Why Managing a City Is Like Designing a Spaceship: Exploring Complex Systems

Recent coverage of a question posed to Yuan Jiajun, a former chief of China's Shenzhou spacecraft programs and current Chongqing Party Secretary, highlighted the similarity between designing a spacecraft and managing a megacity: both are "complex giant systems."

Complex Systems Concept

Complex systems consist of many interacting parts whose collective behavior cannot be predicted simply from the parts themselves. Their key traits include nonlinearity, openness, distance from equilibrium, self‑organization, and emergence .

Nonlinearity : output does not scale proportionally with input.

Openness : exchange of energy, matter, or information with the environment.

Distance from equilibrium : the system operates in a dynamic, non‑steady state.

Self‑organization : internal structure forms without external commands.

Emergence : macro‑level properties arise from micro‑level interactions.

Open complex systems interact extensively with their surroundings, making them highly dynamic and adaptive but also unpredictable.

Cities are prime examples of open complex systems, constantly processing information and resources from residents, businesses, government, and external factors, and adapting to economic, social, technological, and natural changes.

Closed complex systems have limited external interaction, relying mainly on initial conditions and internal rules, which makes their evolution more predictable.

Spacecraft design is a typical closed complex system: it depends on internal mechanisms and resources, requiring high predictability and stability to function reliably in the harsh space environment.

Complex Giant Systems Concept

Complex giant systems are extremely large and intricate, comprising many subsystems with dense inter‑connections, and they exert profound impacts on society and the environment.

Beyond the usual complex‑system traits, they exhibit:

Hierarchical structure : distinct layers of subsystems with different functions.

Dynamic nature : ability to evolve structure and function over time.

Coexistence of uncertainty and predictability : despite internal randomness, analysis can reveal trends.

Urban traffic networks illustrate a complex giant system, where roads, signals, pedestrians, and vehicles interact, leading to congestion and accidents that require holistic optimization.

Modeling approaches include rule‑based models (e.g., cellular automata), network models, differential‑equation models, multi‑level modeling, and agent‑based models (ABM).

Qian Xuesen and Complex Systems

Qian Xuesen, the father of Chinese missiles and a pioneer of aerospace engineering, emphasized system engineering as a cross‑disciplinary method to design, integrate, and manage the overall performance of complex systems, arguing that traditional analysis is insufficient for 21st‑century challenges.

Large Language Models and Complex Systems

Large language models such as OpenAI’s GPT series are themselves complex systems, featuring billions of parameters, high nonlinearity, self‑organization during training, and emergent capabilities like creative text generation.

Understanding complex and complex giant systems—whether ecological, economic, or engineered—helps us model, predict, and control real‑world phenomena, offering more effective solutions to today’s intricate problems.