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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.
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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...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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The amount of force exerted on the sail decreases as a square of the distance (since the amount of light reaching the sail decreases by a square of the distance). We're not talking about 'meaningful acceleration' in anything like our current thinking of space travel -- this isn't "get on this space yacht and a few months down the road you'll get to the other star," but rather "put something on this vessel and several hundred/thousand years from now it'll get to where you wanted it to get."
This isn't about travel.
Either way, the Japanese are trying to make this look cool by saying it's star-faring technology. Probably true, but only because we're not likely to put humans on this thing -- so it's possible we'll do this before we get to Mars, because the expense and risk could be vastly lower.
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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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.
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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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."
I'm surprised that no-one else has mentioned this.
:).
The truth is that a solar sail doesn't get you away from the sun by just having the sail aimed straight at the sun. It does it much more trickily than that
What happens is that you orientate the sail at 45% (or something like that) to the sun. That way, a large amount of the force from the sun actually goes to changing your orbital speed, and not just pushing you away from the sun. By orienting the sail so that it increases your orbital speed, you end up making greater size orbits around the sun, until you are far enough away from the sun and you can do some other tricky stuff to leave the solar system.
But, it works the opposite way too. Orient your sail so that you are decreasing your orbital speed. You go slower, and therefore your orbit size decreases, and you start approaching the sun.
Of course another poster queried why you would want to travel to the sun. Good question. But how about Mercury or Venus ?
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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Ironically, this technology can take us to 'the stars' but not toward our own.
.5 C, it'd take thousands to millions of years to get anywhere. But, at relativistic speeds, it'd still take thousands of years, but to the crew on board, it'd be like mere hundreds or even tens of years.
And, why not?
Sailing ships have sailed "upwind" for many centuries.
In outer space, you are either in orbit, or falling directly towards the nearest large body. A solar sail can be used to slow down or accellerate lateral speed simply by rotating it 45 degrees.
A simple google search turned up this in case you are curious.
Although they are right, in that solar sails do accelerate the entire trip and carry no fuel, I don't think that sails are "the way to go" unless we're talking about a ten thousand year multi-generational ship.
I consider the Bussard RamJet the "only way to fly". It carries no fuel, but is powered by carving a planet-sized swath out of the ambient hydrogen atoms out of interstellar space and fusing them.
With interstellar distances, the real issue is: how quickly can you get to relativistic speeds? Because, at
You need power to get you there in less than hundreds of years - thus the RamJet.
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Unfortunately, it turns out that the interstellar medium is much thinner, in most places and in particular around the Sun, than Bussard thought. Even if you could somehow persuade protons to fuse in the few nanoseconds while they are passing through your ship at nearly the speed of light (and on average it takes about 15 billion years for any given proton to fuse in the core of the Sun), there just aren't many of them around here.
A beamrider of some kind (leave the engines at home and ship momentum up to the spacecraft in some convenient form) or an antimatter rocket are looking like the best ideas at present.
Steve
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.
Where wind sails have Bernoulli to work off of to go against the wind, solar sails have Newton. What the gp is saying is you start off in orbit around a star. If you want to get away from that star, you angle your sail +45 degrees, which reflects the light back along your orbit. Thanks to conservation of momentum you gain tangental velocity which propells you in a spiral outwards as you slowly break the sun's gravitational pull. If you want to go towards that star, you angle your sail -45 degrees, reflecting the light forward along your orbit. You lose tangental velocity and the sun's gravitational pull reels you in. You're right, completely different principles are at work, but you get a similar result.
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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)
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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