An animation of Pluto and its largest moon, Charon, was created using a series of images captured by the New Horizons spacecraft as it continues its long journey to the distant planetoid. Taken from a distance of 422-429 million km, the images are not for scientific study, but for optical navigation between worlds.

Think of it as the NASA equivalent of using a sextant, taking measure of celestial bodies in order to properly steer the spacecraft to its destination. As Emily Lakdawalla explains on her blog at the Planetary Society:


Nearly every deep-space mission uses optical navigation methods to help navigators back on Earth fine-tune their path to the target. We know very well from two-way radio communication the position of spacecraft with respect to Earth. What's less precise is our knowledge of the position of the places we're aiming for. This is particularly true of small or distant targets like asteroids and Kuiper belt objects. You need big telescopes to see them, so we have relatively few measurements of their positions with respect to the stars, and few measurements lead to relatively big error bars on our predictions of their future positions.

The cameras on spacecraft never have the resolving power of our better Earth-based telescopes, so at first we steer spacecraft according to what we've been able to determine from Earth. But at some point on every space mission, a spacecraft approaches close enough to its target that its relatively small camera can do better than the bigger 'scopes back at home.

It's going to be at least February 2015 before New Horizons' highest-resolution camera, the Long Range Reconnaissance Imager (LORRI), will be able to get more detailed photos of Pluto and Charon than Hubble can. But LORRI is already capable of taking optical navigation images that will help us fix Pluto's position with more certainty than we could achieve with Earth-based observations alone.

[Source: The Planetary Society]