Does the ion drive work on Earth?

How electric propulsion is revolutionizing space travel

US President Donald Trump cannot go fast enough when it comes to a trip to Mars. In July, Trump bluntly offended the NASA leadership by making it clear that he thought another moon mission - which his administration had commissioned itself - was unnecessary and that one should go directly to Mars. At a meeting with Australian Prime Minister Scott Morrison last weekend, he rowed back, "Well, we're making the moon. But in reality we're making Mars." The moon is the starting point for a trip to Mars.

"I think Mr. Trump's suggestion was meant: Let's not forget Mars," said Nasa researcher Bryan K. Smith diplomatically. Smith heads the space flight systems division at NASA's Glenn Research Center in Cleveland. The J-2 engine for the Saturn V moon rocket was developed here, as was the ion drive - one of several alternative drives that are intended to revolutionize space travel.

"Our vision is that the next generation of electric drives will bring us to Mars," said Smith in an interview with STANDARD. The NASA researcher gave an opening lecture at the International Electric Propulsion Conference, which took place in Vienna last week, organized by the Wiener Neustadt University of Applied Sciences and its research company Fotec. More than 600 researchers exchanged information on the latest developments in space technology.

Save fuel to the stars

Classic rocket engines are chemical and are based on the combustion of huge amounts of fuel. The alternative is electric propulsion, which also includes ion propulsion. They use the thrust that arises when particles of a fuel are accelerated with the help of electrical energy and repelled in the form of a jet.

"Electric drives are much more efficient than chemical drives," says Smith. "This means that you have to carry less fuel into space, which means that you can take more other things with you, such as scientific equipment. Commercial satellites, for example for telecommunications, can work more profitably with them." In conventional propulsion systems, the fuel and engine often make up more than 50 percent of the mass of probes, especially when they are to leave near-Earth orbits. Electric drives get by with a tenth of the fuel, which means that the launch vehicle can also be made smaller.

Rocket pioneers such as Robert Goddard and Hermann Oberth already had the principle of electric propulsion in mind in the early 20th century. In the 1960s, initial experiments were carried out with cesium and mercury as fuels for ion drives. Today the noble gas xenon is mainly used. The Nasa probe Deep Space 1, which was launched in 1998, tested an ion drive for the first time under real conditions. As with all electric drives commonly used today, the necessary energy was obtained in space via solar panels.

Fine tuning for satellites

Electric drives do not have enough thrust to overcome air resistance and therefore cannot maneuver a rocket from Earth through the atmosphere. However, they are perfectly suited for permanent advancement in space and fine-tuning under vacuum-like conditions. In the past few years, word of this has got around in commercial space travel, where a boom in electric drives has been recorded in recent years - which in turn is fueling research.

"At first the satellite manufacturers were skeptical," says Smith. "The technology is now widely used, for example to bring satellites into other orbits." While industry is interested in small systems for flexible mini satellites in low-earth orbits, scientists are working on durable high-performance propulsion systems that make it possible to advance further and further into space. "To do that, we have to take the technology to a whole new level," says Smith.

Their first appearance in manned space travel is to have high-performance electric drives in the space station Lunar Gateway, a joint project of the major space agencies under the direction of NASA. From 2022 the station is to be gradually built up in a moon orbit until it is to serve "the next man and the first woman on the moon" from 2024, according to the NASA slogan.

"Instead of taking people directly to the moon and back again like in Apollo 11, the idea here is to stay near the moon and set up a sustainable base camp, an outpost," says Smith. "A high-performance electric motor helps to keep the station in an optimal orbit in which the sun is always available as an energy source and constant communication with the earth is possible." According to previous plans, the drive element commissioned from a private company will have an output of 60 kilowatts, a multiple of previous electric drives in space.

Stepping stone to Mars

The lunar orbit is to serve as a springboard for flights to Mars. "Electric propulsion will probably not be able to transport people, it would take too long. But they can propel supply ships, and hybrid variants are also possible," says Smith.

First, electric drives from the Glenn Research Center will lead research probes to asteroids. From 2021, the Double Asteroid Redirect Test will test whether a targeted collision with an asteroid can change its orbit - as a test in the event that an asteroid should fly towards Earth. In the Psyche mission, the metallic asteroid of the same name - possibly the nucleus of a protoplanet - is to be investigated from 2022.

Because the technology is so efficient, it also promises to travel to the outer planets of our solar system and beyond. Because too little solar energy is then available, small reactors on board probes could supply the necessary energy. "Nuclear electric propulsion will open a new era for deep space exploration," says Smith. "But that is still in the distant future." (Karin Krichmayr, September 27, 2019)

background

It is no coincidence that last week the International Electric Propulsion Conference (IEPC) brought together numerous space scientists, technology companies and well-known representatives from all space agencies in Vienna of all places. This year the Wiener Neustadt University of Applied Sciences and its research company Fotec, which have already made an international name for themselves in the development of all-electric drives, were awarded the contract to organize the congress.

The spin-off Enpulsion emerged from Fotec in 2016, which produces new types of ion thrusters for commercial applications in series. The engine, which uses indium as fuel, was ignited in space for the first time in 2018, and numerous engines are now in use. Only recently, Fotec and Enpulsion signed a two-million-euro contract with the European space agency Esa to further develop the technology.

Every year the Austrian Ministry of Transport, which is responsible for space, invests around 70 million euros in the sector through the FFG, mainly in the context of ESA missions. More than 100 organizations from research and business with more than 1000 employees are active in this area. (red)

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