The remaining parts of this chapter establish the design requirements for Category A ordnance and ordnance systems during transportation, handling, storage, installation, testing, and connection at the payload processing facility and launch site area. Category B ordnance and ordnance systems do not have to meet the design requirements identified in this chapter; however, Category B ordnance and ordnance systems shall meet the operational requirements identified in Volume 6 of this publication.
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13.2.1. Ordnance Subsystem Identification. Ordnance systems include the following subsystems. All of these subsystems are subject to the design requirements described below.
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13.2.1.1. Power Source. The power source may be a battery, a dedicated power bus, or a capacitor.
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13.2.1.2. Firing Circuit (the path between the power source and the initiating device). The firing circuit includes the electrical path and the optical path for laser initiated ordnance.
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13.2.1.3. Control Circuit. The control circuit activates and deactivates the safety devices in the firing circuit.
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13.2.1.4. Monitor Circuit. The monitor circuit monitors status of the firing circuits.
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13.2.1.5. Initiating Device. The initiating device converts electrical, mechanical, or optical energy into explosive energy.
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13.2.1.6. Receptor Ordnance. Receptor ordnance includes all ordnance items such as the explosive transfer system (ETS), separation charge, explosive bolt installed downstream of the initiating devices.
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13.2.2. Preclusion of Inadvertent Firing. Ordnance devices and systems shall be designed to preclude inadvertent firing of any explosive or pyrotechnic components when subjected to environments encountered during ground processing including shock, vibration, and static electricity encountered during ground processing.
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13.2.3. Failure Mode Effects and Criticality Analysis. A comprehensive FMECA shall be performed on all ordnance systems in accordance with the requirements of a jointly tailored MIL-STD-882C.
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13.3.1. Ordnance Electrical Circuit General Design Requirements
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13.3.1.1. Ordnance system circuitry shall be protected to preclude energy sources such as electromagnetic energy or from causing undesired output of the system.
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Solutions for protection of ordnance system circuitry include shielding, filtering, grounding, and other isolation techniques that can preclude the energy sources such as electromagnetic energy from the range and/or launch vehicle from causing undesired output of the system.
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13.3.1.2. Category A ordnance systems shall be designed so that the initiating devices can be installed in the system just before final electrical hookup on the launch pad.
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It is understood that the requirement for designing ordnance so that the initiating devices can be installed in the system just before final electrical hookup on the launch pad cannot always be met. Alternative proposed processing scenarios will be supported with the detailed system design and hazard assessments.
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13.3.1.2.1. Initiating device locations shall be accessible to facilitate installation and removal and electrical connections as late as possible in the launch countdown.
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13.3.1.2.2. Access required at the launch complexes shall be identified and demonstrated to accommodate this accessibility requirement.
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13.3.1.3. Separate power sources and/or busses shall be required for ordnance initiating systems.
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13.3.1.4. RF energy shall not be used to ignite initiating devices.
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13.3.1.5. Electrical firing circuits shall be isolated from the initiating ordnance case, electronic case, and other conducting parts of the flight hardware.
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13.3.1.5.1. If a circuit is grounded, there shall be only one interconnection (single ground point) with other circuits. Static bleed resistors of 10 kilo-ohms to 100 kilo-ohms are not considered to violate the single point ground.
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13.3.1.5.2. This interconnection shall be at the power source only.
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13.3.1.5.3. Other ground connections with equivalent isolation shall be identified and assessed individually.
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13.3.1.6. Ungrounded circuits capable of building up static charge shall be connected to the structure by static bleed resistors of between 10 kilo-ohms and 100 kilo-ohms.
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13.3.1.7. Firing circuit design shall preclude sneak circuits and unintentional electrical paths due to such faults as ground loops and failure of solid state switches.
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13.3.1.8. Redundant circuits shall be required if loss of power or signal may result in injury to personnel or be a detriment to safety critical systems.
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13.3.1.9. The elements of a redundant circuit shall not be terminated in a single connector where the loss of such connector will negate the redundant feature.
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Redundant circuits should be separated to the maximum extent possible.
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13.3.2. Ordnance Electrical Circuit Shielding
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13.3.2.1. Shields shall not be used as intentional current-carrying conductors.
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13.3.2.2. Electrical firing circuits shall be completely shielded or shielded from the initiating ordnance back to a point in the firing circuit at which filters or absorptive devices eliminate RF entry into the shielded portion of the system.
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13.3.2.3. RF shielding shall provide a minimum of 85 percent of optical coverage ratio.
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Optical coverage ratio is the percentage of the surface area of the cable core insulation covered by a shield. A solid shield rather than a mesh shield would have 100 percent coverage.
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13.3.2.4. There shall be no gaps or discontinuities in the termination at the back faces of the connectors or apertures in any container that houses elements of the firing circuit.
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13.3.2.5. Electrical shields terminated at a connection shall be joined around the full 360 degree circumference of the shield.
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13.3.2.6. All metallic parts of the initiating ordnance subsystem that are physically connected shall be bonded with a DC resistance of less than 2.5 milliohms.
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13.3.2.7. Firing, control, and monitor circuits shall all be shielded from each other.
