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Optical Levitation, Space Travel, Quantum Mechanics and Gravity

timothy posted about 8 months ago | from the where-is-the-tractor-beam-I-crave dept.

Science 82

An anonymous reader writes "Light doesn't just make things brighter; it can also push things around. Normally this "radiation pressure" force is so small you don't notice it. But if you get a really big mirror then you could use it to power a space ship to the stars. This is the idea behind solar sails. The impact of light is more obvious on small things. Scientists are thinking about levitation of a mirror that would be large enough to see with the naked eye. If this turns out to work, the motion of the floating mirror could be used to probe the physics that connects quantum theory and general relativity."

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light is a bully (0, Offtopic)

turkeydance (1266624) | about 8 months ago | (#47143893)

pushing things around like that. no more light-bullying!

Re: light is a bully (1)

WyldPhyr (3622571) | about 8 months ago | (#47143993)

Thats gonna be the slogan for the futuristic band of genetically mutated vampires... In the future! You can look forward to it.

Re: light is a bully (1)

Anonymous Coward | about 8 months ago | (#47145581)

This site is supposed to be about stuff that _matters_. Why are there articles about _energys_ here??

I doub it (0)

Anonymous Coward | about 8 months ago | (#47143935)

We all know that light makes things heavy [slashdot.org]

That's quite a leap (0)

Anonymous Coward | about 8 months ago | (#47144009)

From getting a big mirror (how big? how reflective? made of what? what prevents it from being pushed back itself?) to a "spaceship to the stars"...

Why does everything always have to be this quixotic "to the stars" nonsense?

Send what to the stars? Which star? For how long? You expect to be alive when it gets to the star?

Re:That's quite a leap (1)

Tablizer (95088) | about 8 months ago | (#47144233)

Okay, "To infinity and beyond!"

Re:That's quite a leap (4, Interesting)

sillybilly (668960) | about 8 months ago | (#47144455)

A trip to the nearest stars with the speeds attained by Voyagers I and II and then some, at the limits of our technology, would take on the orders of 70,000 Earth-years. Should it be done? Hell yeah! Do you expect to be alive? Hell no! But with huge solar panels living off of starlight per person carried, you could take a human colony into orbit to the nearest stars, and they could live there for millions of years. Mind you written history is like 8000 years old (Egyptian Pharaoh's and hyeroglyphs, or 11-13000 if you go with the Sanskrit writings), and modern humans (Omo remains) have only been around for 200,000 years, so a 70,000 year trip is quite a trip. But, you never know, humans on Earth may develop an AI that kills everyone, or a super intelligent genetically modified biotech photosynthetic microorganism that kills everyone and everything including trees, grass, lions, deer, fish.. and emerges as the "winner" back home as the only surviving species, well, at least these folks far away would be safe, at least for a while, till this super intelligent life form chases them down too and eats them too. But at least they get some time to figure out how to defend and stand a chance, possibly by creating their own, friendly superintelligent artificial intelligence silicon/organic android microbe that's better than themselves so it could kill them, but luckily it doesn't, but like a good guard dog, protects them from the attacks of the Earth based microbe, that come after them in say, 1000 years (if they have figured out a 70x faster ways to make the same trip.) See a thousand years is a long time to think things through.

The propulsion system should use extra-solar system harvested hydrogen atoms (they are like 1 H atom per cubic mile or something like that), accelerating it to near speed of light through special cyclotrons, then as the relativistic mass takes over and things get out of sync, special coiled linear accelerators continuing it, and you can get almost any kind of mass out of each atom, and get a great propulsion kick, impulse out of each, for rotation and speed control, or for further accelerating, being mindful that halfway through the trip you have to start decelerating, and such propulsion would still beat the simple light propulsion by orders of magnitude, because the impulse per energy expanded ratio is much better than with simple light. It's true that you're creating mass out of energy as you build the mass of each proton up, and shooting off pure energy as mass is equivalent to shooting off pure light as mass, so there is an optimum velocity, optimum ejection speed dependent on the economics of harvesting each atom from the really thin galactic vacuum vs. economics of not building up too much relativistic mass into it and wasting energy as mass, as in case of a light propulsion. You may have to resort to pure light propulsion in case you cannot find any hydrogen atoms whatsoever within 100 cubic miles or so, such as intergalactic space.

