STRUCTURE

The second stage structure consists of an inter­stage, which links it with the first stage; a thrust structure and aft skirt assembly, which supports and houses the five J-2 engines; an ellipsoidal liquid oxygen tank; a bolting ring, which attaches the liquid oxygen tank to the second stage structure; six aluminum cylinder walls, which are welded

Stacking Stage—Aft skirt, thrust structure, and common bulk­head move on transfer table to new station for further buildup of stage.

lower ring. Four support rings along with an outer skin stiffened with hat sections comprise the basic structure. In addition, eight thrust longerons (two to each panel) extend upward along the conical surface of the thrust structure. The lower circum­ferential ring rests directly over the line of thrust of each of the four outboard engines while the cen­ter engine support beam assembly is directly over the thrust line of the center engine. A rigid heat shield mounted around the five J-2 engine •• to a frame connecting to the thrust structure protects the base area of the stage against recirculation of hot engine exhaust gases and heat from the ex­haust. This heat shield is of lightweight construc­tion protected by low-density ablative (heat-resis­tant) material.

Although assembled separately, the aft skirt and thrust structure when joined become a structural entity and together support the five engines and withstand and distribute the thrust and boost struc­tural loads.

In ado, tion to engines and engine accessories, the
interstage, aft skirt, and thrust structure house electrical and mechanical equipment such as signal conditioners and controllers, telemetry electronics, flight control electronics, service and connecting umbilicals, electrical power control units, power distribution panels and batteries, inverters, propel­lant management electronics, propellant plumb­ing, ordnance installations, and hydraulic pumps and accumulators. Equipment that is not required after second-plane separation is in the interstage which is separated 30 seconds after ignition. Equipment necessary for flight operations is located on the aft skirt, thrust structure, and forward skirt.