Chemical rockets have been the workhorse of the space age and they have had a pretty standard formula for the past 60 years. Get millions of pounds of liquid or solid fuel, light it on fire with the help of an oxidizer and the speed of the rocket shooting at the back gives you enough thrust, or kick (not the one that Salman gets), to get into space. But the problem with the chemical rockets is that fuel is heavy, and for that much weight, it's not very efficient. The fuel’s energy is limited to its chemical bonds and after years of research, they are not going to get better. So, if we want to explore deep space and beyond we need new propulsion systems.
One of the technologies is the Ion Propulsion Systems which has been in development for decades now with many spacecraft already using different variations of it to achieve highly efficient thrust systems.
Taking an example of Dawn, which is a retired spacecraft that went to study two protoplanets (planets in the making who don’t have a spherical shape and found in the vicinity of asteroids) in the asteroid belt-Vesta and Ceres, which also used an ion propulsion system.
This spacecraft used xenon as a propellant because it has a high atomic mass allowing it to provide more kick per atom while being inert and having a high storage density lending itself to long term storage on a spacecraft. The engine releases both xenon atoms and high energy electrons into the ionization chamber, where they collide to produce a positive xenon atom and more electrons. These electrons are then collected by the positively charged chamber walls, while the positive xenon atoms migrate towards the chamber exit which contains two grids. A positive grid called the screen grid, and a negative grid called the accelerator grid. The high electrical potential between these grids causes the positive ions to accelerate and shoot out of the engine at speeds up to 145, 000 km/h.
At that speed, even the tiny xenon atoms can provide a decent bit of thrust, but even still this engine provides a maximum of 92 mN of force. About the same force, a piece of paper will exert while resting on your hand. But in the vacuum of space, there is no air to reduce the precious energy we provide. With no drag or friction to remove energy we gradually build up our kinetic energy and gain speed.
The dawn spacecraft weighed about 1220 kilograms at launch with a dry mass of 750 kilograms after the propellant had been expended, so let's say it has an average weight between the two of 1000 kilograms. Thanks to Newton, we can calculate the acceleration this engine could provide which is 0.000092 m/s^2. A tiny acceleration, but multiple by a week (604800 seconds) and our spacecraft is flying at 55.6 m/s. Multiply it by a year and it’s flying at 2898 m/s.
But here on earth, it has a completely different set of challenges. Air will continuously drain any energy we input into our vehicle through drag, and so we need to create an ion system that can provide more energy than air can remove while travelling fast enough to achieve flight.
In November 2018 MIT researchers flew the first airplane without any moving parts with the help of an ion thruster. It had a series of electrodes which consist of an array of very thin wires at the front, and then an array of aerofoils at the back. Now those thin wires at the front were set at +20,000 volts and that constitutes the source of ions (which is ionized nitrogen from the atmosphere). Now the aerofoils at the back were at -20,000 volts and so that creates an electric field. So the ions go from the positive to the negative colliding all the way with neutral air molecules and creating this wind that goes behind the plane.
Ion Propulsion systems have already made their impact on space exploration and also has the potential to become an alternative to the aircraft propulsion system. And maybe one day it can take us to both New York and Pluto.
One of the technologies is the Ion Propulsion Systems which has been in development for decades now with many spacecraft already using different variations of it to achieve highly efficient thrust systems.
Taking an example of Dawn, which is a retired spacecraft that went to study two protoplanets (planets in the making who don’t have a spherical shape and found in the vicinity of asteroids) in the asteroid belt-Vesta and Ceres, which also used an ion propulsion system.
This spacecraft used xenon as a propellant because it has a high atomic mass allowing it to provide more kick per atom while being inert and having a high storage density lending itself to long term storage on a spacecraft. The engine releases both xenon atoms and high energy electrons into the ionization chamber, where they collide to produce a positive xenon atom and more electrons. These electrons are then collected by the positively charged chamber walls, while the positive xenon atoms migrate towards the chamber exit which contains two grids. A positive grid called the screen grid, and a negative grid called the accelerator grid. The high electrical potential between these grids causes the positive ions to accelerate and shoot out of the engine at speeds up to 145, 000 km/h.
At that speed, even the tiny xenon atoms can provide a decent bit of thrust, but even still this engine provides a maximum of 92 mN of force. About the same force, a piece of paper will exert while resting on your hand. But in the vacuum of space, there is no air to reduce the precious energy we provide. With no drag or friction to remove energy we gradually build up our kinetic energy and gain speed.
The dawn spacecraft weighed about 1220 kilograms at launch with a dry mass of 750 kilograms after the propellant had been expended, so let's say it has an average weight between the two of 1000 kilograms. Thanks to Newton, we can calculate the acceleration this engine could provide which is 0.000092 m/s^2. A tiny acceleration, but multiple by a week (604800 seconds) and our spacecraft is flying at 55.6 m/s. Multiply it by a year and it’s flying at 2898 m/s.
But here on earth, it has a completely different set of challenges. Air will continuously drain any energy we input into our vehicle through drag, and so we need to create an ion system that can provide more energy than air can remove while travelling fast enough to achieve flight.
In November 2018 MIT researchers flew the first airplane without any moving parts with the help of an ion thruster. It had a series of electrodes which consist of an array of very thin wires at the front, and then an array of aerofoils at the back. Now those thin wires at the front were set at +20,000 volts and that constitutes the source of ions (which is ionized nitrogen from the atmosphere). Now the aerofoils at the back were at -20,000 volts and so that creates an electric field. So the ions go from the positive to the negative colliding all the way with neutral air molecules and creating this wind that goes behind the plane.
Ion Propulsion systems have already made their impact on space exploration and also has the potential to become an alternative to the aircraft propulsion system. And maybe one day it can take us to both New York and Pluto.
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