In closer quarters, on rotating cylinder space modules near Earth orbit or Lunar orbit, such propulsion, including light propulsion is pure absolute economic waste, compared to specific impulse gained per size (mass, volume) of the drive, as we have plenty of matter to waste, if nothing else, solar wind close to the Sun is pretty matter rich, visible with things like Aurora Borealis. In particular even a cyclotron drive on a rotation cylinder station may not be the economic optimum to align solar panels and control orientaton, rotation speed and orbit, but instead a liquid oxygen/calcium metal energy cash could be used near the Moon and on the Moon's surface. See life down here on Earth uses ATP (high energy adenosine tri-phosphate) as the energy cash, and all processes within all lifeforms respect the resource limit of energy cash, and all processes either generate ATP with food or light energy from ADP (low energy adenosine di-phosphate) plus P, phosphoric acid, APP + P + energy ---> APPP, or APPP ----> APP + P + energy. So, similarly, near Earth or Moon orbit low energy density solar power or efficient high energy density nuclear power could be used to generate the liquid oxygen/calcium metal energy cash, and used efficiently on spacecraft and other industrial processes, just like fossil fuels (refined crude oil) are used as energy cash/resource limit down on Earth. Up on the Moon there is probably a carbon shortage and no atmosphere anyway, so a fossil fuel economy based on crude oil doesn't work, even hydrogen(difficult to store and liquefy) is scarce, because water evaporates into space vacuum, all rock is vacuum dessicated with a beating Sun heat, but there is plenty of aluminosilicate rock, from which calcium and oxygen can be extracted. Calcium has the highest energy density of all metals with respect to oxygen reaction, but in absence of that, aluminum or silicon can be resorted to, each with greater difficulty, because calcium is relatively soft and can almost be pumped or squeezed into a reaction zone, aluminum is somewhat difficult, and silicon even more. Also calcium can be vaporized easier than either aluminum and silicon, and reacted in a vapor form with oxygen, though magnesium is better in this respect. The reason for the need for the calcium is to generate high pneumatic pressure from liquid oxygen, and pneumatic tools and propulsion systems can be used, either ejecting the gaseous oxygen, or better, ejecting the silicon/aluminum metallic slag rods in a nail gun fashion, together with the waste calcium oxide. Liquid oxygen by itself is not useful, as it takes forever to heat it with a solar panel to adequate pressure, a solar panel which would need to be large, and you can't really afford to lug that around, or to lug a nuclear power plant around with small mobile crafts. The amount of calcium per oxygen is probably very small, something on the order of 1% or 3% calcium by weight compared to liquid oxygen weight (i'm too lazy to do the calculations of how much it takes to heat oxygen from liquid to say 200 C power tool or 600-1400 C pneumatic nailgun drive temperature (i.e. not too much of the siliconaluminum slag surface should melt/react while being shot out of the barrel by high temperature oxygen, that's what sets the upper temperature range, self ignition)). You can't really lug a nuclear power plant around on each small mining craft, and batteries suck at power density, but 3%calcium or magnesium metal / 97% liquid oxygen can give you quite an energy density and pneumatic power.with it, and we got plenty of oxygen to waste near the Moon, at least in the beginning centuries of space station construction. You may also be able to get electricity out of 50% Ca/50% liquid oxygen through a suitable "fuel cell" with (possibly molten) electrolytes that dissolve the Ca 0 metal--->(Ca++) + 2 (e-), then react the electrolyte with oxygen without dissolving the CaO, instead flaking it into a separate floating or submerged mass. Providing the oxygen surface for access to the electrolyte is complicated, possibly a second, unmixable electrolyte.contacting the calcium electrolyte, the oxide separating at the interface. Differing density organic solvents might work, where one dissolves only Calcium ions but no oxygen, the other oxygen without dissolving the calcium, (like hemoglobin, o2 does not have to ionize as long as at least one of the compounds, calcium fully ionizes and has no other way to react, the whole energy is electrolitically harvestable), and in the reaction zone the two could interact in a solvent extraction-like fashion, forming mini-droplets from which the calcium oxide would have to be centrifuged/filtered, the solvents phase separated, and recycled to their reaction zones. Solvents stable and resisting both such oxidizing and reducing conditions and still doing what they are supposed to, are difficult to come up with. So the simply pump/squeeze solid calcium sticks into a tiny bead thermite-like ignited liquid oxygen/calcium reaction zone (possibly of oxygen resisting iridium metal or similar construction), the heat conducted to heat the rest of the liquid oxygen to the desired temperature should work for now until someone can come up with a fuel cell/battery that's still compact enough, and can get direct electricity/motors/nailgun propulsion without heating and ejecting high temperature material into outer space vacuum.

One more thing: submarine like nuclear power is probably the most efficient short term energy solution on the Moon, with one caveat - on a submarine you have infinite amount of coolant available in the form of seawater, but on the Moon you lack a good coolant. Geothermal cooling doesn't really work, because the soil is so insulating, the insides of the Earth stay molten as lava, so you run out of thermal capacity pretty fast when you try to inject heat underground. Air cooling is unavailable either, and the only remaining option is blackbody radiation cooling, which is nasty, it requires a complete redesign of nuclear power, because the heat rejection temperature starts around black-smith red-heat of 600C, the Carnot efficiency with such a high heat rejection temperature being dismal, and possibly only noncorrosive helium gas pebble bed (pebble beds are nasty to construct and can shift) reactors at 1500C to 600C coolant temp are usable, even corrosive liquid sodium at 800C to 600C cooling is no good. So direct electricity solar power shines in respect to this nuclear coolant issue, but for start you still probably have to go with a nuclear power plant, before you can develop a solar panel factory on the Moon itself.

Re:That's quite a leap (1, Interesting)

sillybilly (668960) | about 8 months ago | (#47144491)

A mobile nuclear power plant drilling for geothermal cooling, staying for a while, then moving on could work for start, but you can't return to previous locations as the geothermal region there would still be hot for years, and unavailable as a coolant. But a moderate 100C-200C nuclear heat rejection temperature could be attainable this way, assuming the initial geothermal condition of the Moon is the same as down here on Earth, near 0 C or 20 C, room temperature.

