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Romancing The Sun


Our Sun, like most stars, spews copious amounts of light energy to heat up its immediate neighborhood; but it also spits out a flux of subatomic particles that forms a halo enveloping the whole of the solar system. These particles - mostly protons and electrons - are energetic enough to escape from the hot surface of the Sun: think of them as vapor off the boiling pot. This halo is called rather poetically the "solar wind", as it blows away from the Sun against all the planets around it. The solar wind interacts with the Earth's upper atmosphere and has many interesting effects - from generating beautiful aurorae near the Poles, to occasionally disrupting satellite communication. 

However, the solar wind pales - in terms of energetic content - compared to the amount of light energy that the Sun floods the solar system with. And you may think of the Sun's light as a sort of a solar wind as well: a solar wind of photons - particles of light - streaming through space. There is even enough photon wind in this light to propel a spaceship… 

Much like flowing air or water, flowing light exerts pressure and momentum. A spaceship with a large reflecting surface - i.e. a mirror - can literally sail through the solar system using the Sun's wind of photons! The effect is not a large one, but it can add up over time to generate appreciable speeds. To put things in perspective, the pressure from sunlight near the Earth is about 100 billion times smaller that air pressure; but it is a thousand times greater than pressure arising from the proton/electron solar wind. Most importantly, the pressure and hence propulsion provided by the photon wind is free… 

Recently, there has been several romantic as well as practical attempts at building sailing spaceships that can ride the Sun's light across the solar system. The attached videos describe this technology. The first video is a general discussion of solar wind of the weaker first kind - made of electrons and protons. The second video is about a prototype solar sail based on a blade configuration that uses photon wind for propulsion. The last video describes the first solar sailship that was recently launched into space by Japan. All we now need are a few solar sailship pirates and we'll be back to the Middle Ages…

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