Session
Weekday Session 7: Propulsion
Location
Utah State University, Logan, UT
Abstract
A recent study by the ESA Space Research and Technology Center has identified that "reducing toxicity of propellants" offers the highest potential for reducing commercial space operating costs. Developing a "green" alternative for hydrazine, the most commonly used space propellant, was highly recommended. Hybrid propulsion offers an emerging, low-cost solution, especially for SmallSat propulsion.
Historically, a primary drawback of hybrid systems was a lack of reliable multiple-use ignition methods. Recently, restartability issues were overcome by leveraging unique dielectric breakdown properties of 3-D printed acrylonitrile butadiene styrene (ABS). Additive printing significantly changes thermoelectric properties, and when ABS is subjected to an electrostatic potential, the layered structure allows "arc-tracks" to be carved between the electrodes. Associated Joule-heating pyrolyzes fuel, allowing ignition to spontaneously occur when oxidizer flows.
Arc-ignition has been harnessed to develop a High-Performance Green Hybrid Propulsion (HGHP) family that has capability for reliable on-demand start, stop, and re-ignition. In its most mature form, HPGHP uses gaseous oxygen (GOX). However, unless stored at very high pressures, GOX has low-density, and it is highly desirable to employ higher density, long-term storable oxidizers, such as high-test hydrogen peroxide (HTP), nitrous oxide (NO2), or NO2/GOX blends (Nytrox) to improve volumetric efficiency. Unfortunately, when these oxidizers are "dropped-in" to replace GOX, HPGHP systems have experienced ignition reliability and latency issues resulting from decomposition energy barriers found in both HTP and N2O.
Previously published studies have demonstrated catalytic-assist, using high-atomic-weight metals to decompose the incoming oxidizer and release free oxygen, as effective in increasing ignition reliability. In a typical configuration catalytic materials are supported by a substrate housed in an external pressure vessel placed in-line with the oxidizer flow-path. Unfortunately, in-line catbeds pose a series of technical issues. First, catbeds are heavy and add significantly to the spacecraft dry-mass without increasing propulsive efficiency. Second, in order to be effective, catalysts must be externally heated to high temperatures, often exceeding 300 oC. The required pre-heat energy has a significant impact on the total spacecraft energy budget. Finally, catbeds often self-consume at the high temperatures necessary for efficient decomposition action. There exists a universally limited operating lifetime for the expensive catalyst materials.
The presented research solves this problem. As described, external catalysts are replaced by an internal fuel-blend that mixes catalyst directly into the combustible material. The simple, inexpensive process works by cold-diffusion of 3D-printed ABS fuels with appropriate catalytic materials. The infused catalyst allows for near-instantaneous oxidizer decomposition, releasing gaseous oxygen that, when combined with "spark" energy, provides quick and reliable ignition. No system preheating is required, and the infused catalyst does not reduce the overall system performance. Design options and test results are presented for a 1-N HTP/ABS prototype thruster using potassium permanganate as the catalyst, and a 100-N Nytrox/ABS prototype using Ruthenium as the catalyst. "Drop-in" performance and reliability are demonstrated for both systems.
Cold-Infusion of Catalytic Materials Into 3-D Printed Fuels for In-Space Hybrid Propulsion Performance Enhancement
Utah State University, Logan, UT
A recent study by the ESA Space Research and Technology Center has identified that "reducing toxicity of propellants" offers the highest potential for reducing commercial space operating costs. Developing a "green" alternative for hydrazine, the most commonly used space propellant, was highly recommended. Hybrid propulsion offers an emerging, low-cost solution, especially for SmallSat propulsion.
Historically, a primary drawback of hybrid systems was a lack of reliable multiple-use ignition methods. Recently, restartability issues were overcome by leveraging unique dielectric breakdown properties of 3-D printed acrylonitrile butadiene styrene (ABS). Additive printing significantly changes thermoelectric properties, and when ABS is subjected to an electrostatic potential, the layered structure allows "arc-tracks" to be carved between the electrodes. Associated Joule-heating pyrolyzes fuel, allowing ignition to spontaneously occur when oxidizer flows.
Arc-ignition has been harnessed to develop a High-Performance Green Hybrid Propulsion (HGHP) family that has capability for reliable on-demand start, stop, and re-ignition. In its most mature form, HPGHP uses gaseous oxygen (GOX). However, unless stored at very high pressures, GOX has low-density, and it is highly desirable to employ higher density, long-term storable oxidizers, such as high-test hydrogen peroxide (HTP), nitrous oxide (NO2), or NO2/GOX blends (Nytrox) to improve volumetric efficiency. Unfortunately, when these oxidizers are "dropped-in" to replace GOX, HPGHP systems have experienced ignition reliability and latency issues resulting from decomposition energy barriers found in both HTP and N2O.
Previously published studies have demonstrated catalytic-assist, using high-atomic-weight metals to decompose the incoming oxidizer and release free oxygen, as effective in increasing ignition reliability. In a typical configuration catalytic materials are supported by a substrate housed in an external pressure vessel placed in-line with the oxidizer flow-path. Unfortunately, in-line catbeds pose a series of technical issues. First, catbeds are heavy and add significantly to the spacecraft dry-mass without increasing propulsive efficiency. Second, in order to be effective, catalysts must be externally heated to high temperatures, often exceeding 300 oC. The required pre-heat energy has a significant impact on the total spacecraft energy budget. Finally, catbeds often self-consume at the high temperatures necessary for efficient decomposition action. There exists a universally limited operating lifetime for the expensive catalyst materials.
The presented research solves this problem. As described, external catalysts are replaced by an internal fuel-blend that mixes catalyst directly into the combustible material. The simple, inexpensive process works by cold-diffusion of 3D-printed ABS fuels with appropriate catalytic materials. The infused catalyst allows for near-instantaneous oxidizer decomposition, releasing gaseous oxygen that, when combined with "spark" energy, provides quick and reliable ignition. No system preheating is required, and the infused catalyst does not reduce the overall system performance. Design options and test results are presented for a 1-N HTP/ABS prototype thruster using potassium permanganate as the catalyst, and a 100-N Nytrox/ABS prototype using Ruthenium as the catalyst. "Drop-in" performance and reliability are demonstrated for both systems.
