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New Horizons enters safe mode 10 days before Pluto flyby [UPDATED]

Posted by Emily Lakdawalla

05-07-2015 22:25 CDT

Topics: New Horizons, mission status

[UPDATE] Normal operations are planned to resume July 7; see the end of this post for more.

Welp. New Horizons decided to put on a little 4th of July drama for the mission's fans. It's currently in safe mode, and it will likely be a day or two before it recovers and returns to science, but it remains on course for the July 14 flyby. Here's the mission update in its entirety.

New Horizons Team Responds to Spacecraft Anomaly

The New Horizons spacecraft experienced an anomaly the afternoon of July 4 that led to a loss of communication with Earth. Communication has since been reestablished and the spacecraft is healthy.

The mission operations center at the Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, lost contact with the unmanned spacecraft -- now 10 days from arrival at Pluto -- at 1:54 p.m. EDT, and regained communications with New Horizons at 3:15 p.m. EDT, through NASA’s Deep Space Network. 

During that time the autonomous autopilot on board the spacecraft recognized a problem and – as it’s programmed to do in such a situation - switched from the main to the backup computer. The autopilot placed the spacecraft in “safe mode,” and commanded the backup computer to reinitiate communication with Earth. New Horizons then began to transmit telemetry to help engineers diagnose the problem.  

A New Horizons Anomaly Review Board (ARB) was convened at 4 p.m. EDT to gather information on the problem and initiate a recovery plan. The team is now working to return New Horizons to its original flight plan. Due to the 9-hour, round trip communication delay that results from operating a spacecraft almost 3 billion miles (4.9 billion kilometers) from Earth, full recovery is expected to take from one to several days; New Horizons will be temporarily unable to collect science data during that time.

Status updates will be issued as new information is available.

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:

NASA’s New Horizons mission is returning to normal science operations after a July 4 anomaly and remains on track for its July 14 flyby of Pluto.

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.

“I’m pleased that our mission team quickly identified the problem and assured the health of the spacecraft,” said Jim Green, NASA’s Director of Planetary Science. “Now – with Pluto in our sights – we’re on the verge of returning to normal operations and going for the gold.”  

Preparations are ongoing to resume the originally planned science operations on July 7 and to conduct the entire close flyby sequence as planned. The mission science team and principal investigator have concluded that the science observations lost during the anomaly recovery do not affect any primary objectives of the mission, with a minimal effect on lesser objectives. “In terms of science, it won’t change an A-plus even into an A,” said New Horizons Principal Investigator Alan Stern of the Southwest Research Institute, Boulder.

Adding to the challenge of recovery is the spacecraft’s extreme distance from Earth. New Horizons is almost 3 billion miles away, where radio signals, even traveling at light speed, need 4.5 hours to reach home. Two-way communication between the spacecraft and its operators requires a nine-hour round trip.  

Status updates will be issued as new information is available.

See other posts from July 2015


Or read more blog entries about: New Horizons, mission status


Richard Adams: 07/05/2015 02:19 CDT

Is there any word/early indication as to whether or not this could be similar to the event from several years ago? I *believe* I recall New Horizons entered into a safe mode shortly (a year-ish) after launch (I've obsessively followed this mission from day 0)... a memory error or some such, I think it was. In a sense, I'm not sure if this'd really even be all that reassuring. On the one hand? Maybe today's would be something they've experienced before/already familiar with resolving. On the other - it signals a larger issue might be afoot, in the sense that repetitiveness vis-a-vis hardware/software bugs -especially coming several years apart- ain't exactly a good sign. Considering NH has spent much of the interim in hibernation, if this is a repeat of last time, *and* it's something akin to a memory error, it could spell trouble as the probe's systems become ever more taxed as the "meat+potatoes" science starts/all instrumentation gets switched on, active and recording. With that in mind, I suppose I'll actually be rooting for this to be totally separate and distinct from the event several years ago - mere days before the encounter is not exactly when you want the team to have to be pouring over and rewriting the probe's primary operating system/core instruction set software. Why this couldn't have instead happened back when they did their science "dry run" during the Jupiter encounter/gravity assist, when they basically put NH through its stress test... although, now that I mention it, didn't the *last* safe mode event I mentioned happen within like weeks of that same Jupiter encounter? Final question: Was any new instrumentation/systems turned on today; aka. Did anything different happen in the general vicinity of this error that could perhaps explain things somewhat? Even, say, something like it having had an exceptionally large amount of data (compared to before now) actively stored in memory for transmission to Earth? Fingers crossed moving forward!

