Written by By Piana Garagiola, CNN
Engineers have almost perfected the design for a new generation of solar sail, a system that could make space travel cheaper and more convenient.
During a speech at last week’s Lunar and Planetary Science Conference, NASA chief scientist Ellen Stofan acknowledged that the skies were not yet falling, but warned about what might come if the agency’s research into solar sails doesn’t yield real results.
Solar sails don’t need to be carried into space. An “inkjet” type print-out of the atmosphere can cover the sail’s surface. Credit: NASA Ames Research Center
To understand solar sails, you have to travel back in time. Once researchers understood that the only drawback with current rockets was their maximum speed of about 5 kilometers per second (3.2 miles per second), a rocket industry was born.
Over the years, rockets have gotten faster, more powerful and more expensive — a trend that is set to continue if the universe doesn’t fundamentally change.
Michael Rubenstein, a professor of aerospace engineering at the University of Colorado, has been studying the possibility of solar sails for nearly 20 years. He spent a whole year developing a scale model that he shared at the conference.
“After a few years you stop it from doing any more than losing a little bit of my lunch money, maybe,” Rubenstein said of his solar sail. “The one that is a lot closer to reality is the Synchronous Plasma Sail.”
NASA’s Brain Point spacecraft reaches its destination in retrograde orbit around the sun, May 2017. Credit: NASA Ames Research Center
Design for the SPS began in 1999, but Rubenstein says it took many more years to refine the design. At an initial design level, it’s sort of like a sheet of paper — you only want to use the right parts when you build it.
“NASA thought up the concept of the solar sail, and then a lab in Ohio did a whole lot of math. And they got a lot of different shapes that didn’t line up, so the concept lost favor for a long time. They spent hundreds of millions of dollars on various projects, and nobody was listening to anybody and NASA wasn’t listening to anyone,” Rubenstein said.
NASA engineers at the Jet Propulsion Laboratory tested the SPS concept in July. Credit: NASA Ames Research Center
With the SPS , the solar sails are formed in a lattice instead of a sheet of flat paper. The solar sail would act as a saddle, and the better shape comes from the arrangement of the surface area to the thickness of the rest of the sail.
“There is a bit of a tugging effect on a main body of the sail, which generates inertia. The equal shape, in this case, means that the drag is even, which makes it accelerate faster,” Rubenstein said.
After developing the SPS and working out the details, Rubenstein took it to the high seas. He tried it in the Pacific Ocean, creating a buoys that lift the sail in a slow, gentle process. It may not work the same on the moon, because the moon’s gravity is stronger.
Last year, NASA spent $1.5 million on a series of tests that simulated the conditions on the moon’s surface. Three of the four tests were performed in the sea, where the seas are more viscous.
“We did all the tests we could on the seabed, and we didn’t make it very nice — it was a pea soup,” Rubenstein said. “The longest test was 12 hours. We did the first two simultaneous tests in salt water, we did the third parallel, the fourth in open ocean. We did all of it in space, and we were very happy with what we got. It was about 50% of what we expected, but we would have liked it to be better. But it’s still work in progress.”
Rubenstein cautioned that NASA is researching the SPS just for the sake of space travel. He said that he’s open to exploring potential applications for the system, such as space tourism.
“If someone wants to build a spacecraft to go around the sun to visit the moon, it’s very hard to do that economically right now because of the launch fees — around $30 million a flight.”