Sailing Among The Stars

Discussion in 'Strategic Forces' started by LETHALFORCE, Aug 23, 2010.


    LETHALFORCE Moderator Moderator

    Feb 16, 2009
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    Sailing Among The Stars

    This fall, NASA researchers will move one step closer to sailing among the stars. Astrophysicists and engineers at the Marshall Space Flight Center in Huntsville, Ala., and the Ames Research Center in Moffett Field, Calif., have designed and built NanoSail-D, a "solar sail" that will test NASA's ability to deploy a massive but fragile spacecraft from an extremely compact structure.

    Much like the wind pushing a sailboat through water, solar sails rely on sunlight to propel vehicles through space. The sail captures constantly streaming solar particles, called photons, with giant sails built from a lightweight material. Over time, the buildup of these particles provides enough thrust for a small spacecraft to travel in space.

    Many scientists believe that solar sails have enormous potential. Because they take advantage of sunlight, they don't require the chemical fuel that spacecraft currently rely on for propulsion.

    Less fuel translates into lower launch weight, lower costs and fewer logistical challenges. Solar sails accelerate slowly but surely, capable of eventually reaching tremendous speeds. In fact, most scientists consider solar sailing the only reasonable way to make interstellar travel a reality.

    Of course, it's not as easy as it sounds.

    For scientists to really make use of solar sails, the sails must be huge. Because the particles emitted by the sun are so tiny and the spacecraft is so large, the sail needs to intercept as many particles as possible. It's almost like trying to fill up a swimming pool with rain drops; the wider the pool, the more rain it captures.

    The same is true with solar sails and the sun's energy. In fact, a NASA team in the 1970s predicted it would need a solar sail with a surface area of nearly 6 million square feet - about the size of 10 square blocks in New York City - to successfully employ a solar sail for space exploration.

    That's where NanoSail-D comes in. As the first NASA solar sail deployed in low-Earth orbit, NanoSail-D will provide valuable insight into this budding technology.

    "One of the most difficult challenges solar sails face is trying to deploy enormous but fragile spacecraft from extremely small and compact structures. We can't just attach a giant, fully spread sail to a rocket and launch it into space. The journey would shred the sail to pieces," said Dean Alhorn, NanoSail-D principal investigator and aerospace engineer at the Marshall Center.

    "Instead, we need to pack it in a smaller and more durable container, launch that into space and deploy the solar sail from that container," Alhorn said. "With NanoSail-D, we're testing a technology that does exactly that."

    One objective of the NanoSail-D project is to demonstrate the capability to pack and deploy a large sail structure from a highly compacted volume. This demonstration can be applied to deploy future communication antennas, sensor arrays or thin film solar arrays to power the spacecraft.

    NanoSail-D will be deployed 400 miles up after it's launched this fall aboard a Minotaur IV rocket, part of the payload aboard the Fast, Affordable, Science and Technology Satellite, or FASTSAT.

    The relatively low-deployment altitude means drag from Earth's atmosphere may dominate any propulsive power it gains from the sun, but the project represents a small first step toward eventually deploying solar sails at much higher altitudes.

    When fully deployed, NanoSail-D has a surface area of more than 100 square feet and is made of CP1, a polymer no thicker than single-ply tissue paper. The first big challenge for researchers was to pack it into a container smaller than a loaf of bread and create a mechanism capable of unfolding the sail without tearing it.

    "Think of how easily I can rip a piece of tissue paper with my hands," Alhorn said. "Designing a mechanism to unfurl a space sail about that thick without tearing is no easy task."

    To accomplish their goal, engineers tightly wound the NanoSail-D sail around a spindle and packed it in the container.

    During launch, NanoSail-D is stored inside FASTSAT. Once orbit is achieved, the NanoSail-D satellite will be ejected from the satellite bus and an internal timer will start counting down. When the timer reaches zero, four booms will quickly deploy and the NanoSail-D sail will start to unfold. Within just five seconds the sail will be fully unfurled.

    "The deployment works in the exact opposite way of carpenter's measuring tape," Alhorn explained. "With a measuring tape, you pull it out, which winds up a spring, and when you let it go it is quickly pulled back in. With NanoSail-D, we wind up the booms around the center spindle. Those wound-up booms act like the spring. Approximately seven days after launch, it deploys the sail off the center spindle."

