Compared to its predecessor, Atlas G featured an 81-inch stretch of its first-stage propellant tanks and a new MA-5 engine section on its first stage, increasing its thrust by 7,500 lbf (33,000 N).

The tanks featured extremely thin walls, saving a considerable amount of mass, but also requiring the stage to be constantly pressurized to not collapse.

[3] The booster engines, along with their support structure and plumbing, would drop away around two and a half minutes into flight after the vehicle reached 5.3g of acceleration.

The hydrogen peroxide reaction control system (RCS) was replaced with a hydrazine RCS, a change that would persist up until the Centaur III flying on Atlas V. These controlled stage attitude during coasts between engine burns, as well as providing ullage thrust to settle propellants in the tanks.

The uprated Centaur flown on Atlas G, among other changes, deleted the propellant boost pumps in the interest of greater simplicity and weight-saving.

Although the tank had been designed to accommodate higher pressure, technicians at Convair inexplicably failed to test Centaur 5402 for leaks before shipping it to Cape Canaveral.

Finally, the leak testing program and tools used at Convair were outdated and less reliable than newer methods and the tech personnel in charge of fabricating the Centaur's balloon tanks were badly inexperienced.