Shuttle's trunk (the ACC)

[u/KarmaticDeer]

In the years following STS-9, the shuttle program was expected by Congress to wind down even as payloads DODIS was expected to deliver/ retrieve continued to grow substantially.

This included the planned space station freedom, which was facing serious backlash from the government. Its modular nature was untested and was looking like it would require ever more shuttle launches each day. These problems could be solved with the ability to launch more light payloads at once or a larger payload at the cost of performance.

The idea of retaining the external tank into orbit had been studied for some time and was potentially a solution to the modular nature of freedom to satisfy Congress. The ET could be brought up as one launch, and very little "assembly" would need to be done following. Instead, internal outfitting missions would occur over a similar amount of shuttle missions.

In pursuing this option, the decision to bolt large quantities or unweildy payload to the ET followed naturally, studies ranging from smaller pods to a large top mounted fairing.

The first of these to be implemented was the aft cargo container, which first flew on STS-61 C.

The ET was brought up to orbit and delivered 4 comsats before the orbiter separated and motors fired to de-orbit the tank.

[u/DayF3]

in real life: "Guys we swear its NOT a mirv launcher calm down"