LIGHT SAILS:

Post #70 :

Post #77 :

Post #80 :

Odd that if that is "not what was said"...that it is what is Posted in Post #70!!

Typical...!!!???

edited Post #70...not Post #71...My bad!!!

 

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My bad, Bells - I have changed my Posts to Read Post #70...

what paddoboy said was "Light has momentum:
Putting it simply when a solar sail absorbs a photon it gains momentum, when a solar sail reflects a photon it will gain twice the momentum.
Elaborating on this, due to conservation of momentum laws, Initially while the photon has momentum, after it is reflected, it has twice the momentum. That momentum must be conserved and so the sail gains momentum."

Bells, I posted the following link : http://www.physicsclassroom.com/class/momentum/u4l2b.cfm that clearly states :
" One of the most powerful laws in physics is the law of momentum conservation. The law of momentum conservation can be stated as follows.
For a collision occurring between object 1 and object 2 in an isolated system, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision. That is, the momentum lost by object 1 is equal to the momentum gained by object 2."
above quoted from : http://www.physicsclassroom.com/class/momentum/u4l2b.cfm

Yes I was mistaken when I was saying Post #71...that has been corrected.

However, paddoboy did state, in his Post #70 : "Elaborating on this, due to conservation of momentum laws, Initially while the photon has momentum, after it is reflected, it has twice the momentum. That momentum must be conserved and so the sail gains momentum."
He is stating that the Photon "after it is reflected, it has twice the momentum"... twice the momentum is a GAIN!!!
paddoboy then states :"That momentum must be conserved and so the sail gains momentum."

Bells, both the Photon and the Sail cannot gain momentum..."due to conservation of momentum laws"!!!


Bells, I refuse to comment on or reply to the rest of your Post.

 

You are absolutely correct Only Me...My Bad!!!

I meant Post #7o...I have edited my Posts to correct my "Senior Moment"!!!

Thank you Only Me, for pointing out my error.

 

My reference obviously [after the first sentence, was in relation to the sail]
I put that rather poorly admittedly, but I believe the meaning was reasonably clear.
Again dumbest man on earth, why do you not pick up theorist constant on his nonsense, or any of the other trolls and crazies we have spouting misconceptions? Why?
I mean you claim you are a stickler for exactness, proper spelling, and grammar, so why apply it all in my direction?

Maybe I should be ignoring you, as obviously you seem to have a death wish.
And I do not want to be a part of that.
I just thought that needed clearing up.

 

Advantages of Solar/light sails:
[1] No propulsion fuel needed.[lower launch mass]
[2] Cost saving:
[3] Continuous thrust and acceleration:
[4] Unlimited and constant flow of photons:

Disadvantages:
[1] Very large area needed to facilitate reasonable acceleration:
[2] Probably of a very delicate material:

 

An extract from a nice link.....
http://wiki.solarsails.info/index.php?title=Solar_Sailing_101
How Does Light Push a Solar Sail?
Light pressure was predicted in the late 1800s by James Clerk Maxwell using electromagnetism and Adolfo Bartoli using thermodynamics. It was first measured in 1900 by Peter Lebedev and 1901 by Ernest Nichols and Gordon Hull. Before then, the technology didn't exist to measure such a gentle force. Today, quantum mechanics and relativity can also be used to predict light pressure, and mission controllers deal every day with the subtle influence sunlight has on spacecraft.

Electromagnetism

Electric and magnetic field components of sunlight exerting force on a sail
The electromagnetic explanation begins with the description of sunlight as an electromagnetic wave. An oscillating electric field causes a perpendicular magnetic field to form, and vice versa. Together, this self-maintaining electromagnetic wave can travel through space, only losing energy or changing the frequency of oscillation by interaction with solid matter. When the wave is absorbed by a solid object, electric field theory predicts that the electric field will cause an electric current to flow in the surface of the material. Magnetic field theory predicts that the magnetic component of the light wave will exert a pressure into any material with a current flowing through it - just as a magnet pulls on a wire with a current. If the light wave is reflected from the object, the electric and magnetic fields will be in opposite directions as the originals, resulting in a force opposite the direction of the wave - that is, the same direction as the force from the original light wave. Thus, a mirrored object will experience twice the force of one that absorbs all the light.

