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An error in Voyager 2's memory threatened its mission on the edge of the solar system. The 33-year old probe has since been successfully fixed.  (Source: NASA)

Voyager 2 is currently traveling through at the edge of our solar system.  (Source: NASA)
Reset of memory turns out to be just what the computer doctor ordered

Voyager 2 was launched 33 years ago and currently remains on course, traveling out of the solar system.  It is currently 8.6 billion miles (13.8 billion km) from Earth, passing through the heliosphere, a magnetic bubble that surrounds our solar system.  It continues to transmit data, even as it passes through this volatile region.

However, three weeks ago the probe started transmitting garbled messages to Earth.  NASA program administrators put the spacecraft in an engineering mode, restricting it to only sending health updates to Earth, while they diagnosed the issue.

It turns out the problem was caused by a single bit in the probe's memory that had flipped.  The memory was successfully reset to the proper value and normal operations resumed.  In near-Earth satellites, bit flip occasionally occurs due to solar radiation.  Since Voyager 2 was so far from the Sun, though, it's unclear exactly what caused the bit flip instance.

NASA's Voyager 2 project manager Ed Massey comments, "In some spacecraft that are closer to the sun one could think of single event upsets caused by solar activity. But we're so far away, it's hard to say that's what caused it.  We're like 93, 94 AU out."

The command to reset the probe was set on May 19, and by May 22 the probe was back in action talking to Earth in its usual fashion.

Voyager 2 was launched in 1977.  Its primary mission was to study Saturn.  Along the way the craft made flybys of all the other outer gas plants -- Jupiter, Uranus and Neptune -- thanks to a planetary alignment that only occurs once every 176 years.  Even though the probe is leaving the solar system, its sensor measurements are still yielding clues that scientists can use to determine the nature and origin of the heliosphere.

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nuclear power
By hellokeith on 5/29/2010 7:11:16 AM , Rating: 5
It's too lamentable that administration after administration we still refuse to use nuclear power for satellites. One would think that environmentalists would be profoundly happy to see plutonium sent into space where it will never return to earth.

The Voyager spacecraft are a reminder of a braver time..

RE: nuclear power
By BZDTemp on 5/29/10, Rating: -1
RE: nuclear power
By Ranari on 5/29/2010 10:02:07 AM , Rating: 3
Deep space satellites like Voyager 1/2 and New Horizons are nuclear "powered" actually. I use that term loosely, because they're not nuclear powered in the same sense a nuclear submarine would be powered:

Solar panels don't work that far out :)

RE: nuclear power
By mattclary on 5/29/2010 10:40:31 AM , Rating: 5
Besides it is not like plutonium is lying on the ground there is a not very friendly environment process in digging it out and making it useful for fuel.

LOL, science fail. You are right, it's not like plutonium is just lying around on the ground. In fact, you can dig all you want, and you won't find any.

RE: nuclear power
By jhb116 on 5/30/2010 12:31:59 AM , Rating: 1
The reactors on those satellites are so over-designed for launch and reentry scenarios that it is much more likely you'll be killed by booster fragments than the reactor spreading material "all over".

RE: nuclear power
By mcnabney on 5/30/2010 12:48:20 PM , Rating: 4
You pulled that idea out of your butt and you know it.

First off, they don't have anything even 'close' to a reactor. Second, there is no way to be 'prepared' for an accident of that sort. The space shuttle is designed to re-enter the atmosphere and a little chink in the armour obliterated Columbia. All that is required for a disaster is to have the plutonium capsule exposed to re-entry stresses to have highly radioactive debris scattered across a state or two.

RE: nuclear power
By Solandri on 5/30/2010 1:04:36 PM , Rating: 5
There were releases with earlier RTG designs. But the later designs (late 1960s onwards) have all survived re-entry intact with no release (not so sure on the Soviet ones). You know the joke about making the entire airplane out of the same material as the black boxes so it'll survive the crash? That's basically how RTGs are designed.

RE: nuclear power
By gamerk2 on 6/1/10, Rating: -1
RE: nuclear power
By schrodog on 5/29/2010 9:58:17 AM , Rating: 5
They refuse to use nuclear power for satellites that orbit Earth because of the dangers of orbit degradation and nuclear material returning to earth.

