NASA Power Tweak Extends Voyager 2 Mission Even Longer (gizmodo.com) 47
Longtime Slashdot reader canux writes: In an effort to continue to power Voyager 2's five on-board scientific instruments, NASA engineers have devised a software update that disables the probe's electrical supply safety system [to redirect the power to them]. "Although the spacecraft's voltage will not be tightly regulated as a result, even after more than 45 years in flight, the electrical systems on both probes remain relatively stable, minimizing the need for a safety net," according to NASA JPL. "The engineering team is also able to monitor the voltage and respond if it fluctuates too much. If the new approach works well for Voyager 2, the team may implement it on Voyager 1 as well."
The Voyager probes each contain a Multihundred-Watt Radioisotope Thermoelectric Generator for their power which use Plutonium-238 to generate heat to produce electricity with a thermocouple. Plutonium-238 has a half-life of a little over 87 years which means that Voyager 2 has seen a greater than 25% reduction in its power output since it was launched.
The Voyager probes each contain a Multihundred-Watt Radioisotope Thermoelectric Generator for their power which use Plutonium-238 to generate heat to produce electricity with a thermocouple. Plutonium-238 has a half-life of a little over 87 years which means that Voyager 2 has seen a greater than 25% reduction in its power output since it was launched.
Uh oh (Score:5, Funny)
I've seen enough Star Trek to know that things invariably head south the moment the safety protocols get disabled...
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OTOH, the 45-year old scientific instrument really brings more pride than scientific data these days.
Ain't that the truth. And why not, of course. Just imagining the sense of wonder that the people who are still around that put that thing together must have, in in producing a spacecraft that is outliving them. That's something worthy of ginning up some pride.
Just thinking about that brings a big grin to my face.
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You don't need Star Trek to see the same tendency in the real life. OTOH, the 45-year old scientific instrument really brings more pride than scientific data these days.
A working 45 year old instrument in Outer Space seems like a poke in the eye to modern-day engineers that design decrepitude into most of their products (because Marketing wants it that way).
Re:Uh oh (Score:4, Informative)
OTOH, the 45-year old scientific instrument really brings more pride than scientific data these days.
One of the points of TFA is that the data collected by V'ger 1 and 2 is in fact invaluable. These are the only instruments we have that far from the Sun so it's the only direct data we have. Sure we could build much better instruments today but they'd be here on Earth, not in the Heliopause and that doesn't do us any good.
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*Points vaguely to the middle distance* "V'GER!"
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I've seen enough Star Trek to know that things invariably head south the moment the safety protocols get disabled...
*Points vaguely to the middle distance* "V'GER!"
Bill Shatner banging on the door at JPL: "Hel-O-ooooooo! You wan't V'ger? This... is how you get... *dramatic gesture*... V'ger!"
It's not the half-life... (Score:5, Informative)
Re:It's not the half-life... (Score:5, Informative)
Most of the power loss is from the thermoelectric cell degradation and not from the less heat being produced by Pu-238. .
If the half life of Pu-238 is 87 years then 45 years of life is just over half of the half life. Assuming that the thermal output is proportional to the quantity of fissionable Pu then at 87 years the thermal output should be about 50% of its original output. So the >25% reduction in output described is wholly consistent with 45 years of nuclear decay. I couldn't find any documentation describing any significant reduction of output via any modality other than nuclear decay.
Re:It's not the half-life... (Score:5, Interesting)
better data [fandom.com]
> In 2011, 34 years after launch, such an RTG would inherently produce 470 W x 2-(34/87.74) = 359 W, about 76% of its initial power. Additionally, the thermocouples that convert heat into electricity also degrade, reducing available power below this calculated level.
> By 7 October 2011 the power generated by Voyager 1 and Voyager 2 had dropped to 267.9 W and 269.2 W respectively, about 57% of the power at launch. The level of power output was better than pre-launch predictions based on a conservative thermocouple degradation model.
Re:It's not the half-life... (Score:5, Informative)
I love the potential of 232U as an alternative to 238Pu. 238Pu undergoes a single 5,6 MeV, 87,7y alpha decay to 234U. But 238U undergoes:
232U (, 68,9 years, 4,9MeV)
228Th (, 1,9 year, 4,8MeV)
224Ra (, 3,6 day, 4,9 MeV)
220Rn (, 55 s, 5,6 MeV)
216Po (, 0,15 s, 6,9 MeV)
212Pb (, 10,64 h, 569 keV)
212Bi (, 61 min, 2,3 MeV)
208Tl (, 3 min, 5,0 MeV)
208Pb (stable)
And while 238Pu is an expensive manufactured product, 234U is a waste product.
The thing that's kept it out of use is that it doesn't just have alphas in its decay chain, but also some strong gammas, which has two problems: one, it makes handling it on Earth (isolation, manufacturing) more difficult; and two, it exposes your electronics to significant radiation, so you'd need to isolate generation more from electronics.
But for these benefits it provides, it feels like it's underutilized. I mean, that's a lot more energy output per kilogram.
