The Planetary Society is planning to propel a spacecraft using sunlight before the end of next year. Unlike the ill-fated Cosmos 1 solar sail mission of a few years ago, this will be smaller, lighter, and will proceed in three stages.

LightSail 1 will be about the size of a loaf of bread, and that’s before it deploys its sails. The sails are 32 square meters of mylar that will emerge and unfurl on ribs made of exactly the same metal that extends from your average hardware store tape measure. The entire little spaceship weighs 11 pounds. It will take a short trip 500 miles up. Goal: achieve any measurable acceleration from sunlight, and maintain some control of the sail.

LightSail 2 will launch maybe a year later, if all goes well with #1, and will last several days, settling into orbit and then using sunlight to boost itself into a higher orbit. LightSail 3 will go to L1, 900,000 miles out (considerably more distant than the moon) where the Earth’s gravity and Sun’s gravity balance out and it’s easy to stay in one place. LightSail 3 may position a solar storm monitoring station here.

How to sail in space, the short version: Reflected light pressure, caused by photons pushing against the mirror-like sail surface, push the craft and it can be maneuvered by changing the direction of the sail, just like a boat.  Sails can gradually build up some serious speed. A mile-wide sail could cross the entire solar system in five years. According the Planetary Society, this is one known technology that could get a craft up to the speeds needed to leave the solar system and reach another star system in a reasonable time frame (100 years to the nearest stars). It could be helped along by ground-based lasers.

You too can join the Planetary Society and support these efforts. And listen to the highly entertaining Planetary Radio.

Zweimal schon hat die private Planetary Society versucht, den Demonstrator für ein Sonnensegel zu starten, und beide Male versagte die russische Billigrakete (Artikel 301 und A76) – dann tat sich wieder eine neue Option auf. Und jetzt lässt sie eine anonyme Spende von 1 Mio.$ Wirklichkeit werden: Das erste LightSail kann vielleicht schon Ende 2010 abheben! Allerdings ist die Finanzierung (Gesamtkosten: 1.8 Mio.$, alles privat) noch nicht komplett – und Japan könnte dem LightSail 1 mit seinem Projekt Ikaros bereits im Mai 2010 den Rang ablaufen. Dem 32 Quadratmeter großen LightSail 1 (Abb.), das aus zwei gekoppelten CubeSats schlüpft (ein dritter trägt die Elektronik) und in über 800 km Höhe erst einmal das Prinzip testen soll, sollen später zwei ambitioniertere Flüge folgen. Für seinen Start gibt es “several candidate American and Russian launch possibilities” als Co-Passagier – aber ganz sicher keine Volna mehr …

Planetary Society Press Release, Blog und Details und Artikel von Spaceflight Now, New York Times, Space.com, AP, Reuters und Universe Today. NACHTRAG: der New Scientist über’s Sonnensegeln. NACHTRAG 2: das Event rund um die Ankündigung.

The clock stuck twelve. It’s October 30th. In a heartbeat I emerged an adult in the eyes of American law. In an alternate universe, I danced the night into a hazy sunrise. But I left celebration to Haight St. patrons, their addled revelry spilling muffled through the crack in my window. Tonight, we work.

Dawn, a night and two weeks later. It was ready; the design for the both the engine and the drivetrain, encoded in a scattered handful of drawings and documents, one wiki, two heads, and a thousand lines of physical simulation code. The first test: powering a scooter through a staccato ride amid frenzied Manhattan traffic, calculating, by the hundredth second, the will of the engine, and the vehicle’s reply. We’d follow a path devised to track emissions from humming, throbbing combustion engines, byproducts of fuel burnt in tiny explosions sparked every second by the thousands.

But nothing save cool air would our machine exhale. Compressed air, ‘a thermomechanical battery’ of sorts, is cheap, long lasting, and quick to recharge (one need only open a valve, and if impatient, run a pump, the tank will fill in seconds.) What’s more, it’s efficient. A batteries charge begins life in mechanical form, in a spinning turbine if charged off the grid, or in the inertia of a vehicle, during regenerative braking. This is then converted into AC electrical current, which is converted into DC current, which, finally, is converted into mechanical energy, losing power at each step. To power the engine this whole process runs in reverse! But compressing or expanding air keeps mechanical energy mechanical (so long as temperature is kept reasonably constant.) In powering vehicles it is superior to the most advanced battery systems known. That is, in every parameter but one.

Historically, the low energy density of compressed air had crippled any attempt to venture further than a couple dozen miles; physics, it seemed, demanded tanks of excessive proportions to travel longer. At 300 bar (’scuba pressure’), compressed air could release only half a percent as much energy as the same volume of gasoline burnt. We understood, however; it was an efficiency war. We knew that conventional vehicles were incredibly wasteful. There were many battles left to fight.

The Laws of Thermodynamics¹

“You can’t win.”
“You can’t break even.”
“You can’t give up.”

We hunted losses relentlessly. We were repaid with a series of compounding improvements, each building upon another, reversing the conventional patterns of efficiency losses endured by vehicles for more than a century. Finally, in a brilliant and unusually compact layout by Steve Crane, we found room to replace the paltry 1.3 gallon gas tank with one ten times its size. Nights yielded to our toil, and, slowly but surely our enemy routed.

“We’ve cracked the code,” we exclaimed. “The city is ours to conquer.” On the highway, whatever benefit earned by our scooter’s light weight, low rolling resistance and ultra-efficient regenerative braking would be dominated by air resistance.² But air resistance falls quickly with speed, and in the stop-start motion of the city our combined inventions would give our scooter an efficiency historically unmatched.

I keyed in the last few drivecycle parameters, drew a shallow breath, cocked my head, and pressed the enter key. The simulation lasted only a moment, but in that time, my little scooter ran more than one hundred and twenty miles, the equivalent of dozen rides between Wall Street and the Bronx on a single tank. “We’re in business,” I said. With that, and for all of a New York Minute, the questions, worries and restlessness retreated from our hearts. We huffed. “What’s next?”

[1]: To paraphrase C. P. Snow. Hat tip to Jonathan Smith.

[2]: Scooters are not particularly aerodynamic vehicles. Ordinary scooters have a drag coefficient of nearly 0.9, and a frontal area of 0.6 meters squared. We hope to achieve a drag coefficient of 0.6, similar to faired motorcycles ridden upright, but due to the rider’s position this will be difficult: some have described the aerodynamics of a scooter as like a “brick attached to a parachute.”

Our company is going to have graph paper placemats. Jealous?