As the second attempt to launch Artemis I is called off by NASA due to technical problems related to a liquid hydrogen leak, I thought it would be good to dig deeper on the topic of how launch attempts are scheduled.
The earth rotation, the cyclical 27-day movement of the Earth-Moon system, complex trajectories to support the orbital mechanic required for the Earth Orbit, Trans Lunar Injection (TLI) and Lunar Orbit Insertion (LOI) then spacecraft performance combine with mission operational constraints, to further limit the launch opportunities.
If we look back, all the Apollo missions had to deal with the same problem and complexity, so starting from the Apollo Flight Journal website I found the essay “Apollo lunar landing launch window: The controlling factors and constraints” by Robin Wheeler which explains within a somewhat understandable level of details (at least for a space enthusiast like me) how all the factors mentioned above are considered to plan the launch windows.
With that knowledge we can now look at the Artemis I Mission availability page below and better understand the content: https://www.nasa.gov/feature/artemis-i-mission-availability
The following four mission mission specific constraints are mentioned:
1. The launch day must account for the Moon's position in its lunar cycle so that the SLS rocket’s upper stage can time the trans-lunar injection burn with enough performance to successfully intercept the "on ramp" for the lunar distant retrograde orbit. The more powerful Exploration Upper Stage on future configurations of the rocket will enable daily, or near-daily, launch opportunities to the Moon, depending on the orbit desired.
2. The resulting trajectory for a given day must ensure Orion is not in darkness for more than 90 minutes at a time so that the solar array wings can receive and convert sunlight to electricity and the spacecraft can maintain an optimal temperature range. Mission planners eliminate potential launch dates that would send Orion into extended eclipses during the flight. This constraint requires knowledge of the Earth, Moon, and Sun along the planned mission trajectory path before the mission ever occurs, as well as an understanding of the Orion spacecraft’s battery state of charge before entering an eclipse.
3. The launch date must support a trajectory that allows for the skip entry technique planned during Orion’s return to Earth. A skip entry is a maneuver in which the spacecraft dips into the upper part of Earth’s atmosphere and use that atmosphere, along with the lift of the capsule, to simultaneously slow down and skip back out of the atmosphere, then reenter for final descent and splashdown. The technique allows engineers to pinpoint Orion’s splashdown location and on future missions will help lower the aerodynamic breaking loads astronauts inside the spacecraft will experience, and maintain the spacecraft’s structural loads within design limits.
4. The launch date must support daylight conditions for Orion’s splashdown to initially assist recovery personnel when they locate, secure, and retrieve the spacecraft from the Pacific Ocean.References
Origin of the Moon https://people.ast.cam.ac.uk/~wyatt/poa_201415_originofmoon.pdf
Apollo lunar landing launch window: The controlling factors and constraints https://history.nasa.gov/afj/launchwindow/lw1.html
Artemis I Mission Availability https://www.nasa.gov/feature/artemis-i-mission-availability