Photonic Propulsion: Mars in 3 Days?
There’s been all kinds of buzz lately aboutsome new space tech that could send a spacecraftto Mars in 3 days, and maybe even get spaceshipsto exoplanets that are light-years away. Which kind of sounds like something out ofa science fiction novel. But a group of researchers from the Universityof California, Santa Barbara is working ona new way to travel in space. Known as photonic propulsion, it would usea giant set of lasers to push ships along. And if it works, it could eventually be usedto explore other star systems. But that’s a big if. The project is called DEEP-IN, and its goalis to use electromagnetic acceleration toget ships close-ish to the speed of light— fast enough that interstellar travel couldactually make sense. These days, our spaceships use chemical acceleration— in other words, they burn fuel — and theyare fast. They’re just not fast enough to travel toother stars in any reasonable amount of time,which is where electromagnetic accelerationcomes in. Instead of using chemical energy to push itselfforward, a DEEP-IN spaceship would use theenergy from electromagnetic radiation — morespecifically, the energy a huge set of lasers,powered by sunlight. That laser array technology is a whole projectall by itself, called the Directed EnergySystem for Targeting of Asteroids and exploRation,or DE-STAR, and being developed by the sameresearch team. And as you might have noticed from the firstpart of that acronym, DE-STAR would be a lasersystem with multiple uses. Like, destructive uses. DE-STAR is mainly being designed to protectEarth — both by diverting asteroids thatare headed for us, and by vaporizing spacedebris. This photon-driven propulsion thing is justa bonus — a pretty huge one. It’s based on the idea that light has alot of pushing power, which comes from itsmomentum. We might not feel that push from just walkingaround on Earth, but a giant reflector screenin space does feel it. That’s the science behind solar sails, andwe’ve already built spaceships that usethem. When the photons in light bump into a solarsail, their momentum is transferred and thespacecraft is propelled forward a little bit. DE-STAR’s lasers would provide lots of lightthat we could use to take the solar sailsconcept one step further, and start buildingspacecraft that use laser sails. See, solar sails are limited, because thelight coming from the sun only comes withso many photons. But this laser sail willhave a concentrated beam of photons shootingdirectly at it. It’s like the difference between a sprinklerand a fire hydrant. When it gets hit by thatlaser beam, the laser sail — and anythingthat happens to be attached to it, like aspaceship — is going to start zooming throughspace. A ship that used a laser sail wouldn’t haveto carry as much fuel, which would mean thatit could have a much lower mass. It could, also, in theory, go very, very fast. With a huge laser array putting out 50-70gigawatts of power, a 100 kilogram ship — aboutthe size of Voyager 1 — could travel at around1. 5% of the speed of light — nearly 300 timesVoyager’s top speed. But there are still challenges to solve, whenit comes to making spaceships powered by giantlasers. We /could/ send a smaller probe to Mars in3 days, or a larger craft on a trip that wouldtake about a month. But we’d need a giant, square laser arraythat’s 10 kilometers long on each side — whichpresents some obvious problems. Getting stuff to space is expensive, let alone100 square kilometers’ worth of high-poweredlaser equipment. And even if we did get everything to the rightspot, it would be incredibly difficult toassemble. Building a laser sail for this super-fasttrip to Mars would also be tough. According to the researchers, it would haveto be only a micron thick — that’s a thousandthof a millimeter. But to work properly, that whisper-thin lasersail would have to weigh about as much asthe spaceship itself! Meaning that it wouldhave to be a huge, thin sail, but strong enoughto be stable while the ship is moving ridiculouslyfast. And … we also have no idea how to slow thespacecraft down once it gets to wherever it’sgoing. So if we’re talking about sending shipsto Mars in 3 days, we’re probably gettingahead of ourselves a little bit here. Really, the first step to making this researcha reality is building a much smaller set oflasers. The team’s plan — assuming NASA choosesto move forward with their idea — is to startwith a laser array that’s only one metersquare. Then we’d just keep building bigger setsof lasers, until we eventually figured outhow to build one that’s 10 kilometers ona side. Then, we could use that to launch what areknown as wafer sats. These miniature spacecraft would weigh nomore than a gram, but they’d have sensors,a power source, teeny-tiny thrusters, andcommunications equipment. That giant set of lasers could acceleratethese wafer-sats to about 25% of the speedof light, sending them light-years away, wherethey could tell us all about interstellarspace and exoplanets. They might even be able to reach the nearbystar system Alpha Centauri only 15 years afterthey launch. So, there’s still a huge amount of research,technology development, and testing neededbefore we use lasers to propel any sort ofspaceship — even a little wafer one. And it’s going to be a very long time beforewe’re zooming over to Mars in just a fewdays. But it probably is possible. Thanks for watching this episode of SciShowSpace, and thanks especially to our patronson Patreon who help make this show possible. If you want to help us keep making episodeslike this, just go to patreon. com/scishow. And don’t forget to go to youtube. com/scishowspaceand subscribe!