Re: That's quite a leap (0)

Anonymous Coward | about 8 months ago | (#47144511)

that's what she said

Re:That's quite a leap (2)

sillybilly (668960) | about 8 months ago | (#47144531)

Also, providing the oxygen surface to the electrolyte is not that complicated, as the calcium ion dissolving electrolyte might react directly with gaseous oxygen, with the surface scraped, the electrolytic potential harvested as Ca++ concentration difference between the metal and oxygen zones, as in concentration batteries. Yeah, you don't need a second electrolyte bs for oxygen reaction.

Re:That's quite a leap (0)

sillybilly (668960) | about 8 months ago | (#47145525)

Calcium is the universal reductant, but it's not the highest specific energy density material to use in a metal/oxygen electrochemical cell weight-wise. See http://en.wikipedia.org/wiki/F... [wikipedia.org] and http://en.wikipedia.org/wiki/M... [wikipedia.org] –air_electrochemical_cell Beryllium/oxygen leaves everything else in the dust, but in it's very rare, and in its absence the abundant aluminum/oxygen battery is more energy dense weight-wise than calcium/oxygen (though it's harder to find an electrolyte that will ionically dissolve aluminum to later react with oxygen), and even the also abundant magnesium/oxygen is better, weight-wise. This is only a concern when you use 50/50 (or, more exactly the stoichiometric amount) of metal/oxygen in a battery cell to get electricity out of it, with the oxide recyclable through calcium reduction or a separate electrochemical process dedicated to aluminum or magnesium oxide, and is not as relevant when you use the 3% metal/97% liquid O2 pneumatic propulsion system, with the oxide ejected/discarded too, as calcium will be made in large quantitites as the universal reductant of even magnesium and aluminum, both of which will be left intermixed in the metallic residue with each other and oxygen and take extra effort to separate out for use. Also, using aluminum in a direct combustion way may be difficult, and it may have to be finely granulated, because of the protective oxide layer that forms, and it's impossible to vaporize, unlike calcium, which if, necessary, can be used in a vaporized way to react with oxygen in a burner, but nothing beats magnesium in energy density and ease of vaporization, so one may find that the energy cash may actually end up being magnesium metal/liquid oxygen, because of both energy density/weight and also ease of vaporization/combustion considerations.

Re:That's quite a leap (2)

sillybilly (668960) | about 8 months ago | (#47145549)

Oops, made a mistake there, the magnesium/o2 battery is only 2789 Wh/kg, while calcium/o2 is 2990 Wh/kg, according to the wikipedia article, with oxygen included, it's only better if oxygen comes from the atmosphere, like down here on Earth, so no, magnesium is not better in the energy density respect weight wise, only ease of vaporization-wise, but as calcium is so reactive, and also very soft, it is most likely easy to ignite in the solid form with an iridium (or maybe tungsten(burns) or platinum(melts)) resistance wire with oxygen present in the reaction chamber, and also easier to squeeze because of it's softness (though it's harder than lead, and can be cut with a knife only with difficulty.) and if this softness/vaporization becomes an issue, sodium/oxygen may be good, as sodium is even softer and easier to vaporize/liquefy, but the energy density now drops to 1677 Wh/kg, or half.

Re:That's quite a leap (3, Interesting)

Prune (557140) | about 8 months ago | (#47147587)

You like talking to yourself?

Four replies to oneself. I think it's a new slashdot record for a non-AC poster.

More importantly, you need to review some of the things that you wrote, because they don't pass the smell test. An example is the suggestion of using beryllium. There are less than 100 kt of mineable beryllium in the world, and most of that is needed for other applications (nuclear, ceramics, etc.). Beryllium exposure also does very nasty things to human biology. 0 points for practicality.

Re:That's quite a leap (1)

sillybilly (668960) | about 8 months ago | (#47152121)

Yes beryllium is one of those things way off on a tangent asymptote. By the way there are a lot of nonspark tools for explosive fire safety environments made of beryllium-copper bronze, though the beryllium percentage is low. It is very toxic, but has surprising strength and light weight. It's rare, but not as rare as say rhenium or iridium used in high temperature oxidation resistant things like fighterjet turbines and electric sparking resistant switch contacts, or even spark plugs. The toxicity is mainly due to people being unaware of it. There are plenty of highly poisonous mushrooms in the world living symbiotically with many forests and other plants, and as long as people don't ingest it or handle it wrong, they can coexist with us in the world, just like objects made of beryllium, or even nonsparking beryllium bronze.

There are other things that don't pass the smell test, such as solar panels collecting starlight energy - you need like a whole planet's area's worth of solar panel per person, not even talking about the jungle you're taking along, that contains elephants and tigers and ants, and such, Noah's Ark style.

