Ion Thrusters - The Future Of Rocket Propulsion.

  People always wonder why are we still stuck with chemical rockets. Burning of hydrogen or kerosene to generate thrust is the best we can do? Well that's not the case, there are other exotic science fiction-sounding propulsion systems have already been developed which use electromagnetic fields to accelerate atoms, allowing their spacecraft to accelerate for months at a time. I’m talking about ion engines and several spacecraft have already used these ion thrusters to perform some of the most amazing missions in the exploration of the Solar System. 

Why Not Chemically Propelled Rockets ?

I know, chemical rockets seem really primitive. Take tonnes of liquid or solid or maybe hybrid fuels sometimes, burn it with an oxidizer, and then use the speed of the explosive gases as a in the opposite direction. Thanks Newton’s Third Law. But chemical rockets do the jon. Those gases do give  rocket the kick it needs to get into space. Because the rockets bring their own oxidizer with them, they work in the atmosphere and they work in the airlessness of space. The advantage of chemically propelled rockets is that they can deliver enormous amounts of energy in short periods of time, the kind of reaction we need to take tonnes of cargo off Earth and into space. But they’re incredibly inefficient. For a case, a 550 metric tonne Falcon Heavy is carryingalmost 400 tonnes of fuel and oxidizer. The first stage will only burn for 162 seconds (this no. is known as specific impulse of the first stage of the rocket),and the second stage will fire for 397 seconds. That gives us a total burn time of about 9.5 minutes. Well what if we want to make more maneuvers or want to accelerate for days, weeks or even months? Using chemically propelled rockets, its not possible. Yeah, these shortcomings from chemical rockets have made scientists to search for other forms of propulsion systems, especially when we are out in space, and the one of the most successful  is the ion thruster. When you’re working out the rocket equation, an important factor is the velocity that you’re ejecting your propellant. The most efficient chemical rocket can throw hot gases out the back at 5 km/s. Ion engines, on the other hand, can ejectindividual atoms 90 kilometers a second. This high velocity gives the spacecraft amuch more efficient acceleration. The best chemical rockets see a fuel efficiency of about 35%, while ion engines see an efficiency of 90%. Well, thrust is not all about ejection velocity but the momentum of the particles that are being ejected so that the rockets get same momentum in return (ignoring the gravity for small period of time). So it might have become clear to you now that why chemical rockets are used for escaping the Earth's gravity. 

 So how do ion thrusters work?

It’s actually pretty weird, and totally sounds like science fiction. These are atoms or molecules which have an electrical charge because they’ve lost or gained an electron. In the case of an ion engine, they’re emitting positively charged ions which have lost an electron due to the bombardment we do at start with an electron to ionize it. Once you’ve got ions, you can direct them with a magnetic field and speed up using electrical field, accelerating them into space at tremendous speeds. So where do they get all the ions? The thrusters produce them by generating a plasma inside the chamber. They bombard neutral propellant atoms of some gases, like Xenon with electrons. These collisions release even more electrons from the propellant, turning them into positively charged ions. This plasma of electrons and positively charged ions has an overall neutral charge. The electrons are held in the chamber, leadingto more ionizing events, while the positive ions are siphoned out through a grid at the end of the chamber. As they pass through this grid (which is basically an electrode), the high voltage accelerates them out of the back of the spacecraft at speeds of up to 90 km/s. After it has come out of the grid, it is neutralised by an electron so that it does not fall back and thus give no thrust. For each ionized particle that the space craft can kick out, it gets a small kick reciprocally. The whole system is powered by solar panels, so the spacecraft itself doesn’t need to carry any kind of battery or power system, minimising the total weight it has to carry. The big problem is that that kick is really tiny. The thrust of ion engines is measured in milli newtons, like, thousandths of a Newton. Hold a piece of paper in your hand, that’sthe kind of forces involved. But they can operate for days, weeks, even months, accelerating and accelerating long after chemical rockets would have run out of fuel. So if you’re already out of the gravitywell of a planet, they’re very efficient engines for dramatic changes in velocity. 

History of Ion Thrusters.

