Wilfried K. Hofstetter

Affordable Human Moon and Mars Exploration through Hardware Commonality

The Vision for Space Exploration calls for the safe, affordable, and sustainable human exploration of the Moon and Mars. In order to achieve exploration affordability and sustainability, the Mars -back approach was developed. The fundamental principle of the Mars -back approach is that the syste m elements used for lunar exploration are a subset (in terms of design) of those used for Mars exploration; thereby the lunar exploration hardware is directly relevant to the exploration of Mars. After systematic qualitative and quantitative analysis of ov er 1000 lunar and over 1000 Mars exploration architectures using a discrete event simulation tool, two architectures were chosen for further analysis based on overall mission mass, mission risk, and cost: a direct return architecture for lunar exploration, and an architecture similar in concept to the 1993 NASA Mars Design Reference Mission for conjunction -class Mars exploration. Employing the Mars -back approach, the Mars exploration hardware can enable a crewed lunar direct return architecture along with o ne way cargo -delivery capability, such as for a long -duration surface habitat, without the need for additional hardware development. Common system elements include the CEV for short term habitation and Earth entry, long -term in -space and planetary surface habitats, and propulsion stages for Earth departure, deep -space maneuvers, and planetary descent / ascent. Commonality was introduced through design for the most stressing case, typically Mars, when requirements were similar, and through modular, extensibl e solutions when requirements differed more widely. Based on the commonality concept, a hardware development roadmap was laid out for phased development of the hardware; each phase provides increasing mission capability. Hardware development with commonali ty eliminates the need for any significant “development gap” between lunar and Mars exploration missions. The development approach ensures that technology and hardware development for lunar missions is directly relevant to Mars exploration. Also, extensive testing of Mars hardware can be carried out during long -stay lunar missions, thereby increasing operational experience with the equipment to be used for Mars missions and reducing Mars mission risk. As identical hardware is used, lunar missions could stil l be executed during Mars exploration because the production and assembly lines would still be running. Most importantly, the overall lifecycle cost for exploration of the Moon and Mars is significantly reduced by limiting the amount of hardware that must be developed. The drawback of Mars -back commonality is a certain non -optimality in the common system design which leads to increased system dry and wet mass and therefore to a potential increase in recurring cost, mainly in launch and production. Quantitat ive analysis of this commonality penalty shows a modest growth of Initial Mass in LEO, which appears acceptable when set against the significant savings in overall lifecycle cost that would be achieved.

Selection and Technology Evaluation of Moon/Mars Transportation Architectures

Our purpose is to evaluate and select from a large family of Moon-Mars transportation architectures by integrating a general architecture network model with vehicle computational modules. A complete tradespace of 1162 unique transportation architectures for human missions to the Moon and to Mars provided by an Object Process Network based architecture generator has been interpreted and integrated with subsystem models. Three Mars and five lunar architectures are downselected based on total launch mass to LEO, risk, complexity and further criteria. Sensitivity analysis and trades of mass for dierent advanced propulsion types and in-situ propellant production availability are presented.

Design of a Platform-based Surface Mobility System for Human Space Exploration

This paper presents results from an analysis and conceptual design of a manned planetary surface mobility systems platform for use at human exploration sites on the Moon, Mars, and in Earth analog environments such as Devon Island in the Canadian high arctic. A comprehensive analysis of architectural options for pressurized and unpressurized surface mobility systems was carried out based on a set of Design Reference Missions and associated requirements. The analysis resulted in the selection of an innovative surface mobility architecture consisting of 2-person unpressurized rovers and 2-person campers, selfpropelled pressurized vehicles which are guided by unpressurized rovers. This architecture was selected because of superior performance and cost characteristics; however, it also enables more flexible surface exploration operations than architecture based on pressurized rovers because of the ability to leave the camper behind at a distance from a base. For the unpressurized rovers and campers a conceptual design was carried out for the Earth, Moon, and Mars environments using a terrain-vehicle-model taking into account the detailed interaction of the planetary surfaces and the suspension / drive system. Analysis of commonality opportunities between the Earth, Moon, and Mars versions suggests that the surface mobility platform could include the suspensions of the unpressurized rover and the camper, internal outfitting of the camper, energy storage and drive units, as well as avionics and communications systems. The platform approach may lead to significant cost and risk reduction over the lifecycle of the exploration program.

