Paul T. Grogan

A flexible architecture and object-oriented model for space logistics simulation

This paper summarizes the motivation for and the resulting development of a flexible object-oriented software model for simulation and analysis of space exploration campaign logistics. The software model was designed to be applicable to several widely-varying use case scenarios including International Space St ation resupply, support for a long-term lunar outpost and global lunar exploration, and Martian exploration by human and robotic agents. The model includes analysis capability fo r exploration sustainability topics including reusability, reconfigurability, commonality, and repairability. Key additional features include modular demand models that are easily interchanged, element-level models for finegrained demand integration, and reconfigurable system operational states to dynamically change demand models. Other capabilities include generalized impulsive burn maneuvers, surface transportation, abstracted flight transportation, improved support for multidestination scenarios, and multi-user collaboration via online databases.

Space Logistics Modeling and Simulation Analysis using SpaceNet: Four Application Cases

The future of space exploration will not be limited to sortie-style missions to single destinations. Even in present exploration taking place at the International Space Station in low-Earth orbit, logistics is complicated by flights arriving from five launch sites on Earth. The future challenges of space logistics given complex campaigns of interconnected missions in deep space will require innovative tools to aid planning and conceptual design. This paper presents a modeling framework to evaluate the propulsive and logistics feasibility of space exploration from the macro-logistics perspective, which covers the delivery of elements and resources to support demands generated during exploration. The modeling framework is implemented in a versatile and unifying software tool, SpaceNet, for general space exploration scenario analysis. Four space exploration scenarios are presented as application cases to highlight the applicability of the framework across vastly different scenarios. The first case investigates the resupply of the International Space Station between 2010 and 2015 using 77 missions combining NASA, European Space Agency, Japanese Space Agency, Russian Space Agency, and commercial space transportation. The second case models a lunar outpost build-up consisting of 17 flights to achieve continuous human presence over eight years. The third case models and evaluates a conceptual sortie-style mission to a nearEarth object, 1999 AO10. Finally, the fourth case models a flexible path type human exploration in the vicinity of Mars using a combination of human and tele-operated exploration. Taken together these cases demonstrate the challenges and logistical requirements of future human space exploration campaigns during the period from 20102050 and illustrate the ability of SpaceNet to model and simulate the feasibility of meeting these requirements.

Matrix Methods for Optimal Manifesting of Multinode Space Exploration Systems

This paper presents matrix-based methods to determine optimal cargo manifests for supplying resources in a space exploration system. An exploration system consists of transports (both in-space and on-surface) and resource demands occurring during both transportation between nodes and exploration at nodes. Each transport is defined by origin and destination nodes, departure and arrival times, and a cargo capacity. Matrices represent cargo carried by transports, cargo used to satisfy demands, and cargo transferred to other transports. The resulting matrix formulation is equivalent to a network flow problem representing the transportation of resources through a time-expanded network. The formulation allows for evaluating general exploration system feasibility by determining if a solution exists to a linear program (LP). In addition to modeling the manifesting problem, a few metrics, such as the transport criticality index, are formulated to allow for analysis and comparisons. The proposed matrix manifest modeling methods are demonstrated with a notional lunar exploration exploration system comprised of 32 transports including 8 cargo and 9 crewed landings at a base at the Lunar South Pole and several surface excursions to Malapert Crater and Schrodinger Basin. It is found that carry-along and pre-positioning logistics strategies can yield different manifesting solutions in which transport criticality varies. For the specific scenario considered in this study, it is found that transport criticality is larger for a pre-positioning strategy (mean value of 3.02) as compared to a carry-along case (mean-value of 1.99).

Simulating a proactive ad-hoc network protocol for Federated Satellite Systems

Novel distributed space mission concepts such as fractionation and federation promise to transform the design and operations approach of future missions. These paradigms require robust communications networking among other technologies. For the first time this paper explores the specifics of communications network protocols to enable Federated Satellite Systems using an opportunistic resource exchange frame open to all kinds of missions. Within satellite federations, participant spacecraft trade resources on a voluntary basis open to collaborative and/or commercial returns. The heterogeneous, mobile, flexible and scalable environment of satellite federations requires networking technologies capable of handling autonomous node discovery and frequent link disruptions. This work leverages existing Mobile Ad-Hoc Networking techniques to propose an FSS network protocol concept making use of OSLR neighbor sensing and store-carry-and-forward BATMAN routing concepts combined with link availability assessments and predictive topology routing. The performance of this protocol is tested through a dedicated network simulator and the FSS simulation toolkit. Results show the benefits of using FSS under this protocol. For a LEO-based scenario, average content delivery latency is improved from 41 minutes to 3.7 minutes by full usage of federated network benefits. Intermediate scenarios, such as 50% time network usage, present an average latency of 18 minutes. The paper ends by highlighting conclusions and next steps for the development of space communications protocols suitable for FSS.

Multi-stakeholder interactive simulation for federated satellite systems

Federated satellite systems (FSS) are a new class of space-based systems which emphasize a distributed architecture. New information exchanging functions among FSS members enable data transportation, storage, and processing as on-orbit services. As a system-of-systems, however there are significant technical and social barriers to designing a FSS. To mitigate these challenges, this paper develops a multi-stakeholder interactive simulation for use in future design activities. An FSS simulation interface is defined using the High Level Architecture to include orbital and surface assets and associated transmitters, receivers, and signals for communication. Sample simulators (federates) using World Wind and Orekit open source libraries are applied in a prototype simulation (federation). The application case studies a conceptual FSS using the International Space Station (ISS) as a service platform to serve Earth-observing customers in sun-synchronous orbits (SSO). Results identify emergent effects between FSS members including favorable ISS power conditions and potential service bottlenecks to serving SSO customers.

