Search query: Solar sail spacecraft projects
Video title:  and the photons bounce off
instead of being absorbed. And forward you go, with
just the push of light. Japan's IKAROS light
sail uses this phenomenon to even steer their aircraft. What they do is they can
change the reflectivity on the sides of the
solar sail in real time using liquid crystals, similar
to the crystals in your LCD screen. By changing the
reflectivity around one edge of the solar sail,
they can make it so that the shinier
side is pushed more than the other side, and
thus pivot and steer the craft. You don't have to move
anything, and you can steer using liquid crystals. That's ingenious. And fun, Icarus is a
character from Greek mythology that flew too close to the
sun, and the wax on his wings melted off. Oops. Now, I think the coolest
thing about solar sails is that light can
push things at all. It seems pretty straightforward. The photons come in and pelt the
light sail, pushing it forward, just like air molecules in
wind pelt a boat's cloth sail and push it forward. Right? Well, no, because
molecules have mass, unlike photons
which have no mass. They are precisely
zero kilograms. And you learn in physics class
that momentum equals mass times velocity. So no mass means no momentum. But then, quantum
mechanics class comes along and tells you,
well, actually there's another way that you
can get momentum, and it's if
something has energy. And light does have energy,
so it can have momentum. Just another thing
that quantum mechanics came in and turned upside down. And let me just say, solar
sails aren't science fiction. They are the now. In 2008 NASA launched a
small solar sail satellite to orbit Earth, called the
NanoSail-D. D for Dianna. Just kidding. Also in that year,
Japan launched its interplanetary
explorer, IKAROS, which made it all
the way to Venus in less than seven months. This upcoming year,
the Planetary Society plans to launch LightSail,
a crowdfunded satellite the size of a loaf of bread,
which seems pretty small,