O-Rings - Memo Discussing Potential for Disaster

NASA personnel, at the Marshall Space Flight Center in Huntsville, were very concerned about Morton Thiokol's position on the O-ring and clevis-joint design for the Solid Rocket Motor (SRM).  Repeating earlier concerns (from 1977), the NASA officials formally stated their objections to the manufacturer's position in this January 19, 1979 memo. 

Among other things, they worried that:

Excessive tang/clevis movement ... causes the primary O-ring seal to extrude into the gap, forcing the seal to function in a way which violates industry and Government O-ring application practices.

They further pointed out that:

Excessive tang/clevis movement as explained above also allows the secondary O-ring seal to become completely disengaged from its sealing surface on the tang.

These concerns took on even greater meaning after the Challenger disaster - seven years later.

Credits

NASA internal memo, online courtesy NASA.