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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.
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.
I have a reletive who is a CSI guy. I get the impression that 95% of there work is dusting for prints where there was some petty theft then all the paperwork that involves. When there is a major crime they mostly gather the physical evedence then move on to the next crime scene, the tracking down of the suspects is left up to the Detectives. There job is specialized so they can't sit around trying to locate criminals since there is always another crime scene to be worked.
No matter where you go, there you are.
The problem seems to be "These spacecraft are all partially or fully spin-stabilised; the effect is harder to measure accurately with three-axis stabilised craft such as the Voyagers." (quoted from wikipedia). Some other spin stabilized spacecrafts also show the anomaly, however, it is more difficult to be sure of them because most others are too close to the sun.
It's not that simple. We obviously can't account for each chunk of rock orbiting the Sun, but we also don't need to. We instead make very precise measurements of the orbits of the outer planets, and those orbits do reflect every speck of dust in the solar system. What we're seeing is that Pioneer's path does not reflect exactly the same forces that the outer planets agree are present, and that's the part that's hard to explain.
Note that this argument also gives a pretty clear idea of why most scientists don't seriously think that there is new physics involved here -- if (say) gravity operated differently at extreme distances, it would already have shown up in the orbits of the outer planets. Instead we see all of the outer planets in precise agreement about all of the forces, and then Pioneer having a dissenting opinion for some reason. So most of the searching is for Pioneer-specific effects, like dust (which wouldn't measurably slow down somethng the size of a planet) or gas leakages.
ZFS: because love is never having to say fsck
...that what you are talking about is the Pioneer anomaly. That is a well-known name, so when you didn't mention it, you got me thinking there was some other curiosity going on that I had missed.
Swedish plasma phys. PhD student; MSc EE; knows maths, programming, electronics; finance interest; seeks opportunities
"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.
--
.nosig
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