Sailing to the Stars

“Chemistry will get you to Mars, but it won’t get you to the stars.” – Philip Lubin, Astrophysicist at UCSB.

The Planetary Society, NASA, and several aerospace companies are looking to utilize the power of sunlight to sail spacecraft to the stars.

Rendition of LightSail 2 - The Planetary Society
Rendition of LightSail 2 – The Planetary Society

LightSail is a citizen-funded project from The Planetary Society. In 2018, they are launching a small spacecraft on a Space X Falcon Heavy rocket into Earth orbit. Once in orbit, the LightSail 2 spacecraft will be propelled solely by sunlight, aiming to achieve the first controlled solar sail flight in Earth orbit.

LightSail 2 is a three unit cubesat – measuring just 10 x 10 x 30 cm and weighing less than 5 kg. It will deploy a Mylar sail that is roughly the size of two parking spots. The sail captures the momentum of sunlight:  as light reflects off the sail, most of its momentum is transferred, pushing on the sail, and accelerating the spacecraft. Unlike chemical rockets that provide short bursts of trust, solar sails provide a continuous thrust that can result in higher speeds over time.

Tilting the sail steers the spacecraft by changing the angle at which sunlight reflects off it.  The steering technology used in the LightSail 2 demonstration could be used to maneuver cubesats in Earth orbit without fuel. LightSail 2’s performance could also inform NASA’s Near-Earth Asteroid (NEA) Scout solar sail mission which is scheduled to launch in 2019.

Solar sailing is also considered a promising means of interstellar space travel. Last year, the Breakthrough Initiatives announced a plan to send a fleet of small solar sails to Alpha Centauri. An Earth-bound laser array would zap the sails in Earth orbit, accelerating them to 20 percent the speed of light. They would reach the Alpha Centauri system in roughly 20 years and could send back images of the recently-discovered planet Proxima b. One of the first steps is to figure out how to compress a entire spacecraft on to a chip that weighs less than 1 gram.

There has already been some progress on this task. A number of prototype Sprites –  fully functional space probes on a single circuit board weighing just 4 grams.– achieved Low Earth Orbit in June, 2017.