Introduction
The space race is becoming ever more competitive as nations and organizations vie for a piece of the stars. In 2021, the National University of Defense Technology and the Xi’an Satellite Control Center took this to the next level with the 11th edition of the Global Trajectory Optimization Competition (GTOC11). Tasked with the challenge of building a Dyson Sphere – a theoretical mega-structure that encircles a star with platforms orbiting in a tight formation - 94 teams from across the world registered for the competition. In this article, we take a look at the selection of the problem, the design process and the results of the competition. Let's explore how the teams tackled this immense challenge and find out who came out on top.
Exploring the Hypothetical Stellar Civilisation of GTOC11: A Dyson Sphere for the Future
The GTOC11 problem, presented by the ESA and JPL, was designed to bridge the gap between the GTOC9 and GTOCX problems. GTOC9, entitled 'The Kessler Run', imagined a future human civilization in 2060 tasked with the removal of dangerous debris chains to prevent a Kessler Syndrome. GTOCX, 'Settlers of the Galaxy', imagined a future civilisation tasked with designing trajectories of interstellar vessels to travel and settle throughout the galaxy. GTOC11 is a hypothetical futuristic stellar civilisation, where a Dyson sphere could tap the majority of a star's energy.
Exploring the GTOC11 Problem: An Interesting Challenge for Human Minds to Solve
The Kardashev scale is a measure of a civilization's technological advancement, and it is used to distinguish between type-I, type-II, and type-III civilizations. Type-I civilizations are planetary civilizations, while type-II and type-III civilizations are stellar and galactic civilizations, respectively. Inspired by Freeman Dyson's thought experiment, the GTOC11 problem bridges the gap between the GTOC9 and GTOCX problems by envisioning the design of a Dyson ring, consisting of 12 stations uniformly distributed along a circular orbit around the Sun.
The building aspect of the Dyson ring was not discussed in Dyson's original work, so the GTOC11 problem focuses on the astrodynamics involved in material collection and transfer to the desired orbit. To achieve this, an ensemble of 10 mother ships is launched from the Earth toward specific asteroids to collect the necessary construction materials. This is done with the help of a multifunctional asteroid transfer device (ATD), which utilizes the asteroid materials as propellants to provide continuous thrust, pushing parts of asteroids toward the construction orbit.
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This creates a complex trajectory optimization problem due to the trade-offs during combinatorial flybys to target asteroids and during asteroid transfers to the construction orbit and their distribution among the stations. The remainder of the paper provides a mathematical definition of the problem, a preliminary problem analysis, an analysis of the competition results, and a discussion of the verification of the solutions.
To conclude, the GTOC11 problem is an interesting challenge that requires a combination of creativity, problem-solving skills, and an understanding of astrodynamics. It is a great example of the potential of space exploration and the power of the human mind to create innovative solutions.
Competition results
A total of 25 teams participated, and the top 20 teams and their performance indexes were presented in Table 1. The Tsinghua University joint team was the championship, reaching 1.1 AU with 388 asteroids, as shown in the picture. The table shows that the amount of transferred asteroids and the minima mass had a direct correlation with the performance index, as long as the semimajor axis of the Dyson ring stayed the same or approximately the same. The Tsinghua University team was the champion not only due to their performance index, but also due to their superior asteroids and minima mass. What's more, it was revealed that most teams determined the semimajor axis by testing and estimating an approximate value, while only a few teams, such as the rank 2, 14, and 15 teams, determined it through an optimization method. This indicates that it is difficult to perform an overall optimization to determine the best value of the semimajor axis. Thus, the results of the competition indicate that the amount of transferred asteroids and the minima mass have a significant impact on the performance index, as long as the semimajor axis remains
Conclusion
The GTOC11 problem was a unique opportunity for participants to develop a precursor to a Dyson sphere. To meet the challenge, teams had to plan and schedule space trajectories, select and distribute targets, and employ multiple optimization techniques to achieve the objectives of the problem. The teams developed several new methods to overcome the challenging and multifaceted problem. Many of the original objectives were achieved, although the construction of a Dyson sphere at the scale of GTOC11 is still out of reach. Nevertheless, the methods developed for GTOC11 can provide a useful reference for the mission design of building a Dyson sphere when the necessary space technologies are available for future applications like asteroid mining and solar-powered satellites.
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