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Pioneer Anomaly Solved By 1970s Computer Graphics

CmdrTaco posted about 3 years ago | from the whats-your-vector-victor dept.

NASA 169

Frans Faase updated us on a Pioneer Mystery we've been following for many years: something is tugging Pioneer 10 & 11. A few years ago a theory surfaced but now "A new computer model of the way heat is emitted by various parts of the Pioneer spacecraft, and reflected off others, finally solves one of the biggest mysteries in astrophysics. Previous calculations have only estimated the effect of reflections. A computer modeling technique called Phong shading was used to work out exactly how the the emitted heat is reflected (PDF) and in which direction it ends up traveling. Taking into account the reflections on the antenna seem to make the anomaly disappear."

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169 comments

Pong? (-1)

Anonymous Coward | about 3 years ago | (#35678064)

Speaking of 70s graphics... when I saw "Phong" I thought "Pong." Only natural. It did rock the world in its day.

tao of physics?? (0)

ShitSoup (2022948) | about 3 years ago | (#35678090)

So it seems, the mystery ain't a mystery after all... No more hookum about some "unknown" force. Glad to know.

Re:tao of physics?? (1)

John Hasler (414242) | about 3 years ago | (#35678156)

While a mundane explanation has always seemed most likely, why is is "good to know" that an exciting new discovery isn't going to happen?

Re:tao of physics?? (3, Insightful)

Zephyn (415698) | about 3 years ago | (#35678326)

Because focus can now be placed elsewhere instead of continuing to investigate a red herring.

While it is sometimes disappointing that unknown effects don't always turn out to be from unknown causes, having the exciting new discoveries come from the basis of fact rather than imagination is the main difference between actual science versus everything else that claims to be science.

Re:tao of physics?? (1)

gad_zuki! (70830) | about 3 years ago | (#35678672)

I'm not sure how this become the "biggest mystery in astrophysics." Maybe to the ADD addled tech crowd and other casual people who were using it as code for "hey, maybe aliens." It was like a "god of the gaps" argument. Well, "alien of the gaps."

Occam's razor, use it.

Re:tao of physics?? (3, Insightful)

Chris Burke (6130) | about 3 years ago | (#35678996)

Well and every crackpot trying to overturn all of modern physics/cosmology without understanding it first. The number of times I've heard the Pioneer Anomaly brought up as evidence that modern physics was fundamentally broken and the Scientific Clergy refused to admit it is... very large. I think I've even heard EU morons claiming that their plasma cosmology explained the Pioneer Anomaly.

Of course nobody who latched on to the anomaly will be satisfied by this explanation. So it goes...

Re:tao of physics?? (1)

bill_mcgonigle (4333) | about 3 years ago | (#35679706)

Of course nobody who latched on to the anomaly will be satisfied by this explanation. So it goes...

Not so. Since I heard about it, I've allowed the possibility that Newtonian/relativistic physics may have some inaccuracies at very large scales, or that something about space was unknown.

Now this calculation offers a much simpler explanation, so I'll count it as far more likely to be true. I'd previously assumed those writing the papers would have accounted for it.

But until we have a Grand Unified Theory, or at least a provable theory of gravity that works at quantum scales, I'm not going to place any 300-year bets that our current understanding of physics is Correct(tm). Useful tools, definitely, but any higher level of Belief is religious in nature.

Re:tao of physics?? (1)

Kelbear (870538) | about 3 years ago | (#35679168)

Also, it's just plain cool when applied math explains away the mysteries of the world. To my perspective as a layperson, it's incredible how many layers of ingenuity piled up to enable someone to explore and explain some odd phenomenon bouncing off a craft hurtling through space.

Re:tao of physics?? (1)

dkleinsc (563838) | about 3 years ago | (#35678160)

No, clearly this is part of the great conspiracy known as NASA! They're hiding something, I tell you! It's the aliens, the same ones that helped them fake the moon landing! So yeah, this "finding" has to be part of the great cover-up. It couldn't be simply the laws of physics.

(this is the commenter's physician: a sedative has been administered, and he's been returned to his padded cell)

Re:tao of physics?? (4, Insightful)

The Grim Reefer2 (1195989) | about 3 years ago | (#35678218)

So it seems, the mystery ain't a mystery after all...

That tends to happen when you solve them.

Re:tao of physics?? (1)

VGPowerlord (621254) | about 3 years ago | (#35678368)

So it seems, the mystery ain't a mystery after all...

That tends to happen when you solve them.

and like usual, the butler did it!

