Capping a three-billion-mile journey spanning nine-and-a-half years, NASA's New Horizons probe safely raced past Pluto Tuesday, training its cameras and other instruments on the dwarf planet and its large moon Charon and successfully recording high-priority data during a once-in-a-lifetime flyby.
Approaching at nearly 31,000 mph, New Horizons passed within about 7,700 miles of Pluto at 7:50 a.m. EDT, 50 years to the day after NASA's Mariner 4 flew past Mars in the first successful mission to the red planet.
As planned, New Horizons turned away from Earth late Monday to carry out a complex sequence of observations during the critical close-approach phase of the Pluto encounter, kicking off a 21.5-hour communications blackout. While outwardly confident, scientists and engineers spent a somewhat anxious day Tuesday waiting for the spacecraft to phone home.
To the immense relief of the entire team, the probe did just that, turning to aim its high-gain antenna back toward Earth and transmitting a brief stream of engineering data confirming a successful flyby. At that point the spacecraft was more than 400,000 miles beyond Pluto and receding at more than 8.5 miles per second.
The long-awaited signal left New Horizons around 4:30 p.m. EDT (GMT-4) and, traveling across the solar system at 186,000 miles per second, reached the Johns Hopkins University Applied Physics Laboratory control room right on time at 8:52:37 p.m.
"Searching for the frequency," mission operations manager Alice Bowman, call sign MOM, said over an audio loop at the control center. "Stand by. OK, we're in lock with carrier. Stand by for telemetry... OK, copy that, we're in lock with telemetry with the spacecraft!"
Elated engineers and scientists in the Mission Operations Center erupted in cheers and applause as the data trickled in from deep space, prompting equally enthusiastic applause, high fives and hugs in a nearby auditorium where senior managers, dignitaries and journalists were standing by.
Bowman then asked the New Horizons subsystems engineers to report on the status of their systems.
"MOM, this RF (radio) on Pluto 1," an engineer responded a moment later. "RF is reporting nominal carrier power, nominal signal-to-noise ratio for the telemetry. RF is nominal."
The autonomy engineer, overseeing the system responsible for autonomously resolving faults while out of contact with Earth, then reported "no rules have fired," meaning no problems of any significance were encountered throughout the flyby sequence.
Next came the command-and-data-handling system engineer, who reported "nominal status. Our SSR (solid-state recorder) pointers are where we expect them to be, which means we've recorded the expected amount of data."
Likewise, the guidance, navigation and control system reported no problems followed by the propulsion officer, power and thermal subsystems. Bowman then formally called principal investigator Alan Stern, reporting "we have a healthy spacecraft. We've recorded data ... and we're outbound from Pluto."
As planned, no science data were included in the signal. But Stern said fresh imagery and other data are expected early Wednesday.
"We have a pass starting tomorrow morning that'll run for several hours," he said. "It's something we have called 'the New York Times data set,' because we think it's going to be pretty interesting. It begins at 5:50 in the morning.
"Included in that data set will be new imagery at 10 times higher resolution than the spectacular imagery that debuted this morning," Stern said. "Additionally, there'll be information from the two spectrometers, new color data, information on not just Pluto but Charon and small satellites. So there's going to be quite a waterfall of data for us."
The new pictures and other data will be unveiled during an afternoon news conference.
Giving the public a taste of things to come, NASA released a stunning full-frame image of Pluto early Tuesday that was taken Monday afternoon while New Horizons was still 476,000 miles from the dwarf planet.
The image shows a large heart-shaped region seen in earlier photos with hints of circular features that could be eroded or partially snow-covered impact craters -- or something else entirely -- and stark brightness variations across its salmon-colored surface.
"Fifty years ago today, the first spacecraft flew by Mars, it's called Mariner 4," Stern said earlier. "And I think it's fitting that on the 50th anniversary, we complete the initial reconnaissance of the planets with the exploration of Pluto."
The 21.5-hour communications blackout Tuesday added a bit of drama to an already successful mission
Based on observations made during New Horizons' approach to Pluto, engineers calculated a a very remote chance of a catastrophic collision with debris blown into space by past impacts on Pluto's low-gravity moons. The danger was highest during New Horizons' passage through Pluto's equatorial plane.
Bowman admitted to a bit of nervous anticipation.
"We always talk about the spacecraft as being a child, a baby, a teenager, and we lost signal, as planned, (Monday) night at 11:17," she said. All the team could do at that point, "was just to trust that we had prepared it well to set off on its journey on its own and do what it needed to do."
Because New Horizons' instruments and its high-gain antenna are fixed on the body of the spacecraft, the entire vehicle must be re-oriented to aim its cameras and other instruments at Pluto, Charon and the other four known satellites.
As a result, the spacecraft could not communicate with Earth while it was making its highest-priority flyby science observations.
"We loaded up all the commands to the spacecraft about a week ago and it's just ticking down its checklist," Bowman said. "Those commands are firing off at the time the scientists want them to fire off. This is closest approach, this is when you get the best science, so we don't want it to point to Earth and talk to us, we want it to take science. So that's what it's doing."
And it was.