NASA’s budget has been cut.  The last space shuttle has yet to take off (boy, is IT late).  But, we still hope to send exploratory vessels to other planets.  The problem is getting the probes to their destination reliably- when the distance is long.  One possibility relies upon Friedrich Zander’s proposition (1924) that we can use the thrust from photons (light energy) and no other fuel.  His hypothesis was based upon Einstein’s theory (which was confirmed by Peter Lebedev’s experiments) that photons have momentum, so that when absorbed by or reflected from a surface, there would be “radiation pressure”. A large sail may have very little acceleration, but given long time periods, the sail would generate reasonable speeds; as these sails are further from gravitational fields, their acceleration capability becomes viable.

Just this year, Japanese scientists sent a “kite”-type vessel to examine Venus; IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) is a first step.  Now, Drs. Swarzlander, Peterson, Artusio-Glimpse, and  Raisanen from Rochester Institute of Technology have published a more elaborate scheme in Nature Photonics.  Instead of a sail, they propose using a “lightfoil”.  Basically, this is identical to the airfoil the provides lift on the wings of the airplane- except that photons are used in lieu of air flow.  Computer simulations, based upon semi-cylindrical glass rods, were developed to discern what the effect of light beams would be on the system. The results indicated that “lift” certainly was developed- but, also, that the rods would naturally assume certain angle alignments (due to rotational equilibrium), which augmented the lift affect.  But, these were not just computer simulations.

The physicists designed microscopic semi-cylindrical glass rods (on the order of 30 to 50 microns), floating in water.  And, then focused light beams on the rods- which performed virtually identical to the computer simulations.  What makes this revelatory is that even though the rods were floating in water- and, therefore, not optimally aligned towards the light beam, the rotational equilibrium developed did cause them to properly align to obtain the advantage and develop the lift.

Looking at the diagram, you can see the light reach the rod, whereby some of the light gets refracted (at a 20 degree slope or so in the diagram), and some is reflected downward.  Optical lift, to counteract the change in momentum of the light photons (force reaction) follows the direction of the blue arrow.

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