rickray777: 07/05/2015 02:31 CDT

Three Deep-Space Missions 2014-'15: Philae at Comet 67P (largely failed); Dawn at Ceres (still in orbit, hale and healthy); New Horizons at Pluto-Charon (don't count on it!); Oh, well. Better one out of three than none! In any event, NASA, whatever else happens, you DO get your gold star just for trying.

Richard Adams: 07/05/2015 02:52 CDT

Hush with that talk! First: Positive thinking. *Positive!!* But dealing with the issue at hand/facts as are currently known: The probe is still up and running. Communication links remain unsevered, and it was apparently but a momentary glitch detected by the onboard systems that caused a switch over to backups/safe mode until further command from Earth - nothing more. Perhaps the most important thing of all, however: As Emily's post details, even were the probe to remain "on the fritz" for the next couple of days, lost science/irreplaceable data is nil to none. Essentially, NH is still at a point where it's "pictures only" - and whose loss is thusly of little real consequence. So assuming they switch back over to normal operations tomorrow, we'll have lost out on almost nothing. Certainly, nowhere close to the data we lost during Huygen's Titan descent phase, and *FAR* much too early yet to eulogize this mission. We're still going to uncover Pluto with NH over the next two weeks, and it'll be *AMAZING* come then! If insane/detestable politicians couldn't kill this mission, do we really think a mere glitch is going to be able to? Heck no!

MarkRM: 07/05/2015 04:15 CDT

Just curious, what exactly does "the spacecraft is healthy" mean? What kind of data does the safe mode system send back?

LocalFluff: 07/05/2015 06:55 CDT

@Richard Adams The "safe mode" several years ago only lasted for two days, Wikipedia says. Maybe now during the flyby, the entire safe mode software should be disabled? Being in safe mode during the passage would be a mission failure. I hope that the history books won't refer to this as "A James Webb Space Telescope moment".

Messy: 07/05/2015 08:04 CDT

Didn't DAWN go into "safe mode" during it's Mars encounter? There was only one photo released..... Just to reiterate, Rosetta was a major success.

Robert Walker: 07/05/2015 11:47 CDT

Yes, Dawn went into safe mode while leaving Mars on its second flyby. But it didn't lose data as far as I can tell, just missed some instrument calibration tests which it later did. "February 28, 2009 - Dawn Receives Gravity Assist from Mars Dawn flew by Mars on February 17, successfully achieving the gravity assist it needed to help it reach the asteroid belt. The spacecraft passed less than 550 kilometers (340 miles) from the surface of the planet. "As Dawn was leaving Mars, fault detection software put the spacecraft into safe mode and canceled the bonus instrument calibrations. The cause was determined to be an inappropriate software response to an expected temporary loss of valid data from the spacecraft's star tracker in the vicinity of Mars. "The operations team subsequently commanded the spacecraft back to its normal configuration. In addition, they returned the bonus calibration data that had been transferred from the instruments to the main spacecraft computer prior to going to safe mode."

Jerry Hilburn: 07/05/2015 01:47 CDT

Any update? I have a lecture tomorrow for 300+ and would really appreciate an update if possible!

Richard Adams: 07/05/2015 06:20 CDT

@LocalFluff - You do make a good/interesting point that never entered my mind, vis-a-vis disabling all precautionary measures for *the* encounter. Perhaps not a second before, but the 24 hours surrounding the 14th...? This is the entirety of the mission right then and there - getting even a minute worth of data would absolutely beat being in "safe" mode yet again and then only able to view Pluto from the proverbial rear view mirror as NH zooms on out into the Kuiper Belt region. There's absolutely no reason/motivation to preserve the craft's health and vitality for some later date - there *is* no later date to be had. What, miss out on the mission's entire reason for being in order to improve the odds of a later, still undesignated future KBO flyby...? I don't think so. They'd really be fools not to just disable everything precautionary as you suggest, especially given that 9ish hour lag time. A catastrophic fault on the 13th = DOA. Honestly, I'm most concerned about what this means for planetary science moving forward. NH barely made it to launch, and that was when NASA still had a budgetary pulse. Add in Webb, then all these ISS private rocket failures... a failed NH could spell the death knell for NASA planetary exploration in all of our lifetimes. There is a *lot* riding on this month. Unfortunately, the latest news I've just read doesn't sound good - it'll be several days yet, apparently, and this wasn't some "minor" glitch. Ugh, why did this have to happen *right* now? For a mission some decade old already, why not a month from now?

