The Wire
July 6, 2015

In the last mile of its 3,464-day journey and only ten days away from a historic rendezvous with the dwarf planet Pluto, the New Horizons probe experienced an anomaly on July 4 and prompted the on-board computer to switch to ‘safe mode’. The event caused a communications blackout between New Horizons and mission control at the Applied Physics Laboratory, Maryland, for 90 minutes on Saturday. Now, the probe is transmitting telemetry signals that will help scientists fix it – hopefully in time for its encounter with Pluto and its moons.

And until it’s fixed, science missions – including the detailed pictures it’s been taking of Pluto and Charon of late – will be on pause. Not surprisingly, the incident will have the scientists and engineers operating the probenervous. As Alan Stern, the mission’s principal investigator, said in June, “There’s only one Pluto flyby planned in all of history, and it’s happening next month!”

New Horizons was launched by NASA on January 19, 2006, with the primary objective of studying Pluto’s surface and atmosphere up-close, as well as observe its moons Charon, Nix, Hydra, Styx and Kerberos. In order to reduce mission costs at the time of launch, New Horizons was not designed to land on Pluto but to fly by it at a distance of about 13,000 km. On planetary scales, that’s small and excellent enough to fetch the dwarf planet out of the blur.

That historic flyby is supposed to happen on July 14. By then, the on-board anomaly needs to be recognized and fixed or the scientists, and humankind, risk losing years of efforts and patient waiting. Nonetheless, if the issue is fixed after the probe has flown past Pluto, it will still be used to study the Plutonian neighbourhood of which we know little. This is the region of space containing the Kuiper Belt objects, a belt of asteroids like the one between the orbits of Mars and Jupiter but over 20-times wider and denser. They comprise the matter leftover after the Solar System’s planets had formed.

According to Emily Lakdawalla, a planetary scientist affiliated with the Planetary Society, the probe is on the right trajectory even on the safe mode. She also wrote that there were no pictures set to be taken by the probe on July 4, but some on July 5 and 6 that might be missed.

Safe modes are not an uncommon occurrence on the computers operating satellites and probes, and even rovers. They are in effect similar to how a computer running the Windows OS sometimes slips into safe-mode, often to eliminate a bug that threatens some critical function, by reverting to a very primitive state conducive to troubleshooting.

In March 2013, the Curiosity rover on Mars entered into safe-mode following a computer glitch. In the next two days, its controllers transmitted the necessary code for the software running the rover to fix itself, and the rover was back online again. More recently, in April 2015, the Rosetta probe that’s tracking comet 67P/C-G went into safe-mode after its computer lost contact with radio signals from Earth, thanks to dust blown from the comet interfering with the antennae.

However, what makes the troubleshooting tricky is that New Horizons is 4.8 billion km away – a distance that radio signals take 4.5 hours to travel. This means the total time taken for mission control to send a message to New Horizonsand receive a reply is nine hours, and that the problem is likely to be fixed over the course of the next few days. Until then, let’s keep out fingers crossed.

Update: At 8 am (IST) on July 6, NASA put out a statement saying the problem in the computer had been resolved and that New Horizons would be able to revert to its original science plan on July 7.

The investigation into the anomaly that caused New Horizons to enter “safe mode” on July 4 has concluded that no hardware or software fault occurred on the spacecraft. The underlying cause of the incident was a hard-to-detect timing flaw in the spacecraft command sequence that occurred during an operation to prepare for the close flyby. No similar operations are planned for the remainder of the Pluto encounter.

It added that the down-time will have had a minor effect on the probe’s science objectives in the two days.

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