Abstract: A passive communication system includes a first reflector and a modulator unit. The first reflector is disposed at a first location within line of sight of a first satellite. The first satellite is configured to transmit a first signal at a first wavelength. The first reflector includes a reflective surface that reflects at least a portion of the first signal which is incident on the reflective surface back toward the first satellite, and the first satellite includes a detector for measuring reflected signals received at the first satellite. The modulator unit is configured to modulate a reflectivity of the reflective surface of the first reflector between a first reflective state to a second reflective state to adjust the portion of the first signal which is incident on the reflective surface that is reflected back toward the first satellite.