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ED: Apparently Slashdot bans greek letters... the Pb and Tl decays are beta-minus, while the others are all alpha.
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some HTML entities work, some don't. (Parenthesised examples : & alpha ; & ALPHA ; & BETA ; ) Unicode likewise.
Do Latex codes at least display consistently, even if they're not actually decoded? Thus : \alpha, \BETA \gamma? At least providing comprehension, if not correctness.
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ED: "But 232U undergoes..."
"232U is a waste product..."
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Yeah, Rei is good value. Even if he can't properly write his name, complete with thorn (, "& thorn ;", U+00DE, U+00FE, Latex \TH, \th) thanks to Slashcode's inabilities.
That's the second reference to "llamas" I've seen today. Has Dalai, the Welsh Llama, died or something.
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At literally what weight? How much would the instruments be affected by the gamma radiation in particular?
With 238Pu being available almost for free as a by-product of the nuclear murder industry, you'd need to do a cost analysis on building your own isotope-separating production line for 232U. As well as operating your own tuned reactor(s).
Somehow, I bet there would be ... "regulatory pushback".
Re:It's not the half-life... (Score:4, Interesting)
The TEG would have undoubtedly initially produced higher voltage than the systems require, with the planned degradation of the power source producing lower voltage over time. So a voltage regulator would have been necessary to reduce the voltage to what the electronics were designed to consume. Over time the voltage has apparently dropped to the point that the output voltage is now in the range of what the electronics can handle. Voltage regulators always incur some amount of loss, so it is clever to remove it from the equation to save that small bit of energy.
The thing that is most amazing to me is that they can bypass the voltage regulator via software. It's like every circuit on the entire spacecraft can be routed or bypassed after the fact, which is unheard of in consumer type electronics.
Good capacitors (Score:2)
One of the biggest problems found on vintage electronics repair videos on Youtube are the electrolytic capacitors going bad even in sets that have seen very little use. Stuff that is not even as old as this spacecraft, with caps that end up swelling and leaking all over and destroying the other components in the set.
My guess that they are using milspec caps that don't have this problem.
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I bet there wasn't one single electrolytic in the hardware flown. You can achieve capacitance by other means - solid state tants, conductors separated by dielectrics (vacuum has a dielectric constant ; so d
V'GER (Score:4, Funny)
In order to allow the spacecraft to self manage some of its functions, they will upload an AI program. We've all seen the documentary on what happens after that.
Re: V'GER (Score:2)
Good luck doing that with a computer that makes a TRS-80 look high tech in comparison.
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V'GER was just an early Borg capture.
These are the days of miracle and wonderâ (Score:2)
â¦this is the long distance call.
Re:These are the days of miracle and wonderâ (Score:2)
â¦this is the long distance call.
Good reference!
Where can I buy an RTG? (Score:2)
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You could try the black market in ex-Soviet countries, but beware that they may not have adequate shielding. See e.g. Wikipedia:Lia radiological accident [wikipedia.org].
Re: Where can I buy an RTG? (Score:3)
You get yourself a bunch of smoke detectors...
not exactly immediate response (Score:3, Insightful)
"...engineering team is also able to monitor the voltage and respond if it fluctuates too much."
Are they?
Napkin math says the probe is 17 hours away in signal time.
Which means "error detection - remedy" is at best about a day and a half lag.
I'm going to guess that an electrical fault left for a day and a half is likely to be pretty bad.
That said, this was still a good decision; let's just not candy coat it.
Re:not exactly immediate response (Score:4, Insightful)
The output voltage of the TEG should be incredibly consistent - that is unless the laws of physics somehow abruptly change out there. The radioactive source emits at a very stable rate, and the thermoelectric generators similarly convert that radiation to electricity at an extremely stable rate. That power source should be as stable as battery power all in all.
So the only thing that could cause the voltage to change is on the other end of the circuit, which is the consumption of power by the various instruments. Turning an instrument on or off will cause the voltage to change down or up respectively - it's just the Ohms law in practice. Apparently NASA is confident that this configuration of instruments and their power consumption is very stable. If an instrument were to fail then voltage to the others will increase, but NASA must feel this is still within safety limits to not damage the other instruments. Then they can re-enable the voltage regulation in case yet another instrument were to fail thus increasing voltage even further (which might then be in the realm of damaging things).
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The thermoelectric generator can (and did) degrade causing it to produce less
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That is completely predictable and was known half a century beforehand. Do you have a point? I don't think so.
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Yes, the point was the OP mentioned it would be at "an extremely stable rate" so I was bringing up that fact (that as you mention was known to many) which OP seems to have overlooked. Is this your first time on a discussion forum?
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No, the OP didn't overlook anything. The output of the RPG is extremely stable and predictable at all times, even now. It isn't noisy, isn't sporadic, isn't variable under given load.
You only seem to add ignorance and misconceptions to the discussion
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Not sure if trolling or just bad at reading.
Star Trek joke here (Score:2)
But I'm torn between a Janeway joke and a V'ger joke.
Lasting half a century is the kind of record (Score:3)
Greater than 25% loss? Not for the nerds (Score:2)