Analysis of Human Lunar Outpost Strategies and Architectures

Recently published plans for a human lunar exploration campaign as part of the Vision for Space Exploration focus on the establishment of an outpost at the lunar South Pole with the intent of permanent or near-permanent inhabitation. This paper investigates potential lunar exploration alternatives to this strategy based on a small number of so-called campaign elements which could be placed end-to-end to build a lunar exploration campaign. Results indicate that special consideration should be given to campaign strategies that include what we term “intermediate outpost” missions, as such missions can provide significant value for Mars preparation early in the campaign and under certain conditions may obviate the need for a long-term outpost altogether. The paper also includes conceptual design analysis for technical lunar surface architectures based either on a full-size habitat pre-integrated on Earth or on a habitat that is assembled on the lunar surface out of multiple modules. Comparison of campaign performance shows that the differences between the technical surface architectures are small compared to the differences in campaign strategy; technical architectures therefore need to be compared on cost and risk. Based on cost and risk considerations, a lunar surface architecture with a full-size habitat pre-integrated on Earth is preferred. In general, the lunar surface system architecture should be designed to support all or most of the campaign elements in order to provide flexibility and robustness to programmatic change over the next decade before the actual implementation of the campaign.

Extending NASA's Exploration Systems Architecture towards Long-term Crewed Moon and Mars Operations

This paper presents a baseline strategy for extending lunar crew transportation system operations as outlined in NASA’s Exploration Systems Architecture Study (ESAS) report towards longer-stay lunar surface operations and conjunction class Mars missions. The analysis of options for commonality between initial lunar sortie operations and later Moon and Mars exploration missions is essential for reducing life-cycle cost and providing lowinvestment / high-return options for extending exploration capabilities soon after the 7 human lunar landing. The analysis is also intended to inform the development of the human lunar lander and other exploration system elements by identifying enabling requirements for extension of the lunar crew transportation system. The baseline strategy outlined in this paper was generated using a three-step process: the analysis of exploration objectives and scenarios, identification of functional and operational extension options, and the conceptual design of a set of preferred extension options. Extension options include (but are not limited to) the use of the human lunar lander as outpost for extended stays, and Mars crew transportation using evolved Crew Exploration Vehicle (CEV) and human lander crew compartments. Although the results presented in this paper are based on the ESAS elements, the conclusions drawn in this paper are generally applicable provided the same lunar transportation mode (lunar orbit rendezvous) is used.

Opening Space for Humanity - Applying Open Source Concepts to Human Space Activities

With the open source paradigm gaining traction in a variety of fields, the question arises as to in what ways open source concepts can be applied towards space development endeavors. This paper examines the potential for applying open source towards human space activities. We find that open source holds much promise for benefiting space development endeavors. Open source can clearly be applied in the space software area, including modeling and design tools, testing, ground software, and flight software. The paradigm can, however, be extended beyond software, in areas such as system design, compilation of reference data, system verification & validation procedures and associated results, and relevant education and training materials. Many individuals around the world are highly motivated towards contributing to the expansion of humanity into space. Applying open source principles towards space activities can provide them with a means of doing so. A new organization, DevelopSpace, has been created to aid in the advancement of such activities, focused on building up the technical foundations for human space activities, and doing so in an open manner.

Interplanetary Transfer Vehicle Concepts for Near-Term Human Exploration Missions beyond Low Earth Orbit

This paper presents an analysis of architecture alternatives for carrying out near-term human missions beyond Low Earth Orbit (LEO), in particular missions to Near Earth Objects (NEOs). A minimalist approach to near-term human missions beyond LEO was identified based on the development of an Orion-like vehicle providing Earth entry and deep space propulsion (development could be either lead by government or by a commercial entity), a human-rated heavy-lift launch vehicle capable of launching 72 mt or more to LEO and accommodating payloads of up to 35 m height and up to 5 m diameter, a habitation module similar in size to a lunar lander crew compartment, and an adapted Centaur V1 upper stages from existing commercial launch vehicles. This minimalist architecture would enable lunar flyby, lunar orbit, and Sun-Earth Lagrange point missions with a single launch, and missions to Geostationary Earth Orbit (GEO) and to NEOs with two launches. Based on publicly available estimates of development schedules and cost, for example for shuttlederived launch vehicles (as provided to the Augustine Committee in 2009), such a minimalist architecture should be available 5-7 years after start of development at current funding levels. While being minimalist with regard to near-term availability, this approach would also provide important elements which are forward-extensible to human Mars missions, such as the Orion crew module, the human-rated heavy-lift launch vehicle, and possibly the habitation module.

