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Japanese Deploy Solar Sail
Chuck1318 writes "The Japanese ISAS (Institute of Space and Astronautical Science) announced the launch and deployment of the first ever large-scale solar sail. In the news release they state "Because it carries no fuel and keeps accelerating over almost unlimited distances, it is the only technology now in existence that can one day take us to the stars.""
"...it is the only technology now in existence that can one day take us to the stars." Well, unless the Japanese can automate retraction of the sails, it wont reach any stars. While it's powered by solar wind, it will slow down and reverse as it gets farther from the original star and closer to the destination star.
You are confusing me with someone who cares.
Ironically, this technology can take us to 'the stars' but not toward our own. Better not change your mind and want to turn around less than half-way to Alpha Proxima...
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While it's powered by solar wind, it will slow down and reverse as it gets farther from the original star and closer to the destination star.
No, see, that's where Jeff Bridges comes in.
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What I dont understand is how they intend to protect these massive sails from being shot full of holes by meteorites and space dust as it propels its way through space.
Also, seing as how it is powered by solar wind, what happens when the craft is between 2 or more stars which are all exerting equal force on the sails. With no fuel it is doomed to slow down and be 'blown' around in space.
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In case you, like me, didn't know that much about solar sails, there's a great article at How Stuff Works about them: How Solar Sails Will Work. Looks like a pretty interesting technology!
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Anyone care to fill us in on the rate at which the energy received by a surface decreases with distance? I imagine that, given the incredibly weak force applied by light, it would take one HUGE sail to get anything like meaningful acceleration for space travel. Surely be the time you are a few million kilometres from the Sun the amount of force being applied will have dropped off by a huge amount?
Anyway, we should get to Mars and back a few times before we try to get to the stars... baby steps.
Read Pynchon.
...it is the only technology now in existence that can one day take us to the stars.
Orion can take us to the stars, and it can be done with today's technology, not something that's just starting to enter the very earliest test phases. But it's nuk-yu-ler, so it doesn't count.
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Sorry, but that is incorrect. There is a design from the late 60s for an Orion starship that could get to Alpha Centauri in 130 years, for the whopping cost of $1 trillion. Thats much faster than a solar sail could ever hope to do.
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You just have to tack into the solar wind. *grynn*
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The pictures in the article which show the test sail deployed immediately behind the launch vehicle imply the same thing. The following text says that the launch vehicle reentered and splashed down 400 seconds after liftoff. This can only mean that both the LV and the sail experiment were in ballistic flight when the latter was deployed. For a solar sail to work, it would need to be deployed after orbital insertion (or after escaping the magnetosphere.) The article does not mention orbital insertion, nor was there time for this to occur.
Let's all raise a glass of Sake to the engineers behind this project!
They deployed a sail less than two minutes after launch, had it in place less than two minutes, threw it away, deployed a second sail, then less than three minutes later it crashed into the ocean.
Total trip, liftoff to crash-down, less than 7 minutes.
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Just to clarify what people seem to be mistaking, the sail is *not* powered by Solar Wind, it is powered by the light of from the sun. The idea is that each photon of light that reflects off of the surface of the sail transfers a little bit of it's momentum to the sail.
It won't be a viable method of transportation between solar systems until it has an anti-pirate defense system. Giant solar sails just scream "come and get me space pirates."
Um, no. As you approach the destination star, its light pressure will start to counteract your velocity and slow you down. The "brakes" are built in.
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1. Did they get high enough above Earth to enter the inter-planetary "void," and thus avoid the significant effects of Earth's atmosphere? 100, 230, and 400 seconds after liftoff hardly seem "high enough."
2. What happens to such sails when they cross the heliosphere of a regionally prominent star such as Sol? Is it all chaotic photons and miscellanous radiation in the interstellar "void?" Or are conditions regulated by the nearest stellar bodies?
-- In other words, how would one navigate effectively once the prominent wind from Sol fades and is replaced by other forces? Are you doomed to follow your trajectory mainly established by Sol once you leave its heliosphere, possibly modifed by various minor (uncontrollable) forces from other winds in the void? Can you take advantage of such extra-Solar winds to go where you want?
