I wrote a program in C++ to calculate interplanetary trajectories. It looks up the planetary positions in the JPL ephemeris database, and calculates the Keplerian orbital elements of a probe trajectory by Lambert’s theorem. So, given the departure time and arrival time, I can find the unique orbit that fits those two points at those two times. Here is the trajectory of the Soviet probe Venera-1.

I also compared distance values with Soviet ranging data. The first three ranges were measured by the CWFM radar data, measured from the Pluton system in the Crimea. The rest were calculated by their ballistics center.

Russian Value My Calculation
Feb 12, 03:45 GMT 26000 km 23269 km (1st telemetry session)
Feb 12, 11:25 GMT 165000 km 142001 km (2nd session)
Feb 17, 11:35 GMT 1889104 km 1889500 km (3rd session)

Mar 4 00:00 GMT 6.9 million 6953121 km
Mar 25 00:00 GMT 15 million 15243053 km
Apr 13 00:00 GMT 28 million 27796154 km

I believe my early numbers would be better if I was accounting for the Earth’s gravity. The probe would be launched faster than I calculate, but then slow down from the pull of gravity until it assymptotically approached the Lambert orbit.