Heat 'Most Likely Cause' of Pioneer Anomaly 133
astroengine writes "Everything from clouds of dark matter, weird gravitational effects, alien tampering and exotic new physics have all been blamed for the 'Pioneer Anomaly' — the tiny, inexplicable sun-ward acceleration acting on the veteran Pioneer deep space probes. However, evidence is mounting for a more mundane explanation. Yes, it's the emission of heat from the spacecrafts' onboard radioisotope thermoelectric generators (RTGs), slowly nudging the Pioneers off course, that looks like the most likely culprit. It's unlikely that this new finding will completely silence advocates of more exotic explanations, however."
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erotic explanations
Zapp? Zapp Brannigan? Is that you?
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I never wanted to know how V'Ger came into existence. There are certain things I do not want a Rule 34 for.
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According to Gene Roddenberry's novelization, V'ger was not a result of porn but the derelict probe falling through a wormhole and ending-up near a plant of "living machines". They captured the original Voyager 7(?) probe, and upgraded the technology so it could complete its task of exploration.
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They raped Voyager 7.
Again, please refrain from Rule 34'ing it!
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d00d (Score:5, Informative)
hate to tell you this but this is a dupe from like 6 months ago. Next time search the /'s archive.
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This is slashdot. The editors have better things to do than search for dups, fix typos, and check content. Don't know what they are, but it must be important.
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Throwing nerf balls at the glass walls of CmdrTacos corner suite.
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Yeah, the probe collided with a super advanced alien probe and fused and now they're on their way back to Earth to meet their creator.
I think I should sell this novel script, I'll make millions. Maybe they even turn it into a movie.
So ... (Score:1)
VGer was a totally different design (Score:5, Interesting)
The Pioneers were spin-stablizied (like tops), whereas Voyager was 3-axis stabilized (with thrusters).
The first probes fired at the moon were also spin-stabilized. Both the US probes and the Soviet probes missed, by large margins. The Russians were the first to hit the moon - I guess they loaded extra propellant to perform course corrections.
The proper thing to do is launch another spin-stabilized probe on an extragalactic trajectory. I wonder how much that would cost.
What is the "Pioneer Anomaly"... <snip>
Is the same effect seen with the Voyager spacecraft?
The Pioneers are spin-stabilized spacecraft. The Voyagers are three-axis stabilized craft that fire thrusters to maintain their orientation in space or to slew around and point their instruments. Those thruster firings would introduce uncertainties in the tracking data that would overwhelm any effect as small as that occurring with Pioneer.
This difference in the way the spacecraft are stabilized actually is one of the reasons the Pioneer data are so important and unique. Most current spacecraft are three-axis stabilized, not spin stabilized.
- http://www.planetary.org/programs/projects/innovative_technologies/pioneer_anomaly/update_20050720.html [planetary.org]
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The proper thing to do is launch another spin-stabilized probe on an extragalactic trajectory. I wonder how much that would cost.
I think you mean interstellar, not extragalactic.
The cost of Pioneer 10 was about $430 million in 2010 dollars. Since the Pioneer anomaly turned out to be a mistake, it is doubtful that it would be sensible to spend a similar sum on a follow-up. Furthermore, many of the systematic errors involved in measuring a spacecraft's trajectory come from parts of the tracking systems that are not aboard the spacecraft.
If the goal is simply to confirm by some independent technique that the effect is not gravitational,
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I think you mean interstellar, not extragalactic.
Certainly, thanks for that. :)
it is doubtful that it would be sensible to spend a similar sum on a follow-up.
Did you know Explorer 1 was 12 minutes late? The twelve-minute hiatus of Explorer 1 [thespacereview.com]. I just found this response to that article, which concludes that something is indeed amiss...
Deceleration (Score:3)
What's the difference between "sunward acceleration" and deceleration?
I mean, isn't the probe generally traveling away from the sun?
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What? No, both are vector quantities. One is just the negative of the other, they each have just as much 'context'.
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Actually Deceleration would mean a reduction in speed ( |v| ), while Acceleration would mean a change in velocity ( v ). Since you're only decelerating if the magnitude of your velocity is reducing relative to a specific inertial reference frame, then Deceleration is a pretty specific case of acceleration.
