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posted by janrinok on Tuesday July 07 2015, @11:45AM   Printer-friendly
from the software-doing-what-it-should dept.

Days before NASA's New Horizons probe to Pluto experienced a technical issue, the Dawn spacecraft orbiting Ceres "experienced an anomaly":

NASA's Dawn spacecraft is healthy and stable, after experiencing an anomaly in the system that controls its orientation. It is still in its second mapping orbit 2,700 miles (4,400 kilometers) above dwarf planet Ceres.

On June 30, shortly after turning on its ion engine to begin the gradual spiral down to the next mapping orbit, its protective software detected the anomaly. Dawn responded as designed by stopping all activities (including thrusting), reconfiguring its systems to safe mode and transmitting a radio signal to request further instructions. On July 1 and 2, engineers made configuration changes needed to return the spacecraft to its normal operating mode. The spacecraft is out of safe mode, using the main antenna to communicate with Earth.

The Dawn issue is less serious than problems with New Horizons since the third and fourth mapping orbits can be executed whenever NASA is ready, and the final orbit around Ceres will last indefinitely. By contrast, New Horizons will speed past Pluto and reach its closest approach on July 14th at 11:49:57 UTC at a relative velocity of 13.78 km/s. After collecting data from Pluto, NASA will try to steer New Horizons towards one or two Kuiper belt objects within a narrow cone extending from Pluto.

NASA engineers have released an explanation for the July 4th glitch:

To prepare for these final days of its mission, the probe was doing two things at once. First, it was taking the scientific data it has already harvested, compressing it, and writing it to a portion of its 128 Gbit storage (two 8GB solid-state recorders). At the same time the instrument command sequence for the flyby was being uploaded. The combined workload slightly exceeded the processor's capabilities, and triggered a watchdog-like feature. This switched the main computer system over to the backup computer, while putting the main system into sleep mode as a safety measure. The processor is a Mongoose-V: a 12MHz MIPS R3000 CPU hardened against radiation. The R3000 is a 32-bit chip that's pretty similar to the one used in the original 1994-era Sony PlayStation among many other devices.


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  • (Score: 4, Interesting) by VLM on Tuesday July 07 2015, @02:18PM

    by VLM (445) Subscriber Badge on Tuesday July 07 2015, @02:18PM (#206119)

    always supposed to speed by

    Yes. "The mission" is pretty much the time that its local cameras get better images than hubble and thats a couple months. Obviously non-imaging data is important too. A little more than a week till closest approach. I guess you'd say the pluto mission is only about 45% complete so calling this its final days is a little journalistic, but whatever.

    what is now different

    Not much, they've been imaging like crazy on the way in, just in case there's some previously undiscovered moon in the flightpath, they could navigate out of the way, optimistically. But it seems the path is clear. Murphys law if they hadn't spent all this effort looking then hubble would see a bright flash as it hit an undiscovered moon at full speed, LOL. Also they lost a couple days of data, obviously while its in safe mode there's no science downlink and they need the storage space for closest approach, so hopefully we didn't miss any black monoliths or bug eyed monsters or WTF. Also I guess this is one stressful way to prove the watchdog timer works just fine, along with safe mode procedures, and seeing just how far this thing can be pushed to perform. I suppose better now than during closest approach.

    I've been watching this mission for a couple years, thought about taking "the day" off for closest approach, but downlink is going to take hours, data embargoes, etc, so theres probably going to be nothing to actually see for months other than the usual bone they throw to the journalists and I don't need a day off for that.

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