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Photo: The Planetary Society
“Well there’s just a tremendously exciting prospect called solar sailing. And this is a very crude model.” With this introduction by famed astrophysicist Carl Sagan, Johnny Carson begins to clear off his desk to make room. Sagan pulls a large pyramid shaped model out from behind his chair. It looks delicate, consisting of a thin sheet of a shiny material and held together by wooden skewers and string. “It’ll take you where you want to go.”
In 1972 Carl Sagan introduced a plan for a satellite dubbed LightSail on The Tonight Show. Carson joked that there was prime real estate on a massive space sail for cosmic advertisement. 47 years after his interview, the late Dr. Sagen’s Planetary Society has taken a massive step towards realizing his dream. Minus the marketing ploy.
The Planetary Society has just launched its crowd funded CubeSat LightSail 2 from Kennedy Space Center. One of 24 payloads on board SpaceX’s Falcon Heavy, LightSail 2 is a satellite over 40 years in the making. On Tuesday, June 25th 2019, LightSail 2 was delivered to a 720-kilometer (450 mile) orbit with a 24 degree inclination.
Photo: Ryan Bale
LightSail 2 is proof of concept CubeSat that weighs 11lbs and is roughly the same size as a loaf of bread. In the next few days, 4 doors on the long sides of the hull will open exposing solar panels and a compartment containing the solar sail. Four cobalt alloy booms extend out 13 feet, stretching the mylar sail to an eighteen and a half foot square. The unfurling process will take 3 minutes. Roughly the size of a boxing ring, the sail itself is a large target for orbital debris, but rip-stop seams have been placed every few centimeters to contain any tears that may develop.
The Concept of solar sailing dates back to the 1600’s. Kepler theorized that comets in the night sky were accelerated through the cosmos by the sun's energy, and he was right. Just as the wind blows over the earth’s surface pushing boats through the ocean, the sun's solar radiation pushes photons through the vacuum of space exerting radiation pressure on anything in its way.
Photo: The Planetary Society
Kepler was correct, but solar radiation as a means for propulsion was a relatively new and radical idea in the 70’s. What if man could sail through the stars and rendezvous with Halley’s comet? If it sounds like science fiction, that’s because the concept was publicly theorized and published in the 1951 issue of Astounding Science Fiction. The idea is that the sun’s naturally occurring photon emissions could collide with a solar sail in space and could theoretically accelerate a spacecraft attached to it. NASA and Sagen both saw the concepts merits and promoted it.
Once the sail is deployed, LightSail 2 will spend 1 month positioning and repositioning itself broadside to the sun, allowing photon particles to accelerate it and raise its orbit. Within a year the craft is expected to be taken over by atmospheric drag, at which point it will not be able to raise itself back up. It will then fall back to earth, burning up, and completing its mission. In the meantime, amateur radio enthusiasts track it. LightSail 2 will transmit its call sign WM9XPA every 45 minutes on 437.025 MHz in Morse code.