Opportunistic preventive maintenance scheduling for multi-unit reusable rocket engine system based on the variable maintenance task window method

The reusable rocket engine (RRE), recognized as future propulsion system for space transportation, is composed of multiple components of which each one plays an essential role for the whole system. In rocket launches, these components are impaired by severe service conditions while the maintenance actions can only be executed in mission intervals. To program a reasonable maintenance scheme for the RRE system, an opportunistic preventive maintenance (PM) scheduling strategy is proposed: at the component-level, we evaluate the PM intervals dynamically by minimizing the maintenance cost rate over a life cycle under the reliability constraint where two imperfect maintenance actions: maintenance repair and replacement, are taken into account; at the system-level, a variable maintenance task window (VMTW) method is applied to dynamically rearrange maintenance actions when the maintenance opportunities arise. The novel strategy can effectively reduce the PM cost and avoid unnecessary depot maintenance. Its efficiency is validated by a comparison with traditional optimal preventive maintenance schedule derived from the genetic algorithm.