A Minimalist Approach to Crewed Lunar Exploration

NASA’s current plans for returning to the Moon include the build-up of a lunar outpost at the South Pole. Proposed architectures utilize a complex process of offloading, transporting, and assembling the major pressurized elements of outpost in-situ. This process has significant operational and developmental costs and risks associated with it. To “sidestep” the technical challenges of developing the required hardware and incurring the operational risks of assembly, the authors present an alternative lunar outpost architecture that focuses on transporting the crew and supplies across the lunar surface instead of transporting and assembling the habitation modules (also called the “non-connected architecture”). This architecture is made feasible by the use of the Small Pressurized Rovers (SPRs) that are included in the campaign for long-distance surface exploration. This paper includes discussion of the required redesign of the subsystems of the major elements in the architecture (habitat, laboratory, and Pressurized Logistics Module) that both make a “nonconnected architecture” feasible as well as optimize the elements for the new architecture. The programmatic details involving cost, schedule, and risk are discussed in relative terms to NASA’s proposed architecture.

Architectures for an Integrated Human Space Exploration Program

Long-duration missions to the surface of Mars are generally regarded as the ultimate goal for the human spaceflight program in the foreseeable future. In order to make such missions a reality, significant advances in various capabilities need to be achieved. Such advancements will require a sustained, long-term space program to provide steady funding over several decades. It is unlikely that any space agency would be capable of such funding without interim returns on investment through scientific investigations or high-visibility public events. Therefore, it is necessary to carry out missions to other interesting locations in the inner solar system before a mission to the surface of Mars is achieved. This paper describes an approach for developing a sustainable human spaceflight program by investigating the relationships between the capabilities needed for a Mars surface mission and the capabilities required for other destinations for human spaceflight. Nine critical capabilities ranging from long-duration surface habitation to aero-entry and aero-capture technologies are outlined based on a review of NASA’s Mars Design Reference Architecture 5.0. Six destinations which can be visited before reaching the surface of Mars such as Near Earth Objects and the lunar surface are also outlined. By investigating the relationship between the capabilities required for a Mars surface mission and the capabilities required for each mission type, feasible integrated human spaceflight architectures can be constructed. The two main classes of these programs involve developing the capabilities required for Mars which support advanced in-space missions, such as Mars flyby missions, before developing the capabilities to support lunar surface missions and vice-versa.

Analysis of Architectures for Long-Range Crewed Moon and Mars Surface Mobility

This paper presents an architecture-level analysis of a set of planetary surface mobility concepts for human exploration. The motivation for the analysis is two-fold: to gain an understanding of the limitations of different architectures for extended-range surface mobility and to assess the feasibility of global-scale exploration from a single site to reduce the requirements for surface infrastructure emplacement. Four architectural concepts are investigated, including unpressurized and pressurized mobility options. The primary metric for assessing system performance is the ideal exploration radius achievable based on operational and technological constraints, i.e. the exploration radius the system could nominally achieve on a smooth planetary sphere. The analysis results indicate that for both the lunar and Martian environment, significant exploration radii on the order of several 100 km can be achieved from a single location provided that two independent pressurized vehicles are available, and that pre-positioning of supplies and in-situ generation of power in the field is possible. From the perspective of accessible surface area, this makes a single base on a planetary surface superior to a sequence of missions to separate sites. The analysis also indicates that unpressurized mobility can achieve exploration radii on the order of several 10 km when using two independent vehicles and high driving speeds, i.e. the accessible exploration radius of an unpressurized mobility system can increase significantly due to familiarization with the terrain and resulting increased driving speeds. The paper is concluded by a summary of findings and suggestions for future work.