A gas core fission reactor that utilizes americium in place of uranium is examined for potential utilization as a nuclear rocket for space propulsion. The isomer 242mAm with a half life of 141 years is obtained from an (n, γ) capture reaction with 241Am, and has the highest known thermal fission cross section. We consider a 7500 MW reactor, whose propulsion characteristics with 235U have already been established, and re‐examine it using americium. We find that the same performance can be achieved at a comparable fuel density, and a radial size reduction (of both core and moderator/reflector) of about 70%.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87734/2/585_1.pd