NERVA (OT)

NERVA was intended for use from one orbit (like Earth Orbit) to another (for example, Mars orbit). It would not have had the strength to lift a load from a planetary surface, hence, would not have been used in Earth's atmosphere. Basically, it worked by heating a gas to plasma temperature and exhausting it through a nozzle. Major advantages over conventional rockets included an ability to run for longer times at lower forces (if you took Physics in school, recall that time is squared in acceleration formulae). and requiring less reaction mass (the gas to be exhausted) than a regular rocket would need for fuel (much, much less) which means a much bigger payload for the same size of vehicle.
AFAIK, still the best engine we have on the shelf for a mission to Mars and the only one that would be anything like practical for tooling around the asteroids or beyond.

Hank
PS. to be somewhat closer to OT, If you live in someplace like Leadville, you will exceed the maximum yearly dosage of radiation allowed just from cosmic rays, as more get through due to the thinner atmo up there. Wonder what kinds of dosage South Park crews on the High Line accumulated as they spent so much of their time at that altitude or higher?