However, nuclear material is used to power satellites/probes that are headed away from the sun. As these spacecraft get further and further away from the sun, the amount of energy that they can pick up with solar cells gets smaller and smaller, thus making nuclear power the most logical choice for a power source.

RE: nuclear power
By quiksilvr on 5/29/2010 1:12:02 PM , Rating: 5
For the second paragraph, I commend you on that factual assessment.

For the first paragraph, I respectfully have to say as an aerospace engineer you have no idea what the hell you are talking about.

I can't even begin to count the number of times satellites have gone into Earth's orbit and brought back to Earth with Plutonium on board. In fact, they collected the Plutonium, placed it on another satellite, and sent it back up again.

Nuclear satellites are SAFE. It is all PR bullsh*t and there is no scientific or environmental factors hindering nuclear powered, Earth orbiting satellites.

RE: nuclear power
By Solandri on 5/29/2010 1:59:40 PM , Rating: 5
The misconception comes from a fear campaign mounted against RTGs by environmental groups. Solid plutonium is actually pretty safe. It's just an alpha emitter so it can't penetrate past your skin - it'll give you the equivalent of a sunburn if you're exposed to it. Your skin cells peel off in a couple days, and that's the end of it. Eating it is slightly worse, but it'll pass through your system in a day or two and that's the end of it.

The real danger is breathing in plutonium oxide dust. The particles are small enough to lodge in your lungs and stay there, constantly bombarding your lung cells over years or decades, eventually causing lung cancer and killing you.

So to protest RTG launches, the environmental groups pulled out statistics which said one tablespoon of plutonium could kill tens of thousands of people or some such thing, while omitting the little bit about having to first grind it into a fine powder then spread it evenly among all those people and have them inhale it. When someone pointed this out, they theorized that re-entry could cause the plutonium to burn up, presumably aerosolizing it and creating a hazard for lungs around the world. They conveniently overlooked that RTGs are designed to survive re-entry intact.

If you really, truly fear breathing in radioactive particles, you should be demanding all our coal plants immediately be replaced with nuclear plants. Coal contains trace amounts of uranium and thorium (they contain more energy than the coal itself actually), which is released into the atmosphere as a component of coal ash dust. With a nuclear plant, the radioactive materials are stored in solid form where they're easily contained and safe to handle. And at present, none of the renewables except hydro can produce electricity as cheaply, consistently, and in the amounts we need. So nuclear is really the only option.

RE: nuclear power
By icanhascpu on 5/29/2010 6:02:54 PM , Rating: 3
Welcome to the world of religious logic.

RE: nuclear power
By SharkManEXR on 5/31/2010 12:49:23 PM , Rating: 3
here is another example of religious logic

RE: nuclear power
By Shadowself on 5/29/2010 6:48:36 PM , Rating: 4
While the hazards of external exposure are pretty small, they are more than just the equivalent of a sunburn. The issue is lower levels of the skin get the nuclei damaged. This raises the chance of skin cancers above that of a simple sunburn. The risk is still not great, but it is significantly more than just a sunburn.

Ingestion is a huge issue. Plutonium goes to both the major organ soft tissue and to the major bones. About 10% of what is ingested is eliminated from the body in about 24 to 48 hours. About 45% of what is ingested goes to major soft tissue organs (e.g., the liver). The average biological half life for Pu is approximately seven years for those organs. The remaining 45% goes to the bones with the majority of that going to the major bones. The biological half life in the major bones is longer than the radiological half life. Strangely Ca and other metals get swapped out during bone remodeling preferentially to Pu. For some reason, not fully understood yet, the Pu seems to stay and stay. Note the difference in the two terms biological versus radiological half life.

Additionally, since Pu sits on the surface of the bone (versus radium which goes deep into the bones and stays there), Pu is always decaying near the undifferentiated cells that destroy and then rebuild your bones on a continuous basis. Thus the rate of cancer due to Pu is higher than for Ra or U for the same level of activity (number of decays in a given period).

Therefore ingesting Pu is bad. Period.

