Deep-Space Doppler Tracking (2D)

This simulator reproduces the core observable behind Deep Space Network orbit determination: two-way coherent Doppler tracking. A spacecraft coasts on a Kepler orbit — solved exactly frame by frame, not force-integrated — while a rotating ground station measures the line-of-sight range-rate between itself and the craft. That range-rate becomes a real Doppler frequency shift on the X-band or S-band downlink, exactly as it does at Goldstone, Madrid or Canberra. This 2D edition lays the same physics out across three panels: drag the orbit view to rotate its axonometric camera, watch the spacecraft's track sweep across a real azimuth/elevation sky plot, and follow the Doppler shift scroll by on a strip chart that flips color the moment the craft sets below the horizon. Adjust the orbit's semi-major axis, eccentricity and inclination, or switch tracking bands, to see how geometry and frequency both shape the tracking signal.