Although the preparation for bonding was almost identical to the one 

 used for scale models, considerably more difficulties were encountered in the 

 bonding of the large-scale capsule. These difficulties can be placed into two 

 categories: (1) mixing and pouring of large quantities of adhesive and (2) elim- 

 ination of cavities and separation spaces in cast joints. The problem in the first 

 category centered around mixing large quantities of adhesive components 

 without inclusion of air bubbles and at the right temperature so that the mix 

 would not set during pouring into the joints while at the same time retaining 

 the ability to set in the joint within a short span of time. If the chemical reac- 

 tion in the mix progressed too rapidly (because of the large mass of adhesive 

 involved) during pouring, it not only generated an excess of bubbles but the 

 adhesive would set in some portions of the joint prior to filling it completely. 

 When this occurred, access holes had to be drilled through already-set adhesive 

 to permit trepanning the voids in joint spaces so that they could be filled with 

 adhesive by means of a syringe. On the other hand, when the mix reacted so 

 slowly that several hours were required before it set, the components of the 

 mix attacked the acrylic plastic surfaces of the joint causing them to craze. 

 Since the exact temperature was not known to which the components of the 

 mix had to be precooled to prevent premature setting during pouring while 

 still permitting rapid setting in joint, the trial and error approach was utilized. 

 The problem of arriving at a satisfactory mix temperature was further com- 

 plicated by the variation in ambient temperature during the several day-long 

 periods required for casting the joints. As a result, the placement of PS-18 

 into the joint spaces was a continuous trial and error operation. Some of the 

 joint sections were filled with the adhesive without any trouble, while others 

 had voids or separation spaces that had to be laboriously drilled out and refilled 

 because of the too-rapid or too-slow setting of the adhesive. Since considerable 

 shrinkage took place in the large volume of joint space, the tape covering the 

 joint had to be placed over the joint in such a manner that the cast adhesive 

 would develop an external bead over the joint. To form this bead, the tape 

 was partially folded over the joint and, since the heat of the reaction in the 

 cast adhesive may change the shape of the fold in the tape, it was stiffened 

 locally in the fold area by aluminum foil. This aluminum foil provided a 

 further advantage by giving the joint bead a smooth surface. 



The troubles, however, did not terminate with the placement and 

 setting of adhesive in the joint spaces, because small dispersed cavities 

 (Figure 51) and separation spaces (Figure 52) were found in the joint after 

 it had set. The separation spaces generally were found at the boundaries 

 between individual pours. Only after a brief investigation into methods of 

 eliminating them was it found that the removal of the surface skin from the 

 preceding already set pour would in most cases eliminate the separation 

 spaces between neighboring PS-18 pours in the joint. Separation spaces 



77 



