Last September, California Polytechnic State University (Cal Poly)’s CubeSat team and The Planetary Society unfurled a solar-powered sail that some believe could revolutionize satellite propulsion. This was a deployment test and key milestone for the LightSail project. Among those present was Bill Nye — the television personality and science educator known as “The Science Guy” — in a new role as CEO of The Planetary Society.
Lightsail is a Planetary Society initiative with the goal of demonstrating the effective use of solar sails for satellite control and movement. While the concept of solar sailing is not new, it is only relatively recently that the prospect of propelling a satellite through space using only radiation emanated from the sun has become practically feasible. The kite-like, solar-powered spacecraft is being developed by the Society and a team of partners, including Georgia Institute of Technology (Georgia Tech), Cal Poly and Stellar Exploration.
LightSail is a 3U CubeSat with the mission to deploy a square solar sail while in orbit. After more than four years of development and several last-minute delays, the 344-square-foot piece of Mylar foil that looks like stove-top popcorn foil, slowly emerged from a CubeSat — the team of Cal Poly engineering graduates had successfully deployed the LightSail in a key milestone for the $4 million project.
In addition to hosting the deployment test, the Cal Poly team is providing environmental testing support in preparation for launch, and operations through the Earth Station after launch of the nano-satellite technology project.
Flight by Light
The Planetary Society reports on its Web site: “We’re sending two small spacecraft into Earth orbit carrying large, reflective sails measuring 32 square meters. Our first mission is a May 2015 test flight that will pave the way for a second, full-fledged solar sailing demonstration in 2016.
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.
“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.
“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 aboard LightSail will interact with Earth’s magnetic field, orienting the spacecraft. 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.”
Solar Sailing – Mission 1
The LightSail-1 is currently scheduled to launch on May 20, 2015. This first LightSail spacecraft will hitch a ride to orbit aboard an Atlas V rocket for a “shakedown cruise.” It won’t fly high enough above the Earth’s atmosphere for solar sailing, but will be used to test the design and sail deployment sequence, as well as to snap some awesome pictures.
Lightsail-1 is will serve as a technology demonstrator for the sail deployment and control mechanisms. Following launch, it will conduct a several-week mission, during which it will deploy its sail and undertake a series of controlled maneuvers. By manipulating the orientation of the sail with respect to the sun, the force of the solar radiation against the sail can be controlled, which will ultimately result in a measurable change in the satellite’s orbit.
Throughout he mission, CSS at Georgia Tech will be providing technical assistance and will be managing the mission operations from their ground station. Future Lightsail missions will expand upon the experience gained with Lightsail-1 with the aim of continuing to pioneer solar sail technology as a viable means of propulsion.
Sailing in Space – Mission 2
Currently planned for April 2016 on the SpaceX Falcon Heavy, LightSail-2 will be enclosed within Prox-1, a small satellite developed by the Georgia Tech to autonomously inspect other spacecraft. Both satellites will be lifted into orbit by the Falcon Heavy, a heavy-lift rocket built by private spaceflight company SpaceX.
LightSail 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 into open space. Later, it will rendezvous with LightSail and inspect it. When LightSail unfurls its solar sails, Prox-1 will be nearby to capture images of the big moment.
LightSail was built by Stellar Exploration. The integrating contractor for testing and flight readiness is Ecliptic Enterprises. The spacecraft has ground stations at Cal Poly and Georgia Tech. Ground station testing occurs at Cal Poly. The project is managed by Doug Stetson, the founder and principal partner of the Space Science and Exploration Consulting Group. Boreal Space and Half-Band Technologies are contractors to Ecliptic.
The Planetary Society was founded in 1980 by Carl Sagan, Bruce Murray, and Louis Friedman to inspire and involve the world’s public in space exploration through advocacy, projects, and education. It is the world’s largest non-profit space advocacy group.
- Watch a video of the deployment test
- Watch the “LightSail – Flight by Light” video