Mars Science Laboratory Heat Rejection System (HRS) Tubing Retractor

In support of the cruise stage form entry vehicle separation event for Mars science laboratory (MSL), two 3/8" aluminum tubes that are part of the heat rejection system (HRS) must be cut and retracted. Due to size and stiffness of the tubes to be retracted and the mass and volume constraints on MSL, the typical preloaded spring retraction mechanism was deemed to not be the ideal mechanism. Instead a pyrotechnic thruster was designed to perform the job. This thruster was baselined from the design details of an existing 5/8" cable cutter, but highly modified to meet the needs of the retraction device. Due to the added kinetic energy of an increased stroke, as compared to the cutter, a new attenuator to absorb the residual energy at the end of stroke had to be designed to keep the thruster housing from yielding. Volume constraints limited the size of the attenuator so the typical honeycomb crushable was not an option. Instead a collapsing thin walled tube design was analyzed, tested and implemented. Part of the analysis and testing was the process of correlating the difference between static and dynamic flow stresses of the attenuator material as well as the collapse modes of the cylinder walls. Upon completion of the preliminary attenuator design, proof of concept testing was done to validate the design of the retraction system such that the thruster has adequate capability to retract the HRS lines away from the Entry Vehicle. In that process the attenuator was also validated to absorb the majority of the thruster\´s energy as not to yield any other components of the devise.