Between multiple space agencies sending crewed missions to the Moon and commercial entities looking to commercialize Low Earth Orbit (LEO), space exploration is set to experience a major boom. This will include regular missions to cislunar space, the creation of permanent infrastructure on and around the Moon, and increased payload deliveries by commercial providers. As a result, engineering processes and mission architectures must incorporate innovative technologies to ensure cost-efficiency and sustainability.
Currently, many technologies are being explored by the commercial space sector, but not by leading space agencies like NASA. In a recent paper, a team of engineers from Purdue University describes how this gap could be addressed using video games that offer players a high degree of freedom and creativity (aka. sandbox games). Specifically, they note how the popular Kerbal Space Program (KSP) video game and its mods could be integrated with higher-fidelity systems and astrodynamics models to assist with early-mission development.
Rodrigo N. Schmitt, the study’s lead author, is a Doctoral Research Assistant from the School of Aeronautics & Astronautics (SAA) at Purdue University. He was joined by Moacir F. Becker, a Space Systems Engineer and the Coordinator of the Satellite Morazán Project at Purdue; Daniel DeLaurentis, the Bruce Reese Professor of Aeronautics and Astronautics at Purdue; and Kenshiro Oguri, an Assistant Professor with the SAA at Purdue. The paper detailing their proposal was recently published in Acta Astronautica.
KSP & Mission Design
The most significant development in spaceflight in the past twenty years has been the development of reusable rockets. Similarly, On-Orbit Refueling (OOR) is critical for achieving sustainability in cislunar missions. In this respect, SpaceX stands out as the leading innovator in the development of reusable launch vehicles (the Falcon 9 and Falcon Heavy). Their ongoing development of the Starship will also rely on orbital refueling to provide NASA’s Artemis Program with a crucial Human Landing System (HLS) for the Artemis III and IV missions.
As missions to cislunar space become more frequent, space programs must incorporate these and other innovative concepts into their planning and design processes. NASA has contracted with SpaceX, Blue Origin, and other contractors to develop key elements like reusable landing systems. However, even though reusability and OOR have been proposed since the 1960s, there remains a significant lack of space mission planning incorporating these technologies.
Nevertheless, reusable systems and the ability to refuel in cislunar space have always been part of NASA’s “Moon to Mars” mission architecture. As NASA describes the program:
“Our sustainable Moon to Mars exploration approach is reusable and repeatable. Over the next decade, we will build an open exploration architecture with as many capabilities that can be replicated as possible for missions to Mars. The Moon is a testbed for Mars. It provides an opportunity to demonstrate new technologies that could help build self-sustaining outposts off Earth.”
As part of his research, Schmitt has used KSP with the Realism Overhaul mod to generate design concepts and conducted simulations of the Artemis spacecraft. As he and his colleagues explained, the Program has been increasingly recognized as a valuable tool for education and research. Its utility was highlighted in a 2020 study by Andrei V. Chernenkii, “Using the Aerospace Modeling Simulator in the Educational Process,” who extolled KSP as an education tool for teaching spacecraft design principles and orbital mechanics.
Another study they cite is the 2022 study by Dachowicz et al., “Mission Engineering and Design Using Real-Time Strategy Games: An Explainable AI Approach,” which demonstrated how Real-Time Strategy (RTS) games and an Explainable AI (XAI) approach could be used for mission engineering and design. While KSP had already begun collaborating with NASA and SpaceX to create programs for education in aerospace, engineering, and science, KSP has not yet been extensively used for the representation and analysis of mission architectures.
Mission Simulation
As the team explained, KSP could assist designers and planners during the early stages of mission development, allowing them to explore various architectural options simultaneously. The NASA Systems Engineering Project Life Cycle divides this early phase into Pre-Phase A: Concept Studies and Phase A: Concept and Technology Development. For their case study, Schmitt and his colleagues used KSP for a Pre-Phase A design (inspired by the Artemis V mission profile) to examine the interplay between depot location, capacity, and mission architecture.
Several mods were used to augment their simulations’ realism and engineering capabilities. To address the lack of high-fidelity physics required for the final mission analysis, Schmitt and his team introduced a framework with three-body astrodynamics and graphical representations of space systems. This consisted of the Circular Restricted 3 Body Problem (CR3BP) and Cislunar Object-Oriented Systems Modeling and Integration Code (COSMIC).