Furthermore, to specify this acceleration as a deceleration, you must assume that the velocity is directly *away* from the sun, which is likely not the case. So even if you did specify the reference frame (relative to the sun) and the initial velocity (away from the sun but not necessarily in a straight line), you cannot call it a deceleration and still convey the fact that the force is toward the sun.
And by the way, having just attended a lecture on spacecraft thermal design, I can say this is a perfectl
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Acceleration however doesn't need context.
Is this a fancy way of trying to get us to believe that acceleration is NOT a vector? Please define "context". Also considering that the definition of deceleration is acceleration in a direction opposite to velocity or even "negative acceleration" with the negative just being a flag for "the other way, dummy", I would say that your whole argument is on pretty shaky ground. If acceleration doesn't need your undefined, mystical "context" then neither does deceleration. Why don't you let real nerds do the ner
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This sounds wrong to me too, the probe isn't speeding up backwards, it's slowing down.
ie. Speeding up in the direction opposite to current velocity - especially if your frame of reference is the object. Humanities majors should not be allowed to post on slashdot.
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Or at least, they shouldn't be able to post questions on slashdot. God forbid they try to gain some understanding of things they don't know enough about.
And yes, I am an offended BA.
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It's the direction it is accelerating in (Score:4, Insightful)
Remember that any change in velocity over time is an acceleration in the proper sense, and also remember velocity has both a speed and direction component. You accelerate a car to a stop, and you accelerate around corners when you change direction.
I understand that in regular speech it just means "going faster" and the direction component is dropped. Understand that NASA is full of scientists and they may use science terms in a more precise manner.
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I understand that in regular speech it just means "going faster" and the direction component is dropped. Understand that NASA is full of scientists and they may use science terms in a more precise manner.
Quite right. It is just the units of measurement that NASA does not always get right. Miles, kilometers; what's the difference?
Re:Deceleration (Score:4, Informative)
The AC who responded to your comment is completely wrong.
While deceleration is used in common speech to indicate a reduction of velocity, in physics there is no deceleration only acceleration in the opposite direction of the trajectory. Both concepts, acceleration reverse acceleration, require a point of reference, in this case it is the sun.
I would have been disappointed if /. used deceleration, particularly on a space article.
http://en.wikipedia.org/wiki/Acceleration [slashdot.org]
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oops, sorry about responding to myself, but I messed up my link. I'm more of a hardware guy.
http://en.wikipedia.org/wiki/Acceleration [wikipedia.org]
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Acceleration doesn't require a point of reference.
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Directionality doesn't require a point of reference either. The object itself doesn't count as a reference point.
Velocity requires a reference point - if you're floating in deep space with nothing around you, you can't tell if you have any velocity. The question itself doesn't make sense without some other object against which to measure your motion. Acceleration isn't like that.
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Following your logic acceleration would not be detectable either therefore pointless.
In order to detect acceleration, you must take at least 3 sample points of reference of the object in motion. The first to set a starting point, the second in order to set an velocity and the third in order to set a later velocity with this information you can detect the change in velocity.
Without these an object in empty space would never have velocity therefore no potential increase in velocity.
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Sorry, but you're wrong.
In order to detect acceleration, you only need a pendulum, a glass of water or a faceplant against the spaceship hull. The pain you'll feel isn't relative to the frame of reference.
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That would be inertia.
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That would be linked to the spaceship's acceleration.
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Einstein tells us there's no such thing as gravitational acceleration. In general relativity the unaccelerated frame is the one where you fall freely under gravity's influence, NOT the one where you resist it.
Sitting on your couch, you are accelerating at 9.81 m/s^2. Yes it seems weird. Yes, it works out very well.
Re:Deceleration (Score:4, Informative)
Constant velocity is not detectable without a frame of reference. This is relativity (extremely simplified of course!)
Change in velocity (ie: acceleration) IS detectable. You can detect forces acting upon you and therefore compute acceleration (F=ma). If you can measure the force acting on you (which you can if have the right equipment), and you know your mass, then its pretty trivial to calculate your acceleration without needing any external reference frame.
