Sunlight – life on earth could not exist without it! Sunlight is energy, and as well as benefiting from its warming and nourishing of our planet and its lifeforms, in modern times we have started to learn how to use its power in ways never even imagined by previous generations.
Solar energy panels converting light to electricity are now a familiar sight, but the cutting edge of solar energy research in the last decade has been about harnessing the power of light in a rather different way.
In space, the energy of sunlight gently but relentlessly pushes everything in its path away from the Sun. This effect, known as solar radiation pressure, is clearly visible in comets, where the white tail tail of dust particles trails out behind the comet along its orbital path, on the opposite side of the comet to the sun.
And its effects can be seen on a large scale in clusters of stars where the light from the stars can shape and even disperse the clouds of gas around them.
Solar sailing
During the last decade, humankind has succeeded in tapping into this invisible power source in space - spacecraft powered totally by the pressure of sunlight have been a reality since the launch of Japan's IKAROS craft in 2010, and other have followed and are planned, such as the Planetary Society's Light Sail in 2015, and NASAs Near-Earth Asteroid Scout scheduled for 2018.
There are no solar panels on these spacecraft – they simply use a gossamer-like 'solar sail' for propulsion, by directing the power of this gentle pressure by reflection, a bit like the way a sailing ship uses the power of the wind.
And of course they will not be slowed down and limited in distance by having to carry a on-board fuel supply that sooner or later will be used up. For these reasons, some consider them our best hope of for achieving an interstellar mission.
Interstellar Travel?
The concept is already inspiring some incredible ideas and projects – the latest to hit the headlines named 'Breakthrough Starshot', aims to send a fleet of tiny solar-sail-powered sensors as far as the Alpha Centuari system, our nearest neighbour, over 4 light years away. At such a distance from the Sun the power of solar radiation pressure will be far too feeble, so the project proposes creating artificial radiation pressure with the use of powerful lasers to power the sails up to 20% of light speed!
It seems like science fiction and there are many technological challenges to be overcome before such a project can become reality, but the concept is inspiring. As Stephen Hawking said at the project announcement in mid-April, 'Today we commit to this next great leap into the cosmos, because we are human and our nature is to fly.'
http://global.jaxa.jp/projects/sat/ikaros/
http://sail.planetary.org/
http://www.scientificamerican.com/article/lightsail-solar-sailing-launch-date/
http://news.nationalgeographic.com/2016/02/160202-solar-sail-space
https://www.theguardian.com/science/2016/apr/12/stephen-hawking-and-yuri-milner-launch-100m-star-voyage-nasa-exploration/
1.By Philipp Salzgeber - http://salzgeber.at/astro/pics/9703293.html, CC BY-SA 2.0 at, https://commons.wikimedia.org/w/index.php?curid=184641
2.Andrzej Mirecki - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=14656159S
3. NASA