  The first definite interstellar object observed in our solar system was
discovered in October of 2017 and was subsequently designated 1I/'Oumuamua. In
addition to its extrasolar origin, observations and analysis of this object
indicate some unusual features which can only be explained by in-situ
exploration. For this purpose, various spacecraft intercept missions have been
proposed. Their propulsion schemes have been chemical, exploiting a Jupiter and
Solar Oberth Maneuver (mission duration of 22 years) and also using Earth-based
lasers to propel laser sails (1-2 years), both with launch dates in 2030. For
the former, mission durations are quite prolonged and for the latter, the
necessary laser infrastructure may not be in place by 2030. In this study
Nuclear Thermal Propulsion (NTP) is examined which has yet to materialise as
far as real missions are concerned, but due to its research and development in
the NASA Rover/NERVA programs, actually has a higher TRL than laser propulsion.
Various solid reactor core options are studied, using either engines directly
derived from the NASA programs, or more advanced options, like a proposed
particle bed NTP system. With specific impulses at least twice those of
chemical rockets, NTP opens the opportunity for much higher {\Delta}V budgets,
allowing simpler and more direct, time-saving trajectories to be exploited. For
example a spacecraft with an upgraded NERVA/Pewee-class NTP travelling along an
Earth-Jupiter-1I trajectory, would reach 1I/'Oumuamua within 14 years of a
launch in 2031. The payload mass to 1I/'Oumuamua would be around 2.5metric
tonnes, but even larger masses and shorter mission durations can be achieved
with some of the more advanced NTP options studied. In all 4 different proposed
NTP systems and 5 different trajectory scenarios are examined.
