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
This Brief includes a Technical Support Package (TSP).
Hermetic Seal Designs for Sample Return Sample Tubes
(reference NPO-48927) is currently available for download from the TSP library.
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Overview
The document outlines research conducted at NASA's Jet Propulsion Laboratory (JPL) focused on developing hermetic seal designs for sample return tubes intended for future Mars Sample Return (MSR) missions. A key objective of the MSR campaign is to collect and cache samples on Mars for an extended duration—at least five Mars years—without compromising their scientific integrity. Effective sealing of these samples is identified as the most critical factor in preserving their value until they can be analyzed on Earth.
The document details various sealing techniques that have been designed and prototyped for encapsulating samples in approximately 1 cm diameter thin-walled tubes. Six sealing methods are highlighted: a spring-energized Teflon sleeve plug, a crimped tube seal, a heat-activated shape memory alloy (SMA) plug, an SMA-activated cap, a solder-based plug, and a solder-based cap. These methods were developed to ensure that the samples remain uncontaminated and intact during their time on Mars.
Material compatibility studies were conducted to select appropriate tube and seal materials that would not react adversely with potential sample minerals. The document also describes extensive testing, including helium leak tests performed on clean sample tubes and those exposed to Mars simulants. These tests were conducted before and after thermal cycling between extreme temperatures (-135°C to +55°C) to evaluate the seals' hermetic capabilities. The results indicated that the crimped tube, SMA cap, and finned SMA plug seals met industry standards for hermetic sealing.
The research aims to advance the technology readiness level (TRL) of the sealing methods to TRL 5, indicating that they are sufficiently developed for potential use in actual missions. The document emphasizes the importance of these sealing technologies in ensuring that the scientific value of Martian samples is preserved during their collection, storage, and eventual return to Earth.
Overall, this technical support package serves as a comprehensive overview of the methodologies, testing, and objectives associated with the sealing of sample tubes for Mars missions, highlighting the innovative approaches being taken to safeguard extraterrestrial samples for future scientific analysis.
