Now a trip to Mars takes about nine months. But scientists think they can reduce that travel time considerably.

This can be read in a peer-reviewed research article that Arxiv has been published and accepted for publication in the research journal Acta Astronautica† In the article, scientists present a new way of space travel that should make it possible to shorten the journey to Mars by as much as 7.5 months.

How does it work?

A key role here is played by a number of large and powerful lasers that should rise on the Earth’s surface. Those lasers are then used to heat fuel aboard the spacecraft to create thrust.

Lasers instead of a chemical reaction

“Rockets work like this: they eject mass from the spacecraft as quickly as possible,” explains researcher Emmanuel Duplay. Scientias.nl from. That mass consists of hot gases: by ejecting hot gases backwards at high speed, the rocket gets momentum forward. Those hot gases can be generated in several ways, but most rockets use a chemical reaction, where a fuel (for example, rocket kerosene) reacts with an oxidizing agent (for example, oxygen). The result is a kind of controlled explosion, in which hot gases are created that are pushed out of the rocket at high speed, propelling the rocket upwards or forwards.

However, Duplay and colleagues take a different approach: they propose generating thrust using lasers. For this, a spacecraft would first have to settle in orbit around the earth, after which powerful lasers are used to detect the propellant or propellant (for example, hydrogen) on board the spacecraft to generate hot gases that propel the spacecraft to Mars in a very short time. The approach has two major advantages over conventional (chemical) rocket propulsion, says Duplay. “First of all, we are not dependent on a chemical reaction to heat the propellant, which means that we can heat the fuel to much higher temperatures and thus increase fuel efficiency. In addition, the lasers are located on Earth, which means that not all of the mass needed to generate the necessary thrust is on board. And those two advantages allow our spacecraft to travel much faster than would be possible with a conventional rocket equipped with the same amount of propellant.”

45 days

A calculation shows that in this way it should in theory even be possible for a probe to travel to Mars in 45 days. For an unmanned and relatively light space probe, it does require that several lasers with a combined power of about 100 MW be built. And even more powerful lasers are needed to get astronauts to Mars in 45 days. “We believe it is feasible,” said Duplay. “But then you have to scale up the laser power by a factor of 40.”

Important

However, that can be very rewarding. Because the long travel time to Mars will undoubtedly be difficult for people. Not only mentally, but also physically. “Astronauts in interplanetary space would be exposed to significantly more cosmic rays than we experience here on Earth or on Mars itself. And since long-term exposure to this radiation increases the risk of cancer, it would be good if we could shorten the time it takes to travel from one planet to another.”

Challenges

In 45 days to Mars: it almost sounds too good to be true. And Duplay has to recognize that there are still some hurdles to overcome before that. “One of the bigger challenges is how we deal with the hydrogen gas that is heated to a temperature of 10,000 Kelvin by our lasers. How can we build an engine that can handle those temperatures and not melt away? In our study, we did come up with a seemingly feasible solution for this, but the proposed rocket engine is radically different from the rocket engines that are currently operational and requires the latest of the latest materials and cooling techniques.” And then there’s that collection of unparalleled high-power lasers. The underlying technology is already there, says Duplay. “But there is still some work to be done before we can also use lasers in this way.”

Lasers and spacecraft
It is certainly not the first time that researchers propose to use lasers to move spacecraft. Years ago, for example, scientists suggested building a tiny space probe – a nanoprobe – and attaching it to a huge light sail, and then using lasers to bring it up to great speed and set a course for the nearest star system. We are talking about Alpha Centauri, about 4 light-years away from Earth. Using lasers, the small probe should be able to reach a very high speed and fly to Alpha Centauri in ‘just’ 20 years. By comparison, it would easily take several tens of thousands of years to reach the star system with conventional rockets.

Landing

While a 45-day trip to Mars naturally sounds a lot more attractive than the 270 days it takes with conventional rockets, such a laser-powered spacecraft also has a downside. It can be difficult to brake. “The spacecraft is approaching Mars about as fast as it left Earth, so it can’t use conventional rockets to slow itself down. And since there are no lasers on Mars, they cannot be used to slow down the spacecraft. It means there’s only one option left: aerobraking. The resistance encountered by the spacecraft in the Martian atmosphere is used to slow down the spacecraft. It’s not a pleasant maneuver; according to our study, an astronaut in the spacecraft would feel for several minutes that he or she weighs eight times more than it actually does.”

Whether future Mars travelers should actually prepare for such an experience remains to be seen. “Exploring the edges of our solar system – especially if we want to do it through manned missions – will require new propulsion technologies,” said Duplay. “However, there are several candidates in the race.” For example, in addition to propulsion using lasers, nuclear propulsion is also being considered. “Each approach has pros and cons. And I think which one it will ultimately be will depend on what we find the most acceptable scenario: building unparalleled large lasers on the Earth’s surface or strapping a nuclear reactor to a launch vehicle?”