Microfabricated Emitter Arrays for Electrospray Thrusters
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Solution Overview
Problem
Conventional electrospray thrusters for miniaturized satellites face inefficiencies due to large and heavy propellant reservoirs and limited thrust range, making them unsuitable for miniaturized satellite propulsion, while existing microfabricated emitters struggle to achieve uniformity and geometry necessary for efficient Taylor cone formation and thrust generation.
Innovation Solution
Microfabricated emitter arrays with precisely engineered elongated bodies and extractor grids are developed, featuring uniform height, controlled tip geometry, and surface texture to ensure consistent Taylor cone formation and efficient propellant jet emission, utilizing lithography and deep reactive ion etching for manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If conventional electrospray thrusters are used for miniaturized satellites, then propulsion capability is provided, but the system becomes too heavy and large due to propellant reservoirs and feed systems
Solution Approach 1:
The emitter array is divided into multiple individual emitter elements (e.g., 100-1000 emitters) arranged in a grid pattern, with each emitter contributing to the total thrust. This segmentation allows the system to achieve sufficient thrust through collective action of many small emitters rather than requiring a single large emitter with large propellant reservoirs
Solution Approach 2:
The patent extracts and eliminates the large propellant reservoirs and complex feed systems from conventional electrospray thrusters. Instead, propellant is delivered through microfabricated channels integrated directly with the emitter structure, dramatically reducing the weight and volume of the propulsion system while maintaining thrust capability
Solution Approach 3:
The invention transitions from single-emitter or few-emitter configurations to two-dimensional emitter arrays with hundreds or thousands of emitters. This dimensional expansion allows the system to achieve sufficient total thrust through the collective contribution of many small emitters, enabling miniaturization of the overall thruster system
2Manufacturing precision
If externally wetted needle emitters are used, then simplicity of structure is achieved, but uniformity and geometry necessary for efficient Taylor cone formation cannot be achieved
Solution Approach 1:
The patent merges the emitter structure with the propellant delivery system into an integrated microfabricated unit. The emitter elements are formed as part of the substrate structure with propellant channels leading directly to each emitter tip, eliminating the need for separate external wetting systems while achieving precise geometric control through lithographic fabrication
Solution Approach 2:
The invention replaces manual or mechanical emitter fabrication and wetting processes with lithographic and etching processes. This substitution of manufacturing methods enables precise control of emitter geometry (tip radius, height, spacing) and uniformity across large arrays of emitters, achieving manufacturing precision unattainable with conventional mechanical methods
Solution Approach 3:
The patent systematically controls critical emitter parameters including tip radius (1-10 micrometers), emitter height (50-500 micrometers), and spacing between emitters. These parameter specifications and controls are achieved through lithographic patterning and etching processes, ensuring uniform Taylor cone formation across all emitters in the array
3Manufacturing precision
If chemically etched emitters are used, then manufacturing is simplified, but emitter uniformity and height consistency are insufficient for efficient operation
Solution Approach 1:
The patent replaces chemical etching processes with lithographic patterning followed by controlled etching. The lithographic step defines precise emitter locations, dimensions, and heights before etching, ensuring uniformity across the array. This two-step process (lithography + etching) provides superior dimensional control compared to chemical etching alone, while remaining compatible with standard microfabrication techniques
Solution Approach 2:
The invention performs preliminary lithographic patterning to define emitter geometry and locations before the etching process. This preliminary action establishes precise height and dimensional specifications that guide the subsequent etching, ensuring uniform emitter characteristics across the entire array. The lithographic mask serves as a template that controls the final emitter morphology
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 solution enables scalable, efficient, and compact electrospray thrusters capable of generating sufficient thrust with improved thrust density and reduced weight and volume, overcoming previous limitations in emitter array uniformity and performance.
Implementation Method 1
A potential difference of the order of 2-10 kV is applied to generate a strong electric field at the tip of the emitter
Implementation Method 2
Voltages just above a threshold draw the liquid propellant into a Taylor cone and extract charged particles at the apex of the cone
Implementation Method 3
The charged particles are then accelerated to high velocities on the order of tens of kilometers per second by the applied electric field
Implementation Method 4
In some cases the propellant is stored as a solid, melted to flow, and then pulled up the emitter tip by capillary forces
Data Source
AI summary
Micro-emitter arrays and methods of microfabricating such emitter arrays are provided. The microfabricated emitter arrays incorporate a plurality of emitters with heights greater than 280 microns with uniformity of +/â10 microns arranged on a supporting silicon substrate, each emitter comprising an elongated body extending from the top surface of the substrate and incorporating at least one emitter tip on the distal end of the elongated body thereof. The emitters may be disposed on the substrate in an ordered array in an X by Y grid pattern, wherein X and Y can be any number greater than zero. The micro-emitter arrays may utilize a LMIS propellant source including, for example, gallium, indium, bismuth, or tin. The substrate may incorporate at least one through-via providing a fluid pathway for the LMIS propellant to flow from a propellant reservoir beneath the substrate to the top substrate surface whereupon the micro-emitter array is disposed.