Bill’s latest mission proved that the Andromeda CSM, intended for munar missions, is insufficient for meeting the goals set for it. Part of this failure is the insufficient lifting capacity of the Hercules, and with the Andromeda likely to become heavier in this update the rocket will require more capacity as well.
The primary fault with the design of the Andromeda II CSM is the insufficient fuel for the necessary maneuvers for munar missions, especially given KK protocol of using FRT for missions to Mun, which requires longer burns. A secondary fault is that, due to the LV-909 engine lacking an alternator, the electrical capacity of the craft is dangerously low. Fixing the latter issue is simple: adding a pair of Z-100 battery packs to the SM quintuples the electrical charge of the craft. For the former issue, the LV-909 is already the most efficient engine KK engineers have developed, and therefore the only means of improving Andromeda’s capabilities in that regard is by adding additional fuel. Extending the existing fuel tank by 50%, after factoring in the added mass of the tank and the new batteries, gives Andromeda IIa roughly 35% more ΔV over Andromeda II. Since Bill’s mission fell short by less than 200 m/s (prior to engaging the LES to effect his safe return), the added ~700 m/s should be more than enough.
A heavier Andromeda, however, means that Hercules has to lift more mass into orbit, and previous missions have already proven that the Hercules IIb, the most powerful rocket yet designed by KK, does not have sufficient ΔV to complete orbital insertion, robbing Andromeda of fuel that could be essential to the success of the intended mission. [While KK engineers lack the detailed records necessary to prove it, they believe the failure of the Andromeda II to effect the return to Kerbin can be explained by needing to use some of its fuel to achieve its initial parking orbit around Kerbin.] Rather than trying to update the Hercules II design again, KK engineers began work on Hercules III instead.
Opting for a triple stack design at the top, initial designs took that out to six boosters in the first and second stages. The initial stage was six Rockomax BACC solid fuel boosters; stage two was a core of three LV-T30 engines, supported by three LV-T45 engines for additional guidance. The third and final stage was a trio of LV-T45 engines. While this design proved effective, KK engineers knew they could do better, and with the future of the Hercules family on the line they knew they had to.
The final design of the Hercules III performs extraordinarily well in simulation. A triple stack of LV-T30 engines, topped with a set of reaction wheels, form the third and final stage of the rocket. Immediately below that is another trio of LV-T30s, these assisted by the addition of three addition sets of reaction wheels; while the added weight would seem to make the rocket less capable, the reaction wheels provide the necessary control and stability the rocket needs, while the higher thrust of the LV-T30 (as compared to the LV-T45) more than makes up for it. Radially attached to the second stage are three separate boosters, each topped with a single fuel tank but immediately branching into three stacks, driven by three more LV-T30 engines, for a total of 9 LV-T30s in the initial stage.
The end result is a Hercules III that is more than capable of delivering the upgraded Andromeda IIa into LKO and performing the Munar FRT injection burn, and still has fuel left over.