Modular Building Blocks for Manned Spacecraft: A Case Study for Moon and Mars Landing Systems

摘要

A method is presented for the selection of optimal modular building blocks for platforming of manned Moon and Mars landing systems employing modularity on the subsystem level; platforming shall here be defined as the reuse of designs across different systems. The motivation for platforming is the need to reduce overall Moon and Mars exploration architecture lifecycle cost by lowering spacecraft development, test, and fixed production cost, and to provide flexibility in system design to accommodate changes in the exploration architecture. The fundamental idea is to compute the surplus in functional attributes generated by using particular building block (module) sizes, then relate the surplus to a cost function, and finally select the building block sizes with minimal additional cost. Results are presented for modular crew compartments, propellant tanks, and engines. The proposed method is potentially helpful for platforming decision-making, as well as subsystem technology selection in a broad class of engineering systems. Introduction On January 14, 2004, President George W. Bush proposed a new Vision for Space Exploration, which provides a framework for the United States’ manned and unmanned space activities in the next several decades. Among the primary objectives are a return of humans to the Moon no later than 2020, and a human Mars exploration program in the following decade [www.nasa.gov, 2004]. With the Vision for Space Exploration, a five-year budget plan, as well as a long-term budget forecast for NASA was published (see Figure 1). Both exhibit strong constraints on the resources available to NASA for the development of new exploration systems. A large part of the resources necessary for the development and acquisition of new spacecraft will be provided by retiring the Space Shuttle around 2010, and transitioning leadership of the ISS around 2016 / 17 (Figure 1). The cumulative resources available (see Figure 1) for exploration systems development from 2004 to 2020 are between around $40 billion (FY 2004) [www.nasa.gov, 2004]; assuming a funding level of about $10 billion (FY 2004) per year, another $100 billion will be available from 2021 to 2030. These resources are comparable to the $130 billion (FY 2004) estimated for the Apollo program from inception through 1969 [www.nasa.gov, 2004]. Although it might be argued that for the Apollo program technology had to be developed that is already available today, it nevertheless appears imperative to employ design reuse between Moon and Mars exploration systems to the maximum extent feasible in order to fulfill the Vision for Space Exploration’s goals within the budgetary constraints. Two separate point designs for Moon and Mars exploration systems seem to be unrealistic in terms of overall Moon and Mars exploration architecture lifecycle cost, even if they appear desirable from a technical performance perspective. Figure 1: Overview of the NASA budget forecast for the years 2004 to 2020 [President Bush, 2004] Figure 2 shows a hierarchical breakdown of Moon and Mars exploration systems from a landing system perspective. Although the classification of system hierarchy is naturally somewhat arbitrary, it is the authors’ opinion that two major approaches to incorporating design commonality into the exploration architecture can be readily identified in this top-level view: The first approach is reusing the exploration system point design (vehicles, propulsion stages) for Mars (Moon) to the maximum extent possible for Moon (Mars) exploration. This implies a higher level design commonality, and the vehicle or propulsion stage in question would then have to be developed for the most stringent use case (see Figure 2). 0 5,000 10,000 15,000 20,000 25,000 FY04 FY05 FY06 FY07 FY08 FY09 FY10 FY11 FY12 FY13 FY14 FY15 FY16 FY17 FY18 FY19 FY20 FY05 Budget (inflationary growth post 2009) Retire Shuttle Complete Station Research Object ives Crew Exploration Vehicle First Human Lunar Miss io