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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.""
What if it's only reflective on one side?
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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.
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If the destination star has about the same amount of solar wind (or whatever sails use; I forget what exactly) as our sun, the point where it reverses course would be about 1AU from the destination star. I'd say that's close enough to be considered "reaching another star".
And alot sooner than you would think... Once you cross the heliopause, the solar wind is basically moot.
Let's all raise a glass of Sake to the engineers behind this project!
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?
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.
There is probably some engineering trick to work around this. It might be possible to use mirrors to shine on the opposite side of the sail. Almost surely wouldn't be as fast, but seems like it would be doable.
Interesting idea... you wouldn't be able to carry the mirror with you once you turned around (since the mirror would be producing exactly the opposite force of your solar sail), but you could probably drop it in space pointing in the right direction - the mirror would accellerate backwards because of the light pressure but it would still reflect the light forwards which I guess you could use.
http://blog.nexusuk.org
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:
to the crew on board, it'd be like
mere hundreds or even tens of years
Not according to general relativity: they need
to accelerate when leaving, and decelerating when
arriving to destination. Decelerating will almost
reverse any time compression from the
relativistic speed...
It was not my intention to suggest that jettsoning the sail would slow the craft. You use the light from the star you're approaching to slow down. Actually in the case of Forward's design, you detach an outer ring of the sail. This outer ring accelerates faster than the ship and inner circle of sail because it doesn't have the mass of the ship to pull. Once ahead of the ship actuators on the ring bend it slightly to focus on the circle still attached to the ship. Now the laser in sol's orbit can be used to slow the craft much faster than using the light of the destination star, making for a faster overall trip.
I though Forward's book was entertaining. I love his aliens.
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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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Correction: a square-rigged ship is just as capable of sailing against the wind as a ship with triangular sails. I spent a couple of weeks this summer sailing around with about a dozen other squarerigger enthusiasts in an Åfjordsbåd, an old Norwegian type used for fishing. It can comfortably sail about 60 degrees to the wind, which isn't impressive by modern standards, but keep in mind that this type was developed in the 14. century, as a continuation of the technology of the Viking-ships.
"Workhorses" of the 1800s were in fact usually gaff rigged, like clippers, while the war ships were square rigged. Square rigged ships require rather more crew, but are more maneuvrable, so for navies they were preferable until steam-ships became an option.
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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Not true that the sail would have to be massive. Some years back I read a proposal for a aluminum sail as big as the earth but weighing only 100 grams. It would only be 2 atoms thick.
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.