Partial Gravity Load Simulation Using Mechanical Off-Loading and Lower Body Negative Pressure

Abstract

Prolonged exposure to reduced gravity environments can lead to significant deconditioning of the cardiovascular, musculoskeletal, and ocular systems. These effects increase the risk of orthostatic intolerance, bone loss, and conditions such as Spaceflight Associated Neuro-ocular Syndrome (SANS). As spaceflight missions grow longer and more frequent, especially with increased extravehicular activity (EVA) on the Moon or Mars, it is critical to develop effective countermeasures and Earth-based analogs to simulate these gravitational environments and evaluate physiological impacts. This thesis addresses these challenges through two complementary approaches. First, it presents the design and development of the MIT Moonwalker IV, a passive mechanical offloading system that simulates partial gravity by applying vertical support via a spring-cable mechanism. In a treadmill-based pilot study, one participant showed at least a 50% reduction in metabolic demand while running under simulated Martian gravity. These findings validate the Moonwalker IV as a metabolic analog for EVA task simulation. Second, this thesis evaluates a collapsible lower body negative pressure (LBNP) suit as a wearable countermeasure for micro and partial gravity environments. By applying negative pressure to the lower body, the suit helps restore the mechanical loading and hydrostatic fluid gradients typically provided by Earth’s gravity. The suit was tested in both simulated reduced gravity via a head-down/head-up tilt paradigm and and true reduced gravity via parabolic flight. Each condition was evaluated both with and without –20 mmHg of LBNP. Results demonstrated that the collapsible LBNP suit produced cardiovascular responses comparable to those observed in traditional rigid LBNP chambers. It also induced lower body fluid shifts as measured by segmental leg bioimpedance, reduced intraocular pressure, and generated ground reaction forces similar to standing in 1G. These findings support the complementary use of Earth-based analog systems to simulate partial gravity and wearable devices to simulate Earth gravity in reduced gravity environments. They offer valuable tools for preparing astronauts and preserving physiological health during long-duration space missions.