S-IVB (Saturn V) Auxiliary Propulsion System Module

The S-IVB (third) stage of the Saturn V has two Auxiliary Propulsion System modules. They provided three-axis attitude control (yaw, pitch, and roll) during flight and during transposition, extraction, and docking of the Lunar Module; they also performed the ullage burn prior to S-IVB restart at trans-lunar injection.

Two such units were mounted on the S-IVB's aft skirt, 180° apart (see the mounting brackets on the S-IVB on the KSC Saturn V). Each module contained three 150-pound attitude control engines and one 70-pound ullage engine. The engines used monomethyl hydrazine (MMH) as fuel and nitrogen tetroxide for the oxidizer, with Wach APS module carrying about 115 pounds of usable fuel and 150 pounds of usable oxidizer.

The S-IVB (second) stage of the Saturn IB also used two APS modules, although they were smaller (as they were used only during the main engine burn) and lacked ullage engines (as the J-2 was not restarted on Saturn IB missions).

As of now, I have not yet sorted through all of my pictures of the APS module, but some other page references this location. Thus, this is a "place holder" version right now, with only the pictures actually referenced. Come back some time later to see if I've finished up, or drop me an email to request me to prioritize the rest of these pictures.