Among the many[1] spacecraft and satellites ascending to space on Monday’s Falcon Heavy launch, the Planetary Society’s LightSail 2 may be the most interesting. If all goes well, a week from launch it will be moving through space — slowly, but surely — on nothing more than the force exerted on it by sunlight.
LightSail 2 doesn’t have solar-powered engines, or use solar energy or heat for some secondary purpose; it will literally be propelled by the physical force of photons hitting its immense shiny sail. Not solar wind, mind you — that’s a different thing altogether.
It’s an idea, explained Planetary Society CEO and acknowledged Science Guy Bill Nye said in a press call ahead of the launch, that goes back centuries.
“It really goes back to the 1600s,” he said; Kepler deduced that a force from the sun must cause comet tails and other effects, and “he speculated that brave people would one day sail the void.”
So they might, as more recent astronomers and engineers have pondered the possibility more seriously.
“I was introduced to this in the 1970s, in the disco era. I was in Carl Sagan’s astronomy class… wow, 42 years ago, and he talked about solar sailing,” Nye recalled. “I joined the Planetary Society when it was formed in 1980, and we’ve been talking about solar sails around here ever since then. It’s really a romantic notion that has tremendous practical applications; there are just a few missions that solar sails are absolutely ideal for.”
Those would primarily be long-term, medium-orbit missions where a craft needs to stay in an Earth-like orbit, but still get a little distance away from the home planet — or, in the future, long-distance missions where slow...