A solar sailing spacecraft
from The Planetary Society

Solar Sailing

Flight by Light

LightSail® is a citizen-funded project by The Planetary Society, the world's largest non-profit space advocacy group. We’re sending a small spacecraft into Earth orbit carrying large, reflective sails measuring 32 square meters (344 square feet). We successfully completed a test flight in June 2015 that paved the way for a second, full-fledged solar sailing demonstration in 2017.

Solar sails use the sun’s energy as a method of propulsion—flight by light. Light is made of packets of energy called photons. While photons have no mass, a photon traveling as a packet of light has energy and momentum.

Photons have energy and momentum
The photons reflect off the sail, transferring momentum

Solar sail spacecraft capture light momentum with large, lightweight mirrored surfaces—sails. As light reflects off a sail, most of its momentum is transferred, pushing on the sail. The resulting acceleration is small, but continuous. Unlike chemical rockets that provide short bursts of thrust, solar sails thrust continuously and can reach higher speeds over time.

Our Solar Sail

Tiny Spacecraft, Big Design

LightSail is a CubeSat. These tiny spacecraft often hitch rides to orbit aboard rockets carrying bigger payloads. CubeSats have standard unit sizes of 10 centimeters per side. They can be stacked together—LightSail is a three-unit CubeSat about the size of a loaf of bread.

Once in space, LightSail’s solar arrays swing open, revealing the inside of the spacecraft. Four tape measure-like metal booms slowly unwind from storage, unfolding four triangular, Mylar sails. Each sail is just 4.5 microns thick—one-fourth the thickness of an average trash bag.

Three electromagnetic torque rods and a momentum wheel orient LightSail in space. Ground-based lasers will measure the effect of sunlight on the sails. As LightSail breezes around the Earth, its shiny sails will be visible from the ground. We’ll organize viewing campaigns to show people where to look.

LightSail and engineering team members
LightSail team members Alex Diaz (left) and Riki Munakata (right) prepare the spacecraft for a sail deployment test.

The Mission

Sailing In Space

In May 2015, our LightSail 1 spacecraft hitched a ride to space aboard an Atlas V rocket for a shakedown cruise. Our orbit didn't carry us high enough above the Earth's atmosphere for solar sailing, but we tested our deployment sequence and captured a picture of our unfurled sails.

LightSail with solar sails deployed
LightSail 1 captured this image of its deployed solar sails in Earth orbit on June 8, 2015.

In 2017, LightSail 2 will be enclosed within Prox-1, a small satellite developed by the Georgia Institute of Technology (Georgia Tech) to autonomously inspect other spacecraft. Both satellites will be lifted into orbit by the Falcon Heavy, a new heavy-lift rocket built by private spaceflight company SpaceX.

SpaceX Falcon Heavy rocket
Prox-1 and LightSail spacecraft

LightSail 2 and Prox-1 will be released into an orbit with an altitude of 720 kilometers (450 miles), high enough to escape most of the planet's atmospheric drag. Prox-1 will eject LightSail 2 into open space. Later, it will rendezvous with LightSail 2 and inspect it. When LightSail 2 unfurls its solar sails, Prox-1 will be nearby to capture images of the big moment.


LightSail’s primary contractor is Ecliptic Enterprises Corporation. The spacecraft has ground stations at Cal Poly San Luis Obispo and Georgia Tech. Cal Poly provides additional testing and integration support, and the project is managed by Dr. David Spencer of Georgia Tech. Boreal Space and Aquila Space serve as contractors to Ecliptic. LightSail was built by Stellar Exploration, Inc.

Our Partners:

Boreal Space

Support LightSail

Join Us In The Mission

LightSail needs your support! Our LightSail 1 test mission was successfully completed and our Kickstarter campaign ended June 26th, raising $1.24 million dollars for LightSail's 2017 solar sailing mission!

Miss the Kickstarter campaign, but still want to donate? You can! By donating to our project, you’ll be supporting The Planetary Society’s mission to engage and empower the world’s citizens to advance space science and exploration.

You can also help by spreading the word about this exciting mission! Encourage friends, family, and colleagues to join us in the adventure of space exploration and share this website on your favorite social media platform.

Bill Nye

Bill Nye
Bill Nye, CEO of The Planetary Society.

Keep Reading: The Story of LightSail