Okay. This is scary. It's not what the team wanted to be dealing with right now. However, the spacecraft is healthy. There was some brief confusion on Twitter over the phrase "return New Horizons to its original flight plan," but don't fear: the spacecraft is on course. Even if (heaven forbid) the spacecraft never recovered from safe mode, it would still fly past Pluto at the planned distance, speed, and time; no further trajectory correction maneuvers are planned from now until after the flyby. The "original plan" refers to the science plan.

So, if contact was lost at 1:54 p.m. EDT, what are we now missing? That is about 18:00 UT, and those signals left New Horizons about 4.5 hours previously, or 13:30 UT. I don't have detailed information on the science plans being performed now, but I do have a table of optical navigation images that were planned for this period.

The good news: no images were planned at all for July 4. There were a few planned for July 5, some of which will probably be missed. And only one planned for July 6. None of these is critical for navigation; images taken on days before and after will give the mission the information that they need to target future images precisely. Assuming they can get the spacecraft back into normal operating mode relatively fast, the only result of today's safe mode will be an annoying -- but educational -- gap in our approach animations, and a less educational (but not catastrophic) gap in our light curves for Nix and Hydra.

How long will it take? Well, two-way light time between New Horizons and Earth is nine hours. It sounds like they want more information from the spacecraft before determining the best course of action; they had to command that some time after they regained contact at 3:15 pm EDT / 19:15 UT, so they won't get the information until the wee hours of their morning. In the meantime, they'll probably have developed a list of possible explanations for the anomaly. If the further information that they get tomorrow morning matches one of their explanations, and it's a benign thing, they could conceivably return the spacecraft to science with a command sent later tomorrow morning ET -- leaving a science gap of slightly more than one day. If they still aren't sure they understand the spacecraft's condition, it could take at least one more nine-hour round of communication followed by another meeting, resulting in most of another day.

Safe modes are scary and annoying but not uncommon and not, at this moment, anything that New Horizons fans should be freaking out about. I'll willingly admit that I freaked out, just a little bit, when I first heard this news; but I have confidence that the team will handle it and will return the mission to normal operations with no serious loss to science.

I'll post an update when I have any news to report, but with that nine-hour delay, it's going to be a while.

UPDATE: NASA issued a statement at about 19:30 PT / 22:30 ET July 5 / 02:30 UT July 6 saying that the cause of the safe mode is understood, and that New Horizons will resume science operations on July 7: