Flight by Light for CubeSats

LightSail® is a crowdfunded project from The Planetary Society to demonstrate that solar sailing is a viable means of propulsion for CubeSats—small, standardized spacecraft that are part of a global effort to lower the cost of space exploration. Our LightSail 2 spacecraft, launched 25 June 2019, uses sunlight alone to change its orbit, and is currently operating under an extended mission to further advance solar sailing technology.

The Planetary Society's history with solar sailing dates back to the mid-1970s, when co-founder Louis Friedman led a NASA effort to send a solar sail spacecraft to visit Halley’s Comet. Fellow co-founder Carl Sagan promoted the concept on The Tonight Show with Johnny Carson in 1976.

The Planetary Society’s first crowdfunded solar sail mission, Cosmos 1, failed to reach orbit after launching aboard a Russian rocket in 2005. That effort led to the dual-spacecraft LightSail program. LightSail 1, identical to LightSail 2 with a few key differences, completed a successful deployment test in 2015.

LightSail 2 was named one of TIME’s 100 Best Inventions of 2019, and won a Popular Science Best of What’s New award for 2019. The spacecraft carries a disk with names, selfies, and other messages from our members and supporters. Search for your participation certificate here.

West coast of India from LightSail 2
LightSail 2 over India LightSail 2 regularly transmits images from its onboard cameras. These images help engineers track the condition of the sail while providing stunning public outreach images.Image: The Planetary Society

How LightSail 2 works

For launch, LightSail 2 was enclosed within Prox-1, a Georgia Tech student-built spacecraft the size of a large suitcase that was selected to fly as part of the Air Force’s University Nanosat Program. Both spacecraft were attached to the upper stage of SpaceX's Falcon Heavy rocket, which launched 24 spacecraft to orbit for the U.S. Air Force’s Space Test Program 2 (STP-2) mission. Prox-1 and LightSail 2 were delivered into a circular, 720-kilometer orbit with an inclination of 24 degrees.

LightSail 2 launch video from SpaceX The Planetary Society's LightSail 2 spacecraft launched aboard a SpaceX Falcon Heavy rocket on 25 June 2019.Video: SpaceX

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Seven days after launch, Prox-1 ejected LightSail 2. After a checkout period of a few days, LightSail 2 opened its hinged solar arrays. On 23 July 2019, it deployed its 32-square-meter solar sails. Each orbit, LightSail 2 swings its solar sail into and away from the Sun's rays, giving the spacecraft a slight push.

Light is made of packets of energy called photons. While photons have no mass, they have momentum. Solar sails capture this momentum with sheets of large, reflective material such as Mylar. As photons bounce off the sail, most of their momentum is transferred, speeding up the sail in the direction opposite the bouncing light.

Unlike chemical rockets that provide short, powerful bursts of thrust, solar sails provide continuous, slight thrust and can reach higher speeds over time. Sunlight is free and unlimited, whereas rocket propellant must be carried into orbit and be stored onboard a spacecraft.

What is Solar Sailing?

A solar sail, simply put, is a spacecraft propelled by sunlight. Whereas conventional rockets are propelled by the combustion of rocket fuel, a solar sail is pushed forward by light from the Sun.

LightSail 2 sails deployed
LightSail 2 sails deployed Image: The Planetary Society
LightSail 2 panels open
LightSail 2 panels open Image: The Planetary Society

Though the spacecraft orbits Earth higher than the International Space Station, the planet’s atmosphere is still thick enough to counteract the thrust gained from solar sailing. Analyses of orbital data show that LightSail 2’s rate of orbital decay is markedly slower in solar sailing mode, when the craft actively positions itself to get a push from sunlight. During some time intervals, the spacecraft even gains enough thrust to briefly overcome atmospheric drag and raise its orbit.

The LightSail 2 extended mission is expected to continue as long as the spacecraft remains healthy, or until its orbit decays and the spacecraft reenters Earth’s atmosphere many months from now.

LightSail Academic Resources

Our LightSail academic resources include schematics, links to peer-reviewed papers, parts lists, and more.

How to see and track LightSail 2

Naked-eye observing

LightSail 2 is visible to the naked eye for some observers at dusk and dawn. Our mission control dashboard shows upcoming passes based on user location, and includes a link to a page that highlights passes when the sail is more likely to be visible.

