EnMasse

[Hephaestion]

Wanna see some cool.... err... hot?... pictures of the sun?
_________________
"The dignity of an animal is measured by his capacity to revolt in the face of oppression." -- Mikhail Bakunin

[Maestro]

Wow! I guess I'm glad we're a little ways away from the sun, although I realize that when it finally goes into major expansion we'll be crispy in a thousandth of a second (if we're still here).

Still that flare that was first up was pretty spectacular.
_________________
On the wilds of the Drive

[TS.]

Not quite 1/1000th of a second. It would take eight minutes for something moving at just below the speed of light to reach the earth from the sun.
_________________
"Question with boldness even the existence of a God; because, if there be one, he must more approve of the homage of reason, than that of blind-folded fear." - Thomas Jefferson

[Maestro]

[Hephaestion]

The next step in the weaponization of space? US military launch space plane on maiden voyage... but its mission is top secret

[Hephaestion]

Earth from Mars

[Hephaestion]

A gallery of stunning Hubble images from new book
_________________
"The dignity of an animal is measured by his capacity to revolt in the face of oppression." -- Mikhail Bakunin

[Hephaestion]

Scientists detect ice on asteroid:

[Hephaestion]

James Cameron convinces NASA to shoot Mars in 3-D

[Hephaestion]

See Venus, Moon and ISS all in one swell foop!

[Hephaestion]

Why not go back to the moon?

[TS.]

Honestly, I don't see what is to be gained by going back to the moon. Advances in human extra-terrestrial survival are much more likely to be furthered on Mars than on the moon, since Mars is a more likely analogue of exoplanents than the moon is.
_________________
"Question with boldness even the existence of a God; because, if there be one, he must more approve of the homage of reason, than that of blind-folded fear." - Thomas Jefferson

[Corey]

The moon would seem to be a better site for industrial development. Much closer, much lower-gravity. The negligible atmosphere might also be an advantage in some contexts? I'm thinking about erosion.

[Maestro]

[Rufus Polson]

On the moon I'd definitely do my building underground for the most part.

[Vundo Draxon]

[TS.]

[Maestro]

Just to show the problem:



You'd have to go a long way underground before you'd reach safety. Of course there's also the problem of how to protect the construction site from the aerial bombardment, not too mention the radiation.

Some might also ask why build factories on the moon. Makes about as much sense as building factories on the ocean floor on earth. Except it would be a lot easier and cheaper to build them there than on the moon.
_________________
On the wilds of the Drive

[Raos]

Why build factories on the moon? Because it's already most of the way out of Earth's gravity well, and thus a rather cheap place to launch from, which cannot be said of the ocean floor. And if it were an automated operation, wouldn't radiation not really be much of an issue as anything you'd be building would be meant for space and thus would have to be able to function without the protection of an atmosphere and magnetic field anyway.

[Rufus Polson]

Probably not "pure" automated in the sense of self-directed. But not actual humans actually on site either--we're talking mostly waldos, I would expect.

And yeah Maestro, looking at the picture there are a lot of craters. Looks scary, woo! But that's mostly because everything that's hit for the last how many billion years can still be seen. Earth's craters erode away. Plus, the early history of the solar system was more eventful; an awful lot of the big stuff happened way back in the day. So no, I don't think you'd have to go that deep to be pretty safe. Enough for radiation shielding would be enough for impact shielding against anything that happens more often than once in a million years.

[Maestro]

[Rufus Polson]

Depending on your definition of achievement, human existence on earth has achieved nothing that couldn't have been accomplished more safely and cheaply by machines. But here we are.

Even if we take our primary purpose in space as launching unmanned probes into the solar system, they will still be easier to launch from the moon's gravity well than from earth's. But I find simply foreclosing by fiat on all other possibilities annoyingly reductive. It's the same kind of logic whose next step is to ask what is served by finding out about the solar system or the universe anyway.

I do think in the medium term a bit of asteroid mining is plausible--manned or unmanned. Send things over to moderate-sized asteroids, put a bit of thrust on them to alter their orbits so they pass nearby, and yank their resources when they get close. Maybe not, but I'd be interested in having the chance to experiment with it. Moon facilities would help.

