Son of LEM: Lunar Lander Design Today
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A typical NASA project begins with a set of requirements that describe all the functions and performance a spacecraft must possess. A vehicle is then designed to satisfy those requirements. This process produces a design that initially attempts to meet all requirements equally, after which it is difficult to reduce capability if the vehicle is found to exceed mass or cost limitations. Our risk-informed design approach to Altair, the next lunar lander, is different. Our aim has been first to design a vehicle that meets a minimum set of requirements and then incrementally add functions and performance to that initial design. This approach means that the decision to accept each additional requirement will be informed by its individual impact on cost, performance, and risk. This process was derived in part from NASA Engineering Safety Center Report PR-06-108, Design, Development, Test, and Evaluation (DDT&E) Considerations for Safe and Reliable Human-Rated Spacecraft Systems. After defining the minimum functional vehicle in the first lander design-analysis cycle, the Altair team identified major risks that would affect the safety of the crew and the success of the mission in subsequent design cycles. The project team was able to identify the specific performance cost of each increment of crew safety and mission reliability added to the minimum spacecraft design. Residual spacecraft risks will continue to be evaluated as subsequent design cycles assess the performance, cost, and risk impacts of adding additional vehicle functionality and other factors, such as manufacturability and maintainability.
