Photonic Propulsion: Mars in 3 Days?

There’s been all kinds of buzz lately about
some new space tech that could send a spacecraftto Mars in 3 days, and maybe even get spaceships
to exoplanets that are light-years away. Which kind of sounds like something out of
a science fiction novel. But a group of researchers from the University
of California, Santa Barbara is working ona new way to travel in space. Known as photonic propulsion, it would use
a giant set of lasers to push ships along. And if it works, it could eventually be used
to explore other star systems. But that’s a big if. The project is called DEEP-IN, and its goal
is 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 to
other stars in any reasonable amount of time,which is where electromagnetic acceleration
comes in. Instead of using chemical energy to push itself
forward, a DEEP-IN spaceship would use theenergy from electromagnetic radiation — more
specifically, the energy a huge set of lasers,powered by sunlight. That laser array technology is a whole project
all 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 first
part of that acronym, DE-STAR would be a lasersystem with multiple uses. Like, destructive uses. DE-STAR is mainly being designed to protect
Earth — both by diverting asteroids thatare headed for us, and by vaporizing space
debris. This photon-driven propulsion thing is just
a bonus — a pretty huge one. It’s based on the idea that light has a
lot of pushing power, which comes from itsmomentum. We might not feel that push from just walking
around on Earth, but a giant reflector screenin space does feel it. That’s the science behind solar sails, and
we’ve already built spaceships that usethem. When the photons in light bump into a solar
sail, their momentum is transferred and thespacecraft is propelled forward a little bit. DE-STAR’s lasers would provide lots of light
that we could use to take the solar sailsconcept one step further, and start building
spacecraft that use laser sails. See, solar sails are limited, because the
light coming from the sun only comes withso many photons. But this laser sail will
have a concentrated beam of photons shootingdirectly at it. It’s like the difference between a sprinkler
and a fire hydrant. When it gets hit by thatlaser beam, the laser sail — and anything
that happens to be attached to it, like aspaceship — is going to start zooming through
space. A ship that used a laser sail wouldn’t have
to 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 50-70
gigawatts of power, a 100 kilogram ship — aboutthe size of Voyager 1 — could travel at around
1. 5% of the speed of light — nearly 300 timesVoyager’s top speed. But there are still challenges to solve, when
it comes to making spaceships powered by giantlasers. We /could/ send a smaller probe to Mars in
3 days, or a larger craft on a trip that wouldtake about a month. But we’d need a giant, square laser array
that’s 10 kilometers long on each side — whichpresents some obvious problems. Getting stuff to space is expensive, let alone
100 square kilometers’ worth of high-poweredlaser equipment. And even if we did get everything to the right
spot, it would be incredibly difficult toassemble. Building a laser sail for this super-fast
trip to Mars would also be tough. According to the researchers, it would have
to be only a micron thick — that’s a thousandthof a millimeter. But to work properly, that whisper-thin laser
sail would have to weigh about as much asthe spaceship itself! Meaning that it would
have to be a huge, thin sail, but strong enoughto be stable while the ship is moving ridiculously
fast. And … we also have no idea how to slow the
spacecraft down once it gets to wherever it’sgoing. So if we’re talking about sending ships
to Mars in 3 days, we’re probably gettingahead of ourselves a little bit here. Really, the first step to making this research
a reality is building a much smaller set oflasers. The team’s plan — assuming NASA chooses
to move forward with their idea — is to startwith a laser array that’s only one meter
square. Then we’d just keep building bigger sets
of lasers, until we eventually figured outhow to build one that’s 10 kilometers on
a side. Then, we could use that to launch what are
known as wafer sats. These miniature spacecraft would weigh no
more than a gram, but they’d have sensors,a power source, teeny-tiny thrusters, and
communications equipment. That giant set of lasers could accelerate
these wafer-sats to about 25% of the speedof light, sending them light-years away, where
they could tell us all about interstellarspace and exoplanets. They might even be able to reach the nearby
star 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 of
spaceship — even a little wafer one. And it’s going to be a very long time before
we’re zooming over to Mars in just a fewdays. But it probably is possible. Thanks for watching this episode of SciShow
Space, and thanks especially to our patronson Patreon who help make this show possible.
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