Mars.
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Imagine, an immense laser beam shooting from the surface of Earth to blast a spacecraft to an ultra-high speed and send it careening to the surface of Mars in just a little over a month. It sounds like the stuff of science fiction. But some researchers think it could be the future of space travel.
A newly published scientific paper outlines how a giant laser array could be used to propel a spacecraft to Mars in just 45 days.
“It’s using an approach called directed energy,” explained Andrew Higgins, a professor of mechanical engineering at McGill University in Montreal who worked on the study. “We leave the power source back on Earth and we send power to the spacecraft.”
The paper describes using a 10 meter wide laser array — many little lasers put together to create a giant laser – with the power of 100 megawatts to send a craft that weighs roughly as much as a Mars rover to the red planet. To give an idea of how powerful the laser is, Higgins said it projects thousands of times the power of sunlight. It’s a laser array so powerful, it’s essentially unheard of.
“When the laser gets to the spacecraft, it uses its power to heat up propellant on the spacecraft like a giant steam kettle,” said Higgins. “Just like if you heat up water in a steam kettle and the steam shoots out, you get thrust from that.”
The project grew out of Higgins’ interest in Breakthrough Starshot. Starshot is a part of the Breakthrough Initiatives and was co-founded by Stephen Hawking and Mark Zuckerberg. The concept is to send a one gram solar sail with ultra-light cameras to the closest star system, Alpha Centauri, to take a picture of an Earth-sized planet in the star’s habitable zone. A multiple kilometers-wide laser array would propel the sail to high speeds, getting it to the more than 4-light-year-away system in just 20 to 30 years.
“The interstellar concept is sending a very tiny, tiny probe to take a picture,” explained Emmanuel Duplay, a master’s student in aerospace engineering at Delft University of Technology in the Netherlands and first author of the paper. He worked on the research as an undergraduate student of Higgins’ at McGill.
Duplay found himself drawn to the laser-thermal propulsion to Mars concept for its useful purposes. With the concept outlined in his paper, the laser could send payloads, useful hardware, and astronaut crews around the solar system. “That just felt a little more exciting, a little more interesting to me,” he said.
Higgins explained that a real driving factor behind working to get to Mars so fast is concern for astronaut safety. Surrounding Earth is a system of magnetic fields, called the magnetosphere, which effectively blocks solar and cosmic radiation. The International Space Station is inside the magnetosphere and Apollo astronauts’ trips to the Moon only sent them out of the protective field for days at a time.
“Once you’re outside the magnetosphere, you’re getting exposed all the time to cosmic rays,” explained Higgins. “That is a serious concern for astronauts.”
Reducing what would be an up to 10-month-long mission down to 45 days would dramatically reduce astronaut radiation exposure. Philip Lubin, a professor in the physics department at the University of California, Santa Barbara, agrees minimizing the hazard to humans on a trip to Mars is a main benefit to the work.
Higgins worked with Lubin while on sabbatical at UC Santa Barbara in 2018. Lubin worked on the concept behind the laser arrays that would be necessary to enable Breakthrough Starshot. According to Lubin, the question behind both his own work and Higgins is this: “How do we do better than chemistry to get things faster to places in the solar system?”
Engines, he said, aren’t being made to go any faster than they already are. Researchers are now looking to other methods for fast space travel, including with nuclear fusion.
“The work that [Higgins] is doing is unique, and I think it’s quite promising,” said Lubin.
However, he said, the next step is to prove the concept in a laboratory. There’s still challenges to overcome to make the concept a reality. For example, there would also need to be a laser array on Mars to slow down the spacecraft so that it can land on the red planet.
“We’re not saying ‘Oh, this is easy-peasy’,” said Duplay. “There’s still a lot of work to do and it’s definitely still a technical challenge to actually achieve this.”