Another thing that doesn't pass the smell test is the communication to long distances.. I think we lost radio contact with the Voyager space probes, so their twitter account only displays their estimated distance from us, in light-hours or something like that. The Voyager probes slingshotted off of Jupiter's orbit, making Jupiter drop someting like 0.1 nanometer in orbit closer to the Sun, and that energy used to propel the Voyager probes. If one actually does the calculations it's more likely something like one femtometer or attometer closer to the Sun in orbit. Whoever came up with the slingshot idea was a very clever guy, kudos to him. So anyway, radio contact may be impossible even with a highly directional huge solar panel the size of a planet array per person, so we may have to resort to sending flare signals, kind of simplified Morse code, such as they would watch with a telescope for nuke flashes going off near the orbit of Pluto, sufficiently away from the Sun, at a preagreed location, and the sequence of flashes would be tee tee tah tah kind of Morse code. I don't know if they'd have the resources to also signal us with flares. Yes, there are lots of difficulties with going to the nearest stars. But one can dream about a time when we have people and eartian elephants at Alpha Centauri and such stars nearby, a few light years away. And with a cyclotron drive ejecting captured particles near the speed of light, continuous acceleration close to the speed of light might be possible, say 70% cutting total travel time to something like 1000 years.or maybe even 200 years. That's not such a long time, as current space projects with the Voyager probes had to wait for decades before it was time to get the results back, such as outer solar system planet flybys..

Also with the calcium/liquid oxygen energy cash used for power tools and such, an issue is venting, as you can't continuously vent oxygen into the living/working quarters, and upset the 21% O2/79$ He or N2 balance, so all power tools would have a pneumatic power chord/tube that also contained a return chord/tube that would vent the exhaust O2 gas into outer space, or to be recycled.

Also helium generation from hydrogen via neutron bombardment is difficult, and if successful, it would generate so much friggin power and heat, that cooling the ship would be an issue. The neutron absorption cross section for hydrogen 2, i.e. deuterium is very low, and it must be even lower for hydrogen e, i.e. tritium, but each successful tritium neutron capture to "hydrogen 4", that has no other common name, probably generates helium very fast plus a lot of energy.. I'd have to look up the literature, but they say fusion as a power source is not possible with these portable neutron generators, because the rate of neutron generation is so small compared to the energy invested, I mean you're talking 1 or 10 or 100 neutrons per second compared to 6.023x10^23=6.023x100 000 000 000 000 000 000 000 atoms of helium in 4 grams of helium, (which, because of the low balloon density, would be quite a bit of gas.) But even at that very low rate you should still be getting an energy profit, or you wish you would, but it ain't like that in the real world. Neutrons are nice because they can approach nuclei directly without electrostatic repulsion. Maybe there are ways to enhance neutron capture by tritium, such as cryogenic temperatures of outer space, and a heat engine based on a temperature difference of, say 100 K from tritium portable neutron generator bombardment fusion to the 3 K of outer space,( and because the low temperature term is so small in the Carnot formula, the theoretical cycle efficiency is huge) might work.

Yeah I have lots of rambling ideas when I let my mind go on a trip, most of them don't pass the smell test as is, but could be used as inspiration by others, well, then it's worth it.

Re:That's quite a leap (-1)

Anonymous Coward | about 8 months ago | (#47144567)

Sure, sci-fi was fun. When I was 13. Then I grew up. What's your excuse? Do you clutch your copy of The Millennial Project to your chest before going to sleep every night?

Re:That's quite a leap (0)

Anonymous Coward | about 8 months ago | (#47144643)

Step away from the keyboard, take a deep breath, and spend a minute or two thinking about what you're trying to stay.

Re:That's quite a leap (0)

Anonymous Coward | about 8 months ago | (#47144763)

That's the whole thing, he's going to stay right here. So is everyone else.

Re:That's quite a leap (3, Interesting)

sillybilly (668960) | about 8 months ago | (#47144765)

With a 70,000 year trip corrosion is a big issue, so there may have to be a lot of gold used in the construction of the ship, and as the ship has to be quite a sizable thing considering psychological factors of having a society, and minding that all the gold ever mined on Earth fits into like a 2 km cube, there are issues here. Probably something like a 20 walled ship is needed, with vacuum pumped down to absolute vacuum by the 5th wall, and then corrosion is a nonissue there, and the inner 5 layers have to constantly be renewed/replaced, at least once every 1000 years. Also, once the pioneers/settlers arrive, and there's gotta be floating debris or planets around each star even if there is no liquid water bearing planet, how will they know what to do, would they still have the skills to fabricate things? While traveling there, there may be some outer solar system objects we call comets that have crystallized ice on them, going in the same direction with the same speed as the ship, therefore capturable if sufficient steering is available (what a minuscule chance for such a thing), and then skill can be kept up on the way there to dismantle/process "stuff" found in the vast emptiness of outer space, stuff that should be very dense once arrived near that star. Even in absence of that, practice material and laboratories, and mechanical workshops would have to be kept up, with possibly repair spacewalks, leading to a sizable ship. As there is always a chance of hitting small meteorites at say 30-200,000 km/s, and some units leaking to full vacuum, many completely isolated units would have to be maintained, say even 20 or 50, and ending up with only one surviving by the trip end able to carry and sustain the whole crew would have to be considered. If the different 20 walls rotate with respect to each other, then a small meteorite hole may create a leak into the interstitial wall spaces, but as the holes are not lined up, the vacuum pumps might be able to keep up and scavenge the escaping air, even calcium of vacuum tube barium or liquid helium traps that capture any atoms striking them could be a way to save stuff from leaking in the outer layers. The tighter the spacing between the walls, the less the leakage, and as soon as a leak is detected, there could be a certain preprogrammed rotation misaligning the hole away from each other to maximum distance, then a sudden crash, a halt of the relative rotation of the walls to each other, until the holes are patched, and sliding rotation can be restarted. I don't know what the economic optimum number of walls is.

