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The Pluto Probe Went Into Safe Mode, And We Don't Know Why

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The New Horizons spacecraft is rapidly soaring closer to Pluto for our first flyby of the distant almost-planet. But something went wrong on Saturday afternoon, knocking the probe out of communication for over an hour. Now we’re back in touch and trying to figure out what happened.

The facts so far are sparse: the New Horizons spacecraft dropped out of contact with mission operations at 1:54pm on Saturday, July 4th, with communications reestablished by 3:15pm. Sometime during that gap, the spacecraft’s onboard computers detected some yet-to-be-determined anomaly, flipped itself into safe mode, and started trying reinitiate contact with Earth using its backup computer. Now it’s feeding us a steady stream of telemetry in an effort to help us puny Earthlings determine what went sideways, and is withholding science until we figure it out.


The good part of all of this is that New Horizons did exactly what it was supposed to do when things went pear-shaped (or whatever unexpected fruit-shape this turns out to be once the anomaly recovery team untangles the problem), and that we’re back in touch. The spacecraft says it’s completely healthy and totally functional. Even better, all the trajectory manoeuvres to nuzzle into a Pluto close-approach already happened, so the probe is still where we expect and going where we want, and still on-target for the fly-by next week.

The bad part is that we don’t know what went wrong, and it’s going to take time to fully recover science operations. The probe is 4.9 billion kilometers (3 billion miles) from Earth: that means a nine-hour round-trip communications lag between robot and humans will seriously hamper troubleshooting. In a NASA statement, the anomaly team said they expect full recovery is going to take at “one to several days” to diagnose what went wrong and fully recover the spacecraft out of safe mode. With the probe just ten days until its closest-approach to Pluto, it’ll take some dedicated brainpower to not only identify whatever the triggering anomaly was, but get the mission’s research plan of, “Take this photo here, and this measurement there...” back on track in the next 10.5 million kilometers before the Pluto flyby.


I can’t be the only one obsessively watching the Deep Space Network tracker communicate with New Horizons (NHPC) today.

No photographs were scheduled for July 4th, and only a handful on July 5th and 6th. Assuming the team can get everything back on track quickly, the only result is going to be an annoying but not scientifically-hurtful hiccup in the approach animations and maybe a tiny loss of data collection for getting light curves on the tiny moons Nix and Hydra.

While “unexpected” is usually a very exciting term when describing exploration, this is one instance where it’s more nerve-wracking than exhilarating. Good luck to the Anomaly Review Board, and let’s hope for no more hiccups as New Horizons sneaks up on Pluto before venturing into the great unknown!


Update: The problem was a timing flaw in the flyby preparations command sequence; it’s fixable and the science operations are going back online with full functionality expected on Tuesday, July 7th.


Images credit: NASA