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Computer Forensics to Help Solve Pioneer Mystery
Matthew Sparkes writes "Launched 35 years ago on Friday, Pioneer 10 was the first spacecraft to reach the outer Solar System and return pictures of Jupiter, closely followed by Pioneer 11. However, the twin Pioneer spacecraft drifted off course (see number 8) by hundreds of thousands of kilometres during their three-decade mission, and NASA eventually lost contact with them. An international team of scientists, including many amatuer hobbyists, are re-analysing the tracking and telemetry data in the hope of discovering the reason."
As the article states: So if the direction of deceleration is towards Earth, then you might be able to consider the mystery solved and blame it on the process of collecting the data. But if the deceleration is towards the sun or another direction, we have an observation of an unknown effect in physics. If the latter is the case, I think the mystery is just starting to be understood--with a long ways to go and many more observations before we can consider it solved.
My work here is dung.
while it is possible that the explanation will be mundane--such as thrust from gas leakage--the possibility of entirely new physics is also being considered. http://en.wikipedia.org/wiki/Pioneer_anomaly
Strangest of all:
Data from the Galileo and Ulysses spacecraft indicate a similar effect
Libertarian Leaning Political Discussion Forum.
Heh. I think most of us here on Slashdot would want this anomaly to be due to new and k3wl physics rather than some mundane error. The Pioneer anomaly is one of, if not the most interesting unexplained observation I know of.
V'ger.
I suppose it would actually be P'neer, but that just doesn't sound right somehow.
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However, the twin Pioneer spacecraft drifted off course (see number 8) by hundreds of thousands of kilometres during their three-decade mission, and NASA eventually lost contact with them.
This seems to imply that NASA lost contact because the spacecraft drifted off-course. AIU, they lost contact because the signals became too weak to be readable (due to distance and/or degradation of the RTG).
> And another guess, but surely the gentlest squirrel's fart as
> the craft left Earth could translate to huge discrepancies by
> the time they get to the other side of the solar system?
Yes, a one-off measurement error at launch would turn into hundreds of thousands of miles difference years later. However, the positions of the craft all along the way show it is still slowing down too fast.
In your terms, the squirrel must be hiding on board and farting from time to time on a reqular basis and in the direction of travel, slowing it.
(-1: Post disagrees with my already-settled worldview) is not a valid mod option.
We are still in contact with the Voyager probes, and they have, at this point, traveled further out of the solar system than the Pioneer probes. Has the same anomaly been spotted in their trajectories too? That would be of great importance in weeding out possible phenomena.
It just fell off the back of the turtle and found its demise under legs of the elephants holding it!
It seems to be a no-brainer that the most likely cause is gravitaional force from something we didnt know was there. Some kupier belt trash, comet that passed it years ago, who knows. I'm frankly surprised that these types of navigational issues were/are not expected .....
The codes used took into account all the major sources of gravity, including all the planets and major asteroids. These are some of the same codes that have been used to place many, many other probes in proper orbits around planetary bodies as far away as Saturn, and land on tiny things like asteroids and comets.
The damned thing about the Pioneer anomaly is that the acceleration is constant and the measurement is exceedingly simple. It's just position vs. time. There isn't much that can mess with that, and since individual communications with the craft are uncorrelated with each other, there shouldn't be any kind of drift (relativistic clock drifts are taken into account). Since the acceleration is constant over a distance from roughly Jupiter to well past Pluto, and gravity follows a force law that goes like 1/r^2, you can't add a single source of gravity (e.g. a new planet) -- the force wouldn't be constant. You can't make the sun slightly heavier. You can't add dark matter to do it: the dark matter would have to conspire to have a density as a function of distance from the sun that mimicked the constant acceleration. Such a density profile has more dark matter at the edges of the solar system, which would not be stable. It should collapse and concentrate near the sun. The acceleration is approximately the same magnitude as the expansion of the universe, but it's in the wrong direction, and our current understanding of dark energy wouldn't cause such an effect anyway.
Personally, I think we've got gravity totally wrong.
-- Bob
1^2=1; (-1)^2=1; 1^2=(-1)^2; 1=-1; 1=0.
"Seriously, though, how likely is it that the gravitational and orbital calculations were just not quite as precise when they did them 35 years ago?"
Do you think the calculation was done only once? No. It's pretty much a continuous process. While the calculation would have been as accurate 35 years ago as today. (People have known how to multiply and divide out to many decimal places for century's now) What's changes and what limits our ability is that we don't exactly know the exact mass and location of every object in the Solar System. But if you track the spacecraft you can deduce forces acting on it by where it goes. The anomaly here is that we know the force but can't explain it in terms of gravity. The most likely thing is a small leak in the plumbing that acts like a weak jet. It could also be explained by some revolutionary physics. But if you look back in history and count the number of time plumbing has leaked vs. the number of times physics hes been re-written. My money is on the 30 year old plumbing.
It's not a case of not hitting the spot that was aimed for but of watching a curve develop over decades and seeing the curve be a shape that is not quite what one would expect if only gravity were the cause.
The theory proposed by the grandparent (or was it the great-grandparent) poster is almost correct, but is mis-stated somewhat.
It is not that modern proportional typefaces have extra space after the period, it is that typewriters' fixed-fonts padded the period with extra space to make it take up the same space as a 'W', for example. Therefore, if you didn't hit the spacebar twice, it became somewhat difficult, optically, to discern where sentences began and ended.
Since modern typefaces no longer have to pad the period with extra space, the single space is more than sufficient for discerning sentence beginnings and endings.
Note that it has always been AP and Chicago style to put only one space after each sentence-ending character (. ? !).
Here's a link to the cannonical paper on the issue: http://arxiv.org/abs/gr-qc/0104064
Also, if you're interested, and in the New York area, some of the scientists who've been working on this are speaking at the Hayden planetarium in a few weeks: http://haydenplanetarium.org/programs/asimov/
Just to give a feel for what obsessive level of detail we're dealing with, here's a list of the possible causes considered in the paper above. The numbers after each listing are the bias and uncertainty in units of 10^-8 cm/sec^2. Listings with only one number only have an uncertainity, not a bias.
1 Systematics generated external to the spacecraft:
a) Solar radiation pressure and mass +0.03 ±0.01
b) Solar wind ± 10^-5
c) Solar corona ±0.02
d) Electro-magnetic Lorentz forces ± 10^-4
e) Influence of the Kuiper belt's gravity ±0.03
f) Influence of the Earth orientation ±0.001
g) Mechanical and phase stability of DSN antennae ± 0.001
h) Phase stability and clocks ± 0.001
i) DSN station location ± 10^-5
j) Troposphere and ionosphere ± 0.001
2 On-board generated systematics:
a) Radio beam reaction force +1.10 ±0.11
b) RTG heat reflected off the craft -0.55 ±0.55
c) Differential emissivity of the RTGs ±0.85
d) Non-isotropic radiative cooling of the spacecraft ±0.48
e) Expelled Helium produced within the RTGs +0.15 ±0.16
f) Gas leakage ±0.56
g) Variation between spacecraft determinations +0.17 ±0.17
3 Computational systematics:
a) Numerical stability of least-squares estimation ±0.02
b) Accuracy of consistency/model tests ±0.13
c) Mismodeling of maneuvers ±0.01
d) Mismodeling of the solar corona ±0.02
e) Annual/diurnal terms ±0.32