As nitrogen is scarce, but hydrogen and helium are abundant in outer space, diluting oxygen harvested from comet rocks could be done, but not with hydrogen that forms an explosive mixture with oxygen, but with helium. The helium might have to be fusion generated from the harvested hydrogen, if nothing else, through cyclotron or energy inefficient portable neutron generator bombardment. And everyone would get used to the chipmunk sound of helium balloon inhalation you can hear down here on Earth.

Also, communication with the speed of light would take a few years to go back and forth, to exchange hello's, draining quite a bit of power from the ship for dish/antenna use, and in case the crew on this ship messes up and ends up in deep doo doo sending out an SOS to us, we can reply to them with the phrase/video transcript from Mad TV's Dolla Bill Montgomery's Real Motherf****in Talk Mother's Day episode, "Talk to the hand, you're on your own, motherf****!" https://www.youtube.com/watch?... [youtube.com] We can give them advice, but not much else, advice they have to wait 4-8 years for to arrive. For psychological reasons, a reality show transmitted from them and programming transmitted to them would be neat, each without waiting for a reply to arrive, at least not reacting to one for the few years it takes to transmit the message. Their internet ping timeouts would have to be set to the corresponding few years, if they want to be part of the Internet on Earth, as they download something, and hopefully they wouldn't have to get the daily security patches and be constantly told to upgrade upgrade upgrade their computer systems every 6 months, like we're supposed to do it back home on Earth.

Re:That's quite a leap (1)

ByteSlicer (735276) | about 8 months ago | (#47145303)

and minding that all the gold ever mined on Earth fits into like a 2 km cube

It would loosely fit, the latest estimates are a few orders of magnitude less [bbc.co.uk] : 20-50m on each side. Then again, nobody really knows.

Re:That's quite a leap (1)

sillybilly (668960) | about 8 months ago | (#47152151)

As the Moon does not have a molten lava to sink all the tungsten, uranium, iridium, osmium, lead, gold, platinum and or course nickel/cobalt/iron into a solid metallic core, the abundance and minability of these things might be profitable on the Moon even for oceanic Earth-dops of cargo with a parachute.

Re:That's quite a leap (2)

Rockoon (1252108) | about 8 months ago | (#47145757)

With a 70,000 year trip corrosion is a big issue

The biggest issue is that after your 70,000 year trip, you arrive in a star system that humans have inhabited for 69,000 years already. Thats a full stop right there.

Re:That's quite a leap (1)

phorm (591458) | about 8 months ago | (#47147113)

corrosion is a big issue

There are other ways to prevent corrosion - at least rusting - other than gold-plating, and of course any components in an non-oxygenated area don't need to worry about this. You could possibly take advantage of vacuum here, by using airlock mechanisms to rotate airflow between areas which would otherwise be O2 free.

Re: That's quite a leap (1)

Anonymous Coward | about 8 months ago | (#47144963)

are you on drugs?

Re: That's quite a leap (0)

Anonymous Coward | about 8 months ago | (#47145133)

Pretty sure that's cocaine talking and not bill

Re: That's quite a leap (1)

sillybilly (668960) | about 8 months ago | (#47152157)

No, I get a natural, "organic" high and I love it, I can go on mindtrips to the nearest star and back.

Re:That's quite a leap (0)

Anonymous Coward | about 8 months ago | (#47145013)

A trip to the nearest stars with the speeds attained by Voyagers I and II and then some, at the limits of our technology...[SNIPPAGE]

Jesus. Your really really need to get laid. Please. Pretty please. Get fifty bucks and find a prostitute before you end up on CNN. Please.

Re:That's quite a leap (0)

Anonymous Coward | about 8 months ago | (#47145025)

How dare you you Luddite! Don't you realize the species must get off this rock!!??? It's very important!

Re:That's quite a leap (0)

Anonymous Coward | about 8 months ago | (#47146851)

A trip to the nearest star, Proxima Centuri, could be made within the lifetime of an astronaut, using 1950s nuclear pulse technology. If a star is five light years away that doesn't mean it will take five years travelling at the speed of light to reach. Travelling at 0.08c it would take around 50 years in the astronauts frame of reference to reach the nearest star.

Re:That's quite a leap (1)

Gavagai80 (1275204) | about 8 months ago | (#47146975)

Can you get more acceleration out of scooping the interstellar hydrogen atom than you lose from that atom hitting your ship at high speed in the wrong direction?

Re:That's quite a leap (1)

sillybilly (668960) | about 8 months ago | (#47152173)

If you have solar panels harvesting sunlight, and the ratio of energy harvested to impact by interstellar density vaccum gas ( couple atoms per cubig mile?), then whatever you harvest can accelerate up with a cyclotron (aka synchrophasotron) at eject them at very high speed. So in that case the answer is yes, but of course it would be falls if the startlight harvested solar energy were used to propel a boat or other transportation device at the gas-density prevalent in the atmosphere on Earth.

