Space Flight

3/23/08 – 3/29/08
by C. Zaitz

Do you ever look at a bird and wonder how it flies? Or even better, wonder why you can’t? I wondered that the other day watching a hawk swooping and scooping air with its wings. I remembered Icarus of ancient mythology, the man who wore wings so he could fly. The higher he went, the more his giant wings made of wax and feathers melted from the high temperature of the sun.

In modern terms, the story makes no sense at all. First, if Icarus was confined to flying in the sky, he would have gotten colder, not warmer, as he flew higher. Second, if he had actually broken free and reached escape velocity by flapping his home-made wings, he would also have escaped the means of his flight- air pressure! Birds and planes rely on moving air to stay aloft. In space, there is no air, and thus no flight by wing. But the Greeks didn’t know this, and Icarus tumbled to earth with the melted wax and feathers all akimbo, a testament to man’s hubris and the punishment for flying too high.

Nature may not have gifted us with the ability to fly, but she did endow us with giant brains to figure out how to build devices that fly. In space, we have to use different principles to get around. One elegant solution was proposed long ago by Johannes Kepler. He noticed that comet tails were pushed back away from the sun by some force, and proposed that humans could catch that “breeze” to sail the solar system. Centuries later, the idea was proven true. Pressure from photons streaming from the sun can actually accelerate a thin, lightweight material, like a solar sail, to speeds that eventually could outrun our best traditional rockets. The key to their success, however, is patience.

If our traditional rockets are hares, solar sails are the tortoises of space travel. Since they are collecting ephemeral starlight, it takes a long time to get up a full head of steam to go fast. It’s a continual acceleration, unlike traditional rockets that blast off in a hurry but eventually run out of fuel. It may take a while to get “sailing”, but once it does, it will win the race!

Due to the nature of the slow acceleration, solar sails may not be suited for certain types of space travel. But there are so many benefits to using sunlight to propel a spacecraft that there are companies involved in creating materials and designs for commercial use. Launch rockets can be much smaller and more efficient to get the sails off the ground. The sails themselves don’t need fuel other than what they get from the sun. They can be cheaper, faster, easier, and create less waste.

It turns out that solar sails would need to get pretty close to the sun to go fast enough to travel large distances quickly. Like Icarus, they would swoop near the sun, but unlike him, they can use the energy and gravity to swing back out and go flying through the solar system. Perhaps one day, in the not so distant future, our night sky will be filled with sailing ships, off to distant worlds, using the “winds” of light and the wings of modern technology to fly.

Until next week, my friends, enjoy the view.