Re:tao of physics?? (1)

ackthpt (218170) | about 3 years ago | (#35678418)

So it seems, the mystery ain't a mystery after all...

That tends to happen when you solve them.

and like usual, the butler did it!

Ah, ha. But, who is the Butler?

When I first saw the splash paragraph I was expecting a Commodore PET was figuring into this somehow.

Re:tao of physics?? (0)

Anonymous Coward | about 3 years ago | (#35678462)

Butlers do solve everything, don't they? I guess I should look into getting one.

Re:tao of physics?? (2)

Gilmoure (18428) | about 3 years ago | (#35678956)

Real men know how to butle themselves.

Re:tao of physics?? (0)

Anonymous Coward | about 3 years ago | (#35679930)

You'll go blind doing that! Then all the Phong shading in the world won't help you.

Re:tao of physics?? (2)

PPH (736903) | about 3 years ago | (#35678226)

Its that feeling you got in 8th grade algebra when you did all the work and your answer matched the one in the back of the book.

Re:tao of physics?? (3, Insightful)

Kjella (173770) | about 3 years ago | (#35678430)

Sadly, unless it's one of the big unsolved problems or it takes a PhD to even understand the problem it's probably been solved before. We had a math book that so barely mentioned perfect numbers, I spent a lot of time reaching a result that I felt was "new". Eventually it turns out I had recreated a proof that Euler did in the 18th century. At least it wasn't the Greek, every time you feel bright then you learn someone already figured this out 2000 years ago.

Re:tao of physics?? (-1)

Anonymous Coward | about 3 years ago | (#35678440)

Cool story, bro.

Re:tao of physics?? (-1)

Angostura (703910) | about 3 years ago | (#35678984)

I'm more concerned by the fact you think that 2011-1700 is roughly equal to 2000

Re:tao of physics?? (2)

Chris Burke (6130) | about 3 years ago | (#35679028)

Notice how in that sentence he was talking about the Greeks.

Re:tao of physics?? (0)

element-o.p. (939033) | about 3 years ago | (#35679340)

Yeah, but he also said "...it wasn't the Greeks..." So in this case, someone didn't figure it out 2000 years ago; someone figured it out ~300 years ago.

Re:tao of physics?? (4, Informative)

Chris Burke (6130) | about 3 years ago | (#35679462)

Yes, he said "at least it wasn't the Greeks", because of how often he finds out that something he thought was novel was discovered by them. Which would be 2000 years ago. Merely 300 years ago is better. Thus "at least it wasn't the Greeks".

Got it now?

Re:tao of physics?? (1)

Anonymous Coward | about 3 years ago | (#35679274)

When I was 10, while drying the dishes, I realized that the water wasn't actually going away; was just changing position/form. From this, I realized that energy was the same way (thinking about sunshine and how the photons get absorbed/radiated as heat, etc). And then, a few years later, found out someone else had already figured out this thermo dynamics stuff. Decided then and there I'd stop wasting time with this brain thing and devote my life to viewing porn.

Re:tao of physics?? (1)

Kell Bengal (711123) | about 3 years ago | (#35678466)

Clearly the true test was to see which students were smart enough to simply copy the answer from the the back of the book in the first place. It's a strategy that serves me well to this day. Now, if only I could find where I put the answer booklet for members of congress...

Re:tao of physics?? (2)

ColdWetDog (752185) | about 3 years ago | (#35678582)

Now, if only I could find where I put the answer booklet for members of congress...

It's in your wallet.

Re:tao of physics?? (1)

sconeu (64226) | about 3 years ago | (#35678706)

To futher clarify ColdWetDog's answer.

The answer booklet is gray/green hand has a picture of a dead president, or a Founding Father on it.

Re:tao of physics?? (0)

Anonymous Coward | about 3 years ago | (#35678758)

Thank you for shedding light where there was no darkness.

Re:tao of physics?? (1)

robthebloke (1308483) | about 3 years ago | (#35679108)

For you maybe. For me however, the connection between the Queen and Congress wasn't immediately obvious....

Re:tao of physics?? (1)

ColdWetDog (752185) | about 3 years ago | (#35679112)

Don't be so limiting. Politicians also take credit cards, bullion, golf trips, Interns, chickens.... I guess I'll just stop here.

Re:tao of physics?? (1)

sconeu (64226) | about 3 years ago | (#35679728)

Pretty hard to fit any of those, except for credit cards, into your wallet.

How *do* you fit an intern in there, anyways?

Re:tao of physics?? (1)

Machtyn (759119) | about 3 years ago | (#35678804)

Until you found out that the answers in the back of the book were also wrong. Darn interns.