CR3BP models the gravitational forces between the Earth, Moon, and spacecraft. In contrast, COSMOS models the entities and operations in missions to cislunar space, including launch vehicles, propellant depots, and various sub-systems. They chose the Artemis V mission because of its objectives, which include integrating an OOR module with the Lunar Gateway. Known as Lunar View, this ESA-provided refueling module will be the primary propellant depot and refuel reusable landers between missions.
When paired with propellant production facilities on the lunar surface, this will lessen dependency on Earth-launched fuel. Like the Artemis V mission, the team’s simulations consisted of a Launch Element (LE), a Transfer Element (TE), a Lunar Landing Element (LA), and a Refueling Element (RE). In this case, the LE is NASA’s Space Launch System (SLS), the TE is the Orion spacecraft, while the LA and RE were subject to many considerations. The simulated mission was also broken down into five phases, including:
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Orbit Insertion: The mission begins with the launch of the SLS and the Orion’s insertion into LEO.
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Transfer to Halo: Following orbit insertion, the Orion conducts a lunar injection maneuver to rendezvous with the Gateway in halo orbit. This state includes the deployment of the Lunar View and establishes the Gateway as a staging point for lunar and cislunar operations.
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Descent to Lunar Surface: The crew transfers to the Blue Moon lander, which descends from the Gateway to the lunar surface so exploration activities can begin.
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Ascent to Halo Orbit: After completing lunar surface operations, the crew ascends aboard the Blue Moon lander to the Gateway, which is refueled for future missions.
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Earth Reentry: The final phase involves the crew returning to Earth aboard the Orion, which will reenter Earth’s atmosphere and land, completing the mission.
The team simulated all aspects of the cislunar mission using KSP paired with the CR3BP and COSMIC models, starting with the design of the SLS and Orion. They further considered the design of the propellant depot, which included three options: the Lunar View, a Modular Variant, and an Extended Variant. Three designs were similarly considered for the lander element, including the Lockheed Martin HLS, the Blue Moon HLS, and the Dynetics HLS. They also simulated three variations on the Halo Orbit for the Lunar Gateway and the types of transfer maneuvers. As they explained:
“A total of 10,000 points were used for each simulation to ensure a comprehensive exploration of the design space. The LatinHypercubeGenerator class from the OpenMDAO Python library was selected for its efficiency in sampling high-dimensional spaces and ensuring that the entire design space is adequately covered. The primary objectives of this study were to analyze the impact of different design and architectural choices on mission cost, complexity, and performance. Cost is measured in KSP currency, complexity is a non-dimensional metric derived from graph energy, and performance is quantified by the [Time of Flight] in hours.”
Results
The team’s results provided several insights into the utility of sandbox games as strategic design tools. The RO and kRPC mods were also highlighted for their importance. Whereas the RO mod offers a flexible and interactive environment for rapid prototyping and iterative design, the kRPC mod allows users to extract detailed data directly from the game environment—i.e., propulsion, mass, and delta-v. They also note how the game’s direct interaction allows designers to quickly adjust and test different configurations, making it useful for early concept studies. As they summarized:
“[T]he results demonstrate the effectiveness of leveraging game-based simulation platforms for mission design and evaluation, offering a strategic tool for stakeholders in the decision-making process. The extensibility of the presented framework also makes it suitable for a wide range of future space missions, potentially toward reducing the cost and increasing the feasibility of cislunar exploration.”
Their study also demonstrates the integration of a sandbox game with advanced astrodynamics and systems models. Combining KSP’s intuitive design environment with modifications to increase realism, the framework they created assists work in the rapid iterative design, prototyping, and preliminary analysis stages of mission development. Furthermore, promising architectures identified through this process can be refined using more detailed simulations.
In the future, Schmitt and his team hope to expand the framework of their design space to incorporate more advanced space systems and technologies. In particular, they will focus on optimization methods and the potential of SpaceX’s Starship for cislunar missions. This will include on-orbit refueling, the design of which is available through KSP mods like the Starship Expansion Project.
Further Reading: Acta Astronautica
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