How do you run against the solar wind? What are the appropriate forces to run your 'keel' against when you want to track across a solar system (say, to somewhere useful)?
Anyone got any pointers?
First of, I am not a trained professional. I am a high school senior but I believe that I understand the principals behind this technology. The term solar sail is a modern misnomer. Solar sails are only capable of accelerating away from a star. This is because the sail is powered by reflecting solar radiation/solar wind. (I'm not sure, but I believe that this is limited by the inverse square law, which means that every time you double the distance between you and the source of the radiation, you decrease it's power 4 times. AKA it's power decreases exponentially as you travel away from it.) This means that in the expanse between stars, there will be essentially no acceleration, and in fact, depending on the size of your sail, some drag. Because space is not really empty (one hydrogen atom per square meter, which would add up if you need to travel light years with fully deployed several KM wide solar sails.) While the best way to use solar sails would be to put human power behind them, that is to fire lasers at the sails to continue powering them past the heliopause, enabling them to continue accelerating past our solar system. The simple option for travel would be to have a craft capable retracting it's sail, retract its sails once it leaves the area of acceleration, and then deploy them once it arrives in it's target solar system, slowing it down. Solar sails are also impractical for travel in a solar system (with the exception of traveling from an inner plannet straight out to a planet more distant from the sun.) Solar sails can not function like sails on an ocean. The reason sails work on an ocean is because boats have centerboards, solar sail craft do not have centerboards (because space doesn't have the matter to support one) they would simply drift away from the sun. Conclusion: Solar sails, while wonderful and interesting, will never have a practical use transporting humans simply because it would take hundreds of thousands of years to travel between stars. I also believe that if we begin constructing solar sail craft to travel to distant stars, we should (if we don't we are doing something wrong) be able to travel to the star and back before a solar sail craft would get there to begin collecting data. If I screwed up anything flame me as much as you want.
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Rest Mass from Wikipedia
A clover type deployment was started at 100 seconds after liftoff at 122 km altitude, and a fan type deployment was started at 169 km altitude at 230 seconds after liftoff
If I understand solar sails right, they are actually pretty different from the way wind sails work. Contrary to what your NASA links is telling us, most of the force from the sail does *not* come from the wind trapped in the sail pushing it along. Rather, under the pressure of the wind, the sail takes the form of a wing, and Bernoulli forces propel the boat along. This also enables sailing (up to a degree depending on the craft and the rigging) against the wind. I do not see how Bernoulli forces would appear on a solar sail (as the light can't go faster on one side of the sail than on the other).
These solar sails are pretty useless. Here http://solarsails.jpl.nasa.gov/introduction/design -construction.html
are calculations from NASA guys. It looks like this
Japanese sail has acceleration of few mm/s^2 and is not able to get out of sun gravitational field (and, of course, the Earth's one). It would take solar sail 100 years to get
to alpha centauri if it had acceleration 10 m/s^2 (table 3 in the above link, there is "-" in the
table for 5 m/s^2 and less , that is it will never get away from sun ).
There was a good idea though to build a huge mirror to focus sunlight on such sail. This would effectivly increase surface area of a sail and
pressure would not drop as square of the distanse from the sun.
Yes, it keeps accelerating over long distances....but I can make a rocket do the same thing by asymptotically slowing down the rate of fuel burn. A solar sail is doing nothing differnt, while the sail will keep accelerating the accelaration will fall off with the radiation pressure (about 1/r^2).
Personally, I tend to believe things like ion drive are actually much more efficent and likely to work well with stare exploration (ion drive is just a fancy way of saying you shoot very small amounts of mass out the back going very fast. This is important because it means you can get more thrust from the same amount of fuel weight if you have something like a nuclear power source to accelerate the ions).
If you liked this thought maybe you would find my blog nice too:
Those pictures make it look like Vejur, coming to cleanse the carbon-unit infestation from the Creator's planet...
You must think in Russian.
