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By Corey S. Powell
On June 22, a SpaceX Falcon Heavy will take off from the launch pad of the Kennedy Space Center in Florida. It's a colossal rocket – 230 feet tall, over 3 million pounds – but the launch is a big deal mainly because of a tiny spaceship that it will carry: a device from the size of a bread designed to propel itself with gigantic sails that capture the pressure of sunlight.
This craft, nicknamed LightSail 2, could be the prelude to a new era of spaceflight in which spacecraft renounce the rocket engines on which they have relied for decades and simply navigate the sun.
After seven days in space, LightSail 2 will come out of its container, extend four long poles and deploy four mirror-like Mylar plastic sheets in a 340 square foot square sail. Then comes the truly magical part.
The sunlight falling on these sails will exert a tiny force, not exceeding the weight of a trombone resting on the palm of the hand. On Earth, the strength of sunlight is so weak that it is imperceptible. That's why most of us do not even know it exists. In space, where there is no competing air, a slight pressure acts as a light but persistent wind, powerful enough to move a spacecraft.
"This will be the first time we will navigate in the light in Earth orbit," says Bill Nye, CEO of The Planetary Society, a nonprofit organization based in Pasadena that developed and funded LightSail 2. "We hope to increase the number of people in the world. Orbital energy or altitude, and change the tilt of the orbit by pointing the spaceship like a sailboat.
From there, the possibilities are almost limitless. With a solar sail, a spaceship could continue to go on the moon, towards the asteroids, towards Jupiter – wherever the light wind blows, without any fuel.
It's not easy to catch a solar breeze
LightSail 2 is the realization, in the twenty-first century, of an old willingness to navigate in space as navigators navigate the seas. The German astronomer Johannes Kepler noticed, four centuries ago, that comet tails were always at the opposite of the sun and had an inspiration. "Provide ships or sails adapted to the heavenly breezes, and some will even brave this void," he wrote to Galileo in 1608.
In the 1970s, Lou Freedman, a NASA engineer, became convinced that solar navigation was a feasible technology. When he co-founded The Planetary Society in 1980, this idea became part of the group's mission. But finding how to build a huge, lightweight sail and fit it into space with an affordable budget was a tough challenge.
Cosmos-1, the company's first attempt, launched in 2005, was lost after the rocket carrying it in the air failed after 82 seconds of flight. His diminished successor, LightSail 1, successfully deployed his sail in 2015. But it was a technological demonstrator placed in a low orbit, where the drag of the Earth's upper atmosphere submerged the delicate thrust of the sun.
Other future sailors in space have quietly attempted their own attempts, with equally mixed results.
A 2015 test mission called CubeSail, built by the Surrey Space Center (UK), was not deployed properly, NBC News MACH, director of the center, Guglielmo Aglietti, said in an e-mail. Over the past decade, three other small sailing missions – NASA's NanoSail-D, Canada's CanX-7 and Surrey's InflateSail – have worked. But like LightSail 1, they operated near the Earth, where their sails acted as acceleration slides rather than majestic heavenly courses.
Once again in the wind
The biggest triumph in solar navigation to date has been won by Japan's IKAROS (sun-accelerated interplanetary kite accelerator) launched into orbit around the sun in 2010. Once in space deep, the craft opened up its square sailboats and, for the first time in history, began maneuvering and shifting gears while tapping the sun.
"This was one of the most moving moments of my life," Yuichi Tsuda of the Japan Aerospace Exploration Agency (JAXA) told MACH in an email.
Over the next three years, IKAROS measured the acceleration due to low pressure and tested ways to control its movement using liquid crystal in the sail (similar to an LCD electronic display) likely to make it more or less less reflective.
"We have perfectly fulfilled all our goals," said Tsuda, noting that the craft had been able to adjust both its heading and its orientation while sailing in the sun's breeze. The contact with IKAROS ended as planned in 2015, he added, but the spacecraft continues to revolve around the sun between the Earth and Venus, "its orbital shape changing and changing under the effect of the slight pressure ".
In parallel with these successes, however, IKAROS has revealed all the work needed to realize the full potential of lightweight propulsion. Her sail was not big enough to make serious slips in the solar system, taking an average of one full year to increase or decrease her speed in half. IKAROS was therefore designed as a hybrid, increasing the light pressure with more conventional thrusters powered by solar cells generating electricity integrated in the sail.
The sail is becoming widespread
LightSail 2 is intended to solve technical problems and transform light sails into a reliable, economical and no-thruster way of moving in space. Nye is inspired by test pilot Tex Johnston, who, in 1955, proved the flying ability of the Boeing prototype 707 by making a crazy mid-flight run in front of the press. "He allegedly told the press," A test is worth a thousand expert opinions. "That's why we are doing this flight," says Nye.
A team from CU Aerospace, a privately held company affiliated with the University of Illinois at Urbana-Champaign, has adopted the same daredevil spirit. Last December, they launched a pair of satellites called CubeSail (not related to the British experience of the same name) in Earth orbit. When they reach their target location in mid-2020, the two will separate and unearth an 800-foot-long ribbon between them – a brand new type of solar sail.
NASA also participates in the game with a solar navigation mission called Near Earth Asteroid Scout. He will fly aboard the Agency's long-delayed Space Launch System rocket, "at each launch," said lead investigators Johnson, of NASA's Marshall Space Flight Center in Huntsville. Alabama. This could happen at about the time of the CubeSail test.
The plan for NEA Scout is to use an IKAROS sail to reach a specific target and perform a detailed reconnaissance for the first time. "Our technological goal is to demonstrate the ability of a solar sail to propel and direct a spaceship into space," Johnson said. "Our scientific goal is to take pictures and to characterize an asteroid close to the Earth."
Space trucking
If these missions succeed as expected, a light navigation could finally start to take off. The limited pressure of the sun means that sailing motor boats will take a long time to reach their goals, but by releasing fuel, they could be very simple and cheap. The LightSail 2 budget, for example, is $ 7 million, a tiny fraction of a typical NASA mission. And as the sun never fails, light sails can continue long enough. "All you need is patience. Once in orbit, you drive, "said Nye.
With this in mind, JAXA plans to create OKEANOS, a successor to IKAROS, joining a group of mysterious asteroids near Jupiter. Low-cost solar fleets are another possibility. David Carroll, president of CU Aerospace, explains that CubeSail was conceived as a first step towards UltraSail, a huge four-wing sailboat designed by the company for years.
"The beauty of the UltraSail concept lies in its ability to turn the sails, allowing you to navigate the solar system back and forth without any refueling," says Carroll. This could mark a transition from sailboat to tug, creating an interplanetary freight network powered by nothing more than the ruthless sun.
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