Hermetic Seal Designs for Sample Return Sample Tubes
- Created: Sunday, 01 December 2013
- NASA’s Jet Propulsion Laboratory, Pasadena, California
Prototype sample tube seals prevent material loss and maintain sample integrity.
Prototypes have been developed of potential hermetic sample sealing techniques for encapsulating samples in a ≈1-cm-diameter thin-walled sample tube that are compatible with IMSAH (Integrated Mars Sample Acquisition and Handling) architecture. Techniques include a heat-activated, finned, shape memory alloy plug; a contracting shape memory alloy activated cap; an expanding shape memory alloy plug; and an expanding torque plug.
Initial helium leak testing of the shape memory alloy cap and finned shape memory alloy plug seals showed hermetic- seal capability compared against an industry standard of <1×10–8 atm-cc/s He. These tests were run on both clean tubes and dirty tubes dipped in MMS (Mojave Mars Simulant). The leak tests were also performed after thermal cycling between –135 and +55 ºC to ensure seal integrity after Martian diurnal cycles. Developmental testing is currently being done on the expanding torque plug, and expanding shape memory alloy plug seal designs.
The finned shape memory alloy (SMA) plug currently shows hermetic sealing capability based on preliminary tests. The finned SMA plug sealing technique requires a heater to actuate the plug. Materials have been selected to comply with current sample compatibility, contamination control, and planetary protection concerns. Various Nitinol SMA chemistries are currently being investigated that allow the seal to start activating at temperatures as low as 45ºC (if low-temperature sealing is required for sample integrity), and as high as 135ºC (if planetary protection dry heat microbial reduction is required).
The contracting shape memory alloy cap requires a heater to actuate an SMA ring that swages the toothed cap onto the outside of the tube. The expanding SMA plug also requires a heater to actuate a ring that swages the toothed cap into the inside of the tube.
The benefit to the expanding torque plug is that no heat is required to create a seal. All that is needed is a rotating actuator to actuate the plug.
This work was done by Paulo J. Younse of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48927
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