Comparative Usability Study of Two Space Logistics Analysis Tools

Future space exploration missions and campaigns will require sophisticated tools to help plan and analyze logistics. To encourage their use, space logistics tools must be usable: a design concept encompassing terms such as efficiency, effectiveness, and satisfaction. This paper presents a usability study of two such tools: SpaceNet, a discrete event simulation tool and a comparable spreadsheet-based tool. The study follows a randomized orthogonal design having within-subjects evaluation of the two tools with 12 volunteer subjects (eight subjects with space backgrounds, four without). Each subject completed two sessions of testing, each with a 30-45 minute tutorial and a two-part space exploration scenario. The first part tests the creation a model to verify a simple uncrewed mission to lunar orbit. The second part tests the evaluation of an existing model to improve the effectiveness of a crewed mission to the lunar surface. The subjects completed a questionnaire after each session and a semi-structured interview following the second session. The study results indicate that the SpaceNet tool is more efficient for portions of the model creation task including modeling multi-burn transports and the spreadsheet tool is more effective for the model evaluation task. Qualitative evaluation indicates subjects liked the graphical nature and error-detection of the SpaceNet tool, but felt it took too long to edit information and appeared as a “black box.” Subjects liked the ability to view the entire model state within the spreadsheet tool, however were concerned with limited dynamic state feedback and underlying modeling assumptions. Future tools should combine the best features, including allowing modification of the entire model from a single interface, providing visibility of underlying logic, and integrated graphical and error-checking feedback.

The ISoS Modeling Framework for Infrastructure Systems Simulation

Strategic infrastructure design considers long-term and cross-sector objectives to meet societal needs. Designers rely on tools to mitigate limits on human perception and manage complex systems with high-performance requirements. This paper defines the infrastructure system-of-systems modeling framework for heterogeneous simulation models. It formally defines structural and behavioral templates and an interoperability interface using algebraic statements. Infrastructure elements are graph edges, which express functions via operational states. An interoperability interface defines requirements for resource exchanges across system model boundaries. An example application case demonstrates a model instance with 18 infrastructure elements in water, petroleum, electricity, and social system models. Results show flow validity constraint violations arise from acyclic and cyclic dependencies between models. Increasing the number of iterations per time step or shortening the time step reduces error at the cost of execution time.

Process-oriented evaluation of user interactions in integrated system analysis tools

When computer-based tools are used for analysis of complex systems, the design of user interactions and interfaces becomes an essential part of development that determines the overall quality. The objective of this study is to investigate the processes and results of user interactions with integrated analysis tools to synthesize design implications for future tool development. In this study, two space exploration logistics tools are compared in a controlled user experiment. Through a comparative usability analysis, this study evaluated user performance and perception to provide design implications for future integrated analysis tools. For a comprehensive evaluation, multiple methods were used for data collection, including observation, questionnaire and interview. In addition to a result-oriented performance analysis, a process-oriented approach was used for analyzing patterns in user behaviors and errors. Results are presented with reference to the related features embedded in the interfaces of the two tools. Based on the comparative results, synthesized design insights for hierarchical structure, model transparency, automation, and visualization and feedback are discussed for integrated analysis tools in general.

Interactive simulation games to assess federated satellite system concepts

Federated satellite systems (FSS) consist of heterogeneous spacecraft with opportunistic data services. FSS membership is based on voluntary participation by independent actors without the centralized control required for systems engineering methods. New approaches must be developed to identify and assess mechanisms and incentives for collaborative behaviors required in a FSS. Towards this goal, this paper develops an interactive tabletop board game to demonstrate a technical simulation model integrated inside a social decision-making activity. Although simplified in technical detail, the game achieves a level of realism by basing its structure and behavior on a logical model of FSS with hierarchical federation, federate, system, and subsystem constructs. A prototype game provides a physical form using a game board, mats, tokens, counters, and cards to represent key constructs. Play-testing sessions reveal insights regarding FSS including participation based on minimizing opportunity cost, legacy hardware as a barrier to participation, partnerships to overcome the initial actor problem, and frequent under-estimation of network complexity and robustness.

Infrastructure System Simulation Interoperability Using the High-Level Architecture

Infrastructure planners need new methods to exchange technical data in the pursuit of long-term and cross-sector objectives including sustainability. This paper demonstrates a method for infrastructure system simulation interoperability by applying the high-level architecture (HLA) to the infrastructure system of systems (ISoS) modeling framework. The ISoS considers time-aggregated simulations with iterative data exchange periods to resolve cyclic dependencies. Applying the HLA defines object models, operational agreements, federate implementations, and physical infrastructure required for a federated simulation. An example demonstrates the method on a scenario with 18 infrastructure elements across water, electricity, petroleum, and social sectors as individual federates. The cost of interoperability arises from network latency, runtime infrastructure (RTI) overhead, and additional development effort. Results across several RTIs show that a distributed simulation requires 10–100 times longer executions than noninteroperable configurations. Analysis of source code shows that the HLA contributes about 1500 (56%) more software lines of code to implement federation object models and agreements. The value of interoperability arises from new capabilities provided by the HLA: physical distribution and independent control of constituent models. Conclusions describe a role for the HLA in model-based concept exploration during collaborative and interorganizational design activities with live human participation similar to its use for wargames.