The PD-2, a lesser known NASA-DARPA proposal utilizing 3 SpaceX Merlin 1C engines and 3 RL-10 engines for the upper stage5yr ⋅ Sasamj ⋅ r/spacex
Elon Musk discovering yet another way to increase his wealth. (Ca. 2017)6yr ⋅ Sasamj ⋅ r/SpaceXMasterrace