Author Topic: Interesting Neighbor  (Read 25931 times)

Offline DonPMitchell

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Interesting Neighbor
« on: June 29, 2012, 06:43:58 PM »
I discovered a while ago that living a mile or so from me is on of Charlie Bossart's sons.  We've had some interesting conversations about his life.  One of the unsung heros of rocket engineering in my opinion.
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Offline ijuin

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Re: Interesting Neighbor
« Reply #1 on: June 30, 2012, 12:08:40 AM »
Since he is so unsung that some of us may not know about him, how about you tell us a bit about Bossart's contributions to rocketry?

Offline DonPMitchell

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Re: Interesting Neighbor
« Reply #2 on: June 30, 2012, 10:45:44 PM »
Bossart was the chief engineer at Convair who developed the Atlas.  It was his idea to build a thin metal tank supported only by internal pressure.  The atlas was made from type 301 cold-rolled stainless steel, 0.01 inches thick at the top and 0.05 inches thick at the bottom.

Von Braun was intensely jealous of Bossart and tried hard to scuttle the Atlas and the Centaur stages that he and his team designed.  During a visit to Convair, Bossart challenged one of Von Braun's engineers to hit the side of the centaur stage with a sledge hammer.  It bounced off without leaving a dent and almost knocked the engineer out.
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Offline ijuin

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Re: Interesting Neighbor
« Reply #3 on: July 01, 2012, 12:53:31 AM »
The Atlas and Centaur were definitely giant leaps forward in lightweight construction--imagine if they were re-designed today using aluminim/lithium alloy instead of steel--it would be like the comparison between the original Shuttle External Tank and the later Ultra Lightweight Tank. I don't think any other rocket stages have ever beat them in terms of structural strength-to-weight ratio.

As far as supporting something by internal pressure, look at the common 21st century beverage can. It's a thin shell of aluminum with a mass of all of ten grams or so, and when it's empty you can easily crush it in your fingers. However, when filled with a typical carbonated beverage (containing enough carbon dioxide to pressurize the can to twice the pressure of your typical automotive tire), the can is able to withstand hundreds of Newtons of longitudinal compression--a lightweight adult can even carefully balance atop one without it springing a leak. And this engineering wonder is used to hold our beer and cola and be cast aside afterward, with the contents regarded as ten times more valuable than the container, if price is any measure.

Offline DonPMitchell

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Re: Interesting Neighbor
« Reply #4 on: July 03, 2012, 08:48:17 PM »
Yes, if you look at strength/weight, there are lots of new developments.  I'm not sure what the strongest material is, and materials often have quirky behaviors that aren't described by just tensile strength or young's modulus.  For example, Spruce has impressive strength/weight even by modern standards of materials, but of course its too elastic and problematic in many ways to make a rocket out of wood.

Aluminum/zinc and Al/Li are better than Duralumin, so that's been interesting.  You also have advances in steel, carbon-less maraging steel alloys and such.
Never send a human to do a machine's job.
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Offline ijuin

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Re: Interesting Neighbor
« Reply #5 on: July 03, 2012, 11:24:07 PM »
True, but then there's the behavior of materials at cryogenic temperatures--a lot of materials are less elastic at liquid hydrogen or oxygen temperatures than at the more familiar liquid water temperatures. That's one reason why synthetic non-latex rubber is preferred for cryogenic seals--you ever seen those videos where they dip a rubber ball in liquid nitrogen and then shatter it?

Offline DonPMitchell

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Re: Interesting Neighbor
« Reply #6 on: July 07, 2012, 12:57:35 PM »
Fortunately a lot of metals actually become stronger at those low temperatures.  AMg-6 and some stainless steels for example.
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Offline ijuin

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Re: Interesting Neighbor
« Reply #7 on: July 07, 2012, 11:27:25 PM »
Which paradoxically makes steel BETTER than aluminum for some such applications despite being denser . . . yay materials engineering.

Offline DonPMitchell

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Re: Interesting Neighbor
« Reply #8 on: July 09, 2012, 03:26:38 AM »
AMg-6 does well at low temperature.   One of the reasons the Soviets used it so much.  If you get into materials, they are much quirkier than people realize.  Fabricating with stainless steel is a real pain in the butt, because it can be over work hardend or annealed if you so much as look at it the wrong way.  AMg-6 is an engineer's delight, because its strength is relatively unaffect by whatever you want to do with hit -- stamping, welding, cutting, drilling, milling, etc.  BUt ifyou just look at tensile strenght/density, then you would think "Hey, why didn't we build the Sature V out of Balsa Wood?"
Never send a human to do a machine's job.
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Offline madmax

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Re: Interesting Neighbor
« Reply #9 on: September 18, 2012, 07:57:46 PM »
Balsa wood?
Starting to sound like Steam Punk around here.
What me worry?

Offline ijuin

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Re: Interesting Neighbor
« Reply #10 on: September 18, 2012, 10:54:23 PM »
Balsa wood is pretty lightweight and strong, but its heat tolerance is way too low to allow it to come into close contact with engine exhaust or hypersonic airflow in a rocket.