Megatons to orbit & beyond is a critical piece of the K2 puzzle. The other parts are: massive amounts of solar cell production, AI chip production, millions of humanoid (general purpose) robots and a mass driver on the Moon. My guess is that ~1M Optimi plus ~1GW of solar will constitute the first Von Neumann Probe, a system capable of replicating itself entirely from local materials on any sufficiently large planet or moon. This would enable expansion of civilization throughout the galaxy and reaching K3.