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“Apollo Explosive Devices” by
Quest Volume: 27 #1 (2020)
This article describes the use of explosive devices carried by the Apollo spacecraft during the six missions that landed on the Moon. The devices powered one-time events such as opening valves, cutting ties, disconnecting electronics, and deploying parachutes. Explosive devices were used because of their high reliability and low weight, size, and cost compared to electromechanical devices (motors and solenoids).
Explosives were used to separate the parts of the spacecraft. Separation can include structural, electrical, water, coolant, and oxygen disconnection. Structural connections in Apollo were made with nuts and bolts, tension ties, splice plates, and tie-down straps. Before cutting an electrical connection it was “dead-faced.” This was done by circuit interrupters that pulled two connectors apart. The physical wires could then be cut by a guillotine without shorting one circuit to another. Similarly water and oxygen lines were not cut by guillotine until valves had been closed to prevent spillage.
Explosives produce their effects by a chemical reaction. The substances might be single molecules or mixtures of two or more molecules. For instance, gunpowder is a mixture of a nitrate, sulfur, and carbon that reacts when the nitrate oxidizes the sulfur and carbon. Nitroglycerine is an explosive consisting of a single molecule that decomposes rapidly into oxygen, nitrogen,
water, and carbon monoxide.
Some explosives react by a process called deflagration. The reaction generates heat, which ignites the reaction in neighboring regions of the substance. The region of ignition moves due to thermal conduction at subsonic speed. Other explosions proceed by detonation. The reaction propagates by a shock wave that moves at supersonic speed. A substance can begin deflagration
and then change to detonation when temperature and pressure increase.
Numerous graphics and sketches accompany the text and provide additional detail.
Durbin, Edgar. “Apollo Explosive Devices.” Quest: The History of Spaceflight Quarterly 27, no. 1 (2020): 29-50.