For a real world example, go ride a train (preferably between two stops seperated by a relatively straight run of track.) You definitely feel a backward "pull" as the train speeds up, and a forward "pull" as the train slows again for the next stop (plus some sideways pulls if the track curves, but for the sake of simplicity lets assume it doesn't).
During the middle of the trip -- when the train is maintaining a constant velocity -- you don't feel any different than you do when you're standing on solid ground, give or take a factor of imprecision such as a rough track or the operator not maintaining exactly constant speed.
Your entire knowledge of motion is based on a) looking out the window and b) previous experience with trains -- what they sound like, what they look like, how they move relative to the earth (which is the frame of reference you generally care about if you're taking a train somewhere) and so on. None of these factors have anything to do with the train's frame of reference however.
As for creating a frame of reference, you only need two points. Yourself (the observer) and a target (reference point) that you assume to be fixed (or you can consider yourself fixed and the target as moving -- the math is the same, you just get an extra minus sign).
You just continually monitor the distance between yourself and the target and can compute both your speed and your acceleration by comparing the distances over specific time intervals. As you take the interval times to zero, you get better and better approximations of your exact acceleration curve (that's pretty standard calculus -- sample and integrate.)
And finally, for an object in empty space. You're kind of correct. Its not so much that it doesn't have a velocity as much as velocity is simply undefined. You can still have an acceleration (F=ma as above) but what speed you accelerate from and what speed you accelerate to both have absolutely no meaning without a point of reference.
Of course in the real universe, forces (at least the ones we know about) are actions between objects, so the fact that you have an acceleration implies that there's something around that could be used as a reference point (but you have to be able to find it to use it!)
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You just continually monitor the distance between yourself and the target and can compute both your speed and your acceleration by comparing the distances over specific time intervals. As you take the interval times to zero, you get better and better approximations of your exact acceleration curve (that's pretty standard calculus -- sample and integrate.)
And each time you note the position you create a new reference point for the following position.
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Only if you have the ability to leave a marker at that point. However, the marker you dropped off would be moving with approximately the same velocity you are, so you've lost the ability to measure velocity relative to the original object.
You might still be able to compute the velocity relative to the original object (just add up your velocity relative to the original object plus the velocity relative to the marker), but you can't measure it by using an object you yourself left in space.
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Only in theory. In practice, a real gravitational field is centered on a point, and you can use tidal forces to determine if such a point exists (and if you want, triangulate where it lies).
The theoretical concept that Einstein laid out is only true if you have a flat version of gravity. This can be approximated by simply having the gravitational field be so large relative to the sensitivity of the measurement device that the (truly spherical) surface appears flat. But all you need to break that scenario
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Sit down. Feel that on your ass? That's you detecting acceleration.
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Science classes might have been optional for some...
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So you are saying that I can use an accelerometer in order to determine that bulk of mass in the cosmos is accelerating away from us? How do you propose to determine acceleration of an object that you do not have physical access to?
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Wait, what? No, that's not what I meant. It seemed the thread had diverged a bit from the OP, and your statement that you cannot "figure" acceleration without a reference point is patently false in the general case, so I took offense at your invocation of the Nobel Prize for something so simple. Forgive my juvenile use of sarcasm and capitalization, but I was merely defending a perceived slight to Newtonian physics.
I'm sure you remember from high school physics that there are two completely independent
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You should reread the thread. It was not I who invoked the Nobel prize. I do not do ad hominems or taunts, I find rudeness interferes with the promulgation of knowledge.
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Well, let's see. You can feel acceleration. If you pull down the window shades in a plane can you tell when it takes off? You could get a glass of water and observe the angle of the water in the glass (which is actually very appropriate because it's related to a famous thought experiment called Newton's Bucket). You could observe a swinging pendulum. You could use an accelerometer, solid state or gyroscopic, your choice.
There are LOTS of different ways to do it, and no, unfortunately, no Nobel prize.
Be
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The "if you're floating in deep space with nothing around you" is a thought experiment. Einstein put you in an elevator that you couldn't see out of. Newton stuck you in a universe with absolutely nothing in it, not even CMB. Or maybe you just don't have a handy radio telescope with you!
