Via the BBC:
Controllers have sent Nasa's New Horizons spacecraft a final set of commands ahead of its historic flyby of a distant icy world on Tuesday.
The probe's pass of the 30km-wide object known as Ultima Thule will set a new record for the farthest ever exploration of a Solar System body - at 6.5 billion km from Earth.
The upload included a two-second timing correction that ensures New Horizons knows precisely when and where to point its cameras as it sweeps alongside its target at a breathtaking 14km/s.
"The spacecraft is healthy and we're excited!" said mission operations manager Alice Bowman when she briefed reporters at the control centre embedded in the Johns Hopkins University Applied Physics Lab (JHU-APL) in Maryland.
For the latest on New Horizons, the Johns Hopkins APL website has a countdown clock and more. You can also find info from NASA here.
There’s no telling what the fly-by will reveal, and it will take a while for all of the information to get back to Earth, both because of the light-speed lag of the radio transmissions, and the rate at which the data can be sent. New Horizons has been underway for 4728 Days, 18 hours as of this morning at 8:37 EST.
The images have already started coming in as New Horizons has approached Ultima Thule.
...Given Ultima Thule's relatively small size (it's approximately 20 miles across), LORRI didn't actually start to resolve Ultima (that is, see it as more than a point of light) until Dec. 29, when the New Horizons spacecraft closed to within 2 million miles (3 million kilometers). The New Horizons team will start posting LORRI images on Dec. 30, when Ultima should be approximately 1.5 pixels across in the full-resolution ("1x1" mode) pictures.
The resolution will improve each day, so you can watch as Ultima Thule is transformed from a barely resolved object into a new world never seen before. In the images posted on Jan. 1, Ultima is expected to be approximately 3 pixels across, but it will grow to approximately 100 pixels across for the images posted on Jan. 2, and approximately 200 pixels across for the images posted on Jan. 3….
More to come, though it will take months of processing to bring out all the information that can be extracted from the data. The first images from the fly-by will be pretty basic, but it’s still impressive when you think of where they’re coming from.