Steering Solar Sails

Deby Fredericks asked how to steer a solar sail. The short answer is you do so by turning the sails just like a sailboat. In some solar sail designs, the sails simply rotate on their masts. This was the design I went for in my novel, The Solar Sea. Below is an illustration of the solar sail Aristarchus from the novel by Laura Givens. Each of those sail petals can rotate on its mast 360 degrees. If they face the sun full on, they get the full benefit of light pressure. If you turn them 45 degrees, you’ll alter the course of the ship. If you turn them 90 degrees from the sunlight, you won’t get any acceleration.

Aristarchus Sail Array

Some solar sails like NASA’s forthcoming Sunjammer have little triangular extensions of the sails. Those are the parts that turn in that design. The idea is that induce a little roll to the craft, which allows the whole thing to turn.

Sunjammer Sail

Now, we can also look at the way a solar sail might accelerate out of an orbit. A good way to think about solar sailing is that it’s like sailing in water, but where gravity acts like a current and light pressure acts like wind. A body in orbit around a planet or other body is perpetually falling and an orbit is an ellipse.

solar sail orbit

In the case of a solar sail, if it turns its sails to face the sun when it’s at the top of the ellipse, it’ll get a little boost of acceleration away from the sun. Then if it turns its sails out of the sunlight as it comes around to the part of the orbit closest to the planet, it won’t slow down again. When it reaches the top of the orbit it can turn the sails toward the light again for another boost. In this way, each successive orbit gets a little higher and higher until your solar sail is where you want it, or it achieves escape velocity.

The Solar Sea

You can learn more about The Solar Sea at TheSolarSea.com. There you can see lots of Laura Givens’ cool concept art from the novel. For fans of The Pirates of Sufiro and its sequels, you can also get a look at the Rd’dyggians and the Titans. My novel The Solar Sea is available at:

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2 comments on “Steering Solar Sails

  1. Cool, thanks for answering my question.

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