Estimating the Cost to Transition a Space System from Expendable to Reusable

In recent years, the benefit of hardware reuse for space systems has been demonstrated in the launch market as reusable launch vehicles have enabled companies, primarily SpaceX with their Falcon 9 vehicle, to drive down launch costs prompting competitors to include reusability in their future designs to stay competitive. Although several reusable systems are currently being developed, the high cost and technical challenges of developing such systems remain an issue. To reduce these barriers, some organizations have chosen to first develop an expendable version of a system then transition it to a reusable version once the design has been proven. SpaceX used this approach when developing their Falcon 9 and Dragon vehicles with both starting as expendable systems which were transitioned to reusable after several successful missions. This approach allows for the benefits of creating an expendable design, relative simplicity and faster time to market, to be realized while still working towards a reusable vehicle. Although such an approach provides benefit, a significant drawback is the financial risk associated with developing two distinct versions of a system. Thus, there is a need for a method to optimize the design of an expendable space system, which will be transitioned to reusable, to minimize overall development cost. To realize this need, we propose a method to estimate the program development cost by estimating the cost to develop the initial expendable vehicle and the cost to transition it to reusable. This paper first discusses the primary considerations for modifying an expendable system for reuse, focusing on the hardware changes required. The methods used to estimate the initial expendable system cost and the transition cost are then discussed. The expendable system cost estimation uses cost estimating relationships and analogous cost estimating, which are modified by a change factor and technology readiness level growth factor depending on the design of each entity. A discount rate factor is also established for each reusable entity that is included in the expendable design to account for the time value of money and an inflation factor is used to convert to constant-year dollars. The transition cost is estimated by calculating the cost of each entity which is added to or modified from the expendable design. For reusable entities that are modified versions of entities used in the original expendable system, a reliability growth factor is applied to account for the increased reliability necessary for the reusable version. However, if the entity only exists in the reusable design, its cost is estimated using similar methods as for estimating the cost of the expendable system. An Integration & Test (I&T) factor is calculated for each entity added or modified when creating the reusable design to reflect the cost of integrating changes into the expendable design to make it reusable along with associated testing. In future work, this cost estimation methodology will be used in a multidisciplinary design optimization framework to calculate program life-cycle cost objective values for each space system evaluated.