Quit trying to be clever and use your imagination.
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Ah, it's the know it all Slashdotter.
You might want to brush up on basic physics a little bit, or take a slightly more humble attitude.
Just because you've given an example of using a frame of reference to measure an acceleration doesn't mean you HAVE to have a frame of reference. Mistake #1.
Your example is actually wrong as well. According to general relativity, you are accelerating at this moment (in one direction, not "two directions at once"). That direction is commonly called "up." If you were to wa
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That's not correct. Mathematically your resultant acceleration is 0 because, as you pointed out, the forces are exactly opposite and equal. However the forces are there. You ARE accelerating both towards and away from the center of the Earth. Otherwise you have to start believing in magic - the magical earth "detecting" when you are no longer supported by a surface (and hence the normal force) and suddenly applying acceleration to you because of this.
While it's convenient to ignore the balanced forces bec
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So how many meters per second per second is his velocity towards the center of the earth increasing?
Zero?
No acceleration, gotcha.
Force can cause acceleration, force does not equal acceleration.
Precisely, the hangman put the noose on you and you have the force of gravity pulling you down, it is not until he opens the trap door that the force of gravity accelerates you downward to snap your neck.
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In front of me. Behind me. To my left. To my right. The coordinate system can be entirely defined by your own frame of reference and does not require another point.
Imagine you're in a completely empty universe. Nothing but you. Then you fire the rocket pack attached to your back. You'll know you're accelerating, and you'll be able to describe the direction, with no reference point besides yourself.
As another example, have you ever found yourself in pitch blackness? Did you have trouble figuring out
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Deceleration means "a decrease in speed". If the probe is traveling directly away from the sun, and there are no other contributions to the probe's acceleration, a sunward acceleration causes a decrease in speed, and a decrease in speed causes a sunward acceleration. For deceleration to occur, you need the speed to actively decrease. If, for instance, there was a component of acceleration away from the sun overwhelming the sunward component, there would be no decrease in speed [as long as the velocity vecto
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where the vector "something" is often "velocity"
Just to nit-pick, you mean "the direction of movement". Velocity also implies the magnitude as well as the direction, and I don't see why we need to bring magnitude into the argument.
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where the vector "something" is often "velocity"
Just to nit-pick, you mean "the direction of movement". Velocity also implies the magnitude as well as the direction, and I don't see why we need to bring magnitude into the argument.
No, I meant what I said. The noun phrase "<vector X> in the opposite direction of <vector Y>" makes sense for any vectors X and Y, even though it doesn't define a relationship between their magnitudes or otherwise mention them.
do you step on a car's decelerator pedal? (Score:2)
technically, that's what you are doing. compared to some inertial reference frame, you are decelerating.
an easy frame would be to consider the earth, and consider that you drive from west to east. relative to its own axis, earth is spinning east to west. so, yeah. if you drive from los angeles to new york, what you are really doing is trying to 'decelerate' yourself for a couple of days in a row in order that new york can 'catch up with you'.
(yes i may have mixed east with west here... im too lazy to analyz
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I mean, isn't the probe generally traveling away from the sun?
Generally yes, but not exactly, which is why there's a difference between deceleration and sunward acceleration. See this image [wikipedia.org].
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You should know that science fiction is not science at all. You can theorize all you want, but is there a point when a good old phenomenon based on physics laws that we know is enough to explain the phenomenon?
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Science fiction is based on science; if it isn't, then it's fantasy.
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Science fiction is based on science - check
Science fiction isn't science - check
Ok, we are in agreement here.
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Anyone who dares to dream or think outside the box must brace themselves for the snarky to angry remarks from the mental lemmings. Those who refuse to dream or think outside the box are doom to stay in it. Human intelligence is built upon previous works. We just don't have the lifespans to get very far alone. We have to pick up the torch via education, then run with it a ways further on our own. This helps progress us. If you haven't noticed, we need some progression. We have an overpopulated planet and all
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I'm not sure what your point is. I do agree with everything you wrote. I just think that we shouldn't spend too much time trying to find another explanation than the law of gravity to an apple falling off a tree.
Now, when we'll notice something that the law of gravity fails to explain exactly, then we'll theorize on another law, and I'm perfectly fine with it.