How do I know? I was the person who actually did the analysis on a 30+ year study doing a differential analysis of animals for Ra, U and Pu (plus a few side studies of other transuranics).

Yes, everyone talks about lung issues because of the Radon and Radium issues and the natural occurrence of those. They often extrapolate those to Pu and other transuranics. This is not a grossly inaccurate extrapolation. It is just not 100% accurate. However, ignoring other ingested amounts of Pu (extremely rare to happen) is foolish. Ingested Pu can be a significant hazard. It's not a real world risk, but it is a risk.

Actually, from all the open air testing, from all the different countries that have done open air testing (not just the U.S., USSR and China!) if you take a square foot of the Earth you'd get, on average around the globe, approximately two decays per second due to the Pu fallout. A tiny amount but not undetectable.

This is why we built a room years ago made exclusively out of pre WWII steel. The walls, floor and ceiling were made from a pre WWII battleship -- about 12 to 14 inches of solid steel. The background radiation in that room was way below the background outside. When a person walked into that room s/he was the most radioactive thing in there.

The reality is that the amount of Pu from a reentry of an RTG is tiny compared to the background from all the open air testing done in the past six decades.

RE: nuclear power
By Solandri on 5/29/2010 9:12:41 PM , Rating: 3
While the hazards of external exposure are pretty small, they are more than just the equivalent of a sunburn. The issue is lower levels of the skin get the nuclei damaged. This raises the chance of skin cancers above that of a simple sunburn. The risk is still not great, but it is significantly more than just a sunburn.

I was under the impression alpha particles had nowhere near the penetrating power of UV rays. A quick google search seems to bear that out:

Skin penetration of 0.045 mm for alpha particles vs. less than 1 mm for UV rays (several tanning FAQs cite 2mm). While no doubt alpha particles have much more energy and are much more likely to damage and kill off the uppermost skin cells (leading to it peeling off), the less energetic UV rays seem much more likely to merely damage deeper skin cells without killing them, thus leading to melanomas.

Ingestion is a huge issue. Plutonium goes to both the major organ soft tissue and to the major bones. About 10% of what is ingested is eliminated from the body in about 24 to 48 hours. About 45% of what is ingested goes to major soft tissue organs (e.g., the liver).

Thanks for the update. The previous information I had was that less than 1% was absorbed, and most of it passed through. Do you by chance have a link to the study(ies)? 45% absorption seems unusually high for a heavy metal.

RE: nuclear power
By Mclendo06 on 5/29/2010 7:51:22 PM , Rating: 4
Allow me to apply some nucleophobe editing to your comments...

The misconception comes from a fear campaign mounted against RTGs by environmental groups. Solid plutonium is actually pretty safe. It's just an alpha emitter so it can't penetrate past your skin - it'll give you the equivalent of a sunburn if you're exposed to it. Your skin cells peel off in a couple days, and that's the end of it. Eating it is slightly worse, but it'll pass through your system in a day or two and that's the end of it.

translates to...

Solid plutonium is ... an alpha emitter... [I]f you're exposed to it, your skin ... [will] peel off in a couple days, and that's the end of [you]. Eating it is ... worse... [Just] a [single] day [until] the end...

RE: nuclear power
By FaaR on 5/30/2010 9:22:36 AM , Rating: 2
Funny. I giggled to myself.

Regardless, the dangers of plutonium should not be trivialized... It's a heavy metal and is innately extremely biologically toxic. Nobody should consider it (relatively) harmless when ingested because it "only" fires off alpha particles when it decays. :)

Like pretty much any other heavy metal, it's just plain bad news when it gets into our bodies.

Firing plutonium (or similar) up into space atop of rockets may be fairly safe on the whole, but should we put it into common practice undoubtedly something bad would happen one day, regardless how well contained the radioactive material is. It's just a matter of statistics (and the prone-ness of humans to make mistakes, either by laxness or incompetence or otherwise.)

For satellites in earth orbit, just sticking a couple solar panels on 'em is going to be a much simpler option from an engineering point of view, and it's certainly going to be A LOT cheaper also. The sun provides plenty power for the satellite's instruments. Increased safety is really just a bonus.