Re:tao of physics?? (-1)

Anonymous Coward | about 3 years ago | (#35678508)

One less straw for Space Nutters to grasp at. We have a very good understanding of physics, and no space mining or colonization will be practical under our current understanding of physics and technology.

To be fair... (4, Informative)

cobrausn (1915176) | about 3 years ago | (#35678116)

The technique for Phong Shading was introduced in 1973 as an improvement to Gouraud Shading, but was too computationally intensive to be used for graphics back then. This is no longer the case [valvesoftware.com].

Re:To be fair... (5, Interesting)

BitterKraut (820348) | about 3 years ago | (#35678270)

It is also interesting to note that Phong shading is based on an empirical formula. That means it has not been derived from any known (i.e. accepted) "laws of nature". It is used in Computer Graphics because it can be calculated efficiently and approximates what we see or measure closely enough. Strictly speaking, it is not possible to scientifically explain any phenomenon by showing that Phong shading explains it. But as it seems, the whole scenario is so complex that showing its compatibility with the Phong model must already be regarded as a remarkable achievement.

Re:To be fair... (0)

Anonymous Coward | about 3 years ago | (#35678404)

If you're dealing with point light sources, it's possibly the case that Phong approximates the actual behaviour fairly well. However, I do wonder about the accuracy of the calculations. We're talking about quite a long distance between the light source and the surface!

Re:To be fair... (3, Informative)

Dr. Gamera (1548195) | about 3 years ago | (#35678646)

It's not the radiation pressure from the sun that they're calculating, it's thermal effects from the on-board plutonium on the back of the antenna. So the source of the slowing is a very short distance away.

Re:To be fair... (1)

j00r0m4nc3r (959816) | about 3 years ago | (#35679486)

the whole scenario is so complex that showing its compatibility with the Phong model must already be regarded as a remarkable achievement.

I think what is remarkable is that the monolith is able to make its effect on the probes look identical to phong shading.

Re:To be fair... (2)

Dr. Gamera (1548195) | about 3 years ago | (#35678682)

The whole "1970s computer graphics technique" thing is sort of silly anyway. If anything, it's surprising that the technique was invented so recently. "Area under curve in Second Life calculated by 1600s mathematics technique..."

Re:To be fair... (2)

dachshund (300733) | about 3 years ago | (#35679078)

The technique for Phong Shading was introduced in 1973 as an improvement to Gouraud Shading, but was too computationally intensive to be used for graphics back then. This is no longer the case.

And the saddest thing is that Phong died shortly after completing his dissertation. So he never knew the impact his techniques had on the field.

But... Phong is wrong (3, Interesting)

pyalot (1197273) | about 3 years ago | (#35678200)

everybody knows that. A much better aproximation to real life surfaces are the Oren–Nayar or Cook-Torrance models of the family of BRDFs.

Re:But... Phong is wrong (0)

Anonymous Coward | about 3 years ago | (#35678346)

Yes, i totally agree with you.

Re:But... Phong is wrong (1)

cobrausn (1915176) | about 3 years ago | (#35678372)

Phong is only 'wrong' in graphics if it produces something other than what you expect as the result. Ah, computer graphics. It should be added to that old saying, 'Close only counts with horseshoes, hang grenades, and now, computer graphics.'

Re:But... Phong is wrong (2)

pyalot (1197273) | about 3 years ago | (#35678806)

So Phong is "right" for the probe, because it incidentally matches what they're seeing better? Alright, I propose a better solution, how about we invent some imaginary matter with exotic properties permeating the space, but that can't be seen, which incidentally has exactly the right properties to fit the measured data?

Saying Phong is right after fitting the calculated data to the measured data just suspect.

Re:But... Phong is wrong (1)

cobrausn (1915176) | about 3 years ago | (#35678842)

I should point out that I was only referring to the 'computer graphics' part of Phong Shading, not the application mentioned in the article. I also find the result suspect - the Phong method is 'right' here only because it fits the data, which is interesting, but proves nothing until they can explain why.

Re:But... Phong is wrong (3, Informative)

tnk1 (899206) | about 3 years ago | (#35679720)

They did explain why. Thermal effects. The only thing that Phong shading did was to remove an obstacle to that hypothesis that was merely due to built-in inaccuracies in how they accounted for those effects initially.

In other words, the shading increased the accuracy of the calculations and it was found that when it was applied the most likely solution became even more likely.

While it is true that the Phong solution is still likely "wrong" due to being not perfectly accurate, it's still a lot less wrong than thermal effects uncorrected, and much, much less wrong than assuming aliens or an entirely new discovery in gravitation.

