New Horizons is now just days away from passing Pluto. (EPA/NASA/JHUAPL/SwRI)

This post has been updated.

After causing quite a stir over the weekend and putting scientific observations on hold for three days, NASA's New Horizons spacecraft seems to be recovering. On July 4, NASA reported that New Horizons -- which is just days away from a historic encounter with Pluto after nine years of travel -- was experiencing an anomaly. The craft went into safe mode and lost communications with Earth for an hour.

[Newest photos of Pluto reveal a peachy dwarf planet]

The $728 million mission is meant to give us our first real observations of Pluto, the mysterious dwarf planet that sits on the edge of our solar system. It's been zipping toward its goal since 2006, and the end -- July 14 -- is in sight. By July 15, the public should have access to an image of Pluto on par with shots of Earth taken from space.

For the first time, we're about to get a close look at Pluto and its cold, outer region of the solar system. The Post's Joel Achenbach explains NASA's New Horizons mission. (Tom LeGro/The Washington Post)

But this hiccup is a reminder that no space mission is a guarantee -- and the July 14 flyby will require all the stars to align.

[Graphic: 9 years and 3,000,000,000 miles to Pluto]

For now, NASA reports, things are back to normal. In fact, the spacecraft won't even have to change its science mission plans, which would have been the case had any software or hardware been damaged during the anomaly. Normal science operations will recommence July 7, and mission scientists say that nothing vital will be lost because of the down time.

“In terms of science, it won’t change an A-plus even into an A,” New Horizons Principal Investigator Alan Stern said in a statement.

And while some were spooked by NASA's July 4 statement that the craft had to be returned to its "original flight plan" -- which some took as an indication that the spacecraft had been knocked off course -- NASA was referring to the science plan, not a physical trajectory.

At a news conference on Monday, NASA representatives explained that the anomaly occurred sometime on Saturday morning when New Horizons strained its processing power by working on two tasks at once -- making a second copy of its command sequence for the encounter while simultaneously compressing previously acquired data to make room for all its future finds. But the two tasks proved too much for the spacecraft to handle.

"And then the spacecraft did exactly what it was supposed to do," New Horizons project manager Glen Fountain said: It went into safe mode and sent a distress call back to Earth, which was received in the afternoon. It took about an hour for mission control to get back in touch with the spacecraft, during which time tensions were high -- after all, they had no idea what the problem might be. But once New Horizons phoned home, Fountain and his team could see exactly what had happened.

There's no reason to think that this particular anomaly will happen again. And if the spacecraft is forced to switch from its primary computer to its backup while it's in "encounter mode" -- the chain of commands that will carry it from July 7 through its Pluto flyby -- it will keep collecting scientific data instead of entering safe mode. Right now, the spacecraft is designed to keep itself safe until it enters the Pluto flyby sequence. Once that sequence begins, the continuous collection of data will be the craft's top priority.

Everything is set for the sequence to start on July 7, NASA representatives told the media. Until then, the science collection hiatus will continue.

"New Horizons is operating flawlessly, on course, and so are all of the instruments in the payload," Jim Green, director of Planetary Science for NASA, said on Monday. "In fact in the last few days we’ve been receiving tremendous data, and I couldn’t be happier with what we’re already seeing from this great distance."

At the press conference, New Horizons principal investigator Alan Stern listed the 30 individual observations lost during the craft's downtime, but emphasized that they were a drop in the bucket compared with the science New Horizons will be doing in the next week. Some of the planned observations -- like collections meant to observe the planet's atmosphere -- weren't even expected to yield useful data, since the spacecraft is still too far out to detect most of the things NASA is hoping to detect.

"It's much more important to focus on the flyby than to collect science 8 or 9 million miles from the target," Stern said. "Our assessment is that the weighted loss is far less than 1% [of the overall science mission]."

We may lose a few of our anticipated images and animations because of the downtime this weekend and Monday. But soon enough, we should have unprecedented access to Pluto's secrets -- assuming the nervous anticipation doesn't kill us all first.

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