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Performance Sensitivity To Telescope Aperture



The performance of any directed (beamed) telescope system is a very sensitive function of telescope aperture size, particularly in the visible regime. This can be seen as follows for a symmetrical telescope system with mirror diameter "d":


1. The maximum usable transmitter power is approximately d2.
2. The Effective Isotropic Radiated Power (EIRP) d2.
3. The received power Pr d2.
4. The rejection of Planckian radiation from nearby stars d2.


Thus, the performance of a small visible wavelength telescope could be proportional to d8. This means that a factor of 10 increase in the size of the mirrors could lead to a change in recovered SNR of between 60 and 80 dB, depending on Planckian radiation levels and bandwidth. Clearly, the performance of a symmetrical optical interstellar communications link, particularly one operating in the visible region of the spectrum, is so sensitive to mirror size assumptions, that a small change in mirror diameter produces a drastic change in system performance. Compared to a 10 m diameter mirror system, 10 cm diameter mirrors could reduce the system performance by 160 dB!


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