Re:But... Phong is wrong (1)

Anonymous Coward | about 3 years ago | (#35679672)

Alright, I propose a better solution, how about we invent some imaginary matter with exotic properties permeating the space, but that can't be seen, which incidentally has exactly the right properties to fit the measured data?

Oh, oh! I know! Let's call it "Dark Matter"!

Re:But... Phong is wrong (1)

Anonymous Coward | about 3 years ago | (#35678506)

No need to use models. Just measure the BRDFs (bidirectional reflectance distribution function [wikipedia.org]) of the materials that Pioneer is made of and then use photon mapping to calculate an even better approximation of the energy transfer. Or, you know, don't overdo it and use the Phong approximation because it's good enough when you don't know the exact surface condition after decades in space.

Re:But... Phong is wrong (1)

pyalot (1197273) | about 3 years ago | (#35678748)

Clearly this problem needs more effort to solve conclusively. For this purpose I'd propose constructing a probe that's as close to perfectly spherical as you can get, with a surface that's carefully adjusted to be perfectly diffuse according to the phong model, and which includes self-measuring capabilities (something like retractable cameras) to measure their own reflective properties after prolonged exposure to the solar medium.

Re:But... Phong is wrong (3, Insightful)

fatphil (181876) | about 3 years ago | (#35678998)

And the earth isn't round either. It's just a closer approximation to reality than
saying the earth is flat. Or saying that Pioneer is a spherical cow. Scientists aren't looking for something that is right rather than wrong, they are looking for something that bounds the error term in a significantly tighter way. Phong apparently does this. Presumably any ad-hoc model that approximated reality closer than what was done before would have also decreased the error bounds.

And Oren-Nayar? Have you mistaken Pioneer for a slab of concrete?

Phong shading? (1)

Anonymous Coward | about 3 years ago | (#35678222)

Instead why don't they solve the radiosity equation at a 1 mm^2 resolution? That should be feasible with today's computing power, and indisputably give the correct answer.

Re:Phong shading? (1)

Splab (574204) | about 3 years ago | (#35678294)

Because the "room" they are shading is rather large, think universe size.

Also, since the Phong shading did the trick why bother?

Re:Phong shading? (1)

maxwell demon (590494) | about 3 years ago | (#35678644)

The universe could well be modelled by a small black box around Pioneer with temperature 2.7 Kelvin. It "absorbs" any radiation going into it and sends 2.7 Kelvin thermal radiation. Indeed, probably they neglected the 2.7K radiation anyway, so all that remains is a black box. That's about the easiest part to model.

However I guess Pioneer has not completely diffuse reflection (it probably has some shiny metal parts), and that would be a problem for radiosity.

Re:Phong shading? (0)

Anonymous Coward | about 3 years ago | (#35679196)

Your post got me thinking... is it possible to design an object that will continuously gain momentum in space in some given direction, purely because of the interaction between the CMB and the object's asymmetric shape and material?

Re:Phong shading? (3, Informative)

camperdave (969942) | about 3 years ago | (#35679736)

They don't have to worry about the radiation of the universe. Pioneer has a radioactive battery which serves not only to power the on board electronics, but to keep them from freezing. The heat from the Warm Electronics Box is soaking through the craft and being emitted as infrared photons. These photons are bouncing off the back of the radio dish antenna and are slowing down the craft.

Re:Phong shading? (1)

TerranFury (726743) | about 3 years ago | (#35678590)

The article posted by Intron here [slashdot.org] seems to indicate that they did spend some time solving something like Laplace's equation. I haven't read the paper, so I don't know whether radiative transfer between different components of the spacecraft was considered, or just conduction.

Excuse my ignorance (0)

Anonymous Coward | about 3 years ago | (#35678224)

But how exactly is heat contributing to this? Unlike most Slashdotters, I'm no self-professed rocket scientist. My understanding of space propulsion is that you throw some mass in the opposite direction of the one you want to travel in

Re:Excuse my ignorance (0)

Anonymous Coward | about 3 years ago | (#35678278)

Mass or energy, since they're both the same thing. Infrared radiation is energy after all.

Re:Excuse my ignorance (0)

Anonymous Coward | about 3 years ago | (#35678300)

> But how exactly is heat contributing to this?

The heat in question is nuclear power.

This heats reflection off of the superstructure of the craft is the source.

Re:Excuse my ignorance (1)

utoddl (263055) | about 3 years ago | (#35678302)

Right, well, heat is energy, which as Einstein showed, is mass. So, figure out the net "heat emitted" vector and you've got your opposite reaction thingy right there.

