Abstract: Systems and methods for performing quantum key distribution (QKD) using one or more high-altitude platforms (HAPs) are disclosed. The system includes a second QKD station (Alice) supported by the HAP so as to be in free-space communication with the first QKD station (Bob) over an optical path (OP) via an optical quantum communication channel that carries quantum signals (P1?), an optical synchronization channel that carries synchronization signals (PS) and optionally classical communication signals (PC), an optical beacon channel that carries beacon signals (PB), and a radio-frequency (RF) channel that carries RF signals. The beacon signals are used to detect changes in the optical path and correct the synchronization signals (PB) so as to gate the first and second SPD pairs to correspond to arrival times of the quantum signals at said first and second SPD pairs. The system does not require a Pockels cell for quantum signal modulation, thereby improving the security of the system.