[Symmetry]

Well, some fallout. Orion is designed to to use small, single stage atomic bombs even if it does use lots of them to get out of the atmosphere. Those individually produce much, much less fallout than the huge fission-fusion-fission bombs that are mounted on ICBMs. Getting Orion to space would produce less fallout than the Bikini Atoll test. But then again there was a reason the various nuclear powers agreed to stop testing atomic weapons in the open air.