Challenges in Quantifying Heel-Lift During Spacesuit Gait

Area of Science:

• Space exploration engineering
• Biomechanics
• Wearable sensor technology

Background:

• Heel-lift is a common, unquantified fit issue in planetary spacesuit boot prototypes.
• Inertial measurement units (IMUs) are susceptible to integration drift, complicating their use for precise motion analysis.

Purpose of the Study:

• To evaluate the efficacy of IMUs and drift-correction algorithms (zero-velocity updates and zero-position updates) in quantifying heel-lift during spacesuited gait.
• To assess the accuracy of IMUs in measuring heel-lift magnitude under various spacesuit padding conditions.

Main Methods:

• Utilized data from Fineman et al. (2018) with IMUs on spacesuit lower legs and operator's shanks.
• Applied discrete wavelet transforms to identify gait phases (foot-flat, heel-off).
• Calculated heel-off timepoint differences and estimated IMU drift rates before and after applying ZVUs and ZPUs.

Main Results:

• Observed instances of both spacesuit-delayed and operator-delayed heel-off, indicating potential measurement inaccuracies.
• Drift correction algorithms suggested a time bound of 0.03 s for measuring heel-lift magnitude with 1 cm accuracy.
• Operator-delayed heel-off suggests spacesuit lower leg expansion may create false acceleration signals.

Conclusions:

• IMUs, as applied in this study, may be inappropriate for accurately quantifying spacesuit heel-lift.
• Spacesuit lower leg (SLL) expansion can interfere with IMU readings, creating erroneous heel-off signals.
• Improved IMU mounting or alternative sensor technologies are necessary to reliably quantify heel-lift in spacesuits.