This is going ahead in my view. Trying to reinvent an existing theory based on nothing other than the will to reinvent it is fine. I just think we sho
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I am a habitual gun jumper, I will admit that. I like to leap on things, they tend to not squirm away as easy.
Ok, here is probably where I train wrecked. Pioneer is slowing down. That is a given, right? They are fielding this "heat" theory, but not quite 100% about it either, but it sounds good, right? Didn't the boys do the long math and say, "nope it's not perturbations of gravity?" Then didn't someone mention it was slowing at exponential rates? Exponential rates?? Wouldn't that mean its going to come to
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Nope. Ok, somebody may have mentioned it, but he would be wrong. There are some good information at Wikipedia [wikipedia.org], the acceleration is 8.74(+-)1.33*10^(-10) m/s2.
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What was that you were saying about grasping at straws?
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Ah yes, well lets hear your hypothesis? Or do you have the balls to put one out here? Or can you even formulate one? Even a extremely convoluted one? Anonymous Coward is rightly named.
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I was married 13 years, /. flames bounce off my upper atmosphere after that kind of conditioning.
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Any sort of Aether/"fabric" theory has been pretty much completely ruled out by experiment [wikipedia.org] over a century ago.
There are lots of other explanations [wikipedia.org] proposed however, though the Wikipedia page doesn't list any of the more crackpot theories like alien tampering.
One of these is dark matter, which could somewhat sound like what you're suggesting, but DM is definitely not a "fabric" of spacetime in any sense. Its "normal" matter that happens to not interact with the electromagnetic, weak or strong forces. That
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Thanks for not remarking like a condescending prick.
Pioneer is the first point of view that isn't taken from within our solar system. Besides, as far as being ruled out by these experiments, isn't the fact that they were conducted within the solar system's sphere of influence tainting them? Wouldn't we have to work out where Pioneer is with these experiments to really qualify them?
Also, pardon my 5 minute analysis of the presented information. A mystery such as what is up with Pioneer to me is exciting. If
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This probe is far enough out that it shouldn't be dicked with anything from the solar system.
You're wrong. The Pioneer is still within the Sun's gravitational sphere of influence. Good luck with your lunacy though.
Heat to blame? (Score:1)
Loss of mass (Score:3)
It's a bit tough to estimate, because the power output of the RTGs has diminished over the years, and I'm not interested in doing integrals this early in the morning. Their electrical output at launch was about 155 W [wikipedia.org], meaning that the heat output was probably more than 1 kW. Because it's an easy number to work with, let's estimate using 1 kW average thermal output over the mission life:
1 kW * 60 sec/min * 60 min/hr * 24 hr/day * 365.25 day/yr * 39 yr = 1.2e12 Joules
As a lovely demonstration of just how big a number the speed of light is, using E=mc^2 equates that energy to a whopping 13 micrograms.
So, yes, they have lost measurable mass. But, no, it is probably insignificant to the orbital mechanics at work. The rest of Pioneer weighed over 250 kg at launch. It probably picked up more than 13 ug in dust and solar wind.
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That's 14 milligrams, not 13 micrograms. And it may not be negligible if the mass is ejected directionally.
Google "1 kW / c / 250kg". The momentum of 1kW of photons could accelerate the Pioneer by 10^-8 ms^-2, if it were all emitted in one direction.
The anomalous acceleration we want to explain is about an order of magnitude smaller than this figure. Hence, TFA.
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kW are not proper units for momentum. /.ers...)
In any case, the thing you're talking about is force, not momentum.
F (of the photon flux) = m (of the spacecraft) * a (of the spacecraft).
(I believe you know this, but for the sake of other physics-challenged
My question is, why would the photon flux have a preferred direction? Is the RTG shielded asymmetrically?
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Not news to me (Score:1)
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Put that on a sandwhich at eat it all up !! Costs you nothing so why not believe it ?!
If it turns out to be wrong (specifically the "no one ever will" part) then it costs me my chance to know the real answer.
If "no one knows" then you don't really know whether or not it's truly knowable, so by your own rules, please shut up.
The rest of us will find purpose in searching.
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