 Subsequent discussions with their American counterparts ended with an agreed-upon final distance of , which has stuck since.The Soviet Mars 2 and Mars 3 landers each had a small 4.5 kg Mars rover on board, which would have moved across the surface on skis while connected to the lander with a 15-meter umbilical.Two small metal rods were used for autonomous obstacle avoidance, as radio signals from Earth would have taken too long to drive the rovers using remote control.