Solarsail

[mental_avenger]

<font color="yellow"> One problem is if you get any where neer that speed in our solar system you are in big trouble due to all th "junk" in orbit around the sun. You must be in clean Intersteller space. </font><br /><br />The interstellar medium would be fatal to a normal spacecraft at any fraction of c above about .2c. A solar sail would be destroyed long before it attained anywhere near .3c, let alone .7c. Collisions with even microscopic particles at those velocities would vaporize solar sails and spacecraft hulls alike.<br /> <div class="Discussion_UserSignature"> <p style="margin-top:0in;margin-left:0in;margin-right:0in" class="MsoNormal"><font face="Times New Roman" size="2" color="#ff0000"><strong>Our Solar System must be passing through a Non Sequitur area of space.</strong></font></p> </div>

 

[mental_avenger]

<font color="yellow"> One thing that I find amazing is that the sail gets pushed twice, once as the light hits, and one more time when it is emitted from the angle of incidence. </font><br /><br />Incorrect. There is no magic creation of energy. When a photon strikes a molecule, it is absorbed, the wavelength and vector information stored in the spins of electrons of the molecule. The molecule then emits a photon with the same characteristics of the original photon. There is no “push” created from the emission of a photon. <br /><br />Currently, there is still a debate about whether a photon provides “push” when it strikes an object. The classical “radiometer”, so often cited as an example, may operate on a different principle.<br /> <div class="Discussion_UserSignature"> <p style="margin-top:0in;margin-left:0in;margin-right:0in" class="MsoNormal"><font face="Times New Roman" size="2" color="#ff0000"><strong>Our Solar System must be passing through a Non Sequitur area of space.</strong></font></p> </div>

 

[nacnud]

We've had this discussion before; unfortunately the crash wiped it all away. <br /><br />Are you still going on about the billowing of the sail causing it to only move away form the light source? I showed you that was wrong back then. Any control mechanism capable of steering the sail such as small movable sails at the corners or a weight on a stick is capable of changing the centre of force or the centre of mass, or both, to account for this very small effect.<br /><br />Also I showed that the radiometer does work by light pressure, so long as it is in a very good vacuum, other wise a different process occurs see: Crook’s Radiometer [wikipedia] for a full description.<br />

 

[henryhallam]

<font color="yellow"><br />Currently, there is still a debate about whether a photon provides “push” when it strikes an object. <br /></font><br /><br />There is no debate about this. It is the principle of operation of all tested types of hydrogen bomb.<br /><br />Photons are massless but have momentum p = h/wavelength.<br /><br />It follows by conservation of momentum that if the light is incident to, and reflected from the sail at some angle to the normal then the sail will experience a force in the direction of the normal, i.e. at an angle to the direction of the light source.<br /><br />I do agree that billowing and rotation of the sail may be problematic, but presumably simulations of this can be carried out.<br /><br />It has been demonstrated using a device similar to a Crookes radiometer (in a very high vacuum, different to the kind sold as toys which operate due to something similar to eddy currents in the thin atmosphere) that nearly twice the force is experienced when using a reflective surface as opposed to an absorbing surface. <br /><br />This is consistent with the hypothesis that the emission of a photon provides a push (and this makes perfect sense given that photons have momentum). <br /><br />Edit: typo

 

[CalliArcale]

I noticed this question didn't get answered earlier, so I'll answer it. <img src="/images/icons/wink.gif" /><br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>1) do we have plans of building a real solar sail at all? or is Russia in charge<br />of the sailing <p><hr /></p></p></blockquote><br /><br />Russia is not in charge of this mission at all. A non-profit mostly-American group called the Planetary Society (founded by Carl Sagan, hence the spacecraft name "Cosmos") is entirely responsible for the spacecraft and its mission. Russia is merely providing the initial boost from a Volna missile. It's effectively a commercial flight as far as they're concerned. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[chebby]

Mental, I don't know, I just took that website yurkin posted for its face value. Nevertheless, I never assumed energy is created. I thought that reflected light’s wavelength would slightly increase (lose energy) and that where the energy would come from (using p = h/wavelength)<br /><br />Btw, I found a website that shows that most of the sun's intensity is in the visible spectrum or lower frequency. Therefore there is no reason to worry about higher frequencies not being reflected, they don’t amount to that much push. So disregard that part of my previous post.<br /><br />http://csep10.phys.utk.edu/astr162/lect/light/****-sun-ant.gif<br />

 

[mental_avenger]

