Solar sail to deploy this weekend on a journey of starlight
One of the problems with space flight is you need to throw stuff out of the back of your spacecraft in order to make it go. You could throw rocks out the back, but you wouldn’t get very far, or go very fast.
So, we’ve decided that, for now, the best thing to do is to create controlled explosions and channel those through a nozzle of some sort. Really big explosions are needed to get you off the ground and into space, but then you can use smaller explosions to adjust course and get where you want to go.
Now, as you may have noticed, rockets are big. I mean, really big. That’s because it takes a lot of fuel, tons of it, just to get out of the reach of Earth’s gravity. So, the science payloads (rovers, cameras, etc.) tend to be tiny and the vast majority of the fuel is used up just getting the rest of the fuel off the ground.
It’s a problem.
One solution that’s being explored is the concept of a “Solar” or “Light” Sail. This is literally a sail, similar to what you’d find on an old-timey ship, except that it’s pushed through space by the force of the light coming off the Sun.
The advantage is pretty obvious: Once you get out into space, your “fuel” is all around you. The Sun never stops shining, so you never stop accelerating.
The problems however, are numerous. First, the “pressure” from sunlight is tiny. I mean really tiny. So tiny I couldn’t find a human-scale metaphor to relate it to. However, it’s constant. So, once you get your Solar Sail up and running, it’s constantly accelerating, which makes it good for long term missions…like maybe ferrying supplies to colonists on Mars.
But, because the acceleration is tiny, the sail itself has to be huge. Several hundred square meters at least, just to move a tiny payload around. Larger payloads, like supplies for colonists, would require sails that were hundreds of square kilometers in size.
And, because the pressure is tiny, and the sizes are huge, the material the sail is made of has to be incredibly thin and light. Think Mylar sheets, and then make it a little thinner.
And because it’s thin and huge and it’s in space with micro meteorites whizzing around, it has to be tough enough to take hits and not shred into millions of tiny pieces.
And then there’s the deployment part. You can’t launch a 100 square kilometer sail from the ground fully deployed. So you have to pack it up, shove it in a conventional rocket, throw it into orbit and then unfurl the entire thing in space. If you’ve ever unfurled even a brand new umbrella, you know what a dicey operation that’s going to be.
Still, conventional rocket fuel is expensive and heavy, so lots of people have been working to overcome these issues, and there have been some successes.
In 2010, the Japanese Space Agency (JAXA), launched a successful Solar Sail spacecraft, IKAROS. The sail on IKAROS was about 200 square meters, and it carried a very small set of instruments intended to test how well solar sailing actually worked. While it’s no longer actively doing science, it is still on an orbit around the sun and it occasionally wakes up to transmit data.
Closer to home, the Planetary Society launched “LightSail 2” last month and is aiming to deploy its sail on July 21st. (That’s this weekend!) Once the sail is deployed, you might even be able to see it from the ground! (It’s a big mirror, after all.) The purpose of this mission is also to see how such a craft handles and can maneuver, paving the way for longer missions with bigger sails, and bigger payloads.
Light sails have also been suggested for our first mission to another star system. The “Breakthrough Starshot” concept (which I wrote about in 2016), would use gigawatt lasers to push thousands of tiny light sail probes towards Alpha Centauri in about 20 years’ time. Of course, they won’t be able to stop, or even slow down when they get there, but what a drive by that will be!
Steven W. Disbrow is the proprietor of “Improv Chattanooga” on the South Side of town. He also creates e-commerce systems and reads comic books when he’s not on stage acting like a fool.