When Ikaros unfurled, it unfurled like a spinning top blossoming into a pinwheel. Out in space earlier this month, the center piece of Japan’s solar sail was rotating quickly when it began to extend the arms that had been wrapped up inside. As they stretched out into a stiff X shape, like the stakes that hold a kite taut, the craft slowed to a gentler rotation (a consequence of conservation of angular momentum, like the way a figure skater’s spin slows down when she extends her arms). The JAXA scientists then could let Ikaros stretch the shining sail into a square that spanned 66 feet diagonally.
When Ikaros unfurled, it also breathed new life into a technology that has been dreamed for decades—using the the pressure of sunlight itself to cruise the solar system, and perhaps beyond.
In Brooklyn this week, solar sail enthusiasts gathered for an international symposium. Last night Osamu Mori of the Ikaros team (seen above with a mock-up) was the toast of the party, and a group of experts joined him to celebrate and look forward to a bevy of new explorations. The roster included Planetary Society current director Louis Friedman and director-to-be Bill Nye, NASA’s Les Johnson, Malcolm McDowell of the University of Strathclyde in Scotland, and Roman Kezerashvili of the host New York City College of Technology.
“I feel like they deserve a ticker-tape parade here in New York City,” Friedman said, “rather than just showing up for a scientific conference.”
So far, Mori said, Ikaros has succeeded in stretching out its sail, confirming that it is accelerating under pressure from the sun’s photons, and demonstrating its clever way of steering. Solar cells cover the surface of Ikaros’ sail, which is only microns thick, allowing the craft to create photovoltaic electricity. But the sail also carries small sets of LEDs LCDS. When the Ikaros team changes the color of turns particular lights on and off, they change how much light that side of the sail reflects, which can turn it. “It creates differential torque,” Friedman told me. “That’s very creative.”
While Ikaros prepares to cruise on a flyby of Venus in the months to come, the Planetary Society’s own project nears a launch. Friedman has long been an enthusiast of solar sailing, and the society previously built a craft that was lost during a launch accident—the price of not having hundreds of millions of dollars to launch your own rocket. But now its new LightSail-1 has passed its design review, and Friedman is angling to send the craft, which weighs just about 10 pounds, as a piggyback on a NASA launch next year.
NASA, too, is back in the game. Johnson, of the Marshall Spaceflight Center, said NASA investigated solar sails in the early 2000s, but the work mostly faded into the background. Now, with JAXA having shown that a solar sail can be achieved, NASA’s solar sail scientists are regrouping. In the hopper, Johnson said, are square sail ideas that look very much like Ikaros and LightSail-1. But NASA also has a much wilder design, a ribbon hundreds of meters long but less than one meter across. Surface area is what matters for solar sails, and different engineers will try any number of designs to find the most efficient.
Nye and the other panelists all praised this nascent solar sailing success as a open door to exploration. These missions, Johnson said, are by far the best way to make round-trips in space. “Most other missions run out of gas,” he says. But here, “as long as the sun is shining, you’ve got thrust.”
Dreamers like Friedman and Nye even imagine solar sails as the propulsion mechanism of choice to visit other stars. However, once you get too far from the sun you’d need a new way to push your vessel along: Like, maybe, ultra-powerful lasers in Earth orbit beaming a stream of photons across the expanse of space. As you might imagine, we don’t have ultra-powerful lasers in Earth orbit. Someday, though, we might. “You could be driven all over the universe by the momentum of photons,” Nye said.
We may all be long gone by the time that happens. But after so many years of yearning for this to work, Friedman finally has the chance to soak it in. “Of course,” he told DISCOVER, “I’m tremendously gratified to beat the naysayers.”
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July 22nd, 2010 at 2:41 pm
Bill Nye, The Science Guy of childrens television fame?????? Is that the same Bill Nye they are talking about in the Article? If so then whoa nellie he’s going to be in charge of the Planetary Society???
A few questions about this technology. What about debris hitting the thin membrane for the sail? Goodness knows there’s plenty of natural and man made space junk and debris up there so if the sail gets hit how will it effect the performance of the technology? How fragile is the tchnology itself?
How fast can this sail potentially travel? If it takes 5 years to get to saturn, as a simple example, is it really that wonderous a technology?
July 22nd, 2010 at 3:02 pm
@Chris
1. Yes indeed, the Science Guy himself.
2. I asked Louis Friedman about debris and he said they do worry about it, given that the material’s width can be measured in human hairs. The sails are built with a support system sort of like a grid, which contains any hole and prevents it from spreading (that’s the idea, anyway). Then, if you just had a small hole or two, you could keep going without much performance loss.
3. Speed depends on how big you can make the sail and how light you can make the craft. Somebody in the audience asked Roman Kezerashvili about this and he predicted that far off in the future you could approach 600 to 800 kilometers per second.
July 22nd, 2010 at 6:37 pm
JAXA is on a bit of a hot streak lately. Bringing back Hayabusa, a working solar sail (the first? outside a lab perhaps?). Then there’s that expensive new gravity wave detector they are building, tho’ that’s probably not a JAXA project…
Go Go Gadget!
July 22nd, 2010 at 7:51 pm
Really cool, though I’d like to see a craft that generates it’s own photons as it’s source of thrust.
July 22nd, 2010 at 8:50 pm
Here’s my brilliant idea for reducing the need for heavy structural members – instead of using crossbars, use a springy hoop around the outside. Such hoops can be folded in on themselves multiple times so it can fit inside a capsule – I have a laundry basket that folds into a six inch hoop. There might have to be a way (such as a slowly released string) to slow the folding out to avoid a sudden shock that could tear the membrane. But the hoop need not be very springy, so that might not be an issue. Once the hoop folds out, the membrane (with the ‘rip-stop’ pattern) provides the tensile strength and the hoop provides the stretching force.
July 23rd, 2010 at 9:31 am
@ rabidmob
A Craft which produced its own photons would go backwards. It would have to deal with the recoil of photon emission and then have only a partial chance of the sail capturing a portion of that thrust. A vehicle trhat just produced photons without a sail could work but it would require a large amount of energy to get any thrust due to the low mass of the photons. Sails are useful because there is lots of free energy from the sun and because the technology might be convertible to magnetic sails which would be more useful and powerful.
July 23rd, 2010 at 1:20 pm
Actually, one of the Fathers of this technology was Dr. Robert L Forward, who consulted with NASA and worked at Hughes Research Laboratories. He proposed setting up “ultra-powerful lasers” as mentioned in the article way back in 1962, and his paper, “A Program for Interstellar Exploration” published in the Journal of the British Interplanetary Society, Volume 29, pp. 611 – 632, 1976 is fascinating reading.
As for the speeds, according to Tony Reichhardt in Space Technology: Setting Sail for History, Nature 433, February 2005, it is possible to get to Pluto in 5 years using laser systems. Initially, the effect and speeds are very slow, starting about 160 kph. However, after 100 days, that speed has increased to 16,000 kph, and after 3 years, the craft would be moving at 160,000 kph, fast enough to reach Pluto in less than 5 years. 0.5c maximum velocity within 5-10 years from launch; travel to Alpha Centauri in only 12.5 years. Granted this is with kilometers-wide sails, much bigger than the one from JAXA, but possible in the future.
July 26th, 2010 at 4:04 pm
Steering mechanism is via LCD not LED.
Change “when the Ikaros team changes the color of particular lights” to something like “when the Ikaros team changes the opacity of the LCD segments” and you’ll be on the right track.
July 26th, 2010 at 4:47 pm
@Chris
Thanks for the note—fixed. I misheard Friedman when he was telling me about that.
July 4th, 2011 at 2:21 pm
I like your blog. Fantastic information.