NASA Standard Initiator

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.

Development

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 reliable, 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 redesign 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]

References

1. Proceedings of Electric Initiator Symposium - 1963 (PDF). Franklin Institute, Philadelphia, Pennsylvania: U.S. Army Materiel Command. 1 October 1963. pp. 3-1 –3-22. Archived from the original on 22 August 2022. Retrieved 24 August 2022.
2. Seeholzer, Thomas L.; Smith, Floyd Z.; Eastwood, Charles W.; Steffes, Paul R. (1 January 1995). Applications catalog of pyrotechnically actuated devices/systems (PDF). Cleveland, OH: NASA Lewis Research Center. pp. 66–67. Archived from the original (PDF) on 22 August 2022.
3. Apollo Spacecraft and Saturn V Launch Vehicle Pyrotechnics/Explosive Devices (PDF). Houston, TX: NASA, Johnson Space Center. 1 January 2009. Archived from the original (PDF) on 6 January 2022.
4. Apollo Experience Report - Spacecraft Pyrotechnic Systems (PDF). Houston, TX: NASA, Lyndon B. Johnson Space Center. 1 March 1973. Archived from the original (PDF) on 12 December 2020.

See also

• NASA standard detonator