Vitaliy V. Fitenko¹, Dmitriy Yu. Chetyrkin²

 1, 2 JSC «Corporation «Vega» (Moscow, Russia) 2

 d_chetyrkin@mail.ru

In the Doppler measuring instruments of velocity and altitude (Doppler Landing Radar), used for controlling landing modules, ranging by means of a phase measurement is used, featuring the ambiguity of measurements. For range unwrapping, several modulation frequencies of the radiated signal are used. The efficiency of range unwrapping will be defined by the chosen values of modulation frequencies with features of the reflecting surface and measuring instrument parameters.

The purpose of this work is the justification of chosen nominal values for modulation frequencies in Doppler Landing Radar to measure the velocity and altitude, taking into account the restrictions imposed by range measurement fluctuation errors.

It is shown that the result of unambiguous slant range calculation significantly depends on measurement fluctuation errors, caused by features of the signal, reflected from the underlying surface. Depending on the spacecraft flight altitude, ratios for the calculation of the radiated signal modulation frequencies, which provide necessary probability of the correct range unwrapping, are received. The conclusion is drawn on the influence of the measured ambiguous range fluctuations, caused by the reflection of a signal from the extended underlying surface, on the result of unambiguous range calculation. The calculation formulas of the radiated signal modulation frequencies are received.

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