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13.3.3. Ordnance Electrical Circuits Wiring
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13.3.3.1. Twisted shielded pairs shall be used unless other configurations such as coaxial leads can be shown to be more effective.
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13.3.3.2. For low voltage circuits, insulation resistance between the shield and conductor at 500 volts DC minimum shall be greater than 2 megaohms.
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13.3.3.3. For high voltage circuits, insulation resistance between the shield and conductor at 150 percent of rated output voltage or 500 volts, whichever is greater, shall be greater than 50 mega-ohms.
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13.3.3.4. Wires shall be of sufficient size to adequately handle 150 percent of the design load for continuous duty signals (100 seconds or more) on the safety critical circuit.
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13.3.3.5. Splicing of firing circuit wires or overbraid shields is prohibited.
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13.3.3.6. The use of wire wrap to connect wire shields is prohibited.
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13.3.4. Ordnance Electrical Connectors
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13.3.4.1. The outer shells of electrical connectors shall be made of metal.
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13.3.4.2. Electrical connectors shall be selected to eliminate the possibility of mismating. Mismating includes improper installation as well as connecting wrong connectors.
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13.3.4.3. Electrical connectors shall be of the self-locking type or lock wiring shall be used to prevent accidental or inadvertent demating.
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13.3.4.4. The design shall ensure that the shielding connection for an electrical connector is complete before the pin connection.
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13.3.4.5. Shields need not be carried through a connector if the connector can provide RF attenuation and electrical conductivity at least equal to that of the shield.
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13.3.4.6. Circuit assignments and the isolation of firing pins within an electrical connector shall be so that any single short circuit occurring as a result of a bent pin shall not result in more than 10 percent of the no-fire current. A bent pin analysis shall be performed on all electrical connectors.
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13.3.4.7. There shall be only one wire per pin and in no case shall an electrical connector pin be used as a terminal or tie-point for multiple connections.
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13.3.4.8. Spare pins shall be allowed in electrical connectors except where a broken spare pin may have an adverse effect on a firing or control circuit.
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13.3.4.9. Source circuits shall terminate in an electrical connector with female contacts.
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13.3.4.10. Electrical connectors shall not rely on spring force to mechanically lock mating halves together if they are to be used on safety critical circuits.
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13.3.4.11. Electrical connectors shall be capable of adequately handling 150 percent of the designed electrical load continuous duty signal (100 seconds or more) on safety critical circuits.
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13.3.4.13. Separate cables and connectors shall be used when redundant circuits are required.
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13.3.5. Ordnance Electrical Circuit Switches and Relays
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13.3.5.1. Switches and relays shall be designed to function at expected operating voltage and current ranges under worst case ground environmental conditions, including maximum expected cycle life.
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13.3.5.2. Switches and relays used for inhibits shall not be considered adequate for RF isolation and absorption unless demonstrated by analysis and test for the specific environment of use.
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13.3.6. Ordnance Electrical Monitoring, Checkout, and Control Circuits
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13.3.6.1. All circuits used to arm or disarm the firing circuit shall contain means to provide remote electrical indication of their armed or safe status.
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13.3.6.1.1. These inhibits shall be directly monitored.
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13.3.6.1.2. GSE shall be provided to electrically monitor arm and safe status of the firing circuit at all processing facilities including launch complexes up to launch.
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13.3.6.2. Monitoring, control, and checkout circuits shall be completely independent of the firing circuits and shall use a separate and non-interchangeable electrical connector.
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13.3.6.3. Monitoring, control, and checkout circuits shall not be routed through arm or safe plugs.
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13.3.6.4. The electrical continuity of one status circuit (safe or arm) shall completely break before the time that electrical continuity is established for the other status circuit (arm or safe).
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13.3.6.5. The safety of the ordnance system shall not be affected by the external shorting of a monitor circuit or by the application of any positive or negative voltage between 0 and 35 volts DC to a monitor circuit.
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13.3.6.6. Monitoring and checkout of current in a low voltage electro-explosive system firing line shall not exceed 1/10 the no-fire current of the EED or 50 milliamperes, whichever is less.
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13.3.6.7. Monitor circuits shall be designed so that the application of the operational voltage will not compromise the safety of the firing circuit nor cause the ordnance system to be armed.
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13.3.6.8. Tolerances for monitor circuit outputs shall be compatible with the tolerances specified for the PSWG and Range Safety required parameter to be verified. Tolerances for monitor circuit outputs shall be specified for both RF and hardline.
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13.3.6.9. Maximums and minimums for monitor circuit outputs shall be specified.
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13.3.6.10. No single point failure in monitoring, checkout, or control circuitry and equipment shall compromise the safety of the firing circuit.
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13.3.6.11. Firing circuits that do not share a common fire command shall be electrically isolated from one another so that current in one firing circuit does not induce a current greater than 20 dB below the no-fire current in any firing output circuit. Control circuits shall be electrically isolated so that a stimulus in one circuit does not induce a stimulus greater than 20 dB below the activation level in any firing circuit.
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13.3.6.12. The monitor circuit that applies current to the EED shall be defined to limit the open circuit output voltage to 1 volt.
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