thickness. The 3 locations were required because the overlap max. time was 45 seconds. We desired the "as sprayed" finished condition because it was more durable when exposed to sunlight and the weather conditions in Florida. There was no attempt to create a "pattern" to the finish. We tried for a smooth uniform finish.

The wave like patterns were unique to each tank as a result of the variations in the spray foam insulation process. The spray guns pattern control tip would accumulate a build up of foam causing a less than perfect pattern. There were engineering drawing requirements limiting the peaks and valleys of this finish. The critical area near the nose cone was often machined to obtain a smooth surface using a tool we nicknamed the "pencil sharpener".

I found this photo, on which one can see this tool during the repair work of the hail damage on the ET-124 during the start preparations for the STS-117, in which he was involved too.

Source: NASA

Of course I had asked further questions, including a term "Barber pole", which I found that characterizes the SOFI mode.

"It was a non-stop procedure. The tank was rotating as the guns started spraying a predetermined amount of SOFI. Carriages holding the spray guns traveled (down the rail) at a set speed until the end of the spray operation.

The correct tank rotation, travel of spray carriages, temperature of SOFI components, pressure of component supplied to guns, substrate temperature, cell environment, (temp. & humidity) and the pattern at the gun pattern control tip all determined the thickness and as sprayed condition of the finished product.

"Barber pole" was a shop term to generally refer to the method. The travel of the gun carriages was slow because of the large area (diameter) of the tank. If a smaller cylinder was sprayed (i.e. feed lines) this same method may produce a "spiral-effect" surface."

That these rings actually have a three-dimensional structure can also be seen in this video (unfortunately without sound) which shows an SOFI piece of the ET-93 used in the fateful last Columbia mission STS-107.

Craig commented about this video:

"This was not an optical effect. I would have to see a larger cross section to know exactly where this piece is from. It looks like part of an automatic spray possibly from the aft dome of the LH2 tank. I see two knit lines and it appears the three passes were approx. 1 inch each. SOFI is pliable for about 5 seconds after components are mixed and exit the spray gun. The rough surface in this picture is an example of "roll over" caused when SOFI is formed by an outside force soon after application such as excessive air movement from the direction of the gun."

Furthermore, I have learned from him, that he has worked on every shuttle that has flown,

what I found next to this photo.

"Endeavor the newest shuttle STS-134 (16.05.2011) on the pad. This is ET-122 - we did the mod in February. I've worked on every shuttle that has flown."
A very interesting contemporary witness from that time, I have met in this way.

**beckychestney** · #**1714** 07-05-2018, 07:29 PM

Don't you just love it when stuff like that happens!

**spacerunner** · #**1715** 07-06-2018, 07:46 AM

Hi Becky,
this is a great acquaintance that has helped me a lot to understand the SOFI process better.

**spacerunner** · #**1716** 07-06-2018, 07:52 AM

Hello everybody,

in the meantime another expert and friend of Craig Capdepon has joined our Facebook-Dialog, namely Vince Morales (Sr. Staff QA Engineer) from Louisiana, ie a quality assurance specialist, who among others was also involved in the repair of hail damage at the ET-124 (STS-117) in the KSC.

And he has spontaneously shared more details on my questions.

The rotation of the tank varied during sprays depending on the required SOFI thickness and averaged approximately 2 rpm for the LH2 Tank and up to 6 rpm for the upper part of the LO2 Ogive.

As he said the peak to valley was about 5 inches due to the tanks being sprayed in a shingle pattern (barber pole style), what did confirm my estimated approx. spacing between the wavy rings of about 1 mm (1:144).

The Pencil sharpener was only applied to the most affected area at the top of the LO2 Tank during the repair work on the damaged by hail ET-124.

Due to the high density of golf ball-sized holes at this point, the entire area had to be repaired,

Source: NASA

while the rest of the approx. 1.000-2.000 impacts further down in painstaking detail was repaired hole by hole by hand.

Source: NASA

This amazing tool, mounted on the Lightning Rod on top of the Composite Nose Cone, was be swung all-around for grinding the hand-sprayed SOFI foam.

Source: NASA
Viewed from up close, one can see that the device was a kind of Multi-belt sander.

Source: NASA

And with this speckled ET the Atlantis stack came back to the pad, seen here from the west side,

Source: NASA

and here from the south side,

Source: NASA

and was then ready for launch again.