NASA Expert to Discuss Search for Extraterrestrials, Interstellar Space Travel at The Optical Society Laser Congress

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

WASHINGTON–(BUSINESS WIRE)–#OSA–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.

Like driving in a rain storm—in space

One significant challenge for relativistic spacecraft is radiation
hardening, because “when we begin to achieve speeds close to the speed
of light, the particles in interstellar space, protons in particular,
that you plow into—ignore the dust grains for the moment—are the primary
radiation source,” said Lubin. “Space isn’t empty; it has roughly one
proton and one electron per cubic centimeter, as well as a smattering of
helium and other atoms.”

Smashing into those particles can be significant at high speeds because
while they may be traveling slowly within their own frame of reference,
for a fast-moving spacecraft they make for high-speed impacts.

“When you hit them it’s like driving in a rainstorm. Even if the rain is
coming down straight from the sky your windshield gets plastered because
you’re going fast—and it’s quite a serious effect for us,” Lubin said.
“We get enormous radiation loads on the leading edge as the front gets
just absolutely clobbered, whereas the rest of the spacecraft that is
not the forward edge and facing in different directions doesn’t get hit
much at all. It’s an interesting and unique problem, and we’re working
on what happens when you plow through them.”

In terms of a timeframe for putting directed energy propulsion
technology to work, “We’re producing laboratory demos of each part of
the system,” said Lubin. “Full capability is more than 20 years away,
although demonstration missions are feasible within a decade.”

Getting to Mars quickly

The same core photonics technology in the NASA Starlight program also
allows for extremely rapid interplanetary missions, including missions
to Mars that could transport people in trips as short as one month. This
would dramatically reduce the dangers to humans on the long journey to
the red planet and is currently being studied as one option.

Trillion Planet Survey

Photonics advances also mean that we can now leave a light on for
extraterrestrial intelligence within the universe if we want to be
found—in case there is other intelligent life that also wants to know
the answer to the question, “are we alone”?

Lubin’s students explore this concept in their “Trillion Planet Survey”
experiment. This experiment is now actively searching the nearby galaxy
Andromeda, which has about a trillion planets, and other galaxies as
well as ours for signals of light.

Combining Lubin’s research with his students’ experiment, there are
opportunities for signaling life. When technological advances allow for
the demonstration of lasers powerful enough to propel the tiny
spacecraft, these lasers could also be used to shine a beacon towards
the Andromeda Galaxy in hopes that any life form there could discover
and detect that source of the light in their sky.

The reverse case is more interesting. Perhaps another civilization
exists with similar capability to what we are now developing in
photonics. They may realize, as we do, that photonics is an extremely
efficient means of being detected across vast distances far outside our
galaxy. If there is an extraterrestrial civilization that is
broadcasting their presence via optical beams, like those proposed for
photonic propulsion, they are candidates to be detected by a large scale
optical survey such as the Lubin team’s Trillion Planet Survey.

“If the transmission wavelength of an extraterrestrial beam is
detectable, and has been on long enough, we should be able to detect the
signal from a source anywhere within our galaxy or from nearby galaxies
with relatively small telescopes on Earth even if neither ‘party’ knows
the other exists and doesn’t know ‘where to point,’” Lubin said. This
“blind-blind” scenario is key to the “Search for Directed Intelligence”
as Lubin calls this strategy.

Planetary defense

Perhaps one of the most intriguing uses for photonics—closer to home—is
to tap it to help defend Earth from external threats such as hits
from asteroids and comets.

The same system the researchers are starting to develop for propulsion
can be used for planetary defense by focusing the beam onto the asteroid
or comet. This causes damage to the surface, and as portions of the
surface are ejected during the reaction with the laser light, momentum
would push the debris one way and the asteroid or comet in the opposite
direction. Thus, little by little, it will deflect the threat, Lubin
said.

“The long-term implications for humanity are quite important,” he added.
“While most asteroid threats are not existential threats, they can be
quite dangerous as we saw in Chelyabinsk, Russia in 2013 and in
Tunguska, Russia in 1908. Sadly, the dinosaurs lacked photonics to
prevent their demise. Perhaps we will be wiser.”

About The Optical Society

Founded in 1916, The Optical Society (OSA) is the leading professional
organization for scientists, engineers, students and business leaders
who fuel discoveries, shape real-life applications and accelerate
achievements in the science of light. Through world-renowned
publications, meetings and membership initiatives, OSA provides quality
research, inspired interactions and dedicated resources for its
extensive global network of optics and photonics experts. For more
information, visit osa.org.

Contacts

The Optical Society
Bill Schulz, 202-416-1443
bschulz@osa.org