New photonic devices and directed energy systems are said to be poised to enable the next leap in deep space exploration.

WASHINGTON — (BUSINESS WIRE) — November 1, 2018 — New directed energy propulsion systems may enable the first interstellar missions, with small, robotic spacecraft exploring neighboring solar systems, according to experimental cosmologist Philip Lubin. He will present these and other advances at The Optical Society’s (OSA) Laser Congress, Light the Future Speaker Series, 4-8 Nov. in Boston.

Imagine a wafer-thin spacecraft powered by laser light capable of speeds greater than one quarter the speed of light—fast enough to reach the closest neighboring star to our solar system within 20 years, or something closer to home, like getting people to Mars in a month. By tapping into photonics-driven propulsion, researchers are well on their way to making this seemingly impossible science-fiction achievement a reality, said Lubin, who is a professor of physics at the University of California, Santa Barbara.

The research results Lubin will describe stem from NASA’s Starlight and Breakthrough Starshot programs, both of which support advanced research in photonics. Lubin is director of the Starlight program.

“Photonics, the production and manipulation of light, is already a part of our daily lives—from cellphones to computers to light-emitting-diode (LED) light bulbs to fiber optics that carry your data all over the place—even though you may not see it,” said Lubin. “You can point to practical examples of photonics in everyday life and it appears to have nothing to do with interstellar flight, but in fact it does, because it’s synergistic with the technology you need to achieve interstellar flight.”

One of the greatest challenges in validating this photonics concept as it relates to propulsion is the demonstration of the laser power required to accelerate the proposed/hypothetical spacecraft, according to Lubin.

Synthesized optics for directed energy propulsion systems

Large directed energy systems are not built using a single gigantic laser, but instead rely on beam combining, which involves the use of many very modest power laser amplifiers.

“Our system leverages an established typology called ‘Master Oscillator Power Amplifier’ design,” said Lubin. “It’s a distributed system so each laser amplifier ‘building block’ is between 10 and 1000 Watts. You can hold it in your hand. Instead of building a gigantic laser, you combine a lot of small little laser amplifiers that, when combined, form an extremely powerful and revolutionary system.”

Lubin suggests an analogy with supercomputers, which are built using a large number of central processing units (CPUs). “By coherently combining billions of low poser laser power amplifiers—similar to the same power of a typical modern household LED—you suddenly have this amazingly capable directed energy system,” he said.

Interstellar probes powered via laser light

Directed energy systems may enable interstellar probes as part of human exploration in the not-too-distant future, and they are at the heart of the NASA Starlight program and the Breakthrough Starshot Initiative to enable humanity’s first interstellar missions. The same core technology has many other applications, such as rapid interplanetary travel for high mass missions, including those carrying people; planetary defense; and the search for extraterrestrial intelligence (SETI).

“Our primary focus currently is on very small robotic spacecraft. They won’t carry humans onboard—it’s not the goal for the interstellar portion of our program,” said Lubin. “If humanity wants to explore other worlds outside our solar system, there are no other physically obtainable propulsion options for doing this—with two exceptions.

“One way would be if we could master a technological approach known as antimatter annihilation engines, which are theoretical propulsion systems that generate thrust based on energy liberated by interactions at the level of subatomic particles. But we don’t currently have a way to do that,” Lubin said, “and it involves a number of complexities we do not have a current path to solving.

"The other option is directed energy or photonic propulsion, which is the one we’re focusing on because it appears to be feasible,” Lubin said. In one variant, directed energy propulsion is similar to using the force of water from a garden hose to push a ball forward. Miniscule interstellar spacecraft (typically less than a kilogram and some that are spacecraft on a wafer) can be propelled and steered via laser light, he said.

“Miniaturizing spacecraft isn’t required for all of the mission scenarios we’re considering, but the lower the mass of the spacecraft the faster you can go,” Lubin said. “This system scales in different ways than ordinary mass ejection propulsion."

So far, all of the rockets that have blasted off from Earth are based on chemical propulsion systems whose basic designs date back to World War II. They are just barely able to make it off the surface of the Earth and into orbit. Making a bigger rocket doesn’t make it go faster, it just allows the rocket to carry more mass. Photonic propulsion works differently, because the less dense the payload the faster you go. So you want to lower the mass to go faster.