<font color="yellow"> Are you still going on about the billowing of the sail causing it to only move away form the light source? I showed you that was wrong back then. </font><br /><br />Correction, you presented your opinion. The discrepancy in the model is still there, and for the same reasons.<br /><br /><font color="yellow"> Any control mechanism capable of steering the sail such as small movable sails at the corners or a weight on a stick is capable of changing the centre of force or the centre of mass, or both, to account for this very small effect. </font><br /><br />A “weight on a stick” will not do it. Neither will moveable sections, louvers, etc. I presented the only viable method of allowing a light sail to reduce orbital radius. Do you recall what that was?<br /><br /><font color="yellow"> Also I showed that the radiometer does work by light pressure, so long as it is in a very good vacuum </font><br /><br />Perhaps I worded that badly. What I still have not seen is how that is accomplished. The newest models that show photons being absorbed and new ones emitted (as opposed to being “reflected” or “bounced off”) create questions that the old model does not answer. Exactly what is taking place may be the answer to getting some real efficiency from solar sails.<br /> <div class="Discussion_UserSignature"> <p style="margin-top:0in;margin-left:0in;margin-right:0in" class="MsoNormal"><font face="Times New Roman" size="2" color="#ff0000"><strong>Our Solar System must be passing through a Non Sequitur area of space.</strong></font></p> </div>

 

[mental_avenger]

<font color="yellow"> It follows by conservation[sic] of momentum that if the light is incident to, and reflected from the sail at some angle to the normal then the sail will experience a force in the direction of the normal, i.e. at an angle to the direction of the light source. </font><br /><br />See my above reply to nacnud. Since it is clear that light is not “reflected” from a surface per se, what is really happening there?<br /><br /><font color="yellow"> I do agree that billowing and rotation of the sail may be problematic, but presumably simulations of this can be carried out. </font><br /><br />I have run these simulations, and the result was always the same. I only found one practical way (which does not required input of energy or propellant) to counteract the rotation of the sail.<br /><br /><font color="yellow"> This is consistent with the hypothesis that the emission of a photon provides a push (and this makes perfect sense given that photons have momentum). </font><br /><br />I have always found this to be contradictory, an oxymoron of sorts. People refer to light as electromagnetic waves when it is convenient, and as particles when it is convenient. For instance, it would be difficult to provide an explanation of how an electromagnetic wave would provide “push”. While I understand the basis of the wave-particle duality hypothesis, I suspect that there is something going on there that would explain a lot of things, if we could just figure it out. Wave-particle duality is probably the biggest cop-out by physicists in recent history.<br /> <div class="Discussion_UserSignature"> <p style="margin-top:0in;margin-left:0in;margin-right:0in" class="MsoNormal"><font face="Times New Roman" size="2" color="#ff0000"><strong>Our Solar System must be passing through a Non Sequitur area of space.</strong></font></p> </div>

 

[nacnud]

<font color="yellow">Wave-particle duality is probably the biggest cop-out by physicists in recent history.</font><br /><br />It's not really a cop out it works perfectly well in maths its just the translation into English falls down. I'm a bit rusty but I'll look it up for you, might take a day or so as I'm a bit busy these days - see the thread in FS about the EU.<br /><br />By the way, if the centre of force on the sail from the light is in the same place as the centre of gravity where does your turning moment come from in an angled sail.

 

[gofer]

Too bad there is no page in English, but yes, it's among their projects: http://www.laspace.ru/rus/projects.php I was actually looking for info on their ballute re-entry system and saw the solarsail in there as well. In fact, I believe they'd already built 2 units before, but there were launcher separation (I think another organization is responsible for it) problems? Hopefully, it gets into orbit this time and we can see if the concept is workable.

 

[mental_avenger]

<font color="yellow"> It's [wave-particle duality] not really a cop out it works perfectly well in maths its just the translation into English falls down. </font><br /><br />Not so. If you try to treat light as a wave, as in the current discussion for example, it doesn’t work. Other instances cannot be resolved with light as a particle, such as light being part of the electromagnetic spectrum. There is no “translation” problem, but there is a definition problem. I think that when someone discovers the actual nature of light, and how it is able to be perceived as either a wave or a particle, depending upon the circumstance, then we may have cracked one of the biggest secrets of the Universe. It might even lead to understanding the actual nature of gravity for the first time.<br /> <div class="Discussion_UserSignature"> <p style="margin-top:0in;margin-left:0in;margin-right:0in" class="MsoNormal"><font face="Times New Roman" size="2" color="#ff0000"><strong>Our Solar System must be passing through a Non Sequitur area of space.</strong></font></p> </div>

 

[star_sirius]

Cosmos 1 is scheduled to set sail at 12:46 p.m. PDT /1946 GMT /3:46 p.m. EDT Today. That's about 6 hour and 54 minutes from now!!! <img src="/images/icons/wink.gif" /><br /><br />http://www.solarsail.org/<br /><br />http://www.ctv.ca/servlet/ArticleNews/story/CTVNews/1119285473101_13/?hub=CTVNewsAt11<br /><br />http://www.spaceflightnow.com/news/n0506/21solarsail/<br /><br />http://news.bbc.co.uk/1/hi/sci/tech/4110912.stm <div class="Discussion_UserSignature"> <font size="0" color="#10bdee"><strong>A dazzling bluish luminosity from A distant south pacific.</strong></font><p><br /><img id="cb51e87e-8221-424c-8ff2-78c95122196c" src="http://sitelife.livescience.com/ver1.0/Content/images/store/11/15/cb51e87e-8221-424c-8ff2-78c95122196c.Large.jpg" alt="blog post photo" /></p> </div>