Re:That's quite a leap (1)

sillybilly (668960) | about 8 months ago | (#47176115)

Woah, I think my eyelids were half closed when I wrote that, before passing out asleep.

Re: That's quite a leap (1)

Dishwasha (125561) | about 8 months ago | (#47147457)

Yeah...what that guy said.

Re:That's quite a leap (1)

rossdee (243626) | about 8 months ago | (#47144473)

"Send what to the stars? Which star?"

A nearby star like Barnards Star would be possible (Flight of the DragonFly by Robert L Forward )

But I can see why some people might think its a Crazy Eddie idea

An Old Idea Resurrected - Again (4, Informative)

kenwd0elq (985465) | about 8 months ago | (#47144017)

There's nothing new about the idea of spacecraft being propelled by light pressure. There was an Arthur C. Clarke story published in "Boy's Life" in the early 60's about sunlight powered "sailing yachts" in a race from Earth orbit to the Moon. Or the Niven story "The Fourth Profession", in which an alien trading ship arrives at Earth, wanting humanity to build a launching laser to send the crew on the next leg of their journey.

And it's been 30 years since Niven & Pournelle published "Mote In God's Eye" in which an interstellar probe riding a the combined beam of battery of laser cannons arrive in human space.

So if actual human physicists are finally going to get around to proving the concept, so much the better!

Re:An Old Idea Resurrected - Again (2)

50000BTU_barbecue (588132) | about 8 months ago | (#47144073)

Don' forget Forward's Flight of the Dragonfly. Bonus: about half the novel is a technical addendum of the proposed starship design.

Robert L Forward had the added bonus of being a bona fide physicist and engineer. He didn't goof around, he proposed a terawatt laser system to propel the ship ... with a return stage.

Re:An Old Idea Resurrected - Again (1)

Jason Goatcher (3498937) | about 8 months ago | (#47144295)

I've read all those books, how nerdy is that? :)

Re:An Old Idea Resurrected - Again (1)

Bite The Pillow (3087109) | about 8 months ago | (#47144849)

The Wikipedia article traces it back to Maxwell and Kepler. And proving has been done, since trajectory calculations have included it since the 60's.

It just hasn't had enough potential to use in stead of other tech. It needs a killer app, one for which it is uniquely suited, to take hold. Name that and it is a done deal.

Re:An Old Idea Resurrected - Again (1)

TapeCutter (624760) | about 8 months ago | (#47144959)

Propultion is not the problem, there's a glut of possible technologies that coud drive a ship to a nearby star. Food and water are the problem, the most sphisticated biodomes here on Earth only last about a year before they decay into poisinous organic goop. When we have the technology and political will power to fix the life support systems on spaceship Earth we will have the technology to feed interstellar colonists on their journey, only then then we can talk about getting off the solar merry-go-round. Until that time we are "stuck" with robotic probes.

BTW: Aluminium fizzbies can already be levitated with lasers in the lab, what's left to be "proven"?

Re:An Old Idea Resurrected - Again (1)

kenwd0elq (985465) | about 8 months ago | (#47144987)

"Proven" is, perhaps, the wrong word. "Made to be practical", perhaps. A $5 radiometer from a craft store proves quite readily the idea that light has pressure. The trick will be, as with the nuclear fusion proposals that are perhaps twenty years in the future - and have been "20 years in the future" for thirty years now, to make it big enough and practical enough that we can extract usable amounts of energy from it.

Re:An Old Idea Resurrected - Again (1)

Smallpond (221300) | about 8 months ago | (#47145655)

Except that those don't work from light pressure [wikipedia.org]

Re:An Old Idea Resurrected - Again (0)

Anonymous Coward | about 8 months ago | (#47145007)

You're a loon.

Re:An Old Idea Resurrected - Again (2)

Smallpond (221300) | about 8 months ago | (#47145651)

Sending adult humans on a 70,000 year trip is pointless. If you want a human visit to the stars start thawing the fertilized eggs 20 years before arrival.

Re:An Old Idea Resurrected - Again (1)

Gavagai80 (1275204) | about 8 months ago | (#47147195)

Might as well wait until after landing to thaw.

Hmmm. (4, Informative)

jd (1658) | about 8 months ago | (#47144051)

There are two sorts of solar sail, those that work off photons (and, no, you don't need a mirror, since you can't afford the extra mass) and those that work off ionized particles being emitted from the sun. Ionized particles have much more momentum and are generally considered superior.

A solar sail that is 50 Km in diameter, attached to a 5 Kg probe, would accelerate that probe to 25% light speed by the time you reached the edge of the solar system.

If you built a car whose headlights could accelerate the car in reverse with photonic pressure, the headlights would vaporize a considerable chunk of the planet in front of you. You can do the calculation yourself. The equations are at http://www.physicsforums.com/s... [physicsforums.com]

Re:Hmmm. (2, Informative)

Anonymous Coward | about 8 months ago | (#47144289)

It's just a detail in your post, but I didn't know solar sails got bigger and heavier as they cooled in such a way that their size in kelvin-meter and mass in kelvin-grams stayed constant. Fascinating.