NASA and other space agencies have actually used ion engines very successfully in a range of missions. They had been developing this thruster conceptfor decades but were never willing to risk it on an active mission where a failure could end it. So NASA gathered up a bunch of risky technologies and packaged them together as the Deep Space 1 mission, which was launched in 1998. Deep Space 1 was equipped with 12 differenttechnologies that NASA wanted to test out, including low power electronics, solar concentrator arrays, various scientific instruments, and a solar electric propulsion system. Its engine was run for enormous lengths of time, allowing it to make close observations of asteroids and comets, and even Mars. NASA doubled down on the technology of DeepSpace 1, giving its Dawn Mission three redundant ion engines. These allowed the spacecraft to go into orbit around the asteroid Vesta, make observations, then break orbit and travel to asteroid Ceresand make even more observations. And it could still have fuel in the tank to visit even more asteroids. Just to give a sense of its acceleration,Dawn can go from 0 to 100 km/h in 4 days of continuous thrusting. Ion thrusters were to carry ESA’s Smart1 spacecraft from Earth orbit to lunar orbit, and on the JAXA Hayabusa spacecraft. Ion engines have been tested here on Earth,and successfully operated for more than 5 years continuously. With these successes, we’re going to see even more spacecraft equipped with ion thrusters in the future, but ion thrusters themselves are getting more powerful and resourceful. I said that ion engines produce very little thrust, but there are some ideas which can boost their output. The first is dramatically increase the amountof electricity you’re using to accelerate the ions. Instead of solar panels, NASA considered creating an ion thruster powered by a nuclear reactor. About 19 years ago, NASA considered a mission known as the Jupiter Icy Moons Orbiter Mission. Powered by the Nuclear Electric Xenon IonSystem (or NEXIS) engine, the spacecraft would be capable of exploring each of Jupiter’s icy large moons in sequence: Ganymede, Callisto and Europa. The spacecraft would have been launched into orbit in three separate pieces, which would then be assembled in Earth orbit and launchedoff to Jupiter. The spacecraft would use its 8 ion thrusters to study Callisto and then Ganymede for three months each, and then settle into a finalorbit around Europa. If conditions were right, it could even gointo orbit around Jupiter. Well, we don’t get to have nice things and the mission was cancelled back in 2005.

Present Work

 There are other ways ion thrusters engines output  can be increased. NASA is working on a high thrust version of ion engines known as the X3 hall thruster. This engine is capable of producing 5.4 newtons of force. Again, not large, but remember that previous thrusters top out in the thousandths of newtons. At the highest power levels, this could be the technology that will carry human astronauts to Mars, cutting down the flight times to just a few months. The coolest idea I’ve heard for ion engines is the idea of an air breathing engine under development by the European Space Agency. Instead of carrying any propellant at all,engineers at ESA demonstrated that a spacecraft in low Earth orbit should be able to pull in molecules of air right from the atmosphere, and then ionize them and eject them out of the back. Since the spacecraft would be using unlimited solar electricity for power, and pulling its propellant from the atmosphere, it could operate without refueling for long periods. Spacecraft could operated at lower altitudes,and space stations could remain in low Earth orbit indefinitely without needing to be re-boosted. This is going to be real game changer. This would work in not only Earth but anywhere with an atmosphere. Ion engines have already made an impact on space exploration,and in the next few years, we’re going to see more missions equipped with them. They could even be the engines that carry human astronauts from Earth to Mars in the coming decades. 

Bellatrix which is an Indian start up has recently tested a hall effect thruster which is to be used in Pushpak. This is meant for micro satellites weighing around 50 to 500kg (which is a booming industry right now). It uses Xenon as a fuel but they are also developing their own proprietary fuel which will replace Xenon in future as Xenon is very expensive. It will be more dense (thus ejecting out more particles and hence more thrust) to increase efficiency. Pushpak is their OTV Orbital transfer vehicle. Well you may ask what is this? Ok, let me put this into your perspective. Any rocket is limited to a certain height of orbit due to capability issues. Let's take Skyroot's Vikram 1 for example, Vikram 1 can put 235 kgs into 500km SSPO (Space Solar Powered Orbit) but if someone wants to launch on this to Geo Stationary Orbit which is 36000km away, how will you? For cheap customer, we can use help of OTV 235kg can be total weight VIkram 1 will launch it into a low orbit then Pushpak will it will use its thrusters in this case 4 thrusters of 200 watts power each. In future we may see a more powerfull thrusters.