Satellite QKD Pass — Orbital Link Budget & Secure Key Rate

A quantum-key-distribution satellite doesn't sit still: it rises, crosses the sky and sets again in a few minutes, and the secret-key rate it can deliver to a ground station rides on that geometry. This simulator flies a real circular orbit over a fixed ground telescope and, moment by moment, recomputes the actual link budget — atmospheric absorption scaled by airmass, diffraction loss from the receiving aperture, the resulting quantum-bit-error-rate, and the BB84 asymptotic secure key rate from the binary-entropy formula. Drag the eavesdropper toggle mid-pass and watch the physics do the security proof for you: an intercept-resend attack pushes the QBER past the ~11% threshold and the key rate collapses to zero, exactly as the protocol is supposed to behave.