What is FSPL (free-space path loss)?

Free-space power loss is proportional to the square of the distance between the transmitter and receiver. Free-space path loss (FSPL) is the attenuation between the feedpoints of two antennas of radio energy that results from the blend of the receiving antenna’s capture area plus the obstacle-free, line-of-sight path through free space. The FSPL shows up in vacuum under preferably conditions, for example, a radio communication between satellites.