I'm pretty sure the thing keeping Project Orion from taking off was a treaty to not detonate nukes in space and not necessarily the logistics of detonating nukes in space.
edit: "Danger to human life was not a reason given for shelving the project – those included lack of mission requirement (no-one in the US Government could think of any reason to put thousands of tons of payload into orbit), the decision to focus on rockets (for the Moon mission) and, ultimately, the signing of the Partial Test Ban Treaty in 1963. The danger to electronic systems on the ground (from electromagnetic pulse) was not considered to be significant from the sub-kiloton blasts proposed since solid-state integrated circuits were not in general use at the time."
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