Our journey into the final frontier is still in its infancy. Russian cosmonaut Yuri Gagarin was the first human to venture into outer space in 1961. Fast forward to today and we have men and women living aboard a space station orbiting 249 miles above Earth. Private companies such as SpaceX are pushing the boundaries of what’s possible with reusable rockets. Probes like New Horizons are studying the distant bodies of our solar system. But, how do we take that next step?
One potential answer is photonic propulsion. Basically, using lasers as propulsion.
Professor Philip Lubin from the University of California Santa Barbara gave a talk at the 2015 NIAC Fall Symposium last October. In it, he tackled the prospects of photonic propulsion and what it could mean for interstellar travel and exploration.
Lubin tells us we can already get to relativistic speeds (a speed that is a sizable proportion of the speed of light) in the laboratory. Think the Large Hadron Collider in Europe. That uses electromagnetic acceleration.
Then we get to things we use to travel in everyday life – cars, airplanes and rockets. And “we are pathetically slow,” according to Lubin. This is where photonic propulsion could come into play.
Now, this isn’t your typical propulsion system. Think about NASA’s Dawn and New Horizons spacecraft. The propulsion systems are attached to the spacecraft. What Lubin is proposing is building a laser array to propel a spacecraft. The array and the spacecraft start in low-Earth orbit. But, then the spacecraft is propelled away while the array stays in Earth orbit. Here’s an image that illustrates what’s going on.
You see how the craft is much further away from the laser array? That simulation was using a 20 m diameter array with power of 272 kW propelling a 1 g payload. What makes this system so intriguing is it’s scalable. You could create a bigger array to power a bigger payload.
When the SLS launches in the next few years, it will rise off the launch pad at between 50 and 100 gW (gigawatts). “Turns out, to get to relativistic speeds with the spacecraft we’re talking about, you basically need the same power level,” says Lubin. “And for about the same amount of time. It takes 10 minutes to get to orbit with the shuttle. It takes us 10 minutes to get to 30% the speed of light with about the same power level, just using different technology.”
This technology could propel a 100 kg spacecraft to Mars in three days. Something the size of a shuttle? About a month.
“There are recent advances which takes this from science fiction to science reality,” says Lubin. “There is no known reason why we cannot do this.”
The potential uses for photonic propulsion are nearly endless. From planetary defense to SETI. You can imagine how handy this technology would be for pushing asteroids or comets on a potential impact course away from us.
How do you stop?
And therein lies the rub. “If you ever watched Spaceballs, you know on the back it says ‘we stop for nobody.’ So we stop for nobody,” Lubin joked at his NIAC Fall Symposium talk. One idea is an Alpha Centauri flyby mission.
Getting to Mars in three days sounds great, but placing an object in Mars orbit is trickier. You would need a second array on the surface or orbiting the red planet to slow down the spacecraft. But, using this propulsion for manned missions is a very long ways off. It would be better suited for flybys of objects outside of our solar system.
Watch the entire talk by Lubin to learn more about the ins and outs of photonic propulsion.