Detail of the second stage adapter, taken
between Pos. IV and Pos. III (fuel tank 3 and LOX tank 4 are at center on the
bottom; note the GOX line running up F4's
left side at right). Also note the fuel vent on the forward skirt of F3.
Note the green triplex
spheres (containing nitrogen to pressurize
the fuel tanks), the ends of the spider
beam between the propellant tanks, and how the lines connecting the
spheres pass through holes in the spider beam. Also note the instrumentation
canister forward of F3.
The screen installed over the opening between the S-I stage and its adapter is
presumably to keep the birds out; I don't believe that it was original