Re:Hmmm. (1)

jd (1658) | about 8 months ago | (#47145299)

Space is filled with dust, so yes, as you travel away from the sun, as the solar sail cools (since less heat is reaching it, inverse square law) it does indeed get heavier. It also gets heavier as it accelerates, due to relativity. It would be interesting to determine what the precise function is. The density of space dust is given in Carl Sagan's book, Cosmos, that was a companion to the series.

Re:Hmmm. (3, Informative)

pushing-robot (1037830) | about 8 months ago | (#47144303)

What did you use for the mass of the 50km sail?

Re:Hmmm. (1)

jd (1658) | about 8 months ago | (#47145311)

The calculation was done by NASA and published in a peer-reviewed paper in New Scientist in 1988, I think. As best as I can recall, the solar sail was assumed to also have an initial mass of 5 Kg and to gain mass at a constant rate (since the remnants of the accretion disk should be thinner the further out you go, but you travel through more of it per unit time). I forget what the rate was. As I recall, the paper noted that there would be extreme difficulty in having a sail of such a size that was structurally capable of withstanding impacts at the velocities involved within the permissible mass.

Re:Hmmm. (1)

delt0r (999393) | about 8 months ago | (#47146417)

New Scientist is NOT peer reviewed. It is in fact full of quite a lot of crap.

Re:Hmmm. (0)

Anonymous Coward | about 8 months ago | (#47145457)

What did you use for the mass of the 50km sail?

The calculations are left as an exercise to the reader.

Re:Hmmm. (1)

OglinTatas (710589) | about 8 months ago | (#47146965)

mass of sail = mass of napkin on which the calculations were done

Re:Hmmm. (1, Funny)

Nyder (754090) | about 8 months ago | (#47144367)


If you built a car whose headlights could accelerate the car in reverse with photonic pressure, the headlights would vaporize a considerable chunk of the planet in front of you...

That seems pointless, because you are going in reverse, think you'd want to vaporize the stuff that would be in the way.

Re:Hmmm. (1)

jd (1658) | about 8 months ago | (#47145313)

If you're wanting to get out of Dodge, what could be better than removing Dodge?

Re:Hmmm. (2, Informative)

Anonymous Coward | about 8 months ago | (#47144809)

Actually you absolutely positively DO want a mirror for a photon drive, since it doubles the momentum imparted to you by each photon (sans losses), and only leaves you holding the bag on heat input from those losses, rather than the entire battery of laser cannons. And also somewhat importantly, you can dump most of it to bounce the laser beam back at you and decelerate as you approach your target.

Light does more than push (0)

Anonymous Coward | about 8 months ago | (#47144079)

Yes, light can generate is minuscule amount of push, but it also generates several times more heat.

From what I know, typically by the time you got enough light to push something, you would have generated enough heat to fry it several times over.

Re:Light does more than push (1)

Arkh89 (2870391) | about 8 months ago | (#47144497)

Not if your using a perfect mirror (conductivity going to infinity, no Joule currents).

Re:Light does more than push (-1)

Anonymous Coward | about 8 months ago | (#47145053)

Sorry, Joule ... currents?

http://en.wikipedia.org/wiki/J... [wikipedia.org]

Could you perhaps point me in the direction of what you are trying to get at? The collective wisdom of self-taught slashdot geniuses really is terrifying.

Wagnerrp and his heat-modulated transistors... He should stick to software, that clown.

Khyber and his IPC approved soldering to graphite ... He should stick to his meds.

Laser, Atomic Bomb, (0, Offtopic)

Blaskowicz (634489) | about 8 months ago | (#47144155)

automatic transmission and transistor radio. Also X-ray, general relativity, computer and nuclear reactor. ACME, truck and road intersecting with rail tracks. Dynamite!, rocket engine and jet liner.

Re:Laser, Atomic Bomb, (1)

PolygamousRanchKid (1290638) | about 8 months ago | (#47144527)

No, I'm sorry, contestants must phrase their responses as questions.

Here are some more clues:

Bucky-ball enema moon tube escalator, Jimmy-Carter-built Baba Yaga affordable housing on chicken legs and dephlogistonated Moebius Yorkshire Pudding.

Re:Laser, Atomic Bomb, (1)

Thud457 (234763) | about 8 months ago | (#47149415)

Bucky-ball enema moon tube escalator, Jimmy-Carter-built Baba Yaga affordable housing on chicken legs and dephlogistonated Moebius Yorkshire Pudding.

Great, you just spoiled the whole new season of Dr. Who.
With the exception of flailing the sonic screwdriver around like a magic wand and yelling "RUN!". But those are a given with Moffat.

Re:Laser, Atomic Bomb, (0)

Anonymous Coward | about 8 months ago | (#47144691)


Re:Laser, Atomic Bomb, (1)

wonkey_monkey (2592601) | about 8 months ago | (#47145343)

Is that to the tune of the The Big Bang Theory theme, or Billy Joel's We Didn't Start The Fire?

