In addition to cost, a major design constraint on planetary exploration spacecraft designed at the Jet Propulsion Laboratory has been mass, because of limited launch vehicle capability and the desire to maximize science return. Difficulties in accurately estimating the mass and performance of spacecraft based on their capabilities in the early phases of the design process have contributed to the need for costly mass reduction late in the design process. To help prevent such problems in the future, the process of estimating spacecraft mass has been analyzed and identified in algorithmic form, and software is currently being written to allow trained users to interface with these algorithms in an automated fashion. Such software will potentially lower the cost of preliminary spacecraft design, and the cost-effective ease with which alternative designs can be evaluated should produce better overall mission designs.
As an integral part of this effort, a data base of the appropriate parameters from historical spacecraft is being developed. The software will use the historical data to extrapolate future values of a given time dependent parameter. To obtain the mass moments of inertia and other mass properties, plans call for the current technique of using static graphics to create and modify the initial spacecraft configuration to be replaced by an interactive dynamic graphics configuration builder. The algorithms are to be tested for accuracy by being used to design specific historical spacecraft with the associated data for the spacecraft in question temporarily removed from the data base. The predicted results will then be compared to the actual results. The algorithms developed for mass estimation were found to be part of an algorithmic approach to spacecraft design synthesis that could also provide improved estimates of cost and various other parameters. Future expansions of this work promise to automate the entire conceptual mission design process. Also, the rigorous definition of the spacecraft design process will provide a much needed basis for training and research in the technical discipline of spacecraft systems.