For probes destined for the outer solar system there's of course no alternative to the "nuclear batteries" currently being used. That's a legitimate need, and it should continue to be practiced when needed until the time some less risky alternative becomes available. Cold fusion, perhaps? :D

RE: nuclear power
By Solandri on 5/30/2010 12:53:12 PM , Rating: 2
For satellites in earth orbit, just sticking a couple solar panels on 'em is going to be a much simpler option from an engineering point of view,

It's not quite that simple. Having solar panels means you have to keep them oriented towards the sun, The satellite usually needs to keep an antenna oriented towards the ground for communications, and the angle between that and the sun will constantly be changing. So you need to add moving parts and all the headaches those entail. And you've increased the number of times the satellite will have to change/fine tune its orientation in its lifetime. Hydrazine / reaction mass for maneuvering is precious and irreplaceable in space - when it runs out, your satellite is dead even if it's otherwise fully functional. You also need a battery pack for when the satellite is in the Earth's shadow, and those tend to not last as long as solar panels.

It's still probably cheaper than an RTG for stuff around Earth orbit (or even Mars orbit) or closer. But it adds a not insignificant amount of complexity, and decreases the reliability of the system.

RE: nuclear power
By ZachDontScare on 6/2/2010 2:44:44 PM , Rating: 2

RE: nuclear power
By maven81 on 5/29/2010 4:48:01 PM , Rating: 2
Don't compare reactors to RTGs.
As far as I know no RTG has ever failed. The soviet union has used nuclear reactors in quite a few satellites, and some of those have failed. As I recall there was a re-entry incident in the 70s. But even then it should be noted that the environmental damage was minimal.

RE: nuclear power
By Shadowself on 5/29/2010 6:56:41 PM , Rating: 5
Define "failed".

Several RTGs failed to perform as expected. Is that a failure?

One U.S. reactor, the SNAP10A in the 60s went through a SCRAM event then was not restartable -- but it performed exactly as it was designed to perform. Is that a failure?

There have been more reentries than the reactor from a RORSAT that landed in Canada. That was just the most famous one. For that one the environmental damage was not minimal. No one should ever state it that way. The environmental damage was contained and the cleanup costs were less than $10 million or so (in then year dollars). That region is still being monitored for possible long term effects.

There is a reactor up there leaking radioactive sodium. It is an annoyance to scientists doing deep space research because the trail it has been leaving for years has raised the "background noise" for scientists having to look through that crap to measure what they want to measure.

RE: nuclear power
By Shadowself on 5/29/2010 7:00:50 PM , Rating: 5
There is a formal process in place for either the U.S. Government or a U.S. Commercial Entity (yes, that's right a U.S. Commercial Entity!) to launch a reactor into Earth orbit and operate it in Earth orbit. The legal process whereby it can be done exists. It has existed for about a decade.

How do I know? I lead the technical side of the team that put the process in place from the commercial side. To date no company has filed to do such a launch, but the process to do so is legally on the books.

RE: nuclear power
By hellokeith on 5/29/2010 9:13:25 PM , Rating: 1

Here's an article for reference:

My understanding is that this is a political issue. There is a way for entities to get Plutonium, but the US has not produced it in a long while, so supplies are very limited. Perhaps non-proliferation treaties prevent or complicate the production?

RE: nuclear power
By DesertCat on 5/29/2010 12:32:38 PM , Rating: 2
Well the Cassini probe that was launched in the late 90's and that is currently orbiting Saturn also uses the plutonium powered generators. Like most deployments of this tech, the spacecraft is just too far from the sun to rely on solar panels. I recall a figure of something like 750W of electricity from the 3 plutonium generators on that craft.

Even then, there was a small contingent of people concerned about that spacecraft when it did a fly-by/slingshot maneuver past earth around 1999 (crash/burn up in atmosphere worries).

RE: nuclear power
By rs1 on 5/31/2010 10:07:22 PM , Rating: 5
I disagree. There's no reason at all to use nuclear power on satellites. Probes, yes. If we ever send a manned vehicle to Mars, then yes for that, too. But satellites? Why should a satellite be nuclear powered? Especially given the increasing amount of junk in orbit, and the demonstrable ability of multiple nations to shoot down satellites in orbit. Launching a bunch of nuclear powered satellites would just be stupid.