Special Relativity
Einstein's theory of Special Relativity relates the energy (E) of particles to their mass (m) and momentum (p = mass × speed) by the following equation where c is the speed of light (299,792,458 meters/second):

• E2 = m2 c4 + p2 c2

If the particles have no momentum, then it reduces to the familiar E = m c2. Photons (light particles) have no mass, but they do have energy that is observed when sunlight warms your skin or generates power in a solar array. The equation becomes E = p c, which can be rearranged as p = E / c. Therefore, if you know how much energy there is in the sunlight absorbed and reflected by a solar sail over a period of time, you can calculate the momentum transferred to it. To find the change in speed, divide the momentum by the mass of the spacecraft.

At Earth's distance from the sun, sunlight has an intensity of ~1368 Watts per square meter (Joules per second per square meter). So, if a square meter object absorbs all that sunlight, its momentum will change by (1368 J) / (299,792,458 m/s) = 4.563×10-6 kg m/s2. If the sail also reflects the sunlight, its momentum will change again by the same amount, so the total momentum change will be 9.126×10-6 kg m/s2. That corresponds to a pressure of 9.126×10-6 N/m2 - about 9 micro-Newtons per square meter as stated previously.
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Please note the highlighted section for those Interested. This was what I was trying to get across, and that I believe any sensible average person, without an agenda would have seen.

 

Even the first sentence was suspect...
...if the meaning was "reasonably clear", I would not have commented on it.

paddoboy, there are Posters on this Forum who, for whatever reason, may not have the Knowledge or the ability to accrue it...I do not care to harass those less fortunate than myself.

paddoboy, by your own "Bragging", you are the Local "Cheerleader" and self appointed arbiter of all that is Mainstream Science...
You allow no excuses for any other Posters...but even in this discourse you claim "My reference obviously [after the first sentence, was in relation to the sail]" and "I put that rather poorly admittedly, but I believe the meaning was reasonably clear."
paddoboy you always have excuses for your actions/conduct/erroneous statements...yet you give no quarter to others.

I honestly believe that there may be Members or Readers of SciForums that actually want to learn Science!!
In that respect, we should all be trying to Post to aid learning...not just name-calling and accusations.


Now in response to your "Death Wish"...threat...comment...or whatever it was meant to be : I had numerous surgeries on my spine over the last few years and over Thanksgiving (November 26th) I had open heart surgery for a Quadruple Bypass....death will not come easy for me!!!

I am not sure about yourself, but being Permanently Banned from SciForums would be even less than a "Bruise" or "Sprain" to me...I have a REAL LIFE!!

I only hope to be soon back to teaching/tutoring, instead of laying in Hospital or recuperating at home!!!

 

billvon granted, there are many strange patents, but the one you cited is just for the construction of such a device, no claims are patented as to the method of functioning, or the benefits, and the examiner no doubt did forgo the requirement for a demonstration with super cooling/superconductivity required to be set up in the Crystal City VA offices. My references to "mouse milk" show how little effect is produced with so much effort by the not too heavy sails.

 

Apologies to all in this thread and the Mods...I should not have replied earlier when I did.
Just to clear up the above point as it seems as usual our friend has misinterpreted its meaning...although again, I'm certain that most were awake to what I was referring to.
What I was referring to was......
That since you have been given warnings and threatened with a permanent ban.
By ignoring that, you appear to want to get banned [your death wish] and probably drag me down with you.
I leave you to whatever it is you do best.

 

When solar/light sails are properly mastered, in all likelihood, they will be used in conjunction with gravity assists, and probably a limited form of chemical rocket propulsion also.

 

I tried, paddoboy...

I misinterpreted nothing... I clearly stated : "Now in response to your "Death Wish"...threat...comment...or whatever it was meant to be."
Ergo, I made NO FINAL INTERPRETATION of it, hence the whatever it was meant to be.

paddoboy, I do not want to see you or anyone that relies so much on SciForums for some meaning in their life, Banned.

