Spinal Expansion and Shape Memory Alloy Peristaltic Pump Mechanism
Astronauts report back pain while in a reduced gravity environment. The purpose of this experiment is to observe the effect of microgravity on the forces related to the human spine, and gather preliminary data to enable an understanding cause of the pain. Force probes will measure the tension in the expansion of the spine, and the conductive foam (situated between vertebrae), with electrodes, will indirectly quantify the amount of force the spine undergoes through the change in voltage. The measurements taken by the force probe represent the strain of the back muscles, induced by microgravity; the measurements taken by the conductive foam systems represent the changes experienced by the intervertebral discs. Because muscles and intervertebral discs are the two most likely sources of back pain, we hope to more accurately determine the cause of lower back pain commonly experienced by astronauts.
The International Space Station frequently experiences pump failures. The purpose of this experiment is to study peristaltic pumps as alternatives to conventional pumps mechanisms, with a focus on shape memory alloys as the primary components in these peristaltic pumps. The lateral contraction of wires composed of these alloys will vertically compress a length of tubing in sequence, initiating water flow in a particular direction. Preliminary tests will focus on the functionality and flow rate of such pumps; successive experiments will attempt to optimize design and compression sequence. Because this pump system can be completely controlled using digital mechanisms, and because it contains no moving parts, we hope to develop a pump system to decrease the frequency and hazard resulting from pump failures in microgravity environments.
This experiment is being flown as a part of the High School Students United with NASA to Create Hardware (HUNCH) program. It was designed, fabricated, and documented by the students at North Carolina School of Science and Mathematics in Durham, North Carolina. Our experiment consists of a spinal model including model human vertebrae strung on two 15 ” door springs pried together. The intervertebral discs of the spine were modeled with varying thicknesses of conductive foam, with select discs sandwiched by copper printed circuit board to allow for measurements of compression. Elastic bands serve to model muscles that attach to the spine. The structure is supported by two Lexan boards on bottom and top, which are propped together with six 5/16” rods at the corners and lengthwise edge. These rods will also support the muscles and four force sensors that will be connected to the vertebrae to measure movement. Data will be taken by measuring the change in voltage in the foam pressure sensors, with a lower voltage corresponding to a higher pressure exerted on the sensor. Additional data will be provided by two accelerometers. All foam pressure sensors, voltage probes, and accelerometers will be connected to two Vernier LabQuest devices, which will be attached to the outside of the glovebox, to store data during flight. Additionally, a video camera will be mounted on one side of the spine to observe and record movement visually. The bottom and top Lexan sheets will be strapped to the baseboard of the glovebox, and the experiment will be vertically oriented in a 26” x 23” x 36” vertical glovebox.
In any spacecraft, plumbing is of vital importance. Pump mechanisms used today in the International Space Station are prone to frequent malfunction due to their large number of moving parts. We created an alternate mechanism, a biomimetic pump that employs peristalsis, the sequenced contraction of segments used by the human digestive tract. This peristaltic pump would function by using a pipe embedded with Nitinol, a shape memory alloy actuated by electrically derived resistive heating. This mechanism will entirely eliminate the need for moving parts and would increase the pump reliability, as such a mechanism would only fail if the tubing itself breaks.
We plan to continue project development next year.