Lesson Info:

• Lesson Number: 0591
• Lesson Date: 1998-05-14
• Submitting Organization: JPL
• Submitted by: C. Guernsey/D. Oberhettinger

Subject:

Abstract:

Two satellites with different propulsion system designs were lost in 1993 and 1994 when blow-by from pyrovalves interacted violently with propellants. To prevent detonation of fuel due to the compression of hydrazine and its ignition by pyrovalve blow-by, use non-pyrotechnic valves or a zero blow-by pyrovalve design, or fire a pyrovalve only when there is a vacuum downstream of the valve.

Description of Driving Event:

Two satellites with different propulsion system designs were lost in 1993 and 1994. Limited telemetry was received on the incidents. Subsequent failure investigation focused on possible propulsion feed system design flaws. In both cases, pyrovalves were used to isolate the hydrazine supply until the satellite was separated from the launch vehicle.

[D]

In accordance with a common design practice for engine feed systems, two pyrovalves were placed in parallel to provide redundancy. With the hydrazine tank isolated, pressurized fuel was present upstream of the pyrovalves (e.g., Point A), but only a dry nitrogen "pad gas" at low pressure downstream of the pyrovalves (e.g., Point B). On one spacecraft it was unclear what the gas composition was and whether it was totally vented through the thruster prior to the priming event.

During priming of the hydrazine system, the primary pyrovalve was fired to charge propellant lines leading to the engine. When the propellant reached the thruster valves and stopped, it produced a pressure surge. Under certain conditions, this surge could cause exothermic decomposition of the fuel, and tests were conducted to assess if the prevalent conditions were conducive to exothermic decomposition. This particular failure mode was never observed during the failure investigations. However, when the backup pyrovalve was fired a second later during one test, the blow-by of hot gas into the lines between Points A and B detonated the decomposed fuel; this then breached the fuel lines on both sides of the backup pyrovalve.

The tests did not exhibit this detonation failure mode when, just prior to firing the backup pyrovalve, the pad gas was evacuated to leave a vacuum downstream of both pyrovalves.

Reference(s): GIDEP Advisory No. GH-P-94-01, "Pyrovalve, Titanium, 1/2", Normally Closed Single Initiates," Revised May 1, 1995.

Lesson(s) Learned:

Blow-by from pyrovalves can interact violently with propellants in propulsion systems.

Recommendation(s):

To prevent detonation of fuel in propulsion systems due to the compression of hydrazine and its ignition by pyrovalve blow-by:

1. Use non-pyrotechnic valves such as latching valves, or
2. Use a zero blow-by pyrovalve design, and/or
3. Fire a pyrovalve only when there is a vacuum downstream of the valve.

Evidence of Recurrence Control Effectiveness:

Documents Related to Lesson:

Mission Directorate(s):

Additional Key Phrase(s):

• Energetic Materials - Explosive/Propellant/Pyrotechnic
• Hardware

Additional Info:

Approval Info:

• Approval Date: 1998-06-16
• Approval Name: Carol Dumain
• Approval Organization: 125-204
• Approval Phone Number: 818-354-8242