FlightQualified LowShockSeparation Nut(SN9400 Series) TheHSTCflight-qualified SN9400 SeriesLowShockSeparation Nuts2wereusedontheVikingLander, Mars Pathfinder, SpaceShuttle, DeltaI1andItlLaunch Vehicles, andnumerous otherdomestic andmulti-national spaceprograms. The9400seriesSeparation Nuthasthefollowing general features: •Lowshockoutput •Completely gasandparticle containing •Stronger thanmatingbolt •Ultra-fast release (Under5milliseconds) •Lightweight -predominately aluminum •Actuates onrelatively lowpressure •Thread surfaces andlayingsurfaces drylubricated toM1L-L-46010 Type1 •Multiple in-process coldgasactuations (3-5times,maximum 25times) •Minimum boltinsertion required •Largebolttolerance •Verylowmagnetic influence •Temperature/pressure envelope limitedonlybycartridge TheHSTC9400seriesseparation nutisconstructed ofanodized aluminum andstainless steeltoprovide highresistance tocorrosive environments, andtoprovide thelightestweightcompatible withstrength and otherrequirements. Thestandard aluminum nutscanbeoperated between 93°Cand-87°C. Theefficient designofthisseparation nutallowstheuseofalowactuating pressure, whichinturnallowsthemajority of components tobefabricated ofaluminum whilethehighstressed partsareprecision machined ofstainless steel.Hencetheveryfavorable strength toweightratioisachieved. Actuation oftheseparation nutis accomplished withoneormorepowercartridges. Figure1presents thesequence ofoperations forthe9400 series,0.64-cm (0.25-in) through 3.18-cm (1.25-in), separation nuts. Thelow-shock separation nutdesignreduces mechanical shockbyhavingthelockingpistonmoveaway fromthebaseandstructure uponactuation ratherthantowardthebaseasolderhigh-shock-output separation nuts.Inaddition tothereverse movement ofthepiston,furtherreduction andmitigation canboth beachieved rathereasilybyaddinghoneycomb material, whichcushions theimpactoftheactuation locking pistonontheinsideofthehousing. UltraLowShockSeparation Nut Desiqn Definition Outputshockfromapyrotechnic-actuated separation nuthasthreesources: deflagration ofthepressure cartridge, release oftheboltsstrainsenergy, andinternal collisions ofthemechanical components. Itis generally accepted thatthepyrotechnic shockdelivered bythepressure cartridge contributes lessthan10% ofthetotalshock. Itisprudent thentofocusonthepurelymechanical contributors making uptheother 90%.Depending onthedesign, thecontribution tomechanical shockissplitevenlybetween internal collisions andboltpreload release. ThedesignofHi-Shear's UltraLowShockSeparation Nut3(Figure2) addresses thesetwosources. Thekeytoitsfunction iscontrolofthebolt-preload release time.Arotational element (Rotor)located under thethreaded segments meterspreload release overalongerperiodoftimethanforstandard pyrotechnicactuated separation nuts.Thislongerrelease timeminimizes boltacceleration duringtherelease process, minimizing thecontribution tooverallshockfrompreload release. Bycomparison, Hi-Shear's 9400series nutreleases preload almostinstantaneously duetothesudden ejection oftheretainer byhigh-pressure pyrotechnic gases. Thissudden ejection contributes tomechanical shocktwice:initiallytoovercome high staticfrictionforcesandashorttimelaterwhentheretainer impacts thehousing. Theretainer intheUltra 152