A recycled stack of newspapers 1.2 meters (4 feet) high is enough paper to save one tree?

## Solar Sailing

| Published: November 12, 2009 – 10:29 am

Solar Sails

Among other things, I’m the vice president of a worldwide, medium-sized organization called The Planetary Society. We are launching a series of spacecraft that will be driven through space, not by rocket fuel, but by the pressure of sunlight.

It is surprising at first, at least for most everyone I’ve ever met, that light has momentum. Light has no mass, y’know. Yet it can ever-so-slightly push things.

You probably know or accept that E = mc2. This is to say that if you could convert all the mass in a bit of matter, say the hydrogen in a glowing star, into pure energy, you’d get an enormous amount of it. A kilogram of mass times 300,000 kilometers per second (186,000 miles per hour, as was said back in the 20th Century) is an enormous number of sustained Watts (Watt-seconds or Joules, okay, or foot-pounds).

Well, if you mess around with this equation and insert the idea that moving energy kinetic energy would carry with it a mass and a speed-squared, you can convince yourself that light has momentum. The theoretical limit being established by a physical measurement called Plank’s Constant.

So, we at the Planetary Society are building three very, very low mass sails, solar sails spacecraft. Our solar sail will be pushed through space by the momentum inherent in photons, particles of light, in this case those beaming from our Sun. A photon carries a quantum of energy, the smallest packet of energy we can measure. But with quadrillions of them impacting the sail at every moment, we’ll get a tiny shove. Since the light beams continuously, we hope to build up speed. By the time we build the third sail we hope to have gotten a nice orbit going.

It’s going to be fantastic the first new propulsion system since, well, since the Greek mathematician Heron built his steam jet reaction spinner engine.

We can sail by starlight. How cool is that?

### 7 Responses to “Solar Sailing”

1. Gracie Beck says:

Do you think it would be possible to do a science fair project on this? (sailing by starlight)

2. whens the launch date set ?? will we be able to see any documentries on this ??

3. dahlia says:

you need a video on solar energy!!!!

4. It is startling to me just how many individuals are unaware of the energy probelms that we face. Its really troubling that so many of us either think that there is an unlimited supply of good clean energy, or ignore the issue completely. For others, solar options, as well as many fresh technologies represent a bright light at the end of a very dark tunnel. I highly regard anyone, who in either a strong or small way, takes their valued time to train everyone about their personal chances and duties when it comes to our future, and our grandkids future. When we look back twenty years from now, it will almost be implausible that we were even engaged in this debate. Our energy future is a forgone conclusion, and we all have a function to take on in progressing us toward it.

5. Bailey says:

I wish we reasearched this form of travel and interstellar Ramjets more.

6. Meredith Gold says:

Dear Bill Nye/Planetary Society:
This is gloriously awesome. Being passionate AP Physics student, it’s making me bounce-off-the-walls giddy to realize that I actually know the equations you’re talking about. However, I’m sort of confused–while I understand how this could work, I do want to know–um, why? An orbit around what, exactly? Or is this purely theoretical equations being proved through experiment, somehow, or…? (Okay, I know this was posted approx. forever ago, but I’m just now researching you for a project, and found this…)

–A Bit Confused