The team guiding the New Horizons spacecraft has been able to "nail its position very precisely," guaranteeing the probe will capture a flood of data about Pluto during Tuesday's flyby, a NASA scientist says.

The spacecraft is on track to enter a tiny "box" that measures just 96-by-144 kilometres (60-by-90 miles) and New Horizons "is almost at the centre of it," Glen Fountain, project manager at the Johns Hopkins University Applied Physics Laboratory, said at a briefing on Monday.

There are three important times NASA will be celebrating on Tuesday — the flyby at 7:49 a.m. ET. After that, the spacecraft will send a signal at 4:20 p.m. It should be received on Earth at 8:53 p.m.

The probe will first "go incommunicado" late Monday as it goes to work collecting pre-flyby data.

New Horizons Pluto

Pluto is turning out to be most distant planetary body ever explored, with its four large dark patches near the equator. (NASA)

"Shortly before 9 p.m. [Tuesday], we will hear from it, and that's when we will breathe a sigh of relief and can really call it a successful flyby," New Horizons scientist Alan Stern said.

Scientists are expecting to see the transmission of new colour images of the dwarf planet taken by New Horizons on the same day as the flyby.

Crude images taken from Earth years ago were "just a few pixels across," but as the probe's 9½-year journey progressed, that improvement grew by a factor of 30, Stern said.

'Beyond our wildest dreams'

"We're going to do a hundred times better than that with the images made on Tuesday," he said, adding the team has already seen the "complex and nuanced surfaces" of Pluto and its largest moon Charon "that tell us of a history of these two bodies that is probably beyond our wildest dreams."

NASA-PLUTO/

This image shows a bright heart shape on the rusty-coloured surface of the dwarf planet. (NASA/Reuters)

"The data that we'll be producing and that we're already producing is a gift for the ages, for all mankind," Stern said.

For now, signals take 4½ hours to travel one-way between New Horizons and flight controllers in Maryland.

It will be Wednesday before the closest of Pluto's close-ups are available for release. And it will be well into next year -- October 2016 -- before all the anticipated data are transmitted to Earth.

Over the weekend, New Horizons beamed back black and white images showing a closer view of four dark spots that line up in a row on Pluto's far side. Images of the circular shapes show the side of Pluto that always faces Charon.

The New Horizons team received images of the spots on July 1, photos that were taken from a greater distance, but the new images show a lot more detail.

John Spencer, who leads the New Horizons hazard analysis team at the Southwest Research Institute in Boulder, Colo., told NASA TV on the weekend that scientists should know more about the shapes "in a few days."

"It is just amazing what we are seeing now. It was a gradual approach and every picture is just a little bit better. Now, every day, we just see the whole new view of Pluto, that is telling us things we never knew before.

Pluto New Horizons

New Horizons, which is the size of a baby grand piano,would have come within 12,500 kilometres of Pluto during the flyby. (Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)

"We are seeing these crazy black and white patterns. We have no idea what those mean," Spencer said.

Last Thursday, the probe transmitted a photo of markings on Pluto that look like a whale's tail, near its south pole.

Two days before that, it beamed back a photo of a heart-shaped feature to the right of the darker-coloured "whale."

The spacecraft has travelled 4.7 billion kilometres and will be the first probe from Earth to encounter distant Pluto, capping a reconnaissance of the solar system that began more than 50 years ago.

Astronomers are eagerly looking forward to Tuesday morning, when the spacecraft will take pictures of Pluto from an altitude of only 13,000 kilometres.

New Horizons is travelling at 14 kilometres a second. At that speed, the spacecraft can't go into orbit, but will take as many pictures and gather as much data as it can during the flyby.

"Between this time now and its closest approach, New Horizons will take about 150 observations," team scientist Cathy Olkin told a briefing held at 10:30 a.m. ET on Monday.

The size of a baby grand piano, the spacecraft is set to pass within 12,499 kilometres of Pluto. Fourteen minutes after that flyby, the spacecraft will zoom within 28,857 kilometres of Charon.

Astronomer's ashes on board

Also on Tuesday, Clyde Tombaugh will pass by the icy world he discovered 85 years ago. His ashes are flying on New Horizons.

New Horizons is also carrying a 1991 U.S. postage stamp that's about to become obsolete. The stamp trumpets "Pluto Not Yet Explored."

Also on board are two state quarters, one for Florida, home to the launch site, and the other for Maryland, headquarters for the spacecraft developers and flight control.

In all, nine small mementos are tucked aboard New Horizons. There's a good reason there are nine.

When New Horizons rocketed away from Cape Canaveral in 2006, Pluto was the ninth planet in our solar system. It was demoted to a dwarf planet seven months later.

With files from The Associated Press