IKAROS unfurls first ever solar sail in space

Jun 11, 2010 by Lin Edwards report

(PhysOrg.com) -- Japan's IKAROS has rolled out its solar sail, the first ever deployed in space. JAXA, the Japan Aerospace Exploration Agency, achieved the feat by rotating the craft rapidly and spinning the sail out by centrifugal force. IKAROS is the world’s first solar-powered spacecraft.

The solar sail unfurled by IKAROS (an acronym of Interplanetary Kite-craft Accelerated by Radiation Of the Sun) is an aluminized plastic membrane only 0.0075 mm thick and covered with thin-film solar cells. The sail works through of light reflecting off the sail transferring their forward momentum to the sail to push the attached craft forward.

The four panels of the sail make up a square measuring 20 meters along the diagonal. It was deployed by spinning the craft at up to 20 revolutions per minute, and once unfurled the sail is held flat by the craft’s spinning motion. Dust-counter sensors and steering devices that adjust the angle of the sail to the Sun are also fitted to the sail.

IKAROS is powered only by the abundant photons from the sun and no other or propellant is needed, making the technology ideal for long-distance .

The sail’s solar cells also convert some of the light into photovoltaic electricity, and in future this system could be used to power an engine. The craft is not powered by the , which is made up of much slower ionized particles that create a force of only one percent that produced by photons.

IKAROS is a demonstration craft and as such is designed only to test whether or not the solar sail can work as intended by setting the craft on course towards Venus. After passing Venus in six months' time it will travel the far side of the Sun, arriving in 2013.

JAXA is planning a second mission that will include ion-propulsion engines along with a solar sail 50 meters in diameter. This second mission will aim to use to try to reach the Trojan asteroids orbiting Jupiter.

has confirmed the solar sail is generating power, but it may be several weeks before confirmation is received the sail is moving the craft forward because it will take some time to produce sufficient momentum to start it sailing through space. The acceleration produced by the photons is tiny, but it is continuous, unlike propulsion by chemical engines that fire until the craft reaches cruising speed and then are turned off to conserve fuel. Once in motion the can accelerate the craft constantly and reach high speeds in a short time.

IKAROS was launched from the Tanegashima Space Center on May 20th along with the Akatsuki Venus Climate Orbiter.

Explore further: Video gives astronaut's-eye view inside NASA's Orion spacecraft

More information: IKAROS page: www.jspec.jaxa.jp/e/activity/ikaros.html

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User comments : 18

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Quantum_Conundrum
5 / 5 (4) Jun 11, 2010
Not exactly sure why they chose to use a solar sail to fly TOWARD the sun, as Venus is closer than earth, but whatever. At least someone is actually testing these previously theoretical technologies, unlike the U.S.
zealous
not rated yet Jun 11, 2010
what if Venus isn't in the direction of the sun from us right now? not to mention sail boats can sail into the wind.
Ronan
not rated yet Jun 11, 2010
Zealous: Doesn't sailing into the wind (or whatever it may be) require that the medium you're sailing in be a fluid, though? You have to set up a net higher pressure on a portion of the sail not facing the wind; I"m not sure how one could so that with photons.

That said, perhaps IKAROS is aiming for Venus not by accelerating, but by decelerating. It was launched with nearly the same angular velocity as Earth, remember; if it uses the sun's light to slow itself down, it'll drop down to a lower orbit, and be able to approach Venus. And this really is fantastic news; I'm so used to thinking of solar sails in general as a nebulous, science-fictiony concept, something that'll happen in The Future...and now, it seems, The Future has come a little bit earlier than I expected. Onward to the stars (?)
zealous
not rated yet Jun 11, 2010
OK, just looked up the flight path and its heading more or less directly toward venus with the sun staying pretty much on one side of the craft, just click on the link at the end of the article and you should find the pic easily
Modernmystic
2 / 5 (4) Jun 11, 2010
Moonbases of robots and solar sails.

The United States is going to be a backwater in a few decades. Better to pour all those trillions down a bureaucratic rat hole of social programs than on something as "useless" as science and space exploration....whatevs.
Jermz
5 / 5 (1) Jun 11, 2010
Nobody has mentioned The Planetary Society's LightSail-1?
TegiriNenashi
not rated yet Jun 11, 2010
@Quantum

did you bother to check wikipedia articles about solar sail before making a comment? NanoSail-D is one of the US lead projects, I'm sure there are other initiatives.
Parsec
1 / 5 (1) Jun 12, 2010
Zealous: Doesn't sailing into the wind (or whatever it may be) require that the medium you're sailing in be a fluid, though? You have to set up a net higher pressure on a portion of the sail not facing the wind; I"m not sure how one could so that with photons.

That said, perhaps IKAROS is aiming for Venus not by accelerating, but by decelerating. It was launched with nearly the same angular velocity as Earth, remember; if it uses the sun's light to slow itself down, it'll drop down to a lower orbit, and be able to approach Venus. And this really is fantastic news; I'm so used to thinking of solar sails in general as a nebulous, science-fictiony concept, something that'll happen in The Future...and now, it seems, The Future has come a little bit earlier than I expected. Onward to the stars (?)


