Final Design

Overview

Our final LBNP prototype consists of a two-layer Nomex^®/nylon pant, a rigid 3D printed endoskeleton, and a vacuum assembly. The endoskeleton prevents the airtight pants from collapsing when negative pressure is applied to the suit, minimizes contact between the fabric and the user's body. To permit mobility, a knee hinge mimicking the design of ACL braces allows for around 110° of flexion. Vacuum hoses snap into each leg and connect a vacuum pump to the chamber created by the airtight pants. Velcro attachment points between the pants and endoskeleton prevent the fabric from sliding and misaligning with the knee joint. This device maintains the target pressure of 25 mm Hg (~.5 psi) which is required to safely provide the health benefits of negative pressure to astronauts. The device is comfortable to wear and minimally inhibits movement.

Endoskeleton

The rigid endoskeleton provides internal support for the airtight pants, which together form a flexible vacuum chamber. The current prototype was printed in Polylactic Acid (PLA) on an Creality^® Ender 3 Max, but stronger materials such as carbon infused nylon (Onyx) would be preferable. The endoskeleton is skeletonized to decrease print time and to allow air to flow through to the overlaid pants. The knee joint rotates on 2 sets of geared aluminum shims and contains a knee cap and support rings to prevent fabric from collapsing during flexion. The support rings are attached to a fabric sleeve which holds them in place when the user is standing, and folds like an accordion when bent. Foot straps hold the endoskeleton in place, and provide axial loading when the suit is depressurized.

Airtight Pants

The two layer airtight pants provide the seal that allows negative pressure to accumulate. The outer layer is Nomex^®, a fire-resistant durable fabric that is widely used by NASA, firefighters, and racecar drivers. The Nomex^® is attached at the waist band to an underlayer of airtight, heat sealable nylon. The pants are completely detachable from the endoskeleton, but can be left on via Velcro^® connectors that will keep the suit fully assembled for easy donning. The pants are not sealed at the bottom, but instead fit under a pair of airtight socks that are synched down onto the endoskeleton calf with a Velcro^® band.

Vacuum Assembly

The vacuum assembly connects to a bath shoe strainer which is snap fitted into the endoskeleton. The strainers allow the vacuum access to the inside of the airtight pants, and are attached via two hoses to a tee manifold located on the user's back. This tee manifold connects both legs to the main vacuum tube which feeds directly into the vacuum pump.