Physics Behind Artemis II Return

The trans-lunar-to-splashdown phase of the Artemis II mission is the most unstable part of the flight — the capsule crosses from celestial mechanics into fluid dynamics the moment it hits the atmosphere at 11,000 m/s. This paper builds the governing force equation for that transition and turns it into a working re-entry simulation.

• Models the net force on the capsule as gravity plus a velocity-squared atmospheric drag term dependent on the instantaneous Mach number.
• Uses the barometric formula to model atmospheric density growing exponentially as the capsule descends through its scale height.
• Tracks kinetic energy dissipation and G-load throughout re-entry to check the result stays within the crew's physiological limits.
• Implements the simulation with the Euler-Cromer integration method for a numerically stable, energy-conserving time-step loop.
• Plots velocity decay against altitude and the deceleration G-load curve across the full ~300-second re-entry window.