RE: nuclear power
By aguilpa1 on 6/4/2010 2:34:31 PM , Rating: 2
don't need nuclear power, need error correcting memory.

My heart dances with nerdish joy
By MBlueD on 5/29/2010 6:51:31 AM , Rating: 5
Long Live V'Ger!

RE: My heart dances with nerdish joy
By FaceMaster on 5/29/2010 9:23:06 AM , Rating: 5
'...have you tried turning it off and on again?'

By DFranch on 5/29/2010 3:46:20 PM , Rating: 1
ctrl + alt + delete

By Chernobyl68 on 6/2/2010 6:55:40 PM , Rating: 2
the IT crowd

By AssBall on 5/29/2010 7:28:09 AM , Rating: 2
A bit flipping 93 AU out IS strange for the distance. Also bits take much more energy to occur in the big transistors they used in 1977 memory than in today's electronics.

RE: weird
By Indianapolis on 5/29/10, Rating: -1
RE: weird
By Indianapolis on 5/30/2010 4:43:16 PM , Rating: 1
What??? That's his name!

What is this? Some guy walks into a room with a name tag that says "Hi, my name is AssBall", and I'm not supposed to notice it?

Oh, I forgot. Here on, posters are judged by the content of their comments, and not the appearance of their screen names.**

**Does not apply to "Reader1". No need to read his comments before rating him down.

RE: weird
By maven81 on 5/29/2010 4:50:56 PM , Rating: 2
It's odd that they don't mention cosmic rays... These surely have enough energy to do a bitflip, and in the outer reaches of the solar system there's nothing protecting you from that radiation.

RE: weird
By Shadowself on 5/29/2010 7:06:38 PM , Rating: 4
It was almost certainly a GCR (galactic cosmic ray) event. The LET of those particles can easily flip a bit in 1970s circuits. Even if they did shielding with high-Z materials (a typical method) a high energy GCR would decay in the shielding and the bremstralung radiation could still quite likely flip a bit.

RE: weird
By maven81 on 5/29/2010 10:59:06 PM , Rating: 3
It's great hearing from someone that knows so much about Radiation (I'm not being sarcastic, that was interesting information on shielding).
I just wanted to add that NASA's omission of this explanation is really peculiar because it's not even that rare. I don't have much experience studying the effects of GCRs on computer memory, but I have seen raw data from spacecraft CCD sensors, and they register strikes quite often.

RE: weird
By kattanna on 6/1/2010 11:25:37 AM , Rating: 1
It's odd that they don't mention cosmic rays

they have stated they are not sure yet what caused the glitch. a statement from a real scientist.

now, if they were climate "scientists" they would have stated as fact that it was the worst possible outcome and that they "know" it is so because their computer models said so.

The NASA Help Desk...
By iFX on 5/29/2010 12:07:03 PM , Rating: 5
Engineer: Hi, we're having a problem with our long range space probe, the data stream seems to be corrupted.

Help Desk: Have you rebooted yet?

Engineer: Uhh, I don't see how that would solve our problem, all systems are functioning. Can you send this to a level II engineer please?

Help Desk: I can't escalate this until we do the trouble shooting steps. Please reboot the probe's memory systems and let me know.

Engineer: That's ridiculous, you're just reading from a script, you have no idea what...

Help Desk: Look, if you don't let me help you I can't, just reboot the probe please.

Engineer: *Mumbling* I swear every time I call I get some moron who can't even... Uhhh, looks like everything is working now... uhhh I guess the problem "corrected" itself.. uhhh, thanks, bye.

Help Desk: Another one bites the dust...