In the end, though, sure I'm probably a hopeless romantic. If I can't dance, or fiddle around with space, I want no part of your revolution.

[Maestro]

[Rufus Polson]

I notice you're talking a lot about low earth orbit. I don't recall going on record supporting the space station--in fact I'm not particularly wild about the space station and similar projects. That and this are two different things. The moon is not low earth orbit, it's a place with raw materials of its own. If we get smart enough we can do a bootstrap process that will rely mostly on local resources. It would have to be thought out very carefully, to be sure.

[Hephaestion]

Solar sail launch scrubbed, retry on May 21

[Maestro]

Solar 'sails' are very intriguing, but there seems to be some disagreement as to how they work (or don't work).

There are those who say the sail must be reflective, and those who say it must be absorptive. The 'absorptives' seem to have the upper hand. There is a sort of windmill device that is placed in a near vacuum, having vanes that are alternating reflective and absorptive.

When sunlight is shone on the device, it is the absorptive panels that move away from the light, suggesting they are the ones converting the energy.

The concept seems relatively intuitive, but in searching the web for explanations, one runs into all sorts of opinions, and speculations. Perhaps if the Japanese get this thing off the ground, we'll get the answer.
_________________
On the wilds of the Drive

[Rufus Polson]

So how is it that photons even have momentum, what with being massless particles? I mean, clearly if it wasn't going to work for such a simple reason, physicists would have pointed this out. I'm just wondering *why* it works.

. . . It's probably good that the thing is hybrid, because I don't see how solar sails would allow maneuvering--more like sails on a balloon than in the sea, presumably you'd just be pushed straight down "wind"--no tacking or even reaching possible.

[Maestro]

I'll be honest, my knowledge of particle physics is definitely not up to the job of figuring out solar sails. However, apparently others more knowledgable than I have the same problem. The question of how zero mass particles can deliver energy is hotly debated (no pun intended - well, ok, it was a bit intended).

Here's a different view altogether, one that says solars can't work because of heat transfer.

The solar sail and the mirror

[Raos]

Which makes the experiment all the more exciting!

From my admittedly limited knowledge of physics, I'd have said that it'd work because of wave/particle duality, which means photons DO actually momentum, even without mass. In such a case, whether the surface reflects or absorbs the photons, conservation of momentum would dictate that some kinetic energy is gained by the sail. Which surface would be the better choice would be a matter of efficiency rather than basic utility.

And a quick check on wikipedia for solar sail seems to confirm this.

[Maestro]

Yes. However, the argument is made that a perfect mirror reflects light leaving it with precisely as much energy as it had when it hit the mirror. As Gold says, this would make a perpetual motion machine possible, which it obviously can't.

His suggestion is that the absorptive surface generates some heat when hit by photons, and that does constitute a transfer of energy. He goes on to say, though, that once the temperature of the surface reaches reaches equilibrium with the source of photons, there is no longer a heat transfer, and no work is being done.

I will grant that he seems to be a more or less lone voice, but it's still interesting to me how no one really seems to know for sure. It's like the story of the QWERTY keyboard. There are a million reasons why it may have happened the way it did, but no one seems to know for sure, and each different theory says all the rest are wrong.

So, yes, a real experiment with a solar sail in space will give us the definitive answer as to whether it works. The reasons for it working (assuming it does) may come later.

Yet most seem to be in agreement that solar sails will not work for human space flight. There is not enough power or acceleration to make it feasible.
_________________
On the wilds of the Drive

[Raos]

I don't really know. I'm in that somewhat maddening space where I know enough to say that there's something there, but don't know enough what it is. A perfectly reflective surface reflecting light with precisely the same amount of energy while simultaneously extracting momentum would be a perpetual motion machine which is fundamentally impossible, but a perfectly reflective surface reflecting light with the precisely the same amount of energy backwards without any balancing transfer of momentum in the original direction of the light does not conserve momentum is also thus fundamentally impossible. Perhaps there's just no such thing a perfectly reflective surface and there's always going to be some, if minute, degree of energy transfer at the expense of the photon's frequency?

