NEW HORIZONS to the Kuiper Belt
Although there were backup launch opportunities in February 2006 and February 2007, only the first twenty-three days of the January 2006 window permitted a Jupiter flyby. Any launch outside that period would have forced the spacecraft to fly a slower trajectory directly to Pluto, delaying its encounter by 2–4 years. Fortunately, after some delays, the spacecraft could successfully launch on 19 January 2006 in a direct path towards the outer solar system with a heliocentric speed of 16.3 km/s, which is above solar escape velocity. It used the Atlas V551 rocket with five solid fuel rocket boosters and a third stage added to reach the necessary speed. This third stage is now also in a solar system escape trajectory and must have crossed Pluto’s orbit approximately in October 2015.
The only gravity assist of New Horizons was at Jupiter in February 2007 which increased its speed to 23 km/s. It flew past the Pluto-Charon system in July 2015. Data transmission of the Pluto encounter observations was finally completed in October 2016.
New Horizons is healthy and now on its way further through the Kuiper Belt as displayed in the diagram above (Credit: JHU, NASA). Its mission has been extended to 2021 with a close flyby of Kuiper Belt Object 2014 MU69 on 1 January 2019 and to perform more distant observations of another couple of dozen objects.