Optical Membrane Heating via Perimeter Bus Bars
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Solution Overview
Problem
Existing methods for heating large, irregularly shaped optical membranes in space-based optical systems face challenges in achieving uniform temperature control without compromising optical performance, particularly due to the thinness and poor thermal conductance of the membrane substrates, and the impracticality of using heating grids or radiative proximity heaters.
Innovation Solution
A framed transmissive membrane assembly with a composite membrane featuring a transparent, electrically conducting resistive coating and bus bars around the perimeter, where current is controlled to provide uniform and stable heating through a power supply and controller, ensuring even heat distribution across the membrane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If heating grids are incorporated into or on the surface of the membrane, then heating capability is improved, but optical performance deteriorates due to structure within the optical aperture
Solution Approach 1:
The heating function is extracted from the optical aperture area and relocated to the perimeter region through bus bars positioned around the edge of the membrane. This allows the heating elements to be removed from the optical path while maintaining thermal control capability.
Solution Approach 2:
A transparent electrically conductive coating is introduced as an intermediary layer between the bus bars and the membrane substrate. This coating serves dual purposes: conducting electrical current for heating while remaining transparent to maintain optical performance.
2Area of stationary object
If ITO-based heating systems are used on meter-scale membranes, then heating coverage is improved, but uniformity of heating deteriorates
Solution Approach 1:
The heating function is segmented into multiple discrete bus bars positioned around the perimeter of the membrane. By distributing heating sources at multiple locations rather than using a single continuous grid, the system achieves both large-area coverage and more uniform temperature distribution through controlled current paths.
3Manufacturing precision
If radiative proximity heaters are positioned outside the membrane aperture, then optical performance is preserved, but heating efficiency deteriorates
Solution Approach 1:
The external radiative heating system is replaced with an integrated electrical resistive heating system. The heating function transitions from external radiative sources to internal resistive heating through the conductive coating, eliminating the need for proximity heaters outside the aperture.
4Weight of moving object
If the membrane substrate is made extremely thin to reduce mass, then mass reduction is improved, but thermal conductance deteriorates
Solution Approach 1:
The transparent electrically conductive coating serves as an intermediary thermal pathway. While the substrate remains extremely thin for mass reduction, the conductive coating provides an additional thermal conduction path that compensates for the reduced thermal conductance of the thin substrate.
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 solution allows for uniform and stable heating of large, irregularly shaped optical membranes, maintaining their dimensional integrity and optical performance while avoiding distortion, thus addressing the challenges of temperature control in space-based optical systems.
Implementation Method 1
Current provided by a power supply under the control of a controller is passed between combinations of two or more bus bars, through the electrically conductive coating. The resistive heat generated within the electrically conductive coating is used to heat the membrane substrate.
Data Source
AI summary
Methods and systems for heating a space deployed membrane assembly are provided. The membrane assembly can include one or more framed sections. Each section can include a composite membrane having a membrane substrate and a transparent, electrically conductive resistive coating. The composite membrane is held within a frame. Electrically conductive bus bars are provided and are placed in intimate electrical contact with the resistive coating. The electrically conductive bus bars are generally arranged, on opposite sides of the perimeter of the membrane. A controller passes current between selected bus bars, with different bus bars operative to pass current between them at different times. The magnitude of the voltage applied to the bus bars, the location of the bus bars, the operational sequence of powering the bus bars, and the time over which current is passed between a selected pair of bus bars, are selected to provide substantially uniform time averaged heating of the membrane.