SMA gas release mechanism for the Rosetta Lander's Ptolemy instrument

The Ptolemy instrument on the Rosetta comet lander “Philae” is an advanced gas analyser. The instrument relies on a supply of ultra-clean helium gas to carry cometary matter through a series of gas chromatography columns and high temperature reactors, into a mass spectrometer. The helium is stored in a pair of titanium gas tanks, pressurised to 50 bar. The use of a conventional valve to seal the tanks would lead to a high loss of helium through leakage over the long period of dormancy involved in this mission (15 years from filling to use). Instead, the tanks are sealed with a hollow “frangible pillar”, which is broken with a shape memory alloy (SMA) actuator to release the gas on reaching the comet.This article describes the SMA mechanism, which provided an effective, low mass, low power, clean solution to the problem of helium storage and release.