Re:Laser, Atomic Bomb, (1)

Gibgezr (2025238) | about 8 months ago | (#47145765)

"Things I found in my father's barn."
I'll take "Oddities of English Cooking" for 500, Alex.

gasp! (0)

Anonymous Coward | about 8 months ago | (#47144341)

We could launch a 3D printer now and as it 3D printed a bigger and bigger sail we could build bigger and bigger solar arrays in space with the space elevator!

Golly gee, we really could get to the stars!

Re:gasp! (0)

Anonymous Coward | about 8 months ago | (#47144611)

and the material for the printing would come from ?

Re:gasp! (0)

Anonymous Coward | about 8 months ago | (#47144745)

A 3D printer that prints printing material, dumbass!

Re:gasp! (0)

Anonymous Coward | about 8 months ago | (#47144769)

Fucken A! Anyone who dares to question this is a LUDDITE and will stay on this rock forever!!!!

Re:gasp! (0)

Anonymous Coward | about 8 months ago | (#47144805)

Duh, space is filled with resources like sunlight, asteroids, lunar helium-3 and water. Space is just filled with stuff compared to this rock!

Not just light, ElectroMagnetic radiation (1)

steeleyeball (1890884) | about 8 months ago | (#47144439)

the interesting thing is you can force photons out of the way... effectively creating your own pressure gradient which provides accelleration in a direction of your choosing.

Re:Not just light, ElectroMagnetic radiation (0)

Anonymous Coward | about 8 months ago | (#47144519)

This is very cool and stuff, but you know you can't really do that. Right?

Optical... (0)

Anonymous Coward | about 8 months ago | (#47144749)

Optical computers, genetic catalogues, nano repair modules, forget all of that -
it's when you see a megaton of steel suspended over your head by a thread the thickness of a human hair, that you really find God in technology.

Anonymous Metagenics Dockworker, Morgan-link 3d-vision live interview.

The Facts! (1)

richardclark1985 (3667559) | about 8 months ago | (#47145097)

That is great the levitation theory and radiation pressure using the concept of solar sails is being tested. But, even if this test prove to be a great success, There is no possibility that we will get to see Space Travel in our life times. Ironic Isnt it?

Re:The Facts! (2)

wonkey_monkey (2592601) | about 8 months ago | (#47145335)

Ironic Isnt it?

No, it's not.

Re:The Facts! (0)

Anonymous Coward | about 8 months ago | (#47145351)

There is no possibility that we will get to see Space Travel in our life times. Ironic Isnt it?

I fail to see why that would be ironic. What definition did you use?

"Hard light" (0)

Anonymous Coward | about 8 months ago | (#47145275)

What about that team that managed to make light hand over more energy in the reflection "handshake" than it normally does?

The potential ideas for that hard light sound amazing if they could get it to work outside of a lab.
But space is pretty damn inert, so if you made something cool enough, it is easy to keep that temperature.
So if you were to do it there, could it be re-performed in space?

The only worry is there'd be so much light it would literally explode the damn ship. That is purely theoretical though.

Optical levitation etc (0)

Anonymous Coward | about 8 months ago | (#47145463)

Solar sails are powered by the solar wind, mainly hydrogen atoms, not photons. Light pressure is far too weak, AFIK, to move a space craft. Check your facts from sources that know what they're talking about. Bona fide researchers (not myself).

Usual /. (4, Informative)

hansraj (458504) | about 8 months ago | (#47145519)

The summary (and the headline) unnecessarily highlights space travel as a usage for radiation pressure and delegates the most interesting part as a footnote-ish last line. The /. crowd as usual starts shouting pros and cons of space travel, as if every comment on this page is not saying what has already been said a million time around here, and nobody to talk about the interesting part.

I wish someone with the right background in physics posted something more interesting about the fact that a group of researchers have come up with prediction of how a non-quantized spacetime (gravity) would look in the presence of quantized matter/energy. Apparently this would look different than a quantized background with quantized foreground (IANAP, so I don't know what is this all about) in a measurable way. If they can levitate a tiny but macroscopic mirror using light and balance it then giving it a gentle push would create a pendulum with no friction slowing it down. By probing the frequency evolution one can potentially get closer to actually knowing whether a quantum theory of gravity is the right way to unify QM and GR.

It's fascinating that such things are possible even in principle with existing technology. I wish someone would explain something more related to this.

Re:Usual /. (0)

Anonymous Coward | about 8 months ago | (#47151399)

I think their asking if the oscillation frequency of the mirror representative of a GR model of a pendulum or a QM model. I think they would need to consider the Poynting vector (directional energy flux) as the direction of energy of light is likely not going to be laminar.

I don't get it (1)

slashmydots (2189826) | about 8 months ago | (#47146085)

So it's light smashing into matter and imparting its energy onto it so that it moves. What's quantum about that? That's only Newton level physics.

Re:I don't get it (0)

Anonymous Coward | about 8 months ago | (#47146351)

have you tried plugging the mass of a photon into Newton's equations?

Re:I don't get it (1)

slashmydots (2189826) | about 8 months ago | (#47152449)

Hey moron, energy imparted onto a physical object makes it move. You don't need mass.

OOh don't break that mirror (1)

PyrousLavawalker (1716674) | about 8 months ago | (#47146303)

I imagine you would have more than 7 years bad luck for breaking this mirror!
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