    Researchers designing NanoSail-D have faced more than their fair share of challenges. When the project was commissioned in 2008, NASA set a deadline of just four months to design and test the new technology. The team had to make decisions quickly, often using whatever parts happened to be available.

    "It wasn't a question of going off and doing an exhaustive study of what components to use," Alhorn recalled. "There was no time for that. We said, 'Okay, this is the size of component we need, this is its function' - and as soon as we found one that worked, we used it."

    After months of work in 2008, researchers and engineers finally completed the sail, which was set to launch that August and orbit Earth for one to two weeks. Engineers integrated the flight unit on the Falcon 1, a launch vehicle designed and manufactured by SpaceX of Hawthorne, Calif., but unfortunately the rocket experienced launch failure and NanoSail-D never made it to orbit.

    Fortunately, the team had built a spare. For the past two years, Alhorn and his team have worked to refine the second flight unit, hammering out the manufacturing problems and cleaning up the spool and a few of the other internals.

    In addition to having a higher orbit, the second NanoSail-D will launch into space and remain there for up to 17 weeks, a big increase from the original mission. The new orbit, 400 miles above the earth, also will allow more astronomers to get pictures of the sail as it glides across the night sky.

    Most of the mission has remained the same, however. For example, because the sail will deploy relatively close to Earth, researchers will have a difficult time detecting the slight solar effects.

    After a few months, NanoSail-D will begin to move out of orbit. This de-orbiting process will provide NASA researchers with information about how systems like NanoSail-D might one day be used to bring old satellites out of space. This will provide a means for future satellites to de-orbit after their mission is complete - keeping them from becoming space junk.

    For now, Alhorn and his team are anxiously awaiting NanoSail-D's second attempt.

    "The most exciting thing about the upcoming launch is just being able to do it," he said. To get a second chance is invigorating. You rarely get one like this - that's what motivates me to get up and keep doing this."

    After the NanoSail-D flight, Alhorn hopes to continue developing solar sails for NASA. He's already started to design FeatherSail, a next-generation solar sail that will rely on insights gained from the NanoSail-D mission to take solar sailing to the next level.

    NanoSail-D, managed by the Marshall Center, will be the first NASA solar sail deployed in low Earth orbit. The sail payload was designed and built by NeXolve, a division of ManTech in Huntsville, Ala. The NanoSail-D project is a collaboration with the Nanosatellite Missions Office at Ames Research Center. The experiment is a combined effort between NASA, the U.S. Air Force, Space Development and Test Wing, Kirtland Air Force Base, N.M., and the U.S. Army Space and Missile Defense Command and the Von Braun Center for Science and Innovation, both in Huntsville.

    LETHALFORCE Moderator Moderator

    Feb 16, 2009
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    Setting Sail In The Sun

    Setting Sail In The Sun

    By rigging large pieces of cloth atop boats, early explorers harnessed the wind to voyage across oceans. Now, modern space explorers want to use sails to send spacecraft to the far reaches of the solar system
    and beyond. These sails will be made of large, ultra-thin gossamer plastic sheets that, instead of wind, will be propelled using sunlight.

    Light particles, or photons, exert a small pressure when they bounce off a reflective surface. Ever since James Maxwell proved that light exerts pressure in the 1860s, space exploration visionaries have talked about solar sailing. Exciting new developments this year are making their vision a reality.

    In May, the Japanese Space Exploration Agency successfully launched IKAROS, the first-ever spacecraft to use solar sail for propulsion in space. The spacecraft finished unfurling its sail in June and is now accelerating toward Venus under solar pressure. Two more solar sail launches are on the horizon: NASA plans to launch a sail this fall, while the Planetary Society is aiming for a launch in 2011.

    At the second International Symposium on Solar Sailing (ISSS 2010), which was held at the New York City College of Technology in July, 60 experts from around the world unanimously agreed that "solar sail technology is viable for space flight operations." The panel recommended speeding up development and testing the technology.

    "Solar sailing is the only known technology we have on Earth that will someday take us to the stars," says Louis Friedman, executive director of The Planetary Society.

