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Interstellar Voyages: The Ion Drive
The spacecraft that promises to give mankind new worlds
Ella Alderson
Jul 26, 2020 · 5 min read
An artist’s impression of Proxima b. Image by ESO/M. Kornmesser.
The nearest habitable world is a planet not much larger than Earth, tidally locked as it orbits ‘round its red dwarf star. To be tidally locked means that the same side of Proxima b always faces its star, Proxima Centauri, and the same side of the planet always faces away from it. This is also the case with our moon. As it loyally and lovingly drifts across the night sky, it views us always with the same face. Proxima b sails within its star’s habitable zone where simulations have shown there’s a good chance liquid water sways and bounces on the surface, soaking in the rosy light of our nearest stellar neighbor. Secrets just 4.2 light years away. That ocean could sustain human life in some exciting future, or it could already nurture life of its own. Organisms swimming through Proxima b’s rugged, rocky channels, the beginnings of complex life exploding in shadows our instruments haven’t yet touched.
And what if this world is our future home — this ocean the ocean in which our distant grandchildren play, looking out at the scattering of stars and knowing that somewhere out there lies the Earth. The cradle that birthed them all. They will seek their beginnings as we now seek our future.
But 4.2 lightyears is only small in cosmic terms. To us humans it still presents a formidable distance requiring passion and innovation on our part. We are in the stage of developing the technology that will get us there.
One of the most promising of all is the ion engine.
Hundreds of communication satellites already use ion thrusters to stay in their correct positions above Earth. Image by NASA.
To create an ion you either add or remove an electron from an atom. This gives the atom an electric charge. In the case of ion drives electrons are removed, thus giving an overall positive charge. The result is a plasma of positive ions and negative electrons which together make for a neutral electric charge. It’s important that the overall charge is neutral because a build up of negative charge could cause the ions to be sucked back into the spacecraft, causing damage and compromising the amount of thrust.
A chemical rocket takes off into space.
This first stage is that of ionizing propellant. Chemicals used as propellants in ion drives include krypton and xenon, both colorless and odorless unreactive gases.
Magnetic fields eject the plasma from the back of the craft, providing thrust in the same way that a chemical rocket receives thrust from the combination of fuel and oxidizer. And chemical rockets are powerful in the short-term — they allow our craft to rip out of the gravitational well of Earth, escaping into space where the planet can no longer hold us prisoners. Thrust from an ion engine is too small to escape Earth. It can’t be used to launch us from here and into space. However, once we’re gliding through the cosmos’s cool, dark corridors the ion engine can reach speeds unmatched by any chemical rocket.
At the tail end of the ion thruster is a set of grids textured with thousands of small holes. The plasma exits from these apertures. In the image above an ion thruster fires during a test. Image by ESA.
An ion engine’s speed builds up along the ride so that the longer the craft spends traveling, the faster it can go. While chemical rockets can reach a maximum of 40,000 mph (64,000 kph) , ion thrusters can go five times faster to reach speeds of 200,000 mph (322,000 kph). Not only that but ion thrusters have a fuel efficiency of 90% — or 10 times more thrust per kg of propellant — while chemical rockets have one of only 35%. A craft relying on ion engines experiences a slow but smooth ride, continuing to accelerate for months as its stream of ionized gas plumes into the imperfect vacuum of space.
In 2017, the X3 ion thruster achieved new records for power output and thrust. The X3’s thrust of 5.4 Newtons surpassed a previous record of 3.3 Newtons. It’s a heavy, hope-giving machine. All 500 pounds of it can operate at 100 kW of power. Machines like the X3 could take us to Mars in the next couple of decades as part of a propulsion system for manned missions. Stringing together several X3 engines could result in higher power levels sustained by more advanced solar panels. The solar panels would only suffice for nearby missions, however. Spaceships attempting to voyage farther beyond Earth will need onboard nuclear power. The more electricity available, the stronger the ions can be accelerated behind the ship.
Ion thrusters have operated for almost 6 continuous years on Earth without failure, but they were also an important part of NASA’s Deep Space 1 mission. That is, they’ve already proven themselves in space. The mission extended over 160 million miles to produce beautiful, detailed studies of the asteroid 9969 Braille and the comet Borelly. Once the ion engine was found to be successful it was then later used in NASA’s Dawn mission, covering a total of 4.3 billion miles (6.9 billion km). The mission visited some of the asteroid belt’s largest worlds: Ceres and Vesta. It was the first time we’d visited a dwarf planet and, in the case of Ceres, discovered organics there.
False-color image of Ceres created using data from the Dawn mission. Image by NASA.
Ion thrusters are potential important pieces in the prospect of interstellar travel. They’re fast but also delicate. Their gentle thrust gives pilots more precision as they maneuver through the stars. It could be that these will be the first machines to visit exoplanets like Proxima b, sending back information to Earth while we continue to toil and hammer away at our instruments. Or it could be that this information will be beamed back to Mars, the cloudy red planet which ion thrusters will have helped us reach. Here instead of alien oceans our grandchildren will wipe away traces of alien dust from their helmets, able to look upon Earth as it hangs as a small white pearl in the night sky. The daylight that of our sun, but the soil that of our new home.
