In space, power is everything – supplies are limited and a recharge is difficult or impossible, so renewable energy is critical. And what’s the most abundant source of energy in the galaxy? The sun.
This is hardly a revelation – we’ve tinkered with solar power since the earliest days of the space program, and Carl Sagan envisioned a solar sail for spacecraft back in the 1970s, but the key is long-term sustainability. And the Lightsail 2 is taking a rather unique approach.
The Planetary Societary’s crowdfunded vessel trades quick bursts of acceleration for steady, constant momentum. Our resident G-type main-sequence star has a solar constant of 1,368 W/m2 (watts per square meter) at one astronomical unit, and while solar power fluctuates by distance, the sun’s output is more than enough to provide a perpetual energy source.
The first solar-powered satellite, Vanguard 1, took to the heavens more than 60 years ago (and it still remains in orbit, albeit inactive). But the Lightsail 2 is an altogether different animal, like a modern sailboat compared to an 18th-century schooner.
Particles of sunlight bombard the vessel’s 18.4-foot-wide, 4.5-micron-thick reflective Mylar sails, and the New York Times describes the force as a “continuous nudge,” equivalent to the “weight of a paper clip pushing down on your hand.”
That might not sound very impressive, but that continuous nudge can keep the Lightsail 2 moving almost indefinitely – especially since the 3U CubeSat spacecraft is about the size of a loaf of bread.
And after the vessel raised its maximum orbit by about 900 meters (half a mile) – at 450 miles above the Earth – the Planetary Society declared a mission success.
Bruce Betts, Chief Scientist and LightSail Program Manager at The Planetary Society raved that “The spacecraft has successfully raised its orbit around the Earth using nothing but sunlight.”
But again, we’re talking about a spacecraft no bigger than a toaster. Even on the Earth’s surface, solar power, alone, can’t propel large objects.
So the Lightsail 2 – or anything remotely similar – won’t be ferrying human astronauts anytime soon. The prospective Mars missions are leaning towards nuclear-thermal propulsion, and rocket fuel isn’t going away anytime soon.
But the Lightsail 2 is ideal for permanent missions like monitoring Earth’s poles or long-distance voyages to comets or even another solar system.
For Planetary Society’s executive director, Bill Nye (yes, that Bill Nye), the perfect target could be Earth’s planetary neighbor. We’ll probably use nuclear power to send humans to the Red Planet, but a scaled-up version of Lightsail 2 could tote supplies.
“We’d ferry cargo to Mars and look for signs of life, and change the course of human history. How about that?” Nye said.
The Lightsail 2, itself, will descend to Earth in about a year.