Last part of New Horizons mission to Pluto will be the hardest

Nature : On 14 July, NASA’s New Horizons spacecraft is scheduled to make its first flyby of Pluto. Pluto’s orbit has never been fully mapped because it hasn’t completed an orbit since it was discovered. The fact that no one knows Pluto’s exact location combined with the 9-hour communication lag between New Horizons and Earth means the craft will be essentially approaching the dwarf planet blind. During the flyby, the craft has to pass through a window of space just 100 km by 150 km. The targeted path is only 12 500 km above Pluto, and the spacecraft will be moving nearly 14 km/s. The last chance for mission navigators on Earth to signal New Horizons for a change of course will be 4 July. As the craft approaches Pluto, it is taking daily pictures of the planet, which allows the people guiding it to more accurately calculate Pluto’s position against the background stars. But they still haven’t been able to get an accurate measurement of the distance to the dwarf planet.