Sleeping Bag for Astronauts
Client: Dr. Benjamin Levine,
University of Texas SW Medical Center & NASA
Project: LBNP ( Lower Body Negative Pressure) Sleeping Chamber
Problem: When Astronauts are sleeping in space they can experience ‘eyeball bulging’ over time because of the pressure changes in the body due the zero gravity environment.
Client Request: Design and build a sleeping chamber that can hold negative pressure on test subjects.
3rd Protoype version with rod angles in a “W” shape
Dr. Levine and his team from University of Texas SW Medical center approached me to tackle a structural design issue. They needed a sleeping bag/chamber to maintain negative pressure on the lower half of the body. They had the medical expertise, but needed a structural solution and it had stumped both the internal term and outside contractors. Based on my experience designing tents and sleeping bags, Dr. Levine approached me to brainstorm solutions for a simple structure that could handle the the negative pressure of approximately 30mm Hg. I explored several ideas with a variety of materials used in tents, sleeping bags, and kayaking sprayskirts.
Early design concept shared with UTSW
After initial brainstorming, a single tapered chamber was chosen to give the users freedom to move their legs without any restriction or lengthwise compression.
1st prototype: Built using a plywood top and bottom, separated with steel rings and lengthwise rods, and wrapped in Vinyl. This was a concept and lightweight materials were not used. The upper waist seal was an adaptation of a neoprene kayaking spray skirt. The inspiration for the steel bars came from how some drums are constructed. The reinforced vinyl is used in inflatable river kayaking boats, and is easy to construct air-tight seams using HH-66 adhesive. A single prototype was made.
1st Prototype testing: The first proto collapsed and was not durable enough.
2nd prototype: This unit was built using smarter geometry for the rods and heavier vinyl. Inside the chamber was a seat similar to a swingset seat so the astronaut would not get pulled into the chamber. It was built over a long weekend with two Students from the University.
2nd prototype testing: Before the unit was shipped, we tested it to 15mm Hg using a shop vac, without issues. We also demonstrated ingress and egress using a gantry and an overhead “pull-up” bar. At the university it was used in a series of tests to show how it changed the shape of the patients eyes using Ultrasound measurements. A single prototype of this version was made. However as more testing occurred the prototype started to twist under greater negative pressure.
3rd prototype: This unit addressed the twisting issue of the prior prototype by changing the horizontal rods to be at opposing angles, like a “W”. This is current version being used in testing at UTSW, see article in BBC News, “Space sleeping bag solve astronauts’ squashed eyeball disorder“
3rd prototype testing: Before the unit was shipped I tested it to minus 30mm Hg and held it for two hours. The chamber withstood the pressure without any twisting or structural issues.
Here’s an article posted on CNN, December 12, 2021- “A special sleeping bag could help astronauts with vision issues in space“
Testing chamber currently being used at UTSW
4th prototype FUTURE WORK: This unit has not yet been approved to be constructed, but likely will be a version where lightweight materials are used, and an emphasis on portability and easy assembly will be prioritized. This is where my lateral thinking and experience with backpacking and camping tent construction, and folding chairs should prove valuable.