Both terminals aim at the same ground station from the same satellite, under the same simulated pointing jitter. A radio antenna spreads its power over a wide cone, so even when the beam wanders a few degrees off boresight the ground station is still comfortably inside it — the link stays up, just at a modest, fairly constant data rate. A laser terminal concentrates the same transmit power into a beam only a fraction of a milliradian wide: because usable channel bandwidth scales with carrier frequency, and optical carriers run roughly four orders of magnitude higher than microwave, that narrow beam can carry vastly more data — but it must land within a hair's width of the receiver. The same jitter that RF shrugs off walks the laser spot clean off the ground station, and the link drops to zero until it reacquires.
margin = 1 − (pointing_error / beam_half_width)²
rate = locked ? peak_rate × max(margin, 0) : 0
laser_effective_error = fine_pointing_on ? error × 0.15 : error
- Jitter / turbulence — amplitude of the simulated pointing noise: spacecraft micro-vibration plus, for the laser, atmospheric scintillation.
- Active fine-pointing — a fast steering mirror that tracks out most of the residual error on the laser terminal only, trading mechanical complexity for a much higher tolerable jitter range.
- Focus mode — switches which beam the 3D view and chart line highlight; both links are always computed side by side under identical conditions.
Real missions: NASA's TBIRD demonstrated 200 Gbps from a CubeSat in LEO; LCRD relays laser links between GEO and the ground; the earlier LLCD proved a 622 Mbps lunar downlink. All three needed sub-microradian pointing control to keep the beam locked — exactly the tradeoff visualized here.