Even after 30 months in space, The Planetary Society’s LightSail 2 mission continues to “sail on sunbeams” demonstrating solar sailing technology in orbit around the Earth. The mission provides hard data for future missions hoping to use awnings to explore the cosmos.
LightSail 2, a small cube set, was launched in June 2019 on a SpaceX Falcon Heavy, as a demonstration mission to test how well a sunsail could change a spacecraft’s orbit. One month after launch, when LightSail 2 unfolded its ultra-thin 32-square-foot Mylar sail, the mission was declared a success because the sail raised the orbit of the bread-sized small spacecraft.
“We are going to a higher orbital altitude without rocket fuel, just with sunlight,” The Planetary Society (TPS) CEO Bill Nye told a news conference after the broadcast. “This idea that you could fly a spacecraft and get propulsion in space from nothing but photons, it’s surprising, and to me it’s very romantic that you would sail on sunbeams.”
TPS, whose members funded the $ 7 million mission, said it shares mission data with NASA to help three upcoming solar mission missions: NEA Scout, Solar Cruiser and ACS3. . The NEA Scout is scheduled to take a trip to the lunar space as early as February 2022 on NASA’s Space Launch System rocket during the Artemis I test flight. The mission will use its sun sail to leave the vicinity of the Moon and visit an asteroid.
Solar sails use the power of photons from the Sun to propel spacecraft. While photons have no mass, they can still transmit a small amount of momentum. So when photons hit the sunsail, the vessel is pushed very slightly away from the Sun. Over time, if a spacecraft is out in space with no atmosphere to load it, it can potentially accelerate to incredibly high speeds.
A spacecraft with a awning did not need to carry fuel and could therefore theoretically travel for longer periods as it did not need to refuel.
But LightSail 2 is in orbit around the Earth. As the spacecraft swings its sails into sunlight, it raises its orbit by as much as a few hundred meters a day. But the small spacecraft does not have the means to tilt the sails precisely enough to prevent its orbit from sinking on the other side of the planet. Eventually, LightSail 2 will dive deep into Earth’s atmosphere to succumb to atmospheric resistance. It will go into orbit and burn up.
A recent update from TPS says that LightSail 2’s altitude above the Earth is currently around 687 kilometers.
“Thanks to optimized sail pointing over time, altitude decay rates have been the best of the entire mission in recent months,” wrote TPS’s Jason Davis. “Propulsion even occasionally overcame atmospheric resistance and raised the spacecraft’s orbit slightly. In addition, below-average solar activity has kept the Earth’s upper atmosphere thin for much of the mission, creating less resistance on the sail.”
But the Sun has recently become more active, emitting significant solar flares. The LightSail 2 team believes that this activity is now likely to cause higher orbital decay rates than those seen earlier in the mission. However, mission engineers estimate that the spacecraft may remain in orbit for at least one more year.
And meanwhile, as the spacecraft continues to send incredible images back from orbit, engineers continue to gain insights that can be passed on to future missions.
Note: If you’re planning to visit the Smithsonian in Washington DC, models of LightSail 2 will be part of a new exhibit at the Smithsonian’s FUTURES exhibit, a collection of art and technology that shows the future of humanity. The new exhibition begins on November 20, 2021 in the Arts and Industries Building at the National Mall in Washington, DC and will continue until July 2022. More info from TPS here.
Caption for lead: This image taken by The Planetary Society’s LightSail 2 spacecraft on May 31, 2021 shows Afghanistan, Pakistan and the Arabian Sea. The Caspian Sea is at the bottom left. The shadows of the spacecraft’s solar panels can be seen on the sail. North is approximately at the top left. This image has been color-adjusted, and some distortion from the camera’s 180-degree fisheye lens has been removed. Credit: The Planetary Society