Author: CislunarSpace
Website: https://cislunarspace.cn

Transfer Corridor Design

Transfer Corridor Concept

An Earth-Moon transfer corridor is a collection of reachable trajectories in cislunar space along which a spacecraft can travel from a starting point to a target orbit under given energy constraints.

In the CR3BP model, transfer corridors correspond to invariant manifold tubes that connect regions near LEO to target orbits (such as NRHO) in phase space. These tubular structures form "channels" in state space; trajectories within these channels require only small corrections to reach the target.

Low-Energy vs High-Energy Corridors

Transfer corridors can be divided into two categories based on transfer energy:

High-Energy Corridor (Direct Transfer Corridor):

Corresponds to higher $C_3$ values ( $C_3 \approx -0.3$ to $-0.5$ km $^2$ /s $^2$ )
Short transfer time (3-5 days)
Narrow $\Delta V$ corridor width (approximately $\pm 50$ m/s)

Low-Energy Corridor:

Corresponds to lower $C_3$ values ( $C_3 \approx -0.8$ to $-1.0$ km $^2$ /s $^2$ )
Long transfer time (2-4 weeks)
Wide $\Delta V$ corridor width (approximately $\pm 200-300$ m/s)

The $\Delta V$ difference between the two corridor types is approximately 200-300 m/s, significantly impacting propellant budget.

Pork-Chop Plot

The Pork-Chop plot is a standard tool for TLI launch window analysis, presented as a contour plot showing:

x-axis: Launch date
y-axis: Arrival date (or transfer time)
Contours: Total $\Delta V$ or $C_3$ values

How to read a Pork-Chop plot:

Locate the most indented region of the contours (the lowest-energy launch opportunity)
The launch-arrival date pair in that region represents the optimal window
The density of contours indicates how "steep" the corridor is

Multi-Objective Optimization

Earth-Moon transfer design is a typical time-fuel bi-objective optimization problem with core trade-offs:

Objective	Optimization Direction	Cost
Minimize $\Delta V$	Low-energy corridor	Increased transfer time
Minimize time	High-energy corridor	Increased $\Delta V$
Maximize window width	Compromise solution	Neither objective is optimal

The Pareto frontier represents the set of optimal solutions where both objectives cannot be improved simultaneously in the time-fuel trade-off. Mission planners must select the appropriate operating point based on spacecraft capability and mission requirements.

NRHO Insertion Timing

NRHO insertion after arriving in cislunar space is the final step of the transfer:

Insertion timing is determined by the lunar phase and orbital geometry at arrival
Optimal insertion window width is typically $\pm 1-2$ hours
Insertion $\Delta V$ is approximately 200-400 m/s

Simulation Experiments

You can generate Pork-Chop plots in the Satellite Orbit Simulation Laboratory to observe how transfer energy varies with different launch windows.