Two-Piece Aft Closure for Rocket Motor Cases
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Solution Overview
Problem
Existing rocket motor aft closures made from a single piece of material face challenges in thermal expansion mismatch with the motor case, leading to potential leaks and high manufacturing costs, especially when using materials like titanium, and have issues with strength and weight when using aluminum.
Innovation Solution
A two-piece aft closure assembly with a retaining ring piece made from a material similar to the motor case and a blast tube and closure piece made from a different material, utilizing a specialized sealing system with orthogonal seals to accommodate different thermal expansion coefficients and simplify manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the aft closure is made from titanium to reduce mass, then the strength to weight ratio is improved, but the manufacturing cost increases significantly
Solution Approach 1:
The aft closure is divided into two separate pieces: a titanium retaining ring and an aluminum blast tube assembly. This segmentation allows each component to be optimized independently - the retaining ring uses high-strength titanium where needed, while the blast tube uses inexpensive, easily machined aluminum, thereby reducing overall manufacturing cost while maintaining weight benefits.
Solution Approach 2:
Titanium material is applied locally only to the retaining ring portion where high strength is required for structural integrity and thermal expansion matching with the motor case. The blast tube portion uses aluminum where lower cost and easier manufacturability are priorities, achieving cost reduction without sacrificing critical performance areas.
2Ease of manufacture
If the aft closure is made from aluminum to reduce cost and simplify manufacturing, then the ease of manufacture is improved, but the coefficient of thermal expansion mismatch with the motor case causes potential leaks
Solution Approach 1:
The closure is segmented into a titanium retaining ring and aluminum blast tube, allowing the titanium ring to provide thermal expansion compatibility with the motor case while the aluminum tube provides cost-effective manufacturing.
Solution Approach 2:
The titanium retaining ring acts as an intermediary component between the motor case and the aluminum blast tube. It mediates the thermal expansion mismatch by providing a interface that matches the motor case's thermal properties, preventing leaks while allowing the use of inexpensive aluminum for the blast tube portion.
3Strength
If a single-piece titanium aft closure is used, then the strength is improved, but the manufacturing complexity and cost increase due to intricate details
Solution Approach 1:
The complex single-piece design is segmented into two simpler components. The retaining ring maintains the intricate details for structural strength and thermal compatibility, while the blast tube is a simpler, easily manufactured aluminum component, reducing overall manufacturing complexity.
Solution Approach 2:
Complex titanium features are localized only to the retaining ring where structural strength is critical. The blast tube uses simple aluminum construction where high strength is not required, reducing manufacturing complexity while maintaining adequate structural performance.
4Device complexity
If the aft closure is made from a monolithic piece, then the device complexity is reduced, but the ability to use different materials with different thermal expansion coefficients is limited
Solution Approach 1:
The closure is segmented into two pieces that can be made from different materials. This segmentation enables the use of titanium for thermal compatibility and aluminum for cost-effective manufacturing, providing material selection flexibility while maintaining relatively simple assembly procedures.
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 two-piece design reduces manufacturing costs and complexity while maintaining effective sealing across a range of temperatures, suitable for pressure vessels like rocket motor cases, by using less expensive materials and allowing for different thermal expansion coefficients.
Implementation Method 1
the retaining ring piece made from a first material similar to or having a coefficient of thermal expansion similar to that of the motor case. The aft closure assembly also includes a blast tube and closure piece that can be manufactured from a second material that does not need to be similar to, nor have a coefficient of thermal expansion similar to the motor case and retaining ring piece
Data Source
AI summary
An aft closure assembly manufactured from two separate and distinct pieces made from different materials is provided for a rocket motor case. The aft closure assembly includes at least a retaining ring piece made from a first material similar to or having a coefficient of thermal expansion similar to that of the motor case. The aft closure assembly includes a blast tube and closure piece that can be manufactured from a second material that does not need to be similar to nor have a coefficient of thermal expansion similar to the motor case and retaining ring piece. This is possible because the blast tube and closure piece includes a face seal that seals against a face of the retaining ring.