Deep space

Frontier research explores interstellar travel

Alternatives to chemical engines are being studied: laser technologies could reduce the time to Alpha Centauri from millennia to 15 years

by Leopoldo Benacchio

18 September 2025

Crisalide. Il progetto italiano Crhysalis, un astronave pensata per portare migliaia di persone nello spazio profondo, ha vinto il concorso di idee Hyperion

4' min read

Key points

Nearest star: 41 trillion kilometres
The first launches in the 1970s
A laser propulsion
Aboard 1,500 people for hundreds of years
An Italian project: the 58-kilometre-long spaceship

4' min read

In the world of research, one often thinks about problems that apparently have no solution, and perhaps never will have one. This serves to put one's methods of investigation under stress and to find oneself, perhaps, solving parallel, or partial, problems to the one one had set out to solve in the first place. To take an example in a completely different field, one often sets oneself the problem, like Columbus, of discovering a supposedly mysterious route to the Indies and instead discovers America. But if one does not set out to discover the Indies, no America.

Bombarded by techno-political news about constellations to transmit the Internet from space, rather than concerned about the possible military use of space, all serious topics of geopolitics, a discipline that has so many scholars today, we have, however, forgotten Dante's exhortation that we are made 'to follow vertute and canoscenza'.

Closest star: 41 trillion kilometres

One of the innovative fields in which there are, fortunately, several initiatives being undertaken is that of interstellar travel, so not the Moon, Mars or whatever, but just going among other stars, which, we shall see, entails enormous problems, even if we set ourselves the goal of reaching one of the closest to us, Alpha Centauri.

Let us take this very star, 4.37 light years or 41 trillion kilometres away, as the target of our interstellar flight. We have to put a few more numbers to understand the problem: the space between the stars is the region between the sphere of influence of our Sun and the similar sphere of influence of other stars; both are a large bubble of gas in the plasma state formed by charged particles, the solar wind, that continuously emerge from the star. In both bubbles the star is at the centre along with the planets in the very innermost part, say 40 times the Earth-Sun distance. So to go into interstellar space one must first exit the heliosphere, the sun's zone of influence, which is very extensive.

The first launches in the 1970s

Some spacecraft in interstellar space have also ventured into it, but only Nasa's two Voyager probes, Voyager 1 and 2, have entered it, passing planets, the asteroid belt and tens of thousands of comets. Voyager 1, launched on 5 September 1977, was the first to pass the walls of the solar bubble, in August 2012, while its twin, Voyager 2, which took a different route through the solar system, entered interstellar space on 5 November 2018. In 35 years, therefore, Voyager 1 managed to get only 18 billion kilometres from the sun, 122 times the distance Earth-Sun, practically nothing for our task.

A laser propulsion

The first and most important problem for interstellar travel we understand to be the thrust technology, the engine in short. Whether the carrier rocket is a one-, two- or three-stage, liquid- or solid-fuelled one, you cannot do much more than that with today's chemistry-based engines.

There are several projects that have been under study for years, which have a completely different approach, relying on lasers that from Earth, propel special, lightweight vehicles with speeds that, according to the creators, could be 25% that of light, taking the journey from Earth to Alpha Centauri from the millennia needed today to about fifteen years. Both the Starlight project, which started some fifteen years ago, and the Breakthrough Starshot project, adopt as their basic idea to use high-intensity light, laser beams in essence, to propel vehicles, small and light, the size of a CD-ROM, up to relativistic speeds. Funded by NASA or by robust injections of private capital, the two projects, after a development phase, seem to have stalled, but the basic idea, i.e. not to carry neither engine nor fuel in the vehicle, nevertheless seemed revolutionary and could be taken up again.

Aboard 1,500 people for hundreds of years

Even more visionary and extreme are the three projects that won the Hyperion competition, announced by the Initiative for Interstellar Studies, I4IS, an international group led by Andreas Hein, professor of space systems engineering at the University of Luxembourg. Their headquarters, and this seems auspicious, is housed at the British Interplanetary Society, an organisation that back in 1933 set out to develop space travel, then pure fantasy. The rules of the competition were to be able to go to the nearest stars, to use only existing or soon-to-be-developed technologies, and to transport a crew and possible descendants, since the journey was supposed to be hundreds of years long anyway, of an initial 500 to 1,500 people without harming individuals or the community as a whole.

An Italian project: the 58-kilometre long spaceship

The Italian Crhysalis, a gigantic tube, 58 kilometres long, containing several concentric cylinders where the crew can live with an artificial gravity similar to that of the Earth, wins. This, but also the others, have schools, factories, hospitals, squares inside them. The winner's thrust engine is nuclear fusion, not there today but considered a likely technology in the future.

The Achilles' heel, as always, however, seems to be the human one: will 1500 people be able to survive, reproduce, coexist, one wonders. Probably the first generation will, because it is made up of brave volunteers, but the second and third? Hard to hope so, we risk going from a generous reproduction of Thomas More's Utopia to the climate of a modern suburb of a large capital city.

However, as the big names in contemporary high tech are often reminded, if you don't try, you don't fail, you don't take risks then you don't innovate; and that's the end of it.