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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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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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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?
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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What those who are ignorant of the subject matter think; usually wrong.
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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If you accelerate, you move into a higher orbit (and move away from the star). If you decelerate you move into a lower orbit (towards the star). Sideways vectors are used to change the plane of your orbit.
All this acceleration lasts as long as you have light. So even if the sail only gives you 0.001g of acceleration, after three hours that's as much acceleration as a one second, one gee burn... but you have not used any fuel. This can carry on for many months, and at the end of that time you have as much "fuel" as you started with.
I actually agree that, barring powerful lasers to "push" the sail, solar sails are not an interstellar technology; they don't build up enough speed quickly enough. However it's not true that interstellar debris will slow the sail down substantially. The amount of interstellar material is just not enough to affect it. The density of the local interstallar medium is actually around 10^5 atoms per cubic metre. That is an *incredibly* hard vacuum. One hydrogen atom is about 1.67x10^-27 kg; a 1km square sail will hit 10^14 of these for each kilometre of travel. The sail will have to travel roughly 6x10^12km to encounter one kilo of hydrogen. Alpha Centauri is about 4x10^13km away; in getting there you'll encounter about six kilograms of material.
That's simplifying a bit, as matter is much denser than that before you hit the heliopause. On the other hand, once radiation pressure becomes negligible, turn your sail sideways to the interstellar medium and it won't hit *anything*.
Within a solar system, they are an incredibly efficient means of transportation, because they give constant acceleration with no fuel cost. Outside of the solar system, they are much less useful without the aid of lasers boosting your radiation pressure.
Robert Forward's "Rocheworld" (AKA Flight of the Dragonfly) is SF but covers interstellar use of solar sails fairly well. The SF short "The Wind from the Sun" by Arthur C Clarke (I think I have that title right) gives a good overview of use within a solar system.
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.
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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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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