Beaming of laser power to satellites in space may involve sending laser beams over tremendous distances. For example, sending a laser beam from the earth to satellites in geosynchronous orbit, 35,900 km above the earth’s equator, may involve a trip of about 40,000 km. In the far field at these distances the size of the laser spot is determined entirely by the coherent diameter of the beam director primary mirror from which the laser beam came. It is independent of the mirror’s focal length. Even at shorter distances the attempt to control the beam diameter on the solar cells of the spacecraft by focusing the primary mirror may involve attempting to set the mirror to accuracies that are shorter than the telescopes’ focal range, 4λf2, where λ is the wavelength and f the f/number. For an f/4 system at 0.6 μm wavelength, for example, the focal range is 38 μm. Setting the focus more closely than that accomplishes nothing. However if the spot size is not controlled accurately enough, it may become too small and the laser beam may ruin the solar panels of the space elevator, orbital transfer vehicle, or other satellite being irradiated. This problem can be averted by controlling the effective diameter of the beam director system primary mirror rather than trying to control the focus. By making the primary mirror an adaptive optic and continuously adjusting the size of the segment diameters over which correlation exists, the laser beam from each individual mirror segment can be maintained at the correct diameter on the solar panel at all distances less than the maximum distance for the particular primary mirror diameter.
Laser Spot Size Control In Space
BEAMED ENERGY PROPULSION: First International Symposium on Beamed Energy Propulsion ; 2002 ; Huntsville, Alabama (USA)
AIP Conference Proceedings ; 664 , 1 ; 571-581
14.05.2003
11 pages
Aufsatz (Konferenz)
Elektronische Ressource
Englisch
Laser Spot Size Control in Space
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