Improved feasibility of astronaut short-radius artificial gravity through a 50-day incremental, personalized, vestibular acclimation protocol

Abstract

The "Coriolis" cross-coupled (CC) illusion has historically limited the tolerability of utilizing fast-spin rate, short-radius centrifugation for in-flight artificial gravity. Previous research confirms that humans acclimate to the CC illusion over 10 daily sessions, though the efficacy of additional training is unknown. We investigated human acclimation to the CC illusion over up to 50 daily sessions of personalized, incremental training. During each 25-min session, subjects spun in yaw and performed roll head tilts approximately every 30 s, reporting the presence or absence of the illusion while rating motion sickness every 5 min. Illusion intensity was modulated by altering spin rate based upon subject response, such that the administered stimulus remained near each individual's instantaneous illusion threshold. Every subject (n = 11) continued to acclimate linearly to the CC illusion during the investigation. Subjects acclimated at an average rate of 1.17 RPM per session (95% CI: 0.63-1.71 RPM per session), with the average tolerable spin rate increasing from 1.4 to 26.2 RPM, corresponding to a reduction in required centrifuge radius from 456.6 to 1.3 m (to produce loading of 1 g at the feet). Subjects reported no more than slight motion sickness throughout their training (mean: 0.92/20, 95% CI: 0.35-1.49/20). We applied survival analysis to determine the probability of individuals reaching various spin rates over a number of training days, providing a tolerability trade parameter for centrifuge design. Results indicate that acclimation to a given, operationally relevant spin rate may be feasible for all subjects if given a sufficient training duration.

Keywords: Aerospace engineering; Biological sciences.

Fig. 1. Extended acclimation findings.

CC illusion acclimation pretraining and ending thresholds for (a) 10-day and extended acclimation subjects over the first 10 sessions and (b) extended acclimation subjects over the entire duration of their involvement in the study. In panel a, the previous 10-day investigation subjects are shown in gray, while the current extended acclimation subjects are overlaid in color. In panel b, subjects who completed the study by reaching the investigation’s ending criteria are shown with a black circle at their final data point, while subjects who left the study due to scheduling challenges are denoted with a black “X”.

Fig. 2. Extended acclimation motion sickness results.

Subject averages are denoted with the light blue bars, maximum reports across all sessions are shown with light blue asterisks, and the dark blue bar shows the overall average across all extended duration acclimation subjects. The gray bar shows the 10-day personalized subject group average motion sickness score for comparison. Error bars show 95% confidence intervals about the subject means.

Fig. 3. Staircase of survival analysis findings.

Survival analysis results for (a) 20 RPM and (b) 5, 10, 20, and 30 RPM. In panel a, a 95% confidence interval is plotted with gray dashed lines. The confidence intervals are omitted in panel b. Within both plots, the “X” markers along the staircase show when a subject becomes censored (i.e., when a subject leaves the investigation and additional data are unavailable).