
World's first solar sail unfurled in orbit - joshrule
http://science.nasa.gov/science-news/science-at-nasa/2011/24jan_solarsail/
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noahlt
Not quite. According to the article, the Japanese deployed a solar sail with a
Venus probe. This, though, is the world's first solar sail on a probe designed
for Earth orbit.

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robin_reala
The Planetary Organisation _tried_ to deploy a solar sail back in 2005 (
<https://secure.wikimedia.org/wikipedia/en/wiki/Cosmos_1> ) but the rocket
failed.

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rlpb
In what way is this a solar sail? It's a drag sail. From the article, it seems
to me that the sun doesn't propel it any more than the sun propels my car.

~~~
dandelany
Because it's so close to Earth, the drag force will be much greater than any
propulsion force achieved from solar particles, which means its orbit will
decay and it will fall out of orbit. However, this doesn't preclude it from
being a solar sail, it just means it's not a very efficient sail. Eventually,
we'd like to send these into deep space, where there is no drag from the
atmosphere, allowing the craft to accelerate indefinitely. But for now, it
makes sense to keep it in orbit and study it at close range so we can be sure
the "sail" effect works as predicted.

More info: <http://www.nasa.gov/mission_pages/smallsats/10-109.html>

"The relatively low-deployment altitude means drag from Earth's atmosphere may
dominate any propulsive power it gains from the sun, but the project
represents a small first step toward eventually deploying solar sails at much
higher altitudes... because the sail will deploy relatively close to Earth,
researchers will have a difficult time detecting the slight solar effects."

~~~
jacquesm
> allowing the craft to accelerate indefinitely.

In theory that's all very nice, in practice the power available for
acceleration decreases as the cube of the distance.

Of course a bit of acceleration is better than nothing but this will only work
well if you have very large amounts of time, and since all systems will have
to survive for all that time I don't see this as a practical means of
propulsion. Bussard Ramjets are a lot harder to construct (and shield) but I
think if there ever is going to be a practical means of achieving speeds that
are a significant fraction of lightspeed then I think that's where it's going
to come from, not from solar sails (even though the technology definitely has
its charm).

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jimmyk
>In theory that's all very nice, in practice the power available for
acceleration decreases as the cube of the distance.

This is why any solar sail intended to move very quickly will open up
somewhere closer to Mercury.

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iwwr
It would be interesting to see if the magsail or electric sail concepts are
developed as well. The simplest design appears to be the electric sail, which
only needs radial conductive wires (easy to manufacture and deploy, although
it needs to be launched well outside the Earth's magnetosphere).

<http://en.wikipedia.org/wiki/Magnetic_sail>

<http://en.wikipedia.org/wiki/Electric_sail>

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JacobAldridge
I see that this is expected to, as one outcome, help reduce further space junk
in orbit. I wonder what impact existing space junk - which is predominately
small pieces of metal orbiting the earth at speed - would have on the sails?

Without knowing its altitude, even the 70-120 day lifespan makes it a target.
I wonder how resistant a 10m^2 piece of thin polymer sheet would be to a lazy
2-inch screw hurtling into it?

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dandelany
> I wonder how resistant a 10m^2 piece of thin polymer sheet would be to a
> lazy 2-inch screw hurtling into it?

Presumably, not resistant at all... Even the heavy shielding on the ISS can
only protect from debris less than 1cm in diameter. The question is, would
such a debris hit shred the sail, or would it punch a neat hole, leaving it
mostly intact?

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JacobAldridge
Yes, 'not' is how I would have described the resistance. As long as it were a
fairly direct hit, I imagine a neat hole would be most likely (though these
could add up fairly quickly over time).

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riledhel
"For reasons engineers still don't fully understand, NanoSail-D spontaneously
ejected itself." Best line of the article!

~~~
jarin
I'm going to point people to this article next time some code inexplicably
starts working.

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wingo
Is it a sail or a drag parachute?

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Femur
It is a proper sail propelled by light pressure instead of wind.

<https://secure.wikimedia.org/wikipedia/en/wiki/Solar_sail>

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dedward
"NanoSail-D will remain closer to home. "Our mission is to circle Earth and
investigate the possibility of using solar sails as a tool to de-orbit old
satellites and space junk," explains Alhorn. "As the sail orbits our planet,
it skims the top of our atmosphere and experiences aerodynamic drag.
Eventually, this brings it down.""

Pretty clearly not a solar sail...

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51Cards
"They'd also like to measure the pressure of sunlight on the sail, although
atmospheric drag could overwhelm that effect."

Dual purpose study.

