4. Lunar Architecture 4.1 Summary and Recommendations As defined by the Exploration Systems Architecture Study (ESAS), the lunar architecture is a combination of the lunar “mission mode,” the assignment of functionality to flight elements, and the definition of the activities to be performed on the lunar surface. The trade space for the lunar “mission mode,” or approach to performing the crewed lunar missions, was limited to the cislunar space and Earth-orbital staging locations, the lunar surface activities duration and location, and the lunar abort/return strategies. The lunar mission mode analysis is detailed in Section 4.2, Lunar Mission Mode. Surface activities, including those performed on sortie- and outpost-duration missions, are detailed in Section 4.3, Lunar Surface Activities, along with a discussion of the deployment of the outpost itself. The mission mode analysis was built around a matrix of lunar- and Earth-staging nodes. Lunar-staging locations initially considered included the Earth-Moon L1 libration point, Low Lunar Orbit (LLO), and the lunar surface. Earth-orbital staging locations considered included due-east Low Earth Orbits (LEOs), higher-inclination International Space Station (ISS) orbits, and raised apogee High Earth Orbits (HEOs). Cases that lack staging nodes (i.e., “direct” missions) in space and at Earth were also considered. This study addressed lunar surface duration and location variables (including latitude, longi- tude, and surface stay-time) and made an effort to preserve the option for full global landing site access. Abort strategies were also considered from the lunar vicinity. “Anytime return” from the lunar surface is a desirable option that was analyzed along with options for orbital and surface loiter. The duration, location, and centralization of lunar surface activities were analyzed by first determining the content of the science, resource utilization, Mars-forward technology demon- strations, and operational tests that could be performed during the lunar missions. The study team looked at high-priority landing sites and chose a reference site in order to further inves- tigate the operations at a permanent outpost. With the scientific and engineering activities defined, concept-level approaches for the deployment and buildup of the outpost were created. A comprehensive definition of lunar surface elements and infrastructure was not performed because development activities for lunar surface elements are still years in the future. There- fore, the ESAS team concentrated its recommendations on those elements that had the greatest impact on near-term decisions. 4. Lunar Architecture 75 The mission architecture decisions that most greatly affect near-term NASA development activities are mission mode, propulsion system types, and mission duration. The ESAS team recommends the use of an Earth Orbit Rendezvous-Lunar Orbit Rendezvous (EOR–LOR) mission mode. This mission mode, which can be executed with a combination of the launch of separate crew and cargo vehicles, was found to result in a Low Life Cycle Cost (LCC) and the highest crew safety and mission reliability combination. Further, the study found that pressure-fed Liquid Oxygen (LOX)/methane propulsion should be used for the lander ascent stage as well as the Crew Exploration Vehicle (CEV) Service Module (SM), which should be sized to perform the Trans-Earth Injection (TEI) propulsive maneuver for a lunar mission. The study also concluded that the lunar lander should use a LOX/hydrogen throttleable propulsion system for Lunar Orbit Insertion (LOI) and landing. The two-stage lander should include an airlock and be sized to support a 7-day surface mission with four crew members. 76 4. Lunar Architecture 4.2 Lunar Mission Mode The lunar mission mode is the fundamental lunar architecture decision that defines where space flight elements come together and what functions each of these elements perform. Mission mode analysis had its genesis early in the design of the Apollo Program, with notable NASA engineers and managers such as Wernher Von Braun, John Houbolt, Joe Shea, and Robert Seamans contributing to the decision to use LOR as the Apollo mission mode. This study built on the foundation of the Apollo decision but sought to question whether the LOR decision and overall Apollo mission approach were still valid, given new missions require- ments and technology. The ESAS team researched many of the Apollo lunar landing mode comparison studies as well as more recent studies performed by both NASA and industry. One study of interest, performed by a Massachusetts Institute of Technology (MIT)-Draper Laboratory team as part of a “Concept Exploration and Refinement” (CE&R) contract to NASA, suggested that the Apollo mission mode was no longer valid and that NASA should consider “direct return” modes for future human lunar missions. The ESAS team took special note of this study and sought to challenge all of the Apollo mission assumptions. 