Multi-Stage Solid Propellant Motor Thrust Control
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Solution Overview
Problem
Solid propellant propulsion systems face challenges in achieving variable thrust profiles during flight, as initial high thrust requirements decrease as propellant is consumed, potentially leading to excessive acceleration and damage to payloads or propulsion motor components.
Innovation Solution
A multi-stage solid propellant propulsion motor design featuring a forward and aft propellant grain, with an ablative material layer that ignites the aft propellant grain upon erosion, allowing for staged combustion and variable thrust profiles, including a nozzle structure and burn inhibitor layers to manage the combustion process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single propellant grain is used, then the propulsion motor structure is simple, but the thrust profile cannot be optimized for variable mission requirements
Solution Approach 1:
The propellant system is divided into multiple grains (forward propellant grain and aft propellant grain) with different formulations and burn characteristics. Each grain is separated by a burn inhibitor layer, allowing independent control of combustion phases to achieve optimized thrust profiles for different mission requirements.
Solution Approach 2:
Different propellant formulations are used in different regions of the motor. The forward propellant grain uses a formulation optimized for initial high thrust, while the aft propellant grain uses a formulation optimized for sustained thrust, allowing each region to contribute its specific performance characteristics.
2Force
If high thrust is maintained throughout the burn, then initial acceleration requirements are met, but excessive acceleration damages payloads and components
Solution Approach 1:
The combustion process is divided into distinct phases: an initial high-thrust phase using the forward propellant grain, followed by a transition phase where the ablative material erodes to ignite the aft propellant grain, and finally a sustained-thrust phase. This periodic variation in thrust characteristics allows the system to meet initial acceleration requirements while preventing excessive acceleration damage later in the burn.
Solution Approach 2:
The propellant system changes its operational parameters by transitioning from a high-thrust formulation to a sustained-thrust formulation. The burn rate, pressure, and temperature parameters are naturally varied through the sequential combustion of different propellant grains, allowing optimal performance across different flight phases.
3Adaptability or versatility
If multiple propellant grains are used, then variable thrust profiles are achieved, but the manufacturing and assembly process becomes complex
Solution Approach 1:
The aft propellant grain is positioned within the hollow core created by the forward propellant grain, forming a nested configuration. The burn inhibitor layer and ablative material are integrated into this nested structure, allowing multiple components to be assembled in a compact, space-efficient manner that simplifies the overall manufacturing process.
4Duration of action of moving object
If propellant is consumed continuously, then thrust is maintained, but the initial high thrust decreases leading to potential damage
Solution Approach 1:
The forward propellant grain is designed to burn completely before the aft propellant grain is ignited. This preliminary combustion phase establishes the initial high thrust required for launch, and the complete consumption of the forward grain ensures that the transition to the aft grain occurs at the optimal moment to maintain thrust without causing damage.
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
The design enables optimized thrust profiles throughout flight by transitioning from high initial thrust to lower, sustained thrust, reducing the risk of damage and improving propulsion efficiency, while allowing for weight savings and simplified design compared to complex systems.
Implementation Method 1
the ablative material layer is eroded in response to heat from gaseous combustion by-products from burning the forward propellant grain
Implementation Method 2
Ignition at the bore surface of the solid propellant generates high pressure gas, which is expelled from the bore through a nozzle to generate thrust
Implementation Method 3
a first burn inhibitor layer disposed axially adjacent to the forward propellant grain; a second burn inhibitor layer disposed axially adjacent to an aft end of the aft propellant grain
Implementation Method 4
Ignition at the bore surface of the solid propellant generates high pressure gas, which is expelled from the bore through a nozzle to generate thrust
Data Source
AI summary
A solid propellant propulsion motor may comprise: a forward propellant grain extending along a longitudinal axis of a motor case between a forward end of the motor case and a first burn inhibitor layer in the motor case; the first burn inhibitor layer disposed axially adjacent to the forward propellant grain; an aft propellant grain disposed axially adjacent to the first burn inhibitor layer; a second burn inhibitor layer disposed axially adjacent to an aft end of the aft propellant grain; and an ablative material layer disposed on a radially inner surface of the aft propellant grain.