Variable Burn-Rate Solid Rocket Motor Ignition
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Solution Overview
Problem
Conventional solid rocket motors have a predefined thrust profile, limiting their mission envelope and requiring complex barrier and igniter systems with high mass fraction penalties, making it difficult to achieve variable thrust profiles.
Innovation Solution
Incorporating thermally or electrically conductive wires into the propellant grain to increase the burning surface area, allowing for passive or active ignition and ablation, thereby enhancing the burn rate and thrust of the rocket motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional solid rocket motors use a predefined thrust profile, then the motor structure is simple, but the mission envelope is limited and thrust control is inflexible
Solution Approach 1:
The propellant grain is segmented into multiple independent segments, each with its own conductive wire igniter. This allows selective ignition of individual segments to create variable thrust profiles without requiring complex barrier systems. Each segment can be ignited independently through its conductive wire, providing flexible thrust control.
Solution Approach 2:
The system transitions from a static, predefined thrust profile to a dynamic, controllable thrust profile. Conductive wires embedded in the propellant grain can be activated at different times and positions, allowing the thrust profile to be dynamically adjusted during operation based on mission requirements.
2Adaptability or versatility
If multiple pulse rocket motors are used to allow thrust variation, then the thrust profile can be varied, but the mass fraction penalty of propellant is high
Solution Approach 1:
The igniter and barrier functions are merged into a single conductive wire element embedded directly in the propellant grain. This eliminates the need for separate barrier systems and reduces the overall propellant mass fraction while maintaining the capability for variable thrust profiles through selective segment ignition.
Solution Approach 2:
The conductive wire acts as an intermediary element that directly contacts and ignites the propellant segments. This eliminates the need for complex igniter systems and barrier materials, reducing the mass penalty while enabling precise control over which propellant segments are ignited.
3Productivity
If conductive wires are added to increase burn surface area, then the burn rate and thrust increase, but the device complexity increases
Solution Approach 1:
The conductive wire serves multiple functions simultaneously: it acts as a structural support element, a heat conduction path, and an electrical ignition element. This multi-functionality reduces the need for additional separate components, minimizing the increase in device complexity while achieving increased burn surface area and improved burn rate.
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 use of conductive wires enables flexible thrust control, increasing the burn surface area and burn rate of the propellant grain, allowing for single-pulse or multi-pulse rocket motors with improved thrust profiles and reduced mass penalties.
Implementation Method 1
The thermally conductive wire may be passively activated when the propellant grain is ignited. The burn front of the propellant grain directly impinges the thermally conductive wire to heat the wire.
Implementation Method 2
The electrically conductive wire may be activated in response to an electrical signal such that the wire is activated actively, or on-demand.
Implementation Method 3
The conductive wire is interposed between the propellant inhibited center bore and the propellant grain to increase a burn surface area of the burnable propellant grain via ablation of the propellant inhibited center bore
Data Source
Figure 1
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AI summary
A solid rocket motor uses at least one thermally conductive wire or at least one pair of electrically conductive wires to increase a burn surface area of a propellant grain and thus a thrust of the rocket motor. The rocket motor includes a pulse chamber containing a burnable propellant grain, a propellant inhibited center bore bonded to surfaces of the burnable propellant grain, and at least one conductive wire coupled to the burnable propellant grain and arranged in variable regions along the propellant inhibited center bore. The conductive wire is configured for passive or active activation to ignite the propellant inhibited center bore that subsequently burns in the variable regions. The thermally conductive wire is formed of a refractory metal or refractory alloy material that enables the entire length of the wire to be heated simultaneously or nearly simultaneously when the wire is passively activated.