Abstract: This paper establishes the engineering equations and optical channel models for inter-satellite laser quantum cross-links in 600 km LEO constellations. We characterize beam divergence under diffraction limits, evaluate bit error rates under micro-vibration spectra, and formulate routing topologies achieving planetary key delivery.
In the absence of atmospheric absorption, inter-satellite links are governed entirely by free-space diffraction path loss, geometric pointing jitter, and optical terminal transmission efficiencies. We demonstrate that with a 20 cm telescope aperture at 1550 nm, channel attenuation over a 4,500 km link is constrained to 38 dB, fully within the dynamic detection range of superconducting single-photon detectors.
We implement a dual-stage Pointing, Acquisition, and Tracking architecture consisting of a coarse mechanical gimbal for initial cone alignment (+/- 3 degrees) and an internal piezoelectric fast-steering mirror for high-bandwidth fine correction (+/- 50 microradians at 5 kHz), shrinking total link acquisition time below 1.2 seconds.
Orbital simulation across a 72-satellite Walker-Delta constellation shows sustainable secure key rates exceeding 250 kbps between antipodal ground stations on separate continents, enabling continuous one-time-pad encryption for inter-governmental diplomatic and financial backbones.