I Post here while in Hospital or Recuperating - being Banned is in no way a "DEATH" for me, so your "Death Wish" comment is somewhat strange...to say the least!!!

At any rate, I am not the type of person to "drag" anyone "down with" me.

If you want to see me Banned, paddoboy, goody for you.

 

I also remember reading somewhere that "steering" has yet to be fully mastered?
http://www.nasa.gov/offices/oct/early_stage_innovation/niac/swartzlander_steering_solar_sails.html
This study seeks to look beyond the use of radiation pressure for thrust, and to explore a means of solar navigation whereby a solar craft would be steered by use of radiation pressure. The idea is based on a recent discovery by the study team. They found that transparent refractive objects may settle into a position where they feel a force that is perpendicular to the incoming light direction. This transverse force is akin to the lift experience by an airplane wing and other airfoils. Thus they call it “optical lift”. Objects in their experiments simultaneously thrust forward. The combination of lift and thrust allows for the optical steering of optical wings. In the coming year they will conduct experiments and computer modeling to advance this discovery for future space missions employing solar sails. The long-term goal is to devise a means to allow solar sails to navigate through space using only the power of sunlight. In the short term they will design and fabricate small-scale arrays of optical wings and test them in the laboratory to demonstrate the feasibility of the concept. They will also perform numerical modeling to determine optimal design parameters for optical wings.

Space-related applications of a fully maneuverable solar craft are numerous. For example, a plethora of orbiting space debris now litters the Earth. Solar sails could be used to intercept the space junk, forcing it to descend toward the Earth where it would burn in the atmosphere. The low launch cost of lightweight solar sail receptacles would make the cleanup cost relatively low. Another mission concept under current development is to park a solar sail between the Sun and Earth to serve as an early warning system for solar storms. Variabilities in the space environment will require attitude control, which may be achieved with optical lift forces. Radiation pressure exerted on solar panels of spacecraft has been used for years, and future satellites are being designed with solar sail components. The optical lift capability of specially designed solar sails will likely be incorporated into these plans once the technology matures. In the distant future, one can imagine interplanetary missions and visits to exoplanets benefitting from the advantages of the optical lift force.
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Interesting subject in actual fact.

 

To intercept and de-orbit space junk! Now that would be an Interesting and non expensive method of doing a job that is getting more crucial every day.

 

Not going to try and sort out the word for word....

Paddoboy, if you break the process down into the two steps involved, it may be a little more clear what is happening and resolve the conservation of momentum issue.

1. A photon hits the sail and transfers any momentum it has to an atom and thus the sail the atom is a part of. End of step one.
2. When a photon is reflected, it is actually being emitted. It doesn't actually bounce off of the sail which is what the word reflected implies. What happens is, during the emission process part of an atom's inherent energy is converted into a photon and any momentum associated with that photon. And because of conservation of momentum (and the whole equal and opposite reaction thing), that requires a small part of that energy conversion, add to the sails momentum.

The sail gains some momentum in both cases. In the first the gain comes from the initial photon impacting the sail. In the second it comes from the process of photon emission.

 

From the patent - "a permanent magnet and the magnetic flux created by the magnets are controlled and concentrated to orient the magnetic forces generated in such a manner to do useful continuous work"

That is a claim of a benefit - the ability to do useful work. It, of course, did not do useful work. Hence the patent office does sometimes grant patents on incorrect premises. They have definitely improved since then (they will no longer grant any patents on perpetual motion machines) but I can pretty much guarantee you that with the help of an engineer or scientist in an applicable field you could generate ten patents that don't work at all - and at least one of them will get through if they are written well enough.

That doesn't mean that patents are meaningless - but it does mean that having a patent is no guarantee that the device/process/theory described within works. (And of course the term "patent pending" means nothing at all from either a legal or a functional perspective.)

 

I was looking for a date when they made that policy change, but couldn't find it. The patent you linked was from 35 years ago -- is the policy more recent or did that patent slip though the cracks of the policy?