The close encounter carried out by Voyager 2 over Neptune's north polar region to dive the spacecraft towards Triton robbed Voyager 2 of some forward momentum in relation to the Sun, hence Voyager 1 after the close pass of Saturn which was necessary for a very close Titan pass remained the fastest. read more
Voyagers 1 and 2 are both traveling at speeds close to 17 km/s, with Voyager 1 moving about 10% faster than Voyager 2. These spacecraft were launched separately in 1977, with a rocket (Titan III) providing the initial escape velocity relative to the Earth. read more
New Horizons is traveling at about 15 km/s, 2 km/s slower than Voyager 1, and is still slowing down. When New Horizons reaches the same distance from the Sun as Voyager 1 is now, its speed will be about 13 km/s (8 mi/s). read more