The NASA Standard Initiator (NSI) is a pyrotechnic device used to set off other pyrotechnic devices. It is the central multi-purpose component of a modular system of detonating cords, pyrotechnics and various other explosive charges with many different uses.^[1]

The ignition charge of the device is a blend of zirconium, potassium perchlorate, Viton B and graphite, often abbreviated as ZPP.^[2]

Uses of the device include:

• Setting off pressure cartridges, pocket sized gas generators which in turn pneumatically activate other systems.
• Setting off the NASA standard detonator, which itself activates other systems explosively.
• Triggering Pyrotechnic Circuit Interrupters, severing bundles of electrical cables.
• Triggering explosive valves to open/close pressurization lines or fuel lines.
• Triggering a pyrotechnic pin puller which opens a Marman clamp, separating two spacecraft.
• Acting as an igniter.

The NASA Standard Initiator (NSI) was developed from the Single-Bridgewire Apollo Standard Initiator (SBASI) which was itself based on the Apollo Standard Initiator (ASI).^[3]

To provide additional redundancy and thus make the spacecraft more relieable, a double-bridgewire design was utilized, but during development of the Apollo Standard Initiator it was found that the original design responded unfavorably to RF frequencies. This resulted in a re-design with a single bridgewire which was approved in 1966. This new design introduced several other changes to improve resistance and give the device a longer shelf life, such as switching the Material of the body from 17-4 PH steel to Inconel 718.^[4]
After the Apollo program ended, the Initiator was renamed and re-used on other spacecraft, such as the Space Shuttle.^[3]