How Does the Inverse Square Law Affect Communication with Distant Spacecraft?

[Spakfilla]

G'day
Was just wondering if there are any implications the inverse square law has for the transmission of energy for communicating with spacecraft traveling into the outer regions of the solar system?
Thanks

 

[cepheid]

Welcome to PF,

Such communication is done using radio waves, so we are still indeed talking about the propagation of electromagnetic radiation. However, the inverse square law really only applies if the source of emission is isotropic (i.e. it emits equally in all directions, like a point source). Examples of things that emit like point sources (at least when seen from far away) include stars and light bulbs. However, I imagine that the radio signals in question are transmitted and received using antennae, which means that they are probably directional in nature (i.e. they are "beamed", meaning that they go mostly in one preferred direction and not very much at all in any other direction). Therefore, the power won't fall off with the square of the distance. It will probably decrease less quickly. Even so, it will still decrease with distance. Therefore, you probably have to make sure that your transmitter has enough power and your receiver enough sensitivity for the signal to get through. That's as far as I can go towards answering your question without actually looking into the details of how it is done.

 

[Spakfilla]

Thank you