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The current model of the colloid thruster used in satellitesCite error: The opening <ref> tag is malformed or has a bad name (see the help page).
A colloid thruster is an aerospace launching device that uses colloids, or mixtures of liquids, in electrically charged field to create a repulsion to propel a satellite or rocket into space. It was recently developed in December 2015, by Lockheed Martin, an aerospace company, that redesigned the larger scaled electrospray thruster(for modern day satellites) to a nano thruster. The electrospray thruster, when compared to the colloid, is more dependent on the electricity, where as the colloid thruster is based on the kinematics and dynamics of fluids. This transition of sizes in the thruster was a result of the distance covered in a single space voyage, where the nano thruster allows for a longer satellite life.[1]
Colloids are mixtures where one substance homogenized, or is equally dispersed on any size, throughout another substance. These colloids are used in the thrusters as a way to start the ignition of the satellite. Similar to the electrospray thruster, the colloid thruster transfers electricity through the colloids, in the form of liquid droplets, like aerosol, to allow for a low thrust propulsion. However, after the development of large scale satellites electric propulsion, they realized the amount of energy consumed was unrealistic for longer missions. With the goal of reducing the energy consumed, scientists are beginning to move towards building colloid thrusters as they are preferred in the aerospace industry since they provide smoother altitude control and efficient acceleration for smaller spacecrafts over longer periods of time.[2]
During the 1990s, NASA introduced the idea of creating an electrospray propelled satellite. However, after the development of large scale satellites with that mechanism, they realized the amount of energy consumed was unrealistic for longer missions. For that reason, Busek Company(Busek Co.) proposed the idea of using colloid thrusters for micro or nano propulsions and were accredited and given a contract by NASA for the Phase 1 design in 1998. [3]
In 1999, NASA awarded Busek the Phase 2 design when the research for the micro propulsion applications was completed. After receiving the recognition, Busek Co. became invested in research involving micro-Newton balance and different propellants, such as electrosprays.[3][4]
Busek Co. joined the Jet Propulsion Lab(JPL) on the development of the colloid thruster in 2001. Soon after, JPL and Busek Co. have created designs and models of the colloid thruster from 2003-2007. The two companies developed a few models of the thrusters within the 4 years, testing the various concepts of constant acceleration, low thrust G-force, etc. [4]
Models of early colloid thrusters
2003 and 2004: Prototypes of colloid thrusters at a large scale
2005: First Electron Maximizer(EM) Design
This was the first model to have flow control and EM electronics
This model was the first complete colloid thruster system
Colloid thruster in developmentCite error: The opening <ref> tag is malformed or has a bad name (see the help page).2007: First Flight Design
This model had a 3400 hour flight life test.
There are four thrusters as a cluster
This was the first model to have flight hardware assembled with the system
From the time the first flight tested model was created to 2013, scientists from Michigan Technological University and the University of Maryland led by Kurt Terhune worked on an electrospray system within a transmission electron microscope (TEM). This led to the discovery that the TEM environment formed needle-like structures on the thruster disrupting the way the electrospray system works.[5]
The Space Technology 7 Disturbance Reduction System (ST7-DRS) is composed of a system of thrusters and was launched December 3, 2015 from Kourou, French Guiana. It has been in flight for approximately 1400 hours and completed 100% of its mission. Its purpose was to stabilize the flight of the European satellite, the Pathfinder.[6]
In order to understand the way the colloid thrusters function, it is important to know the components of the thruster and how they function when the entire system is running.
Components of Colloid ThrusterCite error: The opening <ref> tag is malformed or has a bad name (see the help page).
A neutralizer is a field emission cathode, with the foundation of carbon nano tubes to separate the emitter substrate(the colloid), which is isolated from the rest of the parts of the thruster. During the run time of the system, carbon dioxide is released through the nano tubes and will mix with the colloid, but the neutralizer will isolate the colloid from the oncoming carbon dioxide from the tubes in order to keep it pure.[7]
Power Processing Unit:
The power processing unit is the main source of power or energy for the thruster. It provides the initial voltage for the current to run through the other components, like the neutralizer so that the ion droplets will start the release.[7]
Propellant Storage:
A propellant storage is where the carbon dioxide gas is stored from the zeolite crystal chamber, where there is a variable pressure applied. The pressure can be determined by the flow rate for compressing the carbon dioxide gas. This can determine the speed that the gas is released when the system starts.
Flow Rate: Qmax ≅ 3 x 10^-4 mL/min
mL = milliliters
min = minutes
The maximum pressure is approximately 400 torr, where the volume needed is 41 mL which gives about 3000 hours of power for the current model of the thruster.[7]
Latching Valve:
The latching valve minimizes the consumption of power by the propellant storage and feeding system(the input of ion droplets).
Propellant Loading
The goal of the propellant loading system is to rid the system of bubbles, or air trapped within it, leading to the stabilization of the carbon dioxide pressure and the temperature in the zeolite chamber.[7]
The colloid thruster system runs through a series of steps, allowing it to direct itself into Earth's orbit.[7]
Carbon dioxide gas is released from heated crystals which increases the pressure on the propellant(such as aerosol or a gaseous state of a liquid) in steel compartments in the structure
The voltage and current needed to accelerate the thruster are applied
A micro valve opens allowing a propellant to flow to the thruster
A neutralizer within the thruster releases electrons to equalize the ion current
It is a new concept, so it may have flaws in the design
Uses a lower total thrust, or an initial force required to leave the atmosphere
The complexity relative to the electrospray thruster
The colloid thruster is similar to the electrospray thruster for its purpose, but the colloid thruster uses a larger static electric field to lower the voltage and current the thruster receives, causing there to be a lower initial thrust. It is more economical in the long run because it uses less electricity and power, making the transition to colloid thrusters more appealing to aerospace industries. [2][7]
However, unlike the development of the electrospray thruster, that of the colloid needs to be more precise as it is used in the micro and nano scale. Since it is a new design and research topic, it may have some technical mistakes, like the various options of backup energy storage, that would be looked at in future remodeling. When comparing the colloid thruster to the electrospray thruster, it may not seem as complex, but when taking into consideration the components of the satellite, there are many microscopic parts such as the CPU(central processing unit) and the circuit board connected to the electric field.[7]
The future research will determine the characteristics of the particle velocity, using the velocimetry to get measurements of the speed at high magnitudes. It will use two laser sheets, where the particles that travel through will be seen as pairs and will be used to find the average speed. With this speed, the scientists would be able to determine the speed of the particle stream, allowing for the calculation of the particle trajectory. This will later be used to simulate the steam exhaust system for the particles from the neutralizer in the thruster.
