  A sizing procedure for a rocket family capable of fulfilling multiple
missions considering the commonality is presented. The procedure aims to take
full advantage of sharing a common part across multiple rockets whose payload
capability differs entirely, ultimately leading to cost savings in designing a
rocket family. As the foundation of the proposed rocket family design method,
an integrated sizing method with trajectory optimization for a single rocket is
first formulated as a single optimal control problem. This formulation can find
the optimal sizing along with trajectory results in a tractable manner.
Building upon this formulation, the proposed rocket family design method is
developed to (1) determine the feasible design space of the rocket family
design problem (i.e., commonality check); and (2) if a feasible design space is
determined to exist, minimize the cost function within that feasible space by
solving an optimization problem in which the optimal control problem is
embedded as subproblems. A case study is carried out on a rocket family
composed of expendable and reusable launchers to demonstrate the novelty of the
proposed procedure.