With an absorptive surface, I'd expect that while energy is transferred it predominately manifests as waste heat which itself isn't going to provide motive force. The only place I can see where meaningful propulsion would be derived is (again) from the conservation of momentum of the source photons. That would also make sense with regards to the wiki claim of reflected radiation imparting twice as much force, as in both cases momentum equal to the original photon is imparted while a reflective surface would also have to balance out the momentum of the reflected photon with an extra dose of imparted momentum, with the energy of that opposite motion in the case of reflection going into waste heat for an absorptive surface.

Now I'm getting more interested in how this goes, anybody know how the tomorrow's weather is looking in Japan? Shaping up to be a nice day to launch an interplanetary space-kite?

[Q*Bert]

[delurk]

[Rufus Polson]

Oh, clever!

[Raos]

Potentially clever, perhaps too clever.

If I'm reasoning this correctly (and it's entirely possible that I'm not) then even the theoretical ideal efficiency of the system decreases with the mass of the system, to the point of no energy transfer at all at infinite mass.

Imparting X amount of energy as momentum on a mass m will produce a velocity v. To conserve momentum imparting the same X amount of energy on a mass 2m, and only v/2 is produced. Different mirrors getting struck by the same force will accelerate at different rates. To balance the red-shift and maintain the same apparent frequency with the mirror-reference, the photons reflecting off of a mirror of greater mass would need to retain more of their initial energy/frequency since the reference is moving away more slowly. Thus the photons reflecting off of a more massive mirror give up less energy per photon than photons reflecting off of a less massive mirror.

It'd take some calculus to figure out precisely what the relationship would be (and I'm not that masochistic), but that would clearly seem to indicate that the more massive your system the lower the theoretical upper limit for energy extracted gets.

[Hephaestion]

Photo: Space Shuttle Atlantis Docks with ISS, Against the Sun

[Q*Bert]

[delurk]

[Raos]

That's just strange, that means that internal efficiency being equal you'd be better off with 10 separate crafts of 1/10th the mass and sail size than one larger craft. Very perplexing.

[Hephaestion]

Mystery of Martian ice cap's spirals solved

[Q*Bert]

[delurk]

[Tehanu]

Q*Bert! How delightful to see you delurking!

[Fidel]

At NYC sci fest, asking 'What if we're holograms?'

What if we are all 3-D holographic projections of 2-D data that exists in another universe? And what about human consciousness? Brian Greene says, "It's there, too." Ya wherever there is.
_________________
Democracy should more appropriately be referred to as Corporatism because it is a merger of state and corporate power. - George Washington

[Hephaestion]

Alka Seltzer in Spaaaaaaaaaaace!
_________________
"The dignity of an animal is measured by his capacity to revolt in the face of oppression." -- Mikhail Bakunin

[Fidel]

Scientists create artificial mini 'black hole'

[TS.]

The Ikaros experiment is underway, with the unfurling of the solar sail. Hopefully we will get some answers on whether or not it is a viable technology fairly soon.

[Raos]

The solar sail has apparently been a success! Acceleration due to the force of striking photons has been measure. The force is quite tiny, but apparently in the range that the scientists were expecting.

JAXA: Small Solar Power Sail Demonstrator 'IKAROS' Confirmation of Photon Acceleration

[TS.]

Cool! Hopefully there will be some way to make it practical some day.
_________________
"Question with boldness even the existence of a God; because, if there be one, he must more approve of the homage of reason, than that of blind-folded fear." - Thomas Jefferson

[thwap]

Good quality youtube video:http://www.youtube.com/watch?v=LNW4-4uq2C8
_________________
Man! I hate them fancy-lads!

[Raos]

So, Japanese solar sail = total success.
NASA's solar sail? Unknown, since they kind of lost it.

NASA solar sail lost in space

[Raos]

So speaking of space as a frontier, Voyager 1 left the outward solar wind behind 4 months ago and hasn't looked back since.