Re:Excuse my ignorance (2)

maxwell demon (590494) | about 3 years ago | (#35678450)

The important part is not the mass, but the momentum. Total momentum is conserved, therefore to accelerate (i.e. to increase your momentum) you'll have to emit something carrying the momentum difference (because in space, there's nothing else you could transfer your momentum to). One way is just to throw some matter out, which then of course has backwards momentum, thus giving you forward momentum (remember, the sum must be zero). But radiation also has momentum, therefore you can also emit radiation backwards. Indeed, if only looking at the energy needed, the best propulsion method would be to send a strong laser beam out of your ship, because light has the least energy for a given momentum (according to Einstein, E^2 = (mc^2)^2 + (pc)^2, and for light, m=0).

Re:Excuse my ignorance (1)

$RANDOMLUSER (804576) | about 3 years ago | (#35678542)

Then again, it took almost 30 years for the change in momentum to be measurable, so don't expect any guest appearances on Top Gear.

Re:Excuse my ignorance (2)

rubycodez (864176) | about 3 years ago | (#35678726)

eh? The WORST thing is light, because light has so very little momentum for so much energy. Using light in collimated beam, it takes 300MW per newton (0.2 lbs) of thrust. or if you reflect the light off of ship from external source, 150 MW per newton. For photonic rocket thrust equals power divided by C, it's a bitch.

Re:Excuse my ignorance (1)

Chris Burke (6130) | about 3 years ago | (#35679150)

Exactly. Photons have the worst case energy/momentum ratio. The advantage of photon drives is not energy efficiency (because they're completely the opposite), it's that you don't need reaction mass.

So if you only need minute amounts of thrust, and have some long-lasting but light-weight source of energy (like an RTG), you can thrust basically forever.

Re:Excuse my ignorance (1)

rubycodez (864176) | about 3 years ago | (#35679220)

That "thrust basically forever" is good if source is external, then we're talking about solar sails or laser boosting reflectors. But for onboard source it's terrible thing, running a reactor onboard one would be better off using ion thruster, a little fuel with high momentum per particle. The only time photonic propulsion would give massive thrust is with matter-antimatter annihilation, if one could figure out how to reflect gamma rays from one end of the reaction chamber

Re:Excuse my ignorance (1)

Chris Burke (6130) | about 3 years ago | (#35679522)

An ion engine needs a source of energy and reaction mass. It's a very efficient use of reaction mass, but nevertheless. So for the same energy source, you can thrust longer with a photon drive.

Massive thrust is not the point of a photonic drive because they suck at it. Ion drives aren't great at thrust either, but they do have more. So it depends on the particular application which one would be better, though I think for most things we're doing in the near term ion drives are better.

Re:Excuse my ignorance (1)

lxs (131946) | about 3 years ago | (#35678738)

Photons may not have mass, but they do carry momentum, and that's what counts.

Cover Up (0)

Anonymous Coward | about 3 years ago | (#35678358)

I take this to mean they've finally received contact from Nibiru.

And Planet X woulda got away with it... (0)

Anonymous Coward | about 3 years ago | (#35678654)

if it weren't for you meddling kids!

sounds like radiosity too (1)

YesIAmAScript (886271) | about 3 years ago | (#35678664)

Radiosity being a 90s computer graphics term for calculation how radiation (heat and light) hit surfaces and are absorbed or re-emitted by them. It came from earlier studies on this not relating to computer graphics.

You can render your radiosity results using phong shading or other shading techniques.

Re:sounds like radiosity too (1)

robthebloke (1308483) | about 3 years ago | (#35679252)

You can render your radiosity results using phong shading or other shading techniques.

You could, but that would be a very stupid thing to do. Why go to the bother of computing an accurate colour for a point on a surface, to then modulate it with an in-accurate plastic surface approximation? That makes absolutely no sense.

Um, Ray Tracing? (1)

emarkp (67813) | about 3 years ago | (#35679176)

Imagine how well you'd model this using monte-carlo techniques / ray tracing.

Re:Um, Ray Tracing? (1)

Osgeld (1900440) | about 3 years ago | (#35679724)

yea it should take no time at all to ray-trace every source of radiation for a couple billion miles

How close did they get? Error bars? (2)

Moof123 (1292134) | about 3 years ago | (#35679258)

I RTFA, but didn't find the results of their calculation. The old method yielded 67% of the effect, but they didn't say what the new method resulted in (other than get the "right" answer). Also I'd want to know error bars. Does the new answer +/- error bars overlap with the detected phenomena within the error bars of it's value?

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