Hypersonic Optical Window Abrasion Tolerance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Hypersonic windows and their coatings face damage from mechanical, chemical, and thermal stresses, leading to erosion and ablation, which compromises optical performance and requires frequent replacement, especially in harsh environments like high-temperature oxygen exposure.
Innovation Solution
An optical window with multiple alternating layers of different materials, including anti-reflection and band-reject coatings, designed to maintain predetermined optical characteristics even as some layers are removed due to ablation, utilizing materials like MgO, ZrO2, and Dy2O3, with a region of graded optical index to ensure continued performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard anti-reflection or blocking coatings are applied to optical windows, then optical performance is improved, but the coatings erode over time in harsh hypersonic environments
Solution Approach 1:
The coating is divided into multiple alternating layers of different materials (e.g., MgO, ZrO2, Dy2O3) with different erosion resistances. The softer material layers are sacrificial and erode preferentially, while the harder material layers remain to maintain optical performance, allowing the coating to degrade gracefully over time.
Solution Approach 2:
The invention changes the material composition parameters of the coating by using alternating layers with different hardness and erosion resistance properties. This allows the coating to transition from initial high protection to gradual degradation while maintaining functional performance throughout its service life.
2Reliability
If coatings are designed to be highly erosion resistant, then durability is improved, but optical performance (anti-reflection or blocking) deteriorates
Solution Approach 1:
Different regions of the coating (different layers) have different local qualities - some layers are softer and more erosion-prone while others are harder and more erosion-resistant. Each layer type is optimized for its specific function, creating a composite structure that achieves both optical performance and erosion resistance.
3Ease of manufacture
If soft window materials are used, then ease of manufacture is improved, but mechanical durability against abrasion deteriorates
Solution Approach 1:
The coating uses composite material structure with alternating layers of different materials (e.g., MgO, ZrO2, Dy2O3) that combine different properties. This composite approach allows the overall system to achieve both manufacturability and superior abrasion resistance that neither material could provide alone.
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 multi-layer coating allows for extended use and potential reuse of the window by maintaining optical performance despite layer removal, enhancing durability and reducing the need for frequent replacements, while enabling the use of ion-reactive materials that would otherwise be unsuitable.
Implementation Method 1
maintains predetermined optical characteristics as some but not all of the multiple layers, including at least one of the layers of each of the different materials, are removed
Implementation Method 2
a region of graded optical index of refraction
Data Source
AI summary
An optical window for a hypersonic vehicle includes a window substrate and an optical coating on the window substrate, with the coating including multiple alternating layers of different materials. The coating may have many layers, for example having five or more alternating bi-layers and may be configured to still perform its optical function with some of the layers removed, such as by ablation of some of the layers through exposure to hypersonic flow. The different materials of the different layers may have different properties, for example with one of the materials being more resistant to ablation and/or chemical reaction than another of the layers. Coatings for anti-reflection additionally include a region of graded optical index between the sequence of bi-layers and the substrate. The hypersonic vehicle may include an optical sensor which operates by receiving light through the optical window.