March 12, 2017
NASA researcher: What’s next for solar sail technology?
According to Les Johnson, a senior technical advisor for NASA's Advanced Concepts Office at the Marshall Spaceflight Center in Huntsville, solar sails could propel us to the stars one day. We sat in on a recent Vanderbilt University lecture on the future of solar sails and even asked Johnson a few questions.
First of all, the solar sail is a very unique spacecraft in that it has no propellant. When asked how it works, Johnson compared it to playing pool."What you do is you put it out, and it's a big reflector, and it reflects sunlight. Light doesn't have any rest mass, but it does have momentum, and so just like when you play a game of pool, and your cue ball bounces off another ball, you conserve momentum and the other ball moves away. The solar sail will be pushed by the sun, and so you don't use any fuel. Theoretically, it's infinitely more efficient.
"If you deploy it in deep space," he continued, "there's no other propulsion system to date that can match it pound for pound of spacecraft mass in terms of the thrust that it can give you. So anywhere in the inner solar system—Jupiter inward—it works really, really well. And if you want to exit the solar system rapidly, and you can go really close to the sun to start, you can go faster than anything we've ever built through the solar system."
As for the material the solar sail itself is made of, Johnson said it was "originally developed as a paint."
Blast from the past
Prior to looking at the future of solar sails and how they could take us to the stars, Johnson explained that the idea of them isn't exactly a new one—in fact, solar sails have had an interesting past.
In 1964, NASA sent a 135-foot rigidized balloon satellite into orbit to test the solar thrust effect on spacecraft.
In 1992, the Soviet Union decided they wanted to put up huge mirrors in space to light up Siberia at night in order to counteract the health problems associated with the lack of sunlight. The project was called Znamya, and it deployed successfully but was de-orbited after several hours.
Even before Bill Nye came along, the Planetary Society was experimenting with solar sails. In 2005, the Cosmos-1 was launched from a Russian submarine, but a rocket failure prevented it from reaching its intended orbit.
Then, in 2010, the Japanese built IKAROS, which was the first solar sail spacecraft to successfully reach interplanetary space. Though, why they would want to name a spacecraft IKAROS is beyond us. Have they read Greek mythology? (It's a pun on Icarus, in case you're lost.)
So what about the solar sails today?
According to Johnson, both NASA's NEA Scout and the Planetary Society's LightSail-B are in the pipeline. The Near Earth Asteroid Scout, or NEA Scout, will be on the first launch of the SLS in 2018, and after the Orion separates and goes to the moon, the Scout will deploy in deep space and fly to the asteroid 1991 VG. The sail will be 86 square meters and will be the biggest sail to date.
The Scout will take pictures and analyze the asteroid's position in space, its shape, debris field, and more. This mission is low-cost at $20 million, and according to Johnson, "It is the only propulsion system that will let us take a spacecraft the size of a bootbox into interplanetary space and observe the asteroids we want to observe."
The Planetary Society's LightSail-B will attempt to demonstrate controlled solar sailing and will launch sometime in 2016.
As for the ultimate goals for light sail technology, Johnson said he'd like to see them used as "pole sitters". Larger sails can thrust against Earth's gravity and not even be in orbit around the Earth, and a pole sitter could sit continuously over Earth's poles and can provide continuous data on the polar ice caps.
But what Johnson is most excited about was the promise of interstellar travel with these solar sails. Giant sails deployed in space could use the sun's energy—or yes, even LASERS—to go deep into space.
He says the ultimate goal is to reach 250 astronomical units within 20 years of launch, but this is not yet approved.
Feature Image: Planetary Society
Story Images: NASA/Wikimedia Commons