Monte Carlo analysis of a cluster of nuclear thermal rockets have been performed using the Code MCNP (Briesmeister 1986). Three effects of clustering have been analyzed: neutronic coupling, nuclear heating in a shutdown engine, and radiation
scattering. Preliminary analyses indicate that clustering phenomena will not have significant effects on engine design or operation. More detailed analyses should be performed as engine and vehicle designs progress, although the basic conclusions of this study are not expected to change.