Modeling and simulation of permanent on-orbit servicing infrastructures dedicated to modularized earth-orbiting platforms

This research aims to quantify the responsiveness and cost-effectiveness of permanent on-orbit servicing (OOS) infrastructures providing services to multiple serviceable platforms in coplanar medium Earth orbit (MEO) and/or geostationary orbit (GEO). The customer satellites are assumed to be made of elementary units (EUs). EUs are small standardized structural units capable of aggregating with each other and gathering the key functions of a typical satellite within the size of a 6U cubesat. Two OOS infrastructures are modeled in this research. The first one, called “Without depot” (WoD), includes a launch vehicle and a robotic servicer. The second infrastructure, called “With Depot” (WD), includes a launch vehicle, a robotic servicer and an orbital depot of EUs. This research is divided in two parts. The first part quickly developed a Simulink-based event-driven simulation framework to compare the responsiveness of WoD and WD, and provide some insight into their respective cost-effectiveness. The metrics used to quantify responsiveness for this first study are the service completion rate and the average waiting time before an EU is replaced over a 10-year period of operation. It is shown that WD is more responsive thanWoD but is also likely to be more expensive to run. Based on this observation, the second part of this research developed a Python-based event-driven simulation framework capable of capturing a much larger trade space of the WD infrastructure than the Simulink framework does. The Python framework considers more accurate models and includes much more OOS design features, such as the number of servicers, more efficient service dispatch strategies and new space trajectories. For this second study, responsiveness is measured via the average working state of the population of customer satellites, which captures how well the satellites work based on three different failure severities and the number of failures. Cost-effectiveness is measured thanks to the average mass sent to orbit per year required to efficiently run the OOS infrastructures. It is first shown that there exist designs based on propellant optimal trajectories yielding similar levels of responsiveness as designs using Lambert-trajectory-based propellant-time-traded trajectories but at much lower costs. The second conclusion is that finding responsive and cost-effective OOS designs is not intuitive. This has to be done through an exhaustive exploration of the trade space of OOS, given the high number of design variables. This research si believed to be a critical milestone in the design of a responsive integrated space infrastructure dedicated to the development and prosperity of a new GEO/MEO economy

Framework for the design and operations of sustainable on-orbit servicing infrastructures dedicated to geosynchronous satellites

After being a concept for decades, the on-orbit servicing industry is finally taking off, with national space agencies and private organizations developing and planning soon-to-be-launched space infrastructures that will revolutionize the way humans operate in space. The advent of this new industry comes at a time when the geosynchronous orbit (GEO) satellite industry faces various pressures whether it be because of ageing fleets or increased competition from nimbler Low Earth Orbit (LEO) and Medium Earth Orbit (MEO) constellations. A new symbiotic relationship is emerging between early OOS players who seek customers and the GEO satellite operators who aim to revive the competitiveness of their fleets. The first OOS infrastructures will be simple ones, involving a few servicers offering a narrow set of services. These servicers will provide services to a few satellites before running out of propellant and getting discarded in a graveyard orbit or into the atmosphere. However, as technology matures and demand for on-orbit services increases, OOS infrastructures will become more versatile and involve additional elements, such as orbital depots, to enable the sustainable operations of a wide variety of servicers. Thus, planning OOS missions will involve not only finding the best route for every single servicer but also optimizing the in-space supply chain of commodities needed to support the long-term operations of the servicers and their client satellites. This dissertation presents an OOS planning framework that simultaneously computes the optimal route of the servicers and plans the in-space supply chain of the supporting commodities. The second chapter gives the background of OOS in GEO and the literature review for OOS planning relevant to the work presented in this thesis. The third chapter presents the mission scenario investigated in this work. The fourth chapter generalizes the Time-Expanded Generalized Multi Commodity Network Flow (TE-GMCNF) model used in recent state-of-the-art space logistics studies to accurately model the operations of the servicers across a network of customer satellites and orbital depots. The Rolling Horizon (RH) approach is adapted to the OOS context to properly model uncertain service demand arising from customer satellites. The fifth chapter generalizes the mathematical formulation at the core of the framework developed in chapter 4 to model all kinds of user-defined trajectories and servicer propulsion technologies, such as high-thrust, low-thrust, and/or multimodal servicers. (Multimodal servicers are defined to be equipped with both high-thrust and low-thrust engines.) An assumption inherent to chapter 4 and chapter 5 is that the nodes of the networks are all co-located along the same orbit. Chapter 6 relaxes this assumption by extending the framework developed in chapter 4 through the computation of the relative dynamics of network nodes distributed across orbits of various shapes and orientations. Thus, chapter 6, unlike chapter 4 and chapter 5, optimizes the operations of OOS infrastructures over a network with time-varying arc costs.Ph.D

