Submersible designs are not necessarily acceptable for habitat designs 

 because of the more stringent functional requirement due to creep. It would, 

 therefore, be worthwhile investigating a new seal design which would meet 

 the requirements and still reduce cost without compromising the structural 

 integrity of the viewport. A new design or variation of the seal in Figure A-ld 

 is shown in Figure A-2. It is a conventional circularO-ring in a rectangular 

 groove located on the conical face of the viewport. Note that all five designs 

 discussed require retainer rings. 



O-ring - Parker 2 - 457, N-183-9 



nitrile (Buna N) 



90 durometer 

 Note - After machining, anneal at 



175°F for 22 hours; cool at 



5°F per hour. 



Figure A-2. Recommended viewport seal design. 



COMPARISON OF DESIGNS 



The five seal designs described may be compared in three different 

 areas: (1 ) operation, (2) economy, and (3) structure. 



Operation 



Functional requirements for viewport seal systems include sealing 

 under all conditions. As previously observed in the main body of this report, 

 creep occurs in the viewport after a long term submergence. Even after 

 returning to the surface, the viewport does not immediately return to its 



34 



