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Supersonic Laser Rockets Are One Step Closer to Reality

A science fiction favorite takes a leap towards becoming a space staple.
A laser lasing. Image: Pixabay

No vision of the future is complete without laser-powered spaceships zipping around the galaxy. Thanks to a study published in Applied Optics yesterday, it looks like we're one step closer to that dream coming true.

The study's authors propose a model that combines lasers with traditional rocket fuel, which would dramatically reduce the weight set aside for propellant. "One of the principal advantages of laser propulsion is its sufficient decrease in mass of onboard propellant that a vehicle to be launched has to have," co-author and physicist Yuri Rezunkov told me.

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"If the propellant mass of a conventional rocket launcher takes about eighty percent of a total rocket mass, the propellant for a laser propulsion launcher will occupy only ten percent of a total mass," he said. "The rest can be used as a payload."

If it works, it would mean a huge bump in efficiency, one that could reshape our entire approach to aerospace. The constraint of using heavy loads of propellant has been an irksome mainstay of space exploration from its infancy. Removing it would free up space for scientific cargo and life-support systems for larger manned missions.

Laser propulsion could potentially allow aircraft to travel at supersonic speeds, especially as we look to a future of high-flying, high-speed jets.

"The technique of supersonic laser propulsion could increase efficiency of thrust production in hypersonic ramjet engines to accelerate high-altitude aircraft to a velocity with Mach number greater than 10," said Rezunkov.

So when do we get our fancy laser rockets? It could be sooner than you'd think. Laser propulsion has a long history not just in fiction, but as an achievable scientific goal. Rezunkov cited the Lightcraft vehicle developed by Leik Myrabo as the leading prototype of laser propulsion, and it was first launched more than a decade ago.

"In 2002, the first full-scale experiments on launching of a small model of the Lightcraft to an altitude of 100 meters were carried out by using a repetitively pulsed CO2 laser," said Rezunkov. "But, the experiments made by researchers demonstrated essential instability of thrust production."

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This instability problem was what Rezunkov and his colleague Alexander Schmidt tackled in their paper. They proposed using a process called laser ablation, which basically amounts to shooting laser pulses at traditional propellant until it heats into a powerful jet of charged particles, called a plasma plume. The craziest part is that the laser doesn't even have to be a part of the spacecraft—it could theoretically power the vehicle remotely.

In this model, the rocket would still be generating thrust by burning fuel, but the laser-activated plume would produce a more powerful and efficient lift-off than propellant alone. The problem is steadying the wild ejection of supersonic gases from the vehicle's nozzle, and preventing shock waves that stifle the overall thrust.

In their paper, Rezunkov and Schmidt suggested using ablation to reconfigure the plasma plume along the nozzle's inner walls. This would theoretically generate a much more consistent and predictable thrust, though the team's results do still need to be borne out in the lab.

"At present time, to prove the proposed technique of laser propulsion experimentally, we need test equipment that has [combines a] high power CW laser and supersonic shock tube in one place," explained Rezunkov.

Though there is still a lot of work to be done, Rezunkov and Schmidt have an ideal space mission in mind for ablation-powered vehicles. "The particular type of space exploration system [we've considered] is a space mini-vehicle with the laser propulsion system, which we call a Space Laser Cleaner (SLC)," said Rezunkov.

"The vehicle [would] be exploited to remove space debris from geostationary and high altitude orbits, to monitor a large-size space station, to observe near-Earth space, and so on," he continued. "In all listed cases, there is a necessity of using a small mobile spacecraft without a large consumption of propellant."

Yes, this does mean that a super-efficient orbital cleaner, powered by a remote laser, could be on the horizon. It seems fitting that the first generation of laser-powered spacecraft would be deployed to declutter outer space, because we're going to need a clear course for all those Millennium Falcons, Starship Enterprises, and other sci-fi-inspired spaceships that will hopefully follow them.