Pulmonary Contusion Risk Assessment in Astronauts During Off-Nominal Earth-Return Capsule Landings.

Purpose: To investigate injury mechanisms and vulnerable regions for severe pulmonary contusion (PC) in astronauts during off-nominal capsule landings, establishing critical injury thresholds.

Methods: Six distinct high-intensity landing scenarios (≤52.1 g) were simulated using a drop-tower test stand and a Hybrid III anthropometric test device(ATD). The Total Human Model for Safety (THUMS) finite element model (FEM) was utilized to simulate thorax-pulmonary dynamics at a 40° supine posture. Injury risk was assessed using the Viscous Criterion (VC), strain/strain-rate thresholds, and Abbreviated Injury Scale (AIS) criteria.

Results: At 37.1 g impact (VC_max 0.98 m/s), the probability of life-threatening AIS 4 + PC surged to 25%, concurrent with a 19.5% probability of 3 + rib fractures(RF). The medial segment of the right middle lobe (S5) was the most severely affected region, primarily due to compression by the costal arch and liver. Injury to the right lung was more severe compared to the left, and fractures of the 1st, 9th, and 10th ribs exacerbated the lung injury.

Conclusion: This study defines 37.1 g as the critical threshold for AIS 4 + thoraco-pulmonary trauma, elucidating the S5 compression mechanism and its association with high-risk RFs (1st, 9th, 10th). These findings provide a biomechanical foundation for enhancing astronaut survival protocols, enabling rapid post-impact triage, targeted pulmonary intervention (focus right S5 segment), and the design of energy-absorbing countermeasures to mitigate visceral compression.