The spacecraft that promises to give mankind new worlds
Ella Alderson
Jul 26, 2020 · 5 min read
The nearest habitable world is a planet not much larger than Earth, tidally locked as it orbits ‘round its red dwarf star. To be tidally locked means that the same side of Proxima b always faces its star, Proxima Centauri, and the same side of the planet always faces away from it. This is also the case with our moon. As it loyally and lovingly drifts across the night sky, it views us always with the same face. Proxima b sails within its star’s habitable zone where simulations have shown there’s a good chance liquid water sways and bounces on the surface, soaking in the rosy light of our nearest stellar neighbor. Secrets just 4.2 light years away. That ocean could sustain human life in some exciting future, or it could already nurture life of its own. Organisms swimming through Proxima b’s rugged, rocky channels, the beginnings of complex life exploding in shadows our instruments haven’t yet touched.
And what if this world is our future home — this ocean the ocean in which our distant grandchildren play, looking out at the scattering of stars and knowing that somewhere out there lies the Earth. The cradle that birthed them all. They will seek their beginnings as we now seek our future.
But 4.2 lightyears is only small in cosmic terms. To us humans it still presents a formidable distance requiring passion and innovation on our part. We are in the stage of developing the technology that will get us there.
One of the most promising of all is the ion engine.
Hundreds of communication satellites already use ion thrusters to stay in their correct positions above Earth. Image by NASA.
To create an ion you either add or remove an electron from an atom. This gives the atom an electric charge. In the case of ion drives electrons are removed, thus giving an overall positive charge. The result is a plasma of positive ions and negative electrons which together make for a neutral electric charge. It’s important that the overall charge is neutral because a build up of negative charge could cause the ions to be sucked back into the spacecraft, causing damage and compromising the amount of thrust.
A chemical rocket takes off into space.
This first stage is that of ionizing propellant. Chemicals used as propellants in ion drives include krypton and xenon, both colorless and odorless unreactive gases.
Magnetic fields eject the plasma from the back of the craft, providing thrust in the same way that a chemical rocket receives thrust from the combination of fuel and oxidizer. And chemical rockets are powerful in the short-term — they allow our craft to rip out of the gravitational well of Earth, escaping into space where the planet can no longer hold us prisoners. Thrust from an ion engine is too small to escape Earth. It can’t be used to launch us from here and into space. However, once we’re gliding through the cosmos’s cool, dark corridors the ion engine can reach speeds unmatched by any chemical rocket.
At the tail end of the ion thruster is a set of grids textured with thousands of small holes. The plasma exits from these apertures. In the image above an ion thruster fires during a test. Image by ESA.
An ion engine’s speed builds up along the ride so that the longer the craft spends traveling, the faster it can go. While chemical rockets can reach a maximum of 40,000 mph (64,000 kph) , ion thrusters can go five times faster to reach speeds of 200,000 mph (322,000 kph). Not only that but ion thrusters have a fuel efficiency of 90% — or 10 times more thrust per kg of propellant — while chemical rockets have one of only 35%. A craft relying on ion engines experiences a slow but smooth ride, continuing to accelerate for months as its stream of ionized gas plumes into the imperfect vacuum of space.
In 2017, the X3 ion thruster achieved new records for power output and thrust. The X3’s thrust of 5.4 Newtons surpassed a previous record of 3.3 Newtons. It’s a heavy, hope-giving machine. All 500 pounds of it can operate at 100 kW of power. Machines like the X3 could take us to Mars in the next couple of decades as part of a propulsion system for manned missions. Stringing together several X3 engines could result in higher power levels sustained by more advanced solar panels. The solar panels would only suffice for nearby missions, however. Spaceships attempting to voyage farther beyond Earth will need onboard nuclear power. The more electricity available, the stronger the ions can be accelerated behind the ship.
Ion thrusters have operated for almost 6 continuous years on Earth without failure, but they were also an important part of NASA’s Deep Space 1 mission. That is, they’ve already proven themselves in space. The mission extended over 160 million miles to produce beautiful, detailed studies of the asteroid 9969 Braille and the comet Borelly. Once the ion engine was found to be successful it was then later used in NASA’s Dawn mission, covering a total of 4.3 billion miles (6.9 billion km). The mission visited some of the asteroid belt’s largest worlds: Ceres and Vesta. It was the first time we’d visited a dwarf planet and, in the case of Ceres, discovered organics there.
False-color image of Ceres created using data from the Dawn mission. Image by NASA.
Ion thrusters are potential important pieces in the prospect of interstellar travel. They’re fast but also delicate. Their gentle thrust gives pilots more precision as they maneuver through the stars. It could be that these will be the first machines to visit exoplanets like Proxima b, sending back information to Earth while we continue to toil and hammer away at our instruments. Or it could be that this information will be beamed back to Mars, the cloudy red planet which ion thrusters will have helped us reach. Here instead of alien oceans our grandchildren will wipe away traces of alien dust from their helmets, able to look upon Earth as it hangs as a small white pearl in the night sky. The daylight that of our sun, but the soil that of our new home.
