Out in space, as photons of light reflect from the sail, the light gives up a little of its energy and momentum, and that momentum goes into the motion of the sail and it pushes it.This is why solar sails are really cool, and this is why I like them for interstellar travel. Let’s go out the Earth’s distance from the sun, 1 AU, 93 million miles. When you unfurl a sail of any size, say it’s 100 square meters, the sunlight falling on it pushes on it.
If you have a light enough sail, you can get a really big acceleration. If you get well inside the orbit of Mercury and you have a sail that only weighs 1 or 2 grams per square meter—which is about 20 times better than we can do today—and you have a sail that’s like a square kilometer, if you add a laser to boost it, you can get enough thrust to go out of the solar system at a significant fraction of the speed of light, like 10 percent. It’s unbelievable.
When I first saw these numbers, I thought, “That’s great, but we have no material that can stand those loads that’s that lightweight. That material is ‘unobtainium.’” That was pure science fiction. Then in 2004, graphene was found. The discoverers of that got a Nobel Prize for it in 2010. That’s a single layer of carbon. It has all the thermal and mechanical properties you need to build this huge sail; you just have to put something on it to make it reflective, like a layer of aluminum.
Good job Les, get elonmusk to cough up the Starlink in Ukraine, eh.