RE: The NASA Help Desk...
By chagrinnin on 5/29/10, Rating: 0
RE: The NASA Help Desk...
By 440sixpack on 5/29/2010 11:35:11 PM , Rating: 2
And at that distance, how long does it take to send the reboot command, wait for it to execute, then get a message back? Something like 24 hours? That's a long wait for a reboot. :-)

RE: The NASA Help Desk...
By sld on 5/30/2010 2:30:48 PM , Rating: 4
Light takes about 8 minutes to travel from the sun to the earth. That's a distance of 1 AU. The probe is 94 AU away, so a rough calculation gives 12.5 hours?

By spathotan on 5/29/2010 1:06:26 PM , Rating: 2
33 years and still going strong, talk about a damn good investment. Amazing technology and an amazing feat during NASA's finer days. Before the dark times....before presidents started pulling funding and then shoving said funds down the throat of oil tycoons and the chinese.

RE: Amazing
By maven81 on 5/29/2010 5:02:19 PM , Rating: 3
it's not that black and white.
Voyager itself was a scaled down mission. I believe the original was called the grand tour mission, and was meant to be more extensive. Voyager is actually the cut down version.
So even back then there were budget cuts.
The last of the great probes is Cassini and that was launched "only" 13 years ago and should keep functioning for quite a while yet.

RE: Amazing
By geddarkstorm on 5/31/2010 2:09:25 PM , Rating: 2
For over a thousand generations, the Voyager Probes were the guardians of peace and justice in the Old NASA. Before the dark times... before the Empire.

RE: Amazing
By JediJeb on 6/3/2010 6:27:21 PM , Rating: 2
Great probes the Voyagers are. Much information continue to provide they will.

By manofhorn on 5/29/2010 11:55:29 AM , Rating: 3
i bet little green men jumped aboard and switched the bit. just to screw with us.

it was either little green men or oompaloompas.

RE: aliens
By drycrust3 on 5/29/2010 7:19:59 PM , Rating: 2
Ummm ... If bit flipping happens when you get too close to something the emits radiation, like the sun, and a bit flipped in Voyager 2, then does that mean it is close to something the emits radiation? Ignoring the obvious conspiracy theories (as in "an abandoned United States Army Air Corps desert base" a la Capricorn One), since it carries it's own nuke pack, maybe that is slowly going "critical", if so, let's hope no aliens find it before it blows up.

RE: aliens
By geddarkstorm on 5/31/2010 3:31:08 PM , Rating: 2
Oompa loompa doopa dee dee. I'm in your probe on a bit flipping spree.

deep space radiation
By xrror on 5/29/2010 6:43:54 PM , Rating: 2
It would be interesting to see if the unexplained bit flips "so far from the sun" are possibly due to nearing the edges of the heliosphere. I'm guessing one of NASA's goals is to gain more experience with conditions so far out?

It would be interesting to see if/how Voyager I's trajectory exposed it to different conditions than Voyager II.

RE: deep space radiation
By zmatt on 5/30/2010 11:26:31 PM , Rating: 2
That was my first guess. The heliosphere does essentially the same thing our planetary magnetic field does, but for the solar system. Getting close to the edge exposes you to galactic radiation. Something we really don't have a lot of information on? That and Voyager is old so shielding being something that can decay, and the same with electromigration (it's been on 24/7 for 33 years after all) just one bit flip seems par for the course. Luckily it seems NASA is used to this kind of thing.

just my $.02 from a non-expert.

By Pessimism on 5/31/2010 9:36:05 AM , Rating: 2
I hope they used RAM with a lifetime warranty on that probe.

By FPP on 5/31/2010 1:46:43 PM , Rating: 2
What?...33 years not long enough?

Voyagers are still my fav
By NA1NSXR on 5/30/2010 12:08:25 AM , Rating: 3
I was enchanted by its photography as a kid and its nice to hear #2 is still healthy!

reset button FTW
By cokbun on 5/30/2010 3:06:01 AM , Rating: 2
reset buttons are cool

just wondering
By spepper on 5/29/2010 9:20:44 AM , Rating: 1
I'm just wondering what the reaction would be, if an extraterrestrial being encounters the messages on board V'ger for the first time-- especially, that of that fellow from White Plains Georgia: yes, our beloved former President Jimmah Cartah! I'm guessing it would go something like the reaction a dog makes when it hears a strange noise-- staring wide eyed with its head cocked to one side.......

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