    Speedy Sunlit Sails
    Sail-propelled spacecraft could be used to monitor the Earth or hover close to the Sun to study solar storms and flares. They also could be used to adjust the orbits of satellites circling the Earth. But their true reach and potential lie farther away: experts believe they are the best propulsion system for exploring the outer edges of the solar system and someday other stars.

    That is because unlike rockets, they don't require fuel and they gain speed constantly as long as light hits them; they can eventually move spacecraft much faster than a rocket.

    "If you want to go really quickly to the outer edge of the solar system you'd want to use a solar sail," says Les Johnson, deputy manager of The Advanced Concepts Office at NASA's Marshall Space Flight Center. "A chemical system [such as] a rocket would run out of gas long before you get there. With solar sails, as long as you've got the Sun you can keep going."

    Today's solar sails are typically made of aluminum-coated plastic films with a thickness a fraction that of a trash bag. Other lightweight materials such as alumina or carbon fiber are also being tested. To capture as much pressure from sunlight as possible, they need to be big. The Planetary Society's Cosmos-1, which did not reach orbit due to a rocket failure, had a surface area of 600 square meters, about one and a half times the size of a basketball court.

    Going to the fringes of the solar system would require very large sails. Johnson imagines next-generation sails would have to be hundreds of meters on a side. They would be deployed close to the Sun to gain thrust and build up immense speed so they could coast the rest of the way through the solar system.

    In three years, a solar sail could reach speeds of 150,000 miles an hour. At that speed, it could reach Pluto in less than five years. It took NASA's Voyagers over 12 years to reach a similar distance. The latest spacecraft to head toward Pluto, NASA's New Horizons mission, will take nine years to reach its destination using a combination of rocket propulsion and gravity-assistant maneuvers.

    Friedman believes that a sail-propelled spacecraft for exploring the Kuiper Belt is possible within the next ten years. Beyond the orbit of Jupiter, the energy from sunlight gets too weak to keep sails accelerating, so to go beyond our solar system, a craft could need added thrust. For that, he says, light could be provided by a solar-powered laser placed in orbit around the Sun at a mid-point within the solar system.

    Setting Sail for the Future
    NASA's first experience with the concept of solar sailing came in 1974 with the Mariner 10 spacecraft, which was designed to fly by Venus and Mercury. When the craft's direction needed to be changed and it had run out of gas for its jets, controllers turned its solar panels to face the Sun and change the spacecraft's direction with solar pressure.

    Between 2001 and 2005, NASA built two 20-meter sails that were successfully tested on the ground under vacuum conditions. But funding for the projects fell through in 2005. About that same time, affordable compact nanosatellites called CubeSats appeared on the scene, presenting a low-cost opportunity to launch a solar sail.

    The result was NanoSail-D, a diamond-shaped sail three meters on a side that was made of four triangular blades and was packed into a 4.5-kilogram spacecraft about the size of an airplane carry-on bag. In 2008, NanoSail-D was launched aboard a Falcon-1 rocket that failed to reach orbit.

    Scientists at NASA's Marshall Space Flight Center plan to launch NanoSail-D again this fall. Meanwhile, the Planetary Society is building LightSail-1, a 32 square meter sail that will weigh less than 5 kilograms.

    Until the launch of the Japanese IKAROS spacecraft this May, no solar sail had ever been deployed in space primarily for propulsion. IKAROS has a solar power sail that uses the Sun's pressure for propulsion and embedded thin-film solar cells to generate power. The square sail with 10 meter sides was deployed and is kept flat because of the craft's spinning motion and weights attached to its four corners. This is unique to the Japanese design, Friedman says, calling the mission a "great achievement and major step toward solar sail flight."

    The LightSail and NanoSail, by contrast, deploy the sail using a rigid mast or boom to which the sail's blades are attached. This more traditional design tends to be heavier than the IKAROS design.

    Johnson says that the biggest challenge lying ahead for NASA engineers is to make the booms lighter. The lower the sail's overall mass, the more it accelerates from the Sun's force. Researchers are now looking for tough, lightweight materials for the support structure.

    Much as the explorers of the past used sails to search for 'new worlds' on the uncharted seas, perhaps one day solar sail technology will allow humans to travel beyond our solar system and visit new and alien worlds elsewhere in our galaxy.

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