During the Age of Sail, ships circled the world on voyages of discovery and trade. That era ended in the 19th century, when coal-fired steam engines began to replace wind power. We may now be entering a new era of sailing, but this time in space. Reversing history, engines and fuel could be replaced by sails on some spacecraft, powered not by wind but by sunlight.
The idea is still in development, but we know it works. Just a few weeks ago, NASA raised sails on its most ambitious test craft yet, a satellite called the Advanced Composite Solar Sail System (SCA3). It has a 9 meter wide square sail that allows it to adjust its orbital path.
Now, to really get anywhere, you’d need a much bigger sail, and a NASA effort The construction of one of 1,650 square meters was abandoned in 2022 as it was considered unfeasible, given the budget. But that’s an implementation problem, which I’m sure smart humans can solve.
To be clear, this is not like putting photovoltaic panels on your roof to generate electricity. Many spacecraft and planetary rovers already use them. In reality, these are bright, ultra-light candles that pushed by solar radiation. Well, you might be wondering: How the hell can light move a physical object?
comet tails
Good question! After all, when someone says they were “moved” by the beauty of a sunrise, we don’t imagine that they were actually floored. But light bouncing off a surface actually exerts a physical force, no matter how small.
An example is the tail of a comet. You might think of it as a vapor trail that is released when a comet hurtles through space. No. Look, comets are basically big dirty snowballs. When you get close to the sun, some of that ice turns into gas, releasing clouds of dust. Sunlight then pushes that dust into a stream that can extend for millions of miles, sideways to the comet’s path!
Speaking of which, there’s a comet approaching right now that could put on a spectacular show in October. is called Tsuchinshan–ATLASand its tail might even be visible to the naked eye.
electromagnetic waves
Now, light travels in waves, which are a kind of “displacement in motion.” Look at an ocean wave: the water only moves up and down, but that vertical displacement propagates horizontally across the surface. It can surely knock you down if you go into the water.
But light waves are different from ocean waves or sound waves. If we take away the water from the sea, we will not have waves to surf. The same thing happens with sound: there is no wave if there is no atmosphere in which to “wave.” That’s why space is so strangely silent.
Light, on the other hand, can travel through empty space. This is because, in a sense, a light wave is its own medium. The reason is that it is actually composed of two waves: there is an electric field wave and a magnetic field wave. That’s why we call it electromagnetic radiation.
