Pyrotechnic (explosive) devices are used throughout the Gemini mission for switching operations and major configuration changes and in recovery and escape systems. All pyrotechnic systems are designed with inherent redundancies. Pyrotechnic devices are initiated by either pressure, electrically, or by means of a lanyard.
The pyrotechnic devices are installed in such a manner that explosive effects are confined within the device or directed outward and shielded in such a manner as to preclude damage to nearby equipment or inward release of shrapnel
Location and Function of Pyrotechnic Devices
Item Nomenclature Function 1 Separation Assembly, FLSC Sever the spacecraft from the launch vehicle and the adapter equipment section from the adapter retrograde section. 2 Guillotine Cut cables and wire buddies. 3 Cutter-Sealer Cut and crimp seal the OAMS fuel and oxidizer lines. 4 Horizon Sensor Fairing Jettison the horizon sensor fairing. 5 Horizon Sensor Release Jettison the horizon sensors. 6 Ventilation Door Release Jettison the ventilation door. 7 Cartridge, Pyrotechnic Valve Open or close pressurant, propellant, or oxidizer lines. 8 Pyrotechnic Switch Open circuits prior to guillotine operation. 9 Separation Assembly, MDF Separate rendezvous and recovery section from the reentry module. 10 Retrograde Rocket igniters ignite the retrograde rocket motors. 11 Retrograde Rocket Provide thrust for velocity decrement necessary for reentry. 12 Parachute Mortar and Reefing Cutter Parachute mortar deploys parachute in reefed condition, reefing cutters allow complete parachute deployment. 13 Parachute Disconnect Change reentry module suspension and jettison parachute. 21 Separation Assembly, FLSC Sever the reentry module from the retrograde section. Escape Mode
14 MDF initiation System Initiate the hatch actuators. 15 Hatch Actuator Open hatch before ejection seat operation. 16 Rocket Catapult Provide ejection seat propulsion during ejection seat operation. 17 Harness Release Actuator Unlatch seat restraint harness after seat ejection. 18 Seat-Man Separator Separate astronaut from seat. 19 Ballute Deploy and Release Assembly Deploy and release ballute according to altitude. 20 Drogue Mortar-Backboard Jettison Assembly Deploy astronaut drogue parachute. Electrically-initiated devices incorporate cartridges and detonators. They are used in the flexible linear shaped charge assemblies, guillotines, cutter sealers, release assemblies, valves, pyrotechnic switches, mild detonating fuse separation assembly, retrograde rocket initiators, parachute mortars, and parachute disconnects. The cartridges and detonators are provided with one or two independent electrical bridge wire circuits as reliability dictates.
Lanyard-initiated devices are the parachute reefing cutters, mild detonating fuse initiation system, harness release actuators, ballute deploy-ment and release systems, and drogue mortar-backboard jettison assemblies.
Pressure-initiated devices are utilized in the hatch actuators, rocket catapults, and seat-man separators. These devices fire when exposed to pressures between 500 and 3000 pounds per square inch except for the rocket catapult which fires when exposed to 300 to 9000 pounds per square inch.
Flexible linear-shaped charge assemblies are sections of electrically-initiated charges capable of separating sheet metal, wire bundles, straps, and tubes. Three such assemblies are provided to separate the launch vehicle, the adapter equipment section, and the adapter retrograde section from the reentry module. The assemblies completely sever inter-connecting tubes, wires, bundles, titanium straps and structural skin of the sections.
Guillotines are provided for cutting wire bundles, cables, and bolts. These are knife-like devices explosively driven through the item to be severed. Redundancy is provided through use of two guillotines, one on either side of the separation plane. The guillotines used for severing cables or bolts contain two cartridges. Function of either cartridge is sufficient to sever the cable or the bolt.
Cutter-sealers provide for sealing and cutting of the orbit attitude and maneuvering system propellant lines prior to section separation. The lines are sealed to prevent leakage of fuel or oxidizer residue at the same instant that the tubes are severed. Redundant cutting is provided by using two cutter-sealers, one on either side of the separation plane. Each contains one cartridge.
The horizon sensor fairing release assembly is secured to the spacecraft by a cartridge-actvated single-point hold- down device containing two cartridges The cartridge is sufficient to jettison the fairing. The horizon sensor fairing release assembly is enclosed to preclude the escape of any pyrotechnic by-products, thus protecting the delicate horizon sensors against damage during fairing jettison.
The horizon sensor is secured to the spacecraft by two-cartridge, single-point, hold-down device. The function of a single cartridge is sufficient to jettison the sensors and the cartridges from the spacecraft. This is accomplished following retrograde and prior to reentry. The electrical connectors, through which the cartridges are initiated, are disconnected by the force of ejection.
Normally open or normally closed pyrotechnic valves are provided for isolation and control of pressurants and propellants. Normally closed pyrotechnic valves isolate the pressurants and propellants in the tanks of the orbit attitude and maneuvering system and the reentry control system from the remainder of the system during prelaunch. Orbit attitude and maneuvering system valves are pyrotechnically opened shortly before launch. The normally closed reentry control system valves are opened prior to reentry. The orbit attitude and maneuvering system is provided with both normally closed and normally open pyrotechnic valves actuated in the event of pressure regulator malfunction.
Pyrotechnic switches are provided for opening electrical circuits in the wire bundles prior to severing. Each pyrotechnic switch contains a single cartridge with dual bridge wires.
A mild detonating fuse separator is provided to break all bolts that attach the rendezvous and recovery section to the reentry module. The separation assembly contains two detonators and an explosive ring assembly. Booster charges initiated by the detonators cause simultaneous detonation in both mild detonating fuse strands of the explosive ring assembly. Either strand has sufficient energy to break all the attachment bolts.
Each retrograde rocket contains two independent cartridge-actuated igniters mounted adjacent to the rocket nozzle. Each igniter contains an electrically-actuated cartridge, 20 boron/potassium nitrate pellets, and a 0.04-pound solid propellant charge of polysulfide/ammonium prechlorate. When fired, the cartridge ignites the boron/potassium nitrate pellets which in turn ignite the solid propellant charge. The propellant will burn for 0.35 second, discharging its exhaust gases into the retrograde rocket cavity and igniting the basic retrograde rocket. Either of the two igniters provided for each rocket is sufficient to ignite the retrograde rocket.
The parachute mortar which deploys the pilot parachute, contains two electrically-initiated cartridges. Function of a single cartridge is sufficient to eject the pilot parachute from the mortar tube. The pilot parachute is deployed in a reefed condition.
Two lanyard-initiated reefing cutters, incorporating a 6-second pyrotechnic time delay, are provided to complete pilot parachute deployment. Three lanyard-initiated reefing cutters, incorporating a 10-second pyrotechnic time delay, are provided to complete main parachute deployment.
After the main parachute has deployed and the spacecraft is suspended from a single point, a parachute disconnect is actuated to allow the spacecraft to rotate to a two-point suspension. Two parachute disconnects jettison the main parachute upon impact. Each of these disconnects contains two electrically-initiated charges.
Copyright 1997, 1998, 1999 by John
Duncan |