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.""

Comments

Re:Stellar Pong?

[mrchaotica]

What if it's only reflective on one side?

Solar sail

[Uplore]

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.

Re:Solar sail

[whopis]

Ever seen a radiometer? or hear about the radiation pressure equation?

This is a common misconception... one that even Maxwell mistakenly believed. Apparently along with the folks at Encyclopedia Britannica as well.

Pay attention to which way a radiometer turns. If it were turning due to radiation pressure, it should act as if a force were pushing on the white side of the plates. Since the white plates reflect the light, there should be twice as much pressure on them as there is on the black plates which absorb the light. (It takes a greater transfer of momentum for something to bounce off of you than for you to catch it... think of the conservation laws).

The problem with the radiometer is that it turns the wrong directions... it acts as if something is pushing on the black side of the plates. And there is... air pressure. The black side will reach a higher temperature than the white side, and then due to the thermal transpiration, the gas near the edges moves from the hot side to the cool side, and in doing so it pushes the blades along.

Radiometers are in a near vacuum, but there is enough air pressure inside to allow this effect to happen.

What Solar Sails Are

[SlashChick]

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!

Physics

[caitsith01]

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.

Re:Stellar Pong?

[Igmuth]

And alot sooner than you would think... Once you cross the heliopause, the solar wind is basically moot.

Good to see

[T.Hobbes]

It's very good to see this branch of space technology getting funding. I'd rather travel in a starship with warp drive, but until then we need some feasable way to get to other stars. There's no reason, in my mind, why we shouldn't send a few of these off to nearby stars with the sole purpose of taking some close-in measurements and somehow getting the data back here (getting the data back would probably be harder than getting the spacecraft there in the first place). The very fact that it would take hundreds or thousands of years for them to get there is the best reason to start sending them now.

Let's all raise a glass of Sake to the engineers behind this project!

2 questions (Earth altitude, Sol heliosphere exit)

[MMHere]

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?

Just a question...

[ScottZ]

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?

calculations from NASA

[gentoo4ever]

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.

Re:Ironically

[FireFury03]

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.

solar wind

[N3wsByt3]

Solar sails do not use (or not primarely, exept maybe when close to the star, in the beginning) solar wind to propel itself. It uses the reflection of the sunlight; thus, photons, rather then ions.

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.

Limited directions?

[wikdwarlock]

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?