This. This struck me as brilliant. If the scientists and engineers refer to the "bombs" as "fissile fuel", Project Orion MIGHT have been much more developed by now, or at least have some application for sending probes to further destinations. Heck, if some sort of nuclear propulsion system (either Orion or NERVA) has been fully developed, we would have been on Mars by now, and have rovers on Titan (the moon of Saturn) or Europa (the moon of Jupiter), and have probes on Pluto, without waiting for another Grand Alignment (which was the case for Voyager missions). If I was controlling NASA, I'd pursue these propulsion systems first, along with alternative propulsion systems (NERVA, SABRE, hybrid rockets, various electric propulsion systems), then adapting the SLS to launch these into orbit. Next, I would build what I call a modular spacecraft, which is basically a spacecraft that's so large, it has to be launched in segments and assembled in orbit. Then, landers, rovers, manned capsules, labs, probes, and other payloads would be docked to this massive spacecraft and be carried away to other planets, acting as a mothership of some sorts. After the mission, the spacecraft would carry its returning payload back to Earth orbit, detach the manned capsules for reentry, and stay in orbit for for its next mission, with new capsules, new crew, and (possibly) new engines. This way, the WHOLE spacecraft, other than discarded segments due to damage, is recovered, and ready for new missions without launching it to orbit again. I have tried this concept in KSP, and while initial efforts are challenging (it cost me 19 launches, and it has 350+ part count, not including payload), the results are staggering. For every subsequent missions, all I have to do is launch a resupply mission, send manned capsules and landers, maybe a processing lab, and simply set the thing on its way. That same spacecraft did at least a dozen missions before I lost my save and had to start over, and I'm thoroughly impressed by its capabilities. If we are actually going to send manned missions to Mars, this would be essential, especially since sending additional supplies from Earth would take months to arrive. Going there with stockpiles in reach may be a better idea.