For those of you who are - like me - not experts in physics, this technology was featured in the BBC documentary "Space" presented by Sam Neill.
c at ,5,,11,science,831
http://www.imdb.com/title/tt0273608/
http://www.bbcshop.com/invt/bbcdvd1090&bklist=i
One of the chapters discusses how travel to other stars would be possible. As far as I remember there is another technical solution in discussion which would involve nuclear detonations as part of a propulsion system. (I might have confused something there, though)
This website has a list of many advanced propulsion technologies under devleopment by JPL. Considering that we are using chemical rockets which have been known about since the 30's it's good to see that people are looking into new propulsion tech. These systems, some of which can reach the speed of light, include Advanced Chemical Propulsion, Nuclear Propulsion, Antimatter Propulsion, Electric Propulsion, Micro Propulsion, Beamed Energy, Sails, Gravity/AeroGravity Assist, Chemical and Electromagnetic catapults, Tethers Skyhooks and Towers,Extraterrestrial resource utilization,etc.
It's also not correct that solarsails can't be used to reach other suns, because the sun there gives an oposite force. It's quite trivial, when using adaptive (rotating) solarsails, which have only one higly reflective side, to slow down or accelerate when nearing a solarsystem. And even withing a solarsystem; for an interesting project in that regard, see the planetary society where they plan to launch the first non-gov solarsail-powered probe.
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What the hell is wrong with you? You hear of a well-thought-out idea developed, examined, and approved by physicists, and without looking into it, you dismiss it with your first couple of off-the-top-of-your-head thoughts.
OF COURSE it's not shining laser light into the sails from the ship itself, like a sailboat with a fan on it, you unbelievable moron. And as for getting "worse and worse with aim", you DO NOT TRY AND POINT THE LASER AT THE FAST-MOVING AND LIGHT-YEARS-DISTANT SPACESHIP, AND DO COURSE CORRECTIONS BY MOVING THE LASER, you just keep the laser pointed at the destination, and do course correction at the ship.
The problem here is not so much that you completely misunderstood the whole concept, it's that you so vastly overestimate your intelligence and knowledge that you didn't recognize your stunning incapacity to evaluate this suggestion.
So let's review:
1- you're not as bright as you think
2- other people are brighter than you think
3- other people have often evaluated things a lot more thoroughly than you are capable of doing in 30 seconds
4- if you don't understand something, it's more likely your own defect than a problem with the expressed idea
5- sit down and shut the fuck up, you arrogant ignoramus
Now that that's out of the way, there certainly are practical issues with this method of space travel. It's just that they have absolutely nothing to do with what you thought they were.
Hasnt anybody read this story by Arthur C. Clarke about an Earth to Moon race in solar sail powered space ships.
A beautiful story with an excellent description of some problems which may exist.Read the story,i will spare the spoilers.
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There is another existing technology that could travel interstellar distances. NASA's Orion project designed a starship propelled by nuclear weapons and a big pusher plate. And yes, the crew can be properly shielded.
Of course what we really should be working on is actual nuclear rockets - controlled nuclear burn instead of explosives. Nuclear gas core rockets are really not beyond present technology, their exhaust is cleaner than the space shuttle's, and they're so powerful you can build big, heavy, safe vehicles.
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Okay, everyone. Let's calm down. The Japanese, or any other Earthlings, will not have to worry about changing their velocity at Alpha Centari anytime soon. The fact is, all they accomplished was opening two differently shaped pieces of foil above Earth over a 400 second period.
Please. I used to launch Estes rockets with shiny parachutes. Prove to me that it WASN'T photons reflected from the Earth into my solar parachute that were slowing my rocket's descent. So NASA, ISAS, and 14-year-old model rocket enthusiasts have simply proven that gravity will pull anything you launch into the sky back to Earth.
Can someone in the know answer me this:
Since a solar sail needs light pressure to accelerate, can it only accelerate in a direct line away from a star?
also
Isn't there a problem, once the sail gets far enough from its original star, that pressure from other stars will interfere w/ the path?
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I ran across this novel form of propulsion the other day that looks promising if it pans out.
The idea is to entangle two cesium atoms, then send one up into space. Back on earth, excite the one that remains and the one in space will do the same. In theory that could be used as an ion drive while keeping the bulk of your engine back on the ground.