The spacecraft has an orbital inclination of 24 degrees, which will keep it much closer to the equator than LightSail 1. We estimate this will restrict viewing to latitudes within 42 degrees of the equator. You can see a location’s latitude and longitude in Google Maps by right-clicking the map and selecting “What’s Here?” The first number in the resulting information box is your latitude, and must be between 42 and -42 to see LightSail 2.

Radio tracking

Radio trackers can download LightSail 2's beacon structure for help with decoding packets. Here are some additional useful parameters:

WM9XPA | 437.025 MHz | AX.25 | FSK | 9600 bps

Every 45 seconds, the spacecraft transmits its call sign, WM9XPA, in morse code:

.-- -- ----. -..- .--. .-

You can download audio files of the morse code beacon below, and even use them as a ringtone for your phone!

LightSail 2 Morse code beacon, sample (WAV format)
LightSail 2 Morse code beacon, sample (M4R format)
LightSail 2 Morse code beacon, actual as recorded by Justin Foley (WAV format)
LightSail 2 Morse code beacon, actual as recorded by Justin Foley (M4R format)

Other solar sails

Japan’s IKAROS spacecraft, launched to interplanetary space with Venus-bound Akatsuki in 2010, was the first and only spacecraft to have demonstrated controlled solar sailing as a sole method of propulsion.

LightSail 2, which began development in 2009, will demonstrate the technology for CubeSats. CubeSats have revolutionized the space industry thanks to low-cost technology miniaturization, but often lack a means of propulsion. Weighing 60 times less than IKAROS but sporting a sail just 6 times smaller, LightSail 2 will demonstrate that CubeSats can carry solar sails with enough punch for orbital maneuvers, and still have room for science instruments.

We currently don't have plans for a follow-on mission, but The Planetary Society is already helping advance solar sail technology through a Space Act Agreement with NASA. The agency is launching a CubeSat called NEA Scout on the first flight of the Space Launch System to lunar orbit. NEA Scout will use its solar sail to leave the Moon and visit a near-Earth asteroid. NASA is also studying a mission called Solar Cruiser that would survey the Sun from a difficult-to-access polar orbit, using a 1,670-square-meter solar sail for propulsion.

Solar sails are also one of the only known methods that could someday be used to travel to the stars. In 2016, the group Breakthrough Initiatives announced an initiative to send a fleet of laser-powered solar sails to our nearest star, Alpha Centauri.

Project history

The History of Solar Sailing
The History of Solar Sailing Image: The Planetary Society

The Story of LightSail, Part 1

The first installment of our three-part LightSail history series looks back at the origins of solar sailing and a NASA project to send a giant solar sail to Halley's Comet.

The Story of LightSail, Part 2

The second entry in our three-part LightSail history series remembers Cosmos 1, The Planetary Society's first solar sail that launched in 2005 aboard an ill-fated Russian rocket.

The Story of LightSail, Part 3

The final chapter of our three-part LightSail history series details how the loss of Cosmos 1 gives rise to the dream of solar sailing for CubeSats.

Funding and Partners

The LightSail project cost is $7 million from 2009 through March 2019. Funding was provided by Planetary Society members, private citizens, foundations, and corporate partners. A Kickstarter campaign raised $1.24 million in 2015, while two Omaze fundraisers in 2017 and 2018 generated more than $220,000.

Spacecraft design and construction: Stellar Exploration, Inc.
Lead contractor for integration and testing: Ecliptic Enterprises Corporation
LightSail testing facilities and mission control: Cal Poly San Luis Obispo
Ground stations: Cal Poly San Luis Obispo, Georgia Tech, Purdue University, Kauai Community College
Contractors: Boreal Space, Georgia Tech, Purdue, Aquila Space, NXTRAC
Additional support: Air Force Research Laboratory, UCLA, Utah State

LightSail 1 launch provided by NASA’s Educational Launch of Nanosatellites program
LightSail 2 launch provided by University Nanosat Program, Air Force Research Laboratory

Program manager: Bruce Betts, The Planetary Society
Project manager and mission manager: Dave Spencer, Purdue University

Recent articles about LightSail 2:

LightSail 2 Enters Extended Mission Phase

One year after launch, The Planetary Society’s solar sail spacecraft is embarking on an extended mission dedicated to further advancing solar sailing technology.