Memo from A.R. Thompson on the Flight Seal

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Morton Thiokol, Inc

Wasatch Division

Interoffice Memo

2871:FY86:141

22 August 1985



TO:     S.R. Stein

        Project Engineer



CC:     J.R. Kapp, K.M. Sperry, B.G. Russell, R.V. Ebeling,

        H.H. McIntosh, R. M. Salita, D.M. Ketner



FROM:       A.R. Thompson, Supervisor

        Structures Design



SUBJECT:    SRM Flight Seal Recommendation





The O-ring seal problem has lately become acute.  Solutions, 

both long and short term are being sought, in the mean time 

flights are continuing.  It is my recommendation that a near 

term solution be incorporated for flights following STS-27 

which is currently scheduled for 24 August 1985.  The near 

term solution uses maximum possible shim thickness and a 

.292 +.005/-.003 inch dia O-ring.  The results of these two 

changes are shown in Table 1.  A great deal of effort will 

be required to incorporate these changes.  However, as shown 

in the Table the O-ring squeeze is nearly doubled for the 

example (STS-27A).  A best effort should be made to include

a max shim kit and the .292 dia O-ring as soon as it is 

practical.  Much of the initial blow-by during O-ring sealing 

is controlled by O-ring squeeze.  Also more sacrificial O-ring 

material is available to protect the sealed portion of the 

O-ring.  The added cros-sectional area of the .292 dia O-ring 

will help the resilience response by added pressure from the 

groove side wall.



Several long term solutions look good; but, several years are 

required to incorporate some of them.  The simple short term 

measues should be taken to reduce flight risks.



A. R. Thompson



ART/jh

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