4.2.1 Previous Lunar Architecture Study Results Since its inception, NASA has conducted or sponsored numerous studies of human explo- ration beyond LEO. These studies have been used to understand requirements for human exploration of the Moon and Mars in the context of other space missions and Research and Development (R&D) programs. Each exploration architecture provides an end-to-end mission baseline against which other mission and technology concepts can be compared. The results from the architecture studies were used to: • Derive technology R&D plans; • Define and prioritize requirements for precursor robotic missions; • Define and prioritize flight experiments and human exploration mission elements, such as those involving the Space Shuttle, ISS, and other Space Transportation Systems (STSs); • Open a discussion with international partners in a manner that allows identification of participants’ potential interests in specialized aspects of the missions; and • Describe to the public, media, and Government stakeholders the feasible, long-term visions for space exploration. 4. Lunar Architecture 77 Each architecture study emphasized one or more critical aspects of human exploration in order to determine basic feasibility and technology needs. Examples of architectural areas of emphasis include: • Destination: Moon ↔ Mars ↔ Libration Points ↔ Asteroids; • System Reusability: Expendable ↔ Reusable; • Architecture Focus: Sorties ↔ Colonization; • Surface Mobility: Local ↔ Global; • Launch Vehicles (LVs): Existing ↔ New Heavy-Lift; • Transportation: Numerous stages and technologies traded; • LEO Assembly: None ↔ Extensive; • Transit Modes: Zero-gravity ↔ Artificial-gravity; • Surface Power: Solar ↔ Nuclear; • Crew Size: 4 ↔ 24; and • In Situ Resource Utilization (ISRU): None ↔ Extensive. The ESAS team extensively scrutinized the NASA studies that led to the Apollo Program, most notably studies to determine the shape of the Apollo capsule and the mode used for the Apollo missions. Additionally, the team reviewed the findings of human lunar and Mars mission studies performed over the past 15 years. A summary of these studies is shown in Table 4-1. Office of Exploration (OExP) - 1988 Case Studies First Lunar Outpost - 1993 Human Expedition to Phobos Early Lunar Resource Utilization - 1993 Human Expedition to Mars Human Lunar Return - 1996 Lunar Observatory Lunar Outpost to Early Mars Evolution Mars Exploration Missions Design Reference Mission Version 1.0 - 1994 Office of Exploration (OExP) - 1989 Case Studies Design Reference Mission Version 3.0 - 1997 Lunar Evolution Design Reference Mission Version 4.0 - 1998 Mars Evolution Mars Combo Lander (Johnson Space Center (JSC)) - 1999 Mars Expedition Dual Landers – 1999 NASA 90-Day Study - 1989 Decadal Planning Team (DPT)/NASA Exploration Team (NExT) - 2000–2002 Approach A - Moon as testbed for Mars missions Earth’s Neighborhood Architecture Approach B - Moon as testbed for early Mars missions Asteroid Missions Approach C - Moon as testbed for Mars Outposts Mars Short and Long Stay Approach D - Relaxed mission dates Exploration Blueprint - 2002 Approach E - Lunar outpost followed by Mars missions Space Architect - 2003 America at the Threshold - “The Synthesis Group” - 1991 Exploration Systems Mission Directorate (ESMD) 2004–2005 Mars Exploration Science Emphasis for the Moon and Mars The Moon to Stay and Mars Exploration Space Resource Utilization Table 4-1. Summary of Previous NASA Architecture Studies 78 4. Lunar Architecture 4.2.1.1 Summary of Previous Studies 4.2.1.1.1 Office of Exploration Case Studies (1988) In June 1987, the NASA Administrator established the Office of Exploration (OExP) in response to an urgent national need for a long-term goal to reenergize the U.S. civilian space program. The OExP originated as a result of two significant assessments conducted prior to its creation. In 1986, the National Commission on Space, as appointed by the President and charged by the Congress, formulated a bold agenda to carry America’s civilian space enter- prise into the 21st century (number 1 in Section 4.5, Endnotes). Later that year, the NASA Administrator asked scientist and astronaut Sally Ride to lead a task force to look at potential long-range goals of the U.S. civilian space program. The subsequent task force report, “Lead- ership and America’s Future in Space,” (number 2 in Section 4.5, Endnotes) outlined four initiatives which included both human and robotic exploration of the solar system. In response to the task force report, the OExP conducted