Failure Modes

Introduction:

Rocket propulsion systems can fail for many reasons. Many of these failures will have adverse consequences on safety, cost, life and/or schedule. Hence failure prevention is necessary (up to the point where the effort of failure prevention no longer weighs up against the consequences of failure). Many of these failures can be prevented through proper design, testing, and operation. By studying the types of things that can go wrong, we can design and build better equipment and learn how to operate it more safely and effectively. Below, we will present a list of typical failure modes for chemical rocket systems allthough part of the information contained will also be applicable to other rocket systems. This list in part is derived using the information obtained from [IEAS]. But first we will define "failure mode".

Definition

Failure mode essentially describes how a system, subsystem, component, or part fails. It does not say anything on why nor on the effect of the failure.

Failure Modes:

Below some failure modes are listed for rocket propulsion systems. The failure modes are given per major subsystem.

  • Propellant feed system (in case of liquid propellant(s))
    • Valves sticking open or closed (e.g. due to freezing of valves or clogging)
    • Regulator regulating high or low (e.g. due to contamination; may cause overpressure or too low a feed pressure)
    • Regulator leakage (may cause overpressure)
    • Sensor (e.g. temperature or pressure) providing no or faulty reading (e.g. due to freezing of propellant)
    • Blockage of filters, feed lines etc. due to e.g. contamination or freezing of propellants
    • Loss of pressurization (e.g. due to pressurant leakage)
    • Failure of turbo-pump (e.g. due to freezing, turbine blade cracks, bearing spalling[1], imbalance, or lack of lubrication)
    • Rupture of tube/pipe connections
    • Line (tube/pipe) rupture (plumbing breakage) due to mechanical/thermal stress, cryogenic boiling/inadequate venting, or oxidizer/contaminate reactions
    • Failure of pneumatics system (pneumatics subsystem provides pressurised helium to open and close the pneumatic valves) to open and close valve
  • Propellant storage system (In case of liquid propellant(s))
    • Tank shell rupture (due to e.g. improper welding or shell damage during handling etc.)
    • Running out of propellant (due to e.g. tank leakage or expulsion system not working properly)
    • Low fuel (propellant) situation not monitored
    • Level sensor providing a wrong indication (see above)
  • Thrust generation system:
    • Failure to ignite/start (due to e.g. weak ignition or failure of electrical control system)
    • Slow ignition e.g. due to weak igniter,or igniter not inserted properly
    • Chamber shell/vessel rupture (due to e.g. over-pressurization beyond the shells' ultimate limits, insufficient brazing, shell damage, insufficient cooling)
    • Improper propellant mixture (poor performance, or excessive chamber temperatures)
    • "Hard Start" when liquids enter chamber and evaporate before ignition then detonate
    • Weak burn performance
    • Engine structure failure
    • Failure of TVC system (e.g. due to jamming of TVC actuators)

References:

 

                                                  

[1] To break up into chips or fragments.

 

Naam auteur: SSE
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