Evaluating a New Design for the NASA SCAPE Harness

Abstract

The National Aeronautical Space Administration (NASA) uses a backpack system as a form of load carriage in the Self Contained Atmospheric Protective Ensemble (SCAPE) suits. SCAPE suits, which are completely enclosed suits, are required in areas where fuel and an oxidizer are present and can spontaneously ignite on contact (hypergolic atmospheres). Inside the SCAPE suit, a person wears a "backpack", which consists of a 40 pound environmental control unit (ECU) attached to a "backpack" harness. Interviews was conducted with current and former SCAPE employees to identify the body positions assumed while performing common tasks during a SCAPE operation, and to explore issues of discomfort while wearing the harness. The purpose of this research has been to develop and evaluate a new harness by comparing it with the current NASA harness in terms of biomechanical loading and subjective assessment.

A Kelty® Sierra Crest M'S external framed pack was chosen as the harness to modify, because it featured many components that are important to a supportive pack, including an external frame, a padded hip belt, load lifter straps, padded shoulder straps, and an adjustable harness for varied torso lengths. In addition to this basic design, lateral stiffness rods were added to the harness to help transfer the load from the shoulders to the hips.

To test the biomechanical effects of the NASA harness and the new harness on the body, the muscle activity of the trapezius, erector spinae, and rectus abdominus muscles were recorded using surface electromyography (EMG). While wearing each harness, subjects were required to position their torso in four different forward flexion angles, 15, 30, 45, and 60 degrees, while EMG was recorded. The subjects were also asked to fill out subjective surveys based on the comfort level of the shoulders and low back for each harness.

The results for the trapezius muscles showed that there was a significant effect of the interaction of harness type and forward flexion angle on these muscles. The normalized EMG for the trapezius muscles showed there was a 14% and 11% reduction in muscle activity at 15 and 30 degrees, respectively, with the new harness compared to the NASA harness. The results for the erector spinae muscles showed that there was a significant effect of forward flexion angle and the interaction of harness type and forward flexion angle on the these muscles. The normalized EMG for the erector spinae muscles showed there was a 24% and 14% reduction in muscle activity at 15 and 30 degrees, respectively, with the new harness compared to the NASA harness. The rectus adominus muscles did have a significant effect of forward flexion angle, although there was not a distinguishable difference in muscle activity between the new harness and the NASA harness.

The subjective surveys agreed with the EMG results, which showed the new harness was more comfortable with respect to the shoulder and low back areas, as well as overall comfort than the NASA harness. Using a five point Likert scale, (where 1 meant no discomfort, 3 meant moderate discomfort, and 5 meant very uncomfortable) the evaluation of pressure on the shoulders from the shoulder straps showed that the NASA harness scored a 2.6, while the new harness had a score of 1.8. For discomfort felt in the trapezius muscles, the NASA harness scored a 3.1, while the new harness scored a 1.9. For the discomfort felt in the low back area, the NASA harness scored a 2.8, while the new harness scored a 1.9. As far as overall comfort for each harness, the NASA harness scored a 3.1, while the new harness scored a 2.1. Each question also proved to be statistically different between harness type. Collectively, the subjective and objective results show a significant improvement with the new harness system.