Author Topic: Faget's reason for Apollo CM shape: shocking!  (Read 3038 times)

Offline Oersted

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Faget's reason for Apollo CM shape: shocking!
« on: 11/12/2008 03:55 pm »
Here Faget discusses the shape of the Apollo CM capsule:

http://history.nasa.gov/SP-4223/ch14.htm

(Chapter 14 of this book, which is online:)
http://history.nasa.gov/SP-4223/sp4223.htm

- When I read it I just went "WHAT?!"

"There were some other things that we did at that time that helped set the shape. We had a fairly lengthy argument about whether the bottom of the heat shield should be rounded-the point where the heat shield and the conical part intersect. Mercury and Gemini are sharp and in Apollo we rounded that off. I thought it should be sharp because I couldn't see anything wrong with it and it also increased the total drag.

One of the primary things that I think settled the issue was that on the early Saturns, which had been designed primarily as a R&D vehicle down at Huntsville, they designed this vehicle and got the go ahead to put two or three of them into production for test flights without any payload. So they had several old Jupiter nosecones laying around. These are long conical nosecones, and they decided since they had instrumentation in those nosecones they'd make the Jupiter nosecones the payload. But because there wasn't enough room for all the instrumentation in a Jupiter nosecone, they discontinued the conical shape until the diameter got up to 156 inches and said that's going to be the payload. Then they took the upper part of the Saturn IV-B stage, which was being built by Douglas, and put an adapter section on it at the same conical angle as the nosecone and brought that down from the 180 inches to 156 inches. That was the interface between the work going on at Douglas and the work going on at Huntsville. So when we finished our job we had a vehicle that was 14 feet in diameter and we said we'd like to fly this on top of the Saturn and they said "Oh, gee, it'll cost us a million dollars to put a new front end on the Saturn." So we went round and round, and to make a long story short we decided at Langley that it would be a lot easier just to reduce our diameter down to 156 inches than to argue with those guys. And the easiest way to do that was just to round the corners off-we didn't want to change the internal layout, so we rounded off the corners and ended up with 156 inches. Marshall decided that they would put rounded corners on Apollo and I don't think they ever knew why."

Offline SpaceCat

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Re: Faget's reason for Apollo CM shape: shocking!
« Reply #1 on: 11/12/2008 10:24 pm »
LOL- Life was simple then.
Reminiscent of Mercury engineer, Scott Simpkinson, running over to Cocoa Hardware to buy a router-- and doing a little trimming when the first boilerplate capsule arrived at the Cape with its heat shield just a little to large for the booster. :)

Offline Oersted

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Re: Faget's reason for Apollo CM shape: shocking!
« Reply #2 on: 11/13/2008 01:28 pm »
Especially interesting, I think, in the light of the fact that the Orion capsule will be modelled more or less on the Apollo CM!

Offline Kaputnik

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Re: Faget's reason for Apollo CM shape: shocking!
« Reply #3 on: 11/14/2008 10:33 am »
That is interesting.
When I first came to this forum, I remember aksing abuot why NASA was sticking with the Apollo OML- surely in the intervening decades a better design would be possible? After all, we have CFD and much more experience now.
The responses I got were generally that Apollo had huge amounts of data behind it and that it would be a poor use of resources to look at a slightly different shape just in the off chance that it could provide some mass, space, or aerodynamic benefits. Nobody mentioned that the shape was, essentially, an accident!
"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

Offline Oersted

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Re: Faget's reason for Apollo CM shape: shocking!
« Reply #4 on: 11/18/2008 07:50 am »
Just one of those little known space facts.... But in fact a lot of shapes and sizes in our world hark back to old irrelevant reasons, like the British railway gauge, etc...

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