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Mission lead
Planetary Society
Launch Date
25 June 2019
Earth orbit
Current status
In Orbit

LightSail® is a crowdfunded solar sail project from The Planetary Society. Our LightSail 2 spacecraft, launched 25 June 2019, is the first spacecraft in Earth orbit propelled solely by sunlight. On 31 July 2019, we announced we had officially raised LightSail 2’s orbit by a measurable amount, showing 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.

The Planetary Society has championed solar sailing for decades. In 2005 we launched the world’s first solar sailing spacecraft, Cosmos 1, which was lost due to a rocket failure. Ten years later in 2015, our LightSail 1 spacecraft successfully completed a test flight. LightSail 2 launched on 25 June 2019 and deployed its solar sail on 23 July 2019.

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.

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The spacecraft

LightSail 2 has 3 configurations as the mission progresses: Panels Closed, Panels Open, and Sails Deployed.

LightSail 2 panels closed

The Planetary Society

LightSail 2 panels closed
LightSail 2 panels open

The Planetary Society

LightSail 2 panels open
LightSail 2 sails deployed

The Planetary Society

LightSail 2 sails deployed

LightSail 2, panels closed
3-Unit CubeSat
Size comparison: Loaf of bread
Dimensions: 11.3 x 11.3 x 34 cm (4.45 x 4.45 x 13.4 in)
Weight: 5 kg (11 lbs)

LightSail 2, sails deployed
Size comparison: Boxing ring
Sail material: Mylar
Sail thickness: 4.5 microns (less than the width of a human hair)
Sail layout: Four triangular sails forming a square, connected with cobalt-alloy booms that unwind like tape measures
Sail boom length: 4 m (13 ft)
Sail width: 5.6 m (18.4 ft)
Total sail area: 32 sq. m (344 sq. ft)

Prox-1 measurements:
Size comparison: Large suitcase
Dimensions: 61 x 56 x 30 cm (24 x 22 x 12 in)

The LightSail 2 Mission

LightSail 2 mission highlights
This video shows brief highlights from The Planetary Society's LightSail 2 mission.

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The Planetary Society

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.

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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.

LightSail 2 is now swinging its solar sail into and away from the Sun's rays as it circles the Earth, giving the spacecraft enough thrust to raise its orbit. This portion of the mission will last 1 month.

LightSail 2's attitude control system does not have the precision to maintain a circular orbit and continuously fly the spacecraft higher. Therefore, as one side of LightSail 2’s orbit rises, the other side will dip lower, until atmospheric drag overcomes the forces of solar sailing, ending the primary mission. The spacecraft will remain in orbit roughly a year before entering the atmosphere and burning up.

Solar Sailing

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.

See and track

Naked-eye observing

LightSail 2 may be visible to the naked eye for some observers at dusk and dawn. The Planetary Society's 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 Planetary Society

The History of Solar Sailing

The story of LightSail spans five decades and includes Halley’s Comet, a failed rocket launch from a Russian submarine, and the quest to apply solar sailing to 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

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