The dish antenna would be pointed towards the sun. The RTG would then be perpendicular to the spacecraft sun axis. This same configuration applies to the Ulysses and Voyager spacecraft.
Posted on 04/16/2008 8:14:45 AM PDT by AndrewC
What is making NASA's twin Pioneer spacecraft mysteriously drift off course, apparently defying the laws of physics? A rigorous new analysis suggests ordinary heat emission can at least partly explain the wayward probes' strange trajectories.
Pioneer 10 and 11 were launched in the early 1970s and explored the outer solar system. But in 1980, mission scientists noticed that the spacecraft have unexpectedly drifted off course.
Both spacecraft have been pulled a little harder than expected towards the sun, and since their launch, they have drifted off course by hundreds of thousands of kilometres.
...
The uneven heat emission is enough to nudge the spacecraft off course, accounting for 28% to 36% of the anomaly detected when Pioneer 11 was 3750 million kilometres, or 25 times the Earth-sun distance, away from us.
(Excerpt) Read more at space.newscientist.com ...
The dish antenna would be pointed towards the sun. The RTG would then be perpendicular to the spacecraft sun axis. This same configuration applies to the Ulysses and Voyager spacecraft.
If the impact of "heat" from the sun and the re-radiation of said "heat", plus heat generated from the radioisotopic generator, are the source of this thrust, then wouldn't all of it would be imbalanced, some coming at greater leverage and from larger areas than others, imparting an uncontrolled, erratic yaw on the vehicle?
They are spin stabilized, so no, I don't think that yaw would occur until the control systems run out of fuel.
I know... but some of these spacecraft that are displaying this anomaly are far beyond their expected and designed life and probably have long ago exhausted the stabilizing fuel (it would be too expensive in Delta-V to provide a fuel supply that would exceed mission parameters, don't you think?) yet they are still sufficiently oriented toward Earth that we can receive their signal. Also, I think that the control people would have noticed an unusually high number of stabilizing maneuvers as the vehicle re-oriented itself if that were the case. It appears to me that whatever is applying a force to the vehicle is acting on the vehicle as a whole and not preferentially on any of its parts due to size or positional leverage.
Exactly.
Sure, insofar as reflecting infrared light (heat) is pressure...but the Pioneer anomaly is pushing P1 and P2 toward the sun, not away from it.
Stimmt. AndrewC seemed to be poo-poo radiation pressure. The anomaly could simply be the difference between the model of radiation pressure and true radiation pressure. If you model, say, 0.001 kg-meter/sec/sec, plus or minus (say) 0.0001 kg-m/s/s, and the actual radiation pressure is 0.0005, you have an anomaly of 0.0005 kg-m/s/s “towards” the sun, which cannot be “explained” by your model.
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