Cislunar Space

Author: CislunarSpace

Website: https://cislunarspace.cn

Definition

Cislunar space refers to the vast region between the Earth and the Moon, typically encompassing Low Earth Orbit (LEO, below approximately 2000 km altitude), lunar orbits and their vicinity, and all the space in between. From a dynamical perspective, cislunar space is governed by the gravitational field of the Restricted Three-Body Problem (CR3BP) with the Earth and Moon as the two primary bodies, and its boundaries are far more complex than simple geometric definitions.

In a broader definition, cislunar space extends to the entire region within the Moon's sphere of influence (Hill sphere, radius approximately 66,000 km), including periodic and quasi-periodic orbit families near the five Lagrange libration points (L1–L5), as well as the lunar surface and low lunar orbits.

Core Elements

Resource Characteristics

Cislunar space contains abundant resources that can be categorized into three types:

  1. Positional Resources: Specific locations in cislunar space possess unique dynamical properties. For example, the Earth-Moon L1 and L2 libration points serve as natural "gateways" for Earth-Moon travel, and the Distant Retrograde Orbit (DRO) offers long-term stability, making it an ideal staging orbit and space station location.

  2. Material Resources: The lunar surface contains abundant helium-3, rare earth elements, and water ice (within permanently shadowed craters near the lunar poles). Regions near the lunar south pole, such as Shackleton Crater, have been confirmed to contain significant water ice deposits.

  3. Orbital Resources: Cislunar space hosts numerous stable or near-stable orbit families, including DROs, Halo Orbits, Lissajous Orbits, and Lyapunov Orbits. These orbits have important applications in communication coverage, observation relay, and space station deployment.

Dynamical Complexity

The dynamics of cislunar space are dominated by the combined gravitational field of the Earth and Moon, fundamentally forming a Restricted Three-Body Problem. Unlike two-body problems (such as purely Earth-orbiting missions), the three-body system has no general analytical solution, and its phase space structure is extremely complex, containing five libration points, numerous periodic orbit families, and chaotic regions.

Strategic Significance

Cislunar space is humanity's first stepping stone toward deep space and holds profound strategic significance:

  • Deep space exploration gateway: The Moon can serve as a fuel depot and transit base for Mars and beyond.
  • Scientific research platform: The lunar far side is an excellent site for radio astronomy, and the Earth-Moon L2 point can serve as a deep space communication relay.
  • Resource development frontier: In-situ resource utilization (ISRU) on the Moon will significantly reduce deep space exploration costs.
  • Space security domain: Cislunar space situational awareness is an important component of future space security.

Application Value

Research and development in cislunar space has become a strategic priority for major spacefaring nations. China's Chang'e program, the US Artemis program, and the International Lunar Research Station (ILRS) all focus on cislunar space as their primary operational area.

From an orbital design perspective, cislunar missions typically require solving the transfer problem from LEO to target orbits such as DROs, lunar orbits, or libration point orbits. Common transfer methods include Hohmann transfers, Weak Stability Boundary (WSB) transfers, and Lunar Gravity Assist (LGA) transfers. Among these, powered lunar flyby (PLF)-based transfer schemes have received widespread attention due to their good balance between transfer time and energy consumption.

References

  • Wei Z et al., "Research on Lunar Flyby Transfer to Distant Retrograde Orbit Families in the Earth-Moon System", 2026.
  • Whitley R J, Martinez R, "Options for Staging Orbits in Cislunar Space", AAS 16-507, 2016.
  • McCarthy B, Howell K, "Leveraging Invariant Manifolds to Generate Low-Thrust Transfer Trajectories in the Earth-Moon System", AAS 21-658, 2021.