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.
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.”
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