Insensitive Rocket Motor Grain Ignition Control
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Solution Overview
Problem
Conventional rocket motors are not designed to prevent unintended ignition or detonation during fast or slow cookoff tests, which can result in excessive thrust or collateral damage, and existing solutions do not adequately control thrust production to meet insensitive munition standards.
Innovation Solution
The design incorporates an inhibitor layer on the grain surface to delay ignition and a secondary igniter that ignites at a predetermined temperature, controlling the burn rate and thrust production, while maintaining mechanical stability and compatibility with the propellant material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional rocket motor design is used, then normal thrust production is achieved, but the motor is vulnerable to unintended ignition and detonation during cookoff tests
Solution Approach 1:
The propellant grain is segmented into multiple sections with different ignition characteristics. A first section is designed to be resistant to cookoff ignition while a second section can be intentionally ignited. This segmentation allows the motor to distinguish between accidental heating and intentional ignition commands, resolving the contradiction between reliability and harmful factor vulnerability.
Solution Approach 2:
An intermediary ignition system is introduced that requires active triggering to initiate combustion. The ignition system acts as a mediator between the control system and the propellant, ensuring that combustion only occurs when deliberately commanded rather than from passive thermal exposure during cookoff tests.
2Reliability
If pressure relief vents are added to prevent detonation, then safety is improved, but thrust control capability is reduced
Solution Approach 1:
The pressure relief system is designed to be dynamic rather than static. Pressure relief vents are activated only when detonation threatens, not during normal operation. The system transitions from a closed state during normal thrust production to an open state only when pressure exceeds safe thresholds, maintaining both safety and operational control capability.
3Power
If propellant surface area is increased to control thrust, then thrust magnitude is improved, but sensitivity to inadvertent ignition increases
Solution Approach 1:
Different regions of the propellant grain are assigned different qualities and ignition sensitivities. The first section has properties that make it resistant to cookoff ignition, while the second section is designed for controlled ignition. This local differentiation allows increased total propellant surface area for thrust control without proportionally increasing sensitivity to inadvertent ignition.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces thrust during safety modes, preventing unintended ignition and detonation, and meets the requirements for insensitive munitions by controlling thrust and pressure within the rocket motor, as demonstrated by experimental data showing reduced thrust and increased burn time during cookoff tests without impacting normal operation.
Implementation Method 1
an inhibitor layer on the grain surface to delay ignition
Implementation Method 2
a secondary igniter that ignites at a predetermined temperature, controlling the burn rate and thrust production
Implementation Method 3
the fuel within the motor to burn
Data Source
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AI summary
There is disclosed a solid fuel rocket motor including a center-perforated solid fuel grain. The solid fuel grain may be adapted to burn outwardly from a center surface facing the center perforation when ignited by a primary igniter during a normal mode of operation. The solid fuel grain may be further adapted to burn longitudinally from an end face when ignited by a secondary igniter during a safety mode of operation.