Synopsis
The paper provides an overview of the vast region between Earth’s atmosphere and the Moon’s orbit, highlighting key differences in scale, dynamics, observation challenges, and spacecraft operations compared to near-Earth orbits that pose major hurdles for effective utilization by civil, commercial, and military entities. Understanding these unique issues is important as human expansion into cislunar space accelerates in the coming years.
Here is a summary of key points about cislunar space:
Definition and Scope
- Cislunar space is the vast region between Earth’s atmosphere and the Moon’s orbit, about 238,855 miles from Earth on average. It covers over 1,700 times more volume than geosynchronous orbit.
Dynamics and Motion
- Motion in cislunar space is governed by the gravitational forces of the Earth, Moon and Sun, making trajectories complex, unstable and unpredictable compared to orbits closer to Earth.
- Special equilibrium points called Lagrange points and repeating natural orbits exist, but most trajectories do not repeat or remain in a fixed plane over time.
- Traditional methods like two-line elements (TLEs) cannot accurately describe trajectories or enable propagation predictions in cislunar space.
Challenges for Observation and Tracking
- Large distances make objects harder to detect with sensors like telescopes and radar. Long orbital periods require more observations for orbit determination.
- No single vantage point can maintain continuous coverage of cislunar objects due to differences in relative motion. A network of sensors is needed for tracking.
- Placement of sensors at Lagrange points, in lunar orbits, or specialized repeating natural orbits can provide unique perspectives unattainable from Earth.
Spacecraft Operations
- Frequent small maneuvers, often daily, are needed to maintain trajectories due to inherent instability. This drives design of propulsion systems.
- Transfers between trajectories can leverage instability to enable changes with low energy and fuel cost, but take long times from days to years.
- Past missions have used various high and low energy trajectories for transfers between Earth and cislunar space.
In summary, cislunar space poses major challenges in scale, dynamics, observation, and operations compared to near-Earth orbits. Understanding these issues is key to effective utilization by military, civil and commercial entities.
