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quote:Originally posted by bostjanMy E/M professor in grad school told me I was foolish when I asked him about the possibility of harnessing E/M momentum to make a sort of ion engine.
quote:Originally posted by syhprumI find this figure rather high when the designers of space vehicles speak of using sails in the order of square kilometers to propel their vehicles by sunlight which I understand has a power of about 1.3 KW per sqare meter.Is there a different calculation for photons. bouncing of a surface as against locally generated ones. 10^6/3*10^8 = 0.00333 what units are employed ? or did you use a million megawatt laser.
quote:Originally posted by bostjanE/M waves carry linear momentum proportional to Poynting's vector, even in static fields.Think about if you put an electron with finite mass in an e/m field. It accelerates, and thus gains momentum, but where does the momentum come from? It comes from the field. Pretty cool, I think.
quote:Originally posted by syhprumThe NewScientist article quotes the case of a light sail of 600 square meters which would adsorb about 1 MW of sunlight and producing 0.0033N force
quote:Originally posted by lightarrowquote:Originally posted by bostjanE/M waves carry linear momentum proportional to Poynting's vector, even in static fields.Think about if you put an electron with finite mass in an e/m field. It accelerates, and thus gains momentum, but where does the momentum come from? It comes from the field. Pretty cool, I think.Yes, and what generate the field? Other electric charges that acquire a momentum in the opposite direction.
quote:Originally posted by bostjanDue to their movement, their magnetic fields are equal and opposite, but the magnetic forces are not. (Use right hand rule if you wish) How can this be? Momentum must be stored in the fields.
quote:Originally posted by syhprumre photon propelled spacecraftConsidering the mass of the associated power generating eequiptment I do not think there is any future in photon propelled space ships although a very low mass sail might just about work close to a star for instance to propell a vehicle from earth to the Kuiper belt.Pity about the 'Tera' 'Mega' mix up it would work fine if we could use megawatts.
quote:Originally posted by syhprumRe photon drivesI must really disagree the largest mobile power sources that we have are the nuclear power units in submarines, these are certainly less than 100 megawatts electrical probably more like ten and cannot be run for more than a year or two without major maintenance.To drive a terawatt laser (if such a thing could be created ) they would have to be scaled up by a factor of 10^7 at the very least , made maintenance free for hundreds of years for interstellar travel with no great increase in mass.I do not think this is just a matter of technological development I consider it impossible!.Let me see a calculation of the probable mass of a photon drive ship travelling to the nearest known star with a planetary system and what leap in power generation technology would be requiredsyhprum
quote:Originally posted by syhprumI am begining to believe that this is just a money making scam, like cold fusion, homopathy, or the various magic water and Ice tales that we hear.syhprum
quote:Originally posted by syhprumI deserve to have one brownie point deducted!, and I have lectured people on action and reaction on this board.syhprum
quote:Originally posted by NieuwenhoveAcoording to special relativity, it is clear that momentum should be conserved and hence the drive can not work. On the other hand, one could also argue that one should use general relativity since the microwaves bounce of the walls (exerting pressure) and thus accelerate (changing direction). In general relativty however, momentum itself is not strictly defined (" Momentum is the Noether charge of translational invariance. As such, even fields as well as other things can have momentum, not just particles. However, in curved spacetime which is not asymptotically Minkowski, momentum isn't defined at all." ; see ...sorry, you cannot view external links. To see them, please
REGISTER or LOGIN) and thus there might be an opening here for some kind of non-conservation of momentum. Any comments ?
quote:Originally posted by Soul SurferNo, there is a force on the mirror as it reflects light.
quote:...the designer is not taking into account the foreces on the tapered section of the waveguide.