BACKGROUND: With the increase in crewed commercial spaceflight and expeditions to the Moon and Mars, the risk of critical surgical problems and need for procedures increases. Appendicitis and appendectomy are the most common surgical pathology and procedure performed, respectively. The habitable volume of current spacecraft ranges from 4 m³ (Soyuz) to 425 m³ (International Space Station). We investigated the minimum volume required to perform an appendectomy and compared that to habitable spacecraft volumes.METHODS: The axes of a simulated operating room were marked and cameras placed to capture movements. An expert surgeon, chief surgical resident, junior surgical resident, and a nonsurgeon physician each performed a Focused Assessment with Sonography for Trauma and an appendectomy on a simulated patient. Dimensions and volume needed were collected and compared using unpaired t-tests.RESULTS: Mean volume (± SD) needed was 3.83 m³ ± 0.47 m³ for standing and 3.68 m³ ± 0.49 m³ for kneeling (P = 0.638). Minimal volume needed was 3.20 m³ for standing and 3.26 m³ for kneeling. Minimal theoretical volume was 2.99 m³ for standing and 2.87 m³ for kneeling.DISCUSSION: The unencumbered volume needed for an appendectomy is between 2.87 m³ and 4.3 m³. It may be technically feasible to perform an open appendectomy inside the smallest of currently operating spacecraft, at 4 m³ (Soyuz-MS). Space vessels operating without rapid evacuation to Earth will need to consider this volume for potential surgical emergencies. Additional investigation on microgravity and standardization of procedures for novices must be completed.Kamine TH, Siu M, Kramer K, Kelly E, Alouidor R, Fernandez G, Levin D. Spatial volume necessary to perform open appendectomy in a spacecraft. Aerosp Med Hum Perform. 2022; 93(10):760–763.