LightSail® is a crowdfunded solar sail project from The Planetary Society. Our LightSail 2 spacecraft, launched 25 June 2019, aims to become the first spacecraft in Earth orbit propelled solely by sunlight. The goal is to raise 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. On 25 June 2019, a SpaceX Falcon Heavy launched LightSail 2 as part of the U.S. Air Force’s STP-2 mission from Kennedy Space Center in Florida. During launch LightSail 2 was enclosed within Prox-1, a small satellite built by Georgia Tech students. Prox-1 deployed LightSail 2 on 2 July 2019.
LightSail 2 has 3 configurations as the mission progresses: Panels Closed, Panels Open, and Sails Deployed.
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LightSail 2 panels closed
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LightSail 2 panels open
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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)
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.
Seven days after launch, Prox-1 ejected LightSail 2. After a checkout period of a few days, LightSail 2 opened its hinged solar arrays. Next, it will unroll 4 cobalt-alloy booms, which will extend like tape measures to pull the spacecraft's 4 triangular sails from storage. The deployment sequence will take roughly 3 minutes.
LightSail 2 will then begin 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 (technically, the orbit semi-major axis). 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.
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.
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.
See and track
LightSail 2 may be visible to the naked eye after solar sail deployment. Once the sails are out, we will post a dashboard offering pass predictions for your location.
The spacecraft will have 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 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!
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.
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.
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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.
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
LightSail needs your support
Support the LightSail mission and become a Society member today!