Adolf Schaller: 07/05/2015 10:19 CDT

It seems New Horizons will resume normal operations on the 7th. Fortunately the glitch was not a hardware or software fault, but a timing issue.

Adolf Schaller: 07/05/2015 10:28 CDT

@ Jerry Hilburn: New Horizons Plans July 7 Return to Normal Science Operations

jose: 07/06/2015 02:55 CDT

What type of operation caused the anomaly? Or is it a hypothesis?

rickray777: 07/06/2015 07:32 CDT

Whew! New Horizons, don't scare us like that again! But I DO have another concern, however. An atmosphere, sadly, need not be very thick to be completely opaque. Even with our modern-day Cassini at Saturn and Titan, I AM still reeling (somewhat) from that Voyager 1 encounter with Titan back in 1980! True, it may have been over thirty years ago; but I still remember the hurt I felt, as plain as day. If this turns out to be the case: The bright, pinkish areas (clouds) would be methane crystals, high and cold; the lower red-brown areas (another, deeper cloud layer) may be complex organic molecules of the sort that led (some four billion years ago) to the origin of life here on Earth. But what surface features (if any) would be producing these perplexing phenomena that we can already see in the Plutonian cloud cover? Not to mention, What IS the true size and rotational period of the dwarf planet? We would never know. Yes, I AM deeply concerned. Well, by golly, I DO hope to be proven wrong in this case!

LocalFluff: 07/06/2015 09:07 CDT

Spending time in safe mode is okay for an orbiter, but very dangerous for a fly by mission. Voyager 2 had a movable instrument platform (a luxury no later space probes has had) which got stuck during the Saturn flyby back in 1981, but the flyby was still a great success and the spacecraft is alive still today. I read that NH from the beginning indeed has been designed to disable safe modes during the flyby of Pluto. I'm confident they know what they are doing. I think they could save at least half the mission in little more than 9 hours (light travel time), if everything is at stake which it wasn't now. Even if it is out for a couple of weeks now, what is that compared to the 9½ years it has successfully worked? Think positive! It is the journey that is the target not the, ehm, target... No, that doesn't sound right. I don't want to hear it.

Michael Richmond: 07/06/2015 11:50 CDT

@rickray777: Don't worry about a thick atmosphere blocking views of the surface. Over the past decade, astronomers have watched as Pluto passed in front of a distant star. The small decrease in the star's brightness caused by the atmosphere places strong constraints on its density and optical depth. For example, this paper: states in the abstract: "we derive an upper limit for the haze optical depth of 0.0023 in the zenith direction at average CCD wavelengths." The very small value for the optical depth means very little light will be blocked or scattered.

rickray777: 07/06/2015 12:05 CDT

@Michael Richmond: Well,...okay.

Pete Jackson: 07/06/2015 12:58 CDT

I am wondering about any possible effects of the leap second, just inserted at 23:59:60 UTC at midnight on June 30-July 1. The leap seconds are only conjured up about six months in advance, so the NH team would have been unable to incorporate it into their encounter drills which were done more than six months ago. And, while all measures were presumably in place to keep mission time separate from UTC, who knows what might have crept in from other computers people may have been using. Ideally, Alan Stern could have prevailed on IERS (International Earth Rotation Service) to delay this particular LS to Dec 31, even if UT1-UTC temperarily exceeded 0.9 seconds. Hopefully, the cause, whatever it is has been found and we'll have an excellent flyby with excellent scientific results. I have been following this mission ever since launch! And after all flby is over and all the dust settles, I would be eager to hear exactly what the problem was.

emartin149: 07/07/2015 02:16 CDT

>I would be eager to hear exactly what the problem was.< Once it became apparent that the four regularly-spaced black spots weren't natural, the "problem" was implemented :)

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