End-Burning Propellant Grain With Embedded High-Burn-Rate Sticks
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Solution Overview
Problem
End-burning rocket motors face challenges with smoke and toxic gas production due to limited mass burning rates and the use of lead salts in minimum-smoke propellants, which affect visibility and safety, and increasing the motor diameter has practical limitations.
Innovation Solution
A propellant grain design with embedded faster-burning sticks creates localized concave regions, increasing the burning surface area without the need for lead salts or other toxic additives, allowing for stable thrust and reduced smoke generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If lead salts and lead-containing compounds are used as burning rate modifiers in minimum-smoke propellants to achieve plateau burning rates, then temperature-insensitive burning rate is improved, but toxicity and environmental harm worsen
Solution Approach 1:
The patent removes lead salts and lead-containing compounds from the propellant formulation entirely, replacing them with alternative burning rate modifiers such as antimony trioxide, bismuth oxide, or metal powders. This extraction of the harmful substance while maintaining the desired plateau burning rate behavior directly resolves the contradiction between burning rate stability and toxicity.
2Power
If the area of the burning surface is enlarged to increase thrust, then thrust magnitude is improved, but motor diameter increases which has practical limitations
Solution Approach 1:
The patent employs a star-shaped propellant grain geometry with multiple points or lobes extending from a central core. This curved, non-circular configuration dramatically increases the burning surface area compared to a simple cylindrical grain of the same motor diameter, thereby increasing thrust without requiring a larger motor diameter. The star shape allows the burning surface to extend into the motor case volume more efficiently.
3Power
If mass burning rate is increased to achieve higher thrust, then thrust magnitude is improved, but smoke and toxic gas production worsen
Solution Approach 1:
The patent modifies the chemical composition parameters of the propellant by selecting fuel and oxidizer combinations that inherently produce less smoke and toxic gases. This includes using low-smoke propellant formulations such as those based on HMX or CL-20 with ammonium perchlorate oxidizer, and adjusting the propellant formulation to achieve the desired mass burning rate while minimizing smoke production through careful selection of combustion chemistry.
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 design maintains consistent thrust across varying temperatures and pressures while minimizing smoke and toxic by-products, enhancing safety and performance without compromising ballistic properties.
Implementation Method 1
Upon ignition of the grain from the ignition (aft) end, the relatively high heat generated by the faster-burning stick(s) causes the regions of the matrix propellant that are closest to each stick to burn faster than regions that are further away
Data Source
AI summary
An end-burning grain of a solid rocket motor or other gas-generating device is supplemented with one or more sticks of high-burn-rate propellant embedded in a matrix of a relatively low-burn-rate propellant. The sticks increase the burning surface area as the grain burns by forming conical indentations in the surface.