Multi-Fidelity Space Mission Planning and Infrastructure Design Framework for Space Resource Logistics

To build a sustainable and affordable space transportation system for human space exploration, the design and deployment of space infrastructures are critical; one attractive and promising infrastructure system is the in-situ resource utilization (ISRU) system. The design analysis and trade studies for ISRU systems require the consideration of not only the design of the ISRU plant itself but also other infrastructure systems (e.g., storage, power) and various ISRU architecture options (e.g., resource, location, technology). This paper proposes a system-level space infrastructure and its logistics design optimization framework to perform architecture trade studies. A new space infrastructure logistics optimization problem formulation is proposed that considers infrastructure subsystems' internal interactions and their external synergistic effects with space logistics simultaneously. Since the full-size version of this proposed problem formulation can be computationally prohibitive, a new multi-fidelity optimization formulation is developed by varying the granularity of the commodity type definition over the network graph; this multi-fidelity formulation can find an approximation solution to the full-size problem computationally efficiently with little sacrifice in the solution quality. The proposed problem formulation and method are applied to a multi-mission lunar exploration campaign to demonstrate their values.Comment: 34 pages, 3 figures, presented at the AIAA Propulsion and Energy Forum 2019, submitted to the Journal of Spacecraft and Rocket

Framework for Modeling and Optimization of On-Orbit Servicing Operations under Demand Uncertainties

© AIAAThis paper develops a framework that models and optimizes the operations of complex on-orbit servicing infrastructures involving one or more servicers and orbital depots to provide multiple types of services to a fleet of geostationary satellites. The proposed method extends the state-of-the-art space logistics technique by addressing the unique challenges in on-orbit servicing applications and integrates it with the Rolling Horizon decision-making approach. The space logistics technique enables modeling of the on-orbit servicing logistical operations as a Mixed-Integer Linear Program whose optimal solutions can efficiently be found. The Rolling Horizon approach enables the assessment of the long-term value of an on-orbit servicing infrastructure by accounting for the uncertain service needs that arise over time among the geostationary satellites. Two case studies successfully demonstrate the effectiveness of the framework for 1) short-term operational scheduling and 2) long-term strategic decision making for on-orbit servicing architectures under diverse market conditions.This work is supported by the Defense Advanced Research Project Agency Young Faculty Award D19AP00127

Integrated In-Situ Resource Utilization System Design and Logistics for Mars Exploration

© 2020 IAA. Published by Elsevier Ltd.This paper develops an interdisciplinary space architecture optimization framework to analyze the tradeoff on in-situ resource utilization options, identify technology gaps, evaluate the benefits of in-situ resource utilization, and optimize the design of infrastructure for Mars human space exploration scenarios and mission profiles. It performs trade studies from the perspective of space logistics, which takes into account the interplanetary transportation, infrastructure deployment, in-situ resource utilization system operation, and logistics of the produced resources. Our method considers space architecture design and operation from the subsystem level to capture the coupling between in-situ resource utilization technologies and in-space architecture elements for space resource logistics. A case study involving a multi-mission human Mars exploration campaign is performed to evaluate the effectiveness of existing and proposed in-situ resource utilization technology concepts and system designs. The results can provide us with a better understanding of the benefits and costs of different in-situ resource utilization technologies for interplanetary space transportation. A sensitivity analysis is also conducted to understand the impacts of lunar and near-Earth-object’s in-situ resource utilization systems on Mars missions. The results of this analysis can help decision-makers determine and optimize the roadmap for in-situ resource utilization technology development.This material is partially based upon work supported by the funding from NASA NextSTEP program (80NSSC18P3418) awarded to the University of Illinois at Urbana-Champaign, where this work was initiated

