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recently we are witnessing a historic moment: the launch of the first crewed space mission american since 2011.

while the futuristic design of the interior of the Crew Dragon remember a series of science fiction such as The Expanse , engines, rocket launcher, Falcon 9, SpaceX use essentially the same technology as that of the R-7 that placed in orbit the first Sputnik in 1957.

Engines of the launcher Falcon 9 SpaceX – Official SpaceX Photos/Flickr, CC BY-NC

The technology that powers launchers

On a space mission come together countless technologies of high complexity and criticality, but without a doubt the key is the propulsion rocket. It is striking that, while there have been improvements, the pitchers and their benefits have not changed substantially since the beginning of the space age, it is now more than 60 years. Why?

To put in orbit a vehicle is necessary, in the first place, to ascend through the atmosphere defeating the gravity on earth and then, to reach a horizontal speed sufficient.

The rockets have to give a high push force , higher than its weight; otherwise, it would not be possible to take off. This is achieved by making the motor big enough and powerful.

But it is also important that the rockets possess a high specific impulse, or the relationship between thrust and fuel costs, which turns out to be equal to the speed of the jet ejected . A higher specific impulse means lower fuel consumption, and a launcher is more lightweight and economical.

The majority of pitchers of liquid fuel, such as the Falcon 9 and R-7 , used kerosene and liquid oxygen is cryogenic. This mixture gives a specific impulse which varies between 3 and 3.5 km/s.

pitchers of maximum performance as the Ariane 5 , the future Ariane 6 and SLS replaced the kerosene with liquid hydrogen and arrive at the 4.5 km/sec, Although this figure seems high, is much lower than desirable. For this reason, the pitchers are mostly a tank fuel flying. Only a small part of its mass corresponds to the load of payment useful.

Ariane 5 taking off. – THAT

it Is very unlikely that the chemical propulsion to exceed once this range of values, since it is limited by the specific energy of the fuel. There is simply no substances best to burn, that it may bear more heat, and comply with other necessary requirements.

Move out there: space electric propulsion

Already in the space, our needs propulsivas change dramatically: now, it is run bug fixes and changes to orbit , which required a push infinitely less than that of a pitcher.

however, to maximize the specific impulse is still more a priority , since the amount of propellant that we can bring on board is limited. Once we completed completely, you will end up the life of the mission.

Since the mid-TWENTIETH century has developed a way of propulsion a spatial alternative to the chemical, known as electric propulsion or plasma. These engines, instead of relying on the energy of a fuel, using electric power to accelerate directly to the propellant. In this way it is possible to greatly exceed the specific impulse of chemical engines, coming easily to 20-40 km/s . This represents a huge savings in mass and makes possible travel unrealizable with rocket traditional.

To do this, it first ionizes the propellant, turning it into a plasma (a soup of ions and free electrons), to then accelerate it with electric and magnetic fields. On this principle are based a great variety of different technologies, as for example the successful Hall effect thrusters and the ion engines.

today, more than 40% of the satellites geostacionarios you use any of these engines to save hundreds of kilograms of fuel and extend its useful life, especially in the motor Hall. They are also used in low-earth orbit and on interplanetary missions such as Bepi-Colombo , Dawn , or Hayabusa , in which the engines are ion offer exceptional performance.

Motor Hall effect in operation – NASA

Despite its great advantages, the electric propulsion also has drawbacks. The main one is that the thrust produced is limited by the power shipped. With the powers available current (10-20 kW), represents a push very low, typically less than 0.2-1 N. This is less than the weight of a mobile phone in the hand, and means that the electric propulsion cannot be used in fast maneuvers (for example to avoid a collision with space debris). So much less to take off of the Earth!

For all these reasons, electric propulsion does not replace the chemical, but rather complements: it is the best choice to fly efficiently once already in the space, when we have enough time to propulsarnos and the forces are small.

current and future Challenges

The current plans of agencies and private companies to suggest that we are on the brink of a new chapter of the conquest of space, in which all the technologies propulsivas known to play a fundamental role.

The commitment to electric propulsion is clear: the engine Hall are the base station Gateway program Artemis NASA to return to the Moon and settle Mars .

Both Boeing as Airbus have been developed in recent years platforms satellite all-electric that perform all phases of the space mission with these technologies.

finally, a use case that has skyrocketed and lower markedly the production of plasma thrusters are the projects megaconstelaciones.

The electric propulsion is a highly active research field. Some of the most pressing challenges are related to understanding and controlling the physics of the turbulence in plasmas magnetized, responsible for a significant loss of efficiency and the erosion of the walls and electrodes of the engines.

Such problems are well known in the nuclear fusion, where the turbulence directly affects the operation of the reactors. Initiatives such as the – project Prometheus in the Community of Madrid trying to find synergies between these two fields of plasma physics to resolve this cross-cutting issue.

In Europe, the development of the engine Hall is led by projects in the program H2020 as Cheops , directed to the improvement of the magnetic confinement of these engines and their scaling to very large and very small powers.

finally, at the frontier of knowledge, we can find new technologies with innovative mechanisms of generation and acceleration of the plasma that promise great advantages.

In this area include the engines without electrodes with magnetic nozzles, like the engine Helicon , engine VASIMR , or motor CRA . These devices promise a high durability and can operate with virtually any substance as a propellant. Will reduce the high cost of the engines that use xenon (a gas very expensive), and perform interplanetary missions that require you to resupply in situ.

Mario Merino Martínez is a Lecturer in university, Department of Aerospace Engineering, equipment propulsion and space plasmas, Universidad Carlos III

This article was originally published in The Conversation.