It has to speed up to move closer to the sun. Venus moves faster than the earth around the sun.
Ronan
not rated yet Jun 12, 2010
Parsec: True, but were Venus higher up in the sun's gravity well, it would have a lower velocity. Think about the difference between a satellite in orbit, and a satellite that has been, say, magically brought to a standstill above Earth's surface. The satellite with a high lateral velocity will keep on speeding along in its original orbit, while the satellite which has had its velocity dramatically reduced (that is, brought to a standstill) will immediately be forced into a much lower orbit (that is, it'll plummet like a rock). If the satellite that's been stopped is allowed somehow to fall straight through Earth's crust, mantle, and core, accelerating all the while, then by the time it's gotten near Earth's center of gravity it'll be moving at a much faster pace than the satellite in orbit--but that's because it's much deeper into the gravitational well of the body it's orbiting, not because it was given a higher velocity when it was higher up in its orbit.
Thrasymachus
5 / 5 (1) Jun 12, 2010
You're wrong about that Ronan. You're forgetting about the conservation of angular momentum. Any force you could apply in the path of an orbiting object counter to its direction of orbit, even if a magical, immovable wall appeared from nowhere, that force would be translated into a force away from the point around which it orbits. If you're in orbit, and you want to occupy a lower orbit, you have to speed up.
Ronan
not rated yet Jun 12, 2010
Hm. Well, I had been pretty confident, but perhaps I made a mistake. If that's the case, though...well, how should I look at the example I gave? If you want to get into orbit around something, you need to be moving fast enough that you're continually "missing the ground," so to speak, correct? Stop moving, and you don't float up into the sky--you fall. One can only stay in orbit by balancing centrifugal acceleration against gravitational acceleration, and if you slow down, the centrifugal acceleration drops while the gravitational acceleration stays constant--leading you to drop down until you reach a new equilibrium. I don't see an error there, although I may have missed something (and Yes, I know centrifugal force is fictitious. Rephrase it as "the gravitational acceleration must be equal to the centripetal acceleration at that radius and angular velocity," if it makes you happy).
Bradfield
not rated yet Jun 13, 2010
IKAROS will be a very interesting experiment. Photons have no mass so quite how their 'forward' momentum will be transferred to the sail is a bit of a mystery. More than likely the sail will be caught up in the Solar wind, a stream of particles made up of electrons and protons that are ejected from the sun. The speed of these particles varies between 400 km/s and 750 km/s and no doubt it'll be this mass/momentum transferred to the sail. If so its direction will be away from the sun, not towards it or Venus for that matter.

Bradfield
Quantum_Conundrum
not rated yet Jun 13, 2010
Ronan:

The problem is gravity does not remain constant. I appears to remain constant on the surface of the earth because we normally don't change our distance from the CoG enough to notice, but on interplanetary scales it certainly is not constant, but rather changes according to the reciprocal of the square of distance.

This means earth recieves far less radiation and far less gravity from the sun than does Venus.

Which means that even though venus is closer to the sun, it actually must move much faster to keep from being sucked in by gravity.

While the Earth has more gravitational potential energy per unit mass relative to the sun than does Venus relative to the sun, Venus moves much faster.
Javinator
not rated yet Jun 13, 2010
Photons have no mass so quite how their 'forward' momentum will be transferred to the sail is a bit of a mystery.


The momentum of a photon is dependant on the frequency/wavelength of the photon. They don't have measurable mass, but photons do have momentum.

By p=h/lambda I guess it would follow that a transfer in momentum (ie. a reduction in p) would just lead to an increase in wavelength (or a decrease in frequency) of the photon.
abhishekbt
not rated yet Jun 13, 2010
@Javinator - I remember reading the same somewhere.
Even though photons have no mass, they do have momentum. Not sure of the actual physics involved though...
Ant
2 / 5 (1) Jun 14, 2010
abhishekpt
photons having momentum is irrelavent, as without mass there is no way for the momentum energy to be transfered to another body.
Javinator
4 / 5 (1) Jun 14, 2010
From wikipedia:

"There are two sources of solar forces. The first is radiation pressure, and the second is due to solar wind. The radiation pressure is much stronger than the wind pressure. In 1924, the Russian space engineer Friedrich Zander proposed that, since light provides a small amount of thrust, this effect could be used as a form of space propulsion requiring no fuel. Einstein proposed and experiments confirm that photons have a momentum p=E/c, and hence each light photon absorbed by or reflecting from a surface exerts a small amount of radiation pressure. This results in forces of about 4.57x10−6 N/m2 for absorbing surfaces perpendicular to the radiation in earth orbit, and twice as much, if the radiation is reflected. It was proven experimentally by Russian physicist Peter Lebedev in 1900."
wither
not rated yet Jun 15, 2010
An often missed detail in the speculation on solar wind sails is the potential to accelerate much faster than is usually considered and achieve a speed several multiples faster than the solar wind itself. Just as an iceboat with a sufficient L/D ratio can beat a balloon to the finish line in a race oriented directly downwind by a factor of 3-4.5, a solar sail with a magnetic field could actually accelerate past the speed of the solar wind by a large factor. The actual speed limit at an angle would be equal to the MHD field efficiency, and the velocity made good over a given course would simply be a function of the MHD efficiency, the speed of the wind (relative to the source, for example), and the angle of the course from the solar wind direction. The magnetic field could be static, and the torque from the MHD interaction would be offset by placement pf mass relative to the center of mag flux.

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