On-Orbit Servicing Optimization Framework with High- and Low-Thrust Propulsion Tradeoff

© AIAAThis paper proposes an on-orbit servicing logistics optimization framework capable of performing the short-term operational scheduling and long-term strategic planning of sustainable servicing infrastructures that involve high-thrust, low-thrust, and/or multimodal servicers supported by orbital depots. The proposed framework generalizes the state-of-the-art on-orbit servicing logistics optimization method by incorporating user-defined trajectory models and optimizing the logistics operations with the propulsion technology and trajectory tradeoff in consideration. Mixed-integer linear programming is leveraged to find the optimal operations of the servicers over a given period, whereas the rolling horizon approach is used to consider a long time horizon accounting for the uncertainties in service demand. Several analyses are carried out to demonstrate the value of the proposed framework in automatically trading off the high- and low-thrust propulsion systems for both short-term operational scheduling and long-term strategic planning of on-orbit servicing infrastructures.This work is supported by the Defense Advanced Research Project Agency Young Faculty Award D19AP00127

Space architecture design for commercial suitability: A case study in in-situ resource utilization systems

© 2020 IAA. Published by Elsevier Ltd.Space Agencies are increasingly interested in stimulating non-traditional players to participate more broadly in the space enterprise. Historically, high barriers to entry in the space market have included challenges of working with the government customer and high technical and financial risks associated with the complexity of space exploration. More recently, agencies have used inducements (e.g., new contracting mechanisms, access to testing facilities) to mitigate these barriers. While these efforts mainly focused on reducing barriers to participation in existing exploration architectures, this paper explores the viability of an alternative strategy. Instead of providing inducements, which essentially subsidize participation, we propose a new strategy for space agencies to treat “commercial suitability” as another “-ility” and make it an explicit criterion of the initial architecture selection. This can be an effective option when multiple equivalent architectures (as evaluated against traditional cost, schedule, and performance measures) differ on their “commercial suitability.” As a proof-of-concept for this strategy, we develop a case study with lunar in-situ resource utilization plant systems as a basis for comparing the architectures with dedicated mass-wise optimal design (selected using traditional architecting strategies) vs. standardized mass-produced modular ISRU (selected using commercially-suitable strategies). The results show that architecture selection that considers commercial suitability upfront can achieve increased commercial participation without compromising cost performance compared with the baseline architecture. This serves as an existence proof for the potential value of this new strategy.This material is partially based upon work supported by the funding from NASA (80NSSC17K0329) awarded to the University of Illinois and George Washington University, where this work was initiated

Semi-analytical model for design and analysis of on-orbit servicing architecture

Robotic on-orbit servicing (OOS) is expected to be a key technology and concept for future sustainable space exploration. This paper develops a semi-analytical model for OOS systems analysis, responding to the growing needs and ongoing trend of robotic OOS. An OOS infrastructure system is considered whose goal is to provide responsive services to the random failures of a set of customer modular satellites distributed in space (e.g., at the geosynchronous equatorial orbit). The considered OOS architecture is comprised of a servicer that travels and provides module-replacement services to the customer satellites, an on-orbit depot to store the spares, and a series of launch vehicles to replenish the depot. The OOS system performance is analyzed by evaluating the mean waiting time before service completion for a given failure and its relationship with the depot capacity. Leveraging the queueing theory and inventory management methods, the developed semi-analytical model is capable of analyzing the OOS system performance without relying on computationally costly simulations. The effectiveness of the proposed model is demonstrated using a case study compared with simulation results. This paper is expected to provide a critical step to push the research frontier of analytical/semi-analytical models development for complex space systems design.Comment: 21 pages, 8 figures, Accepted by Journal of Spacecraft and Rocket