1. Joined
    06 Mar '12
    Moves
    625
    22 Apr '12 08:04
    The various exotic explanations for Pioneer's anomalous trajectory have now been ruled out in favour of a more mundane explanation:

    http://arxiv.org/abs/1204.2507

    Support for the thermal origin of the Pioneer anomaly
    …..
    (Submitted on 11 Apr 2012)
    We investigate the possibility that the anomalous acceleration of the Pioneer 10 and 11 spacecraft is due to the recoil force associated with an anisotropic emission of thermal radiation off the vehicles. To this end, relying on the project and spacecraft design documentation, we constructed a comprehensive finite-element thermal model of the two spacecraft. Then, we numerically solve thermal conduction and radiation equations using the actual flight telemetry as boundary conditions. We use the results of this model to evaluate the effect of the thermal recoil force on the Pioneer 10 spacecraft at various heliocentric distances. We found that the magnitude, temporal behavior, and direction of the resulting thermal acceleration are all similar to the properties of the observed anomaly. As a novel element of our investigation, we develop a parameterized model for the thermal recoil force and estimate the coefficients of this model independently from navigational Doppler data. We find no statistically significant difference between the two estimates and conclude that once the thermal recoil force is properly accounted for, no anomalous acceleration remains.


    the above doc is only a brief summary. If you want more detail, you would need to go to:
    http://physicsworld.com/cws/article/news/2012/apr/16/exotic-explanation-for-pioneer-anomaly-ruled-out
    -but you would need to sign-up to view that.
  2. Subscribersonhouse
    Fast and Curious
    slatington, pa, usa
    Joined
    28 Dec '04
    Moves
    52619
    22 Apr '12 18:21
    Originally posted by humy
    The various exotic explanations for Pioneer's anomalous trajectory have now been ruled out in favour of a more mundane explanation:

    http://arxiv.org/abs/1204.2507

    [quote] Support for the thermal origin of the Pioneer anomaly
    …..
    (Submitted on 11 Apr 2012)
    We investigate the possibility that the anomalous acceleration of the Pioneer 10 and 11 spacecraft ...[text shortened]... /exotic-explanation-for-pioneer-anomaly-ruled-out
    -but you would need to sign-up to view that.
    It makes sense, it has a small nuclear power supply on board. One would expect that acceleration to die down as the energy inside gets smaller and smaller and eventually not being able to produce enough power to keep the transmitter going. That might be another ten years however.

    They really built those craft well back then! It has turned into a photon rocket!

    Not very energy efficient as a propulsion system but it wasn't designed for that anyway.

    A powerful laser can be a rocket propulsion system on its own.

    I imagine ion rockets would be a lot more energy efficient in the long run but you can't beat particles flying off at the speed of light for a rocket!

    Ion rockets can't get even a fraction of that kind of velocity and that limits the ultimate velocity you can attain with X amount of fuel onboard.

    Optical rockets could theoretically be made that are just big mirrors, light sails, where you get free propulsion just from solar radiation, it turns out the amount of energy coming in from the sun that would power such a large solar sail gets less and less as you go away from the sun but so does the gravitational pull of the sun and so it pretty much balances out, you don't need as much energy from the sun in a solar sail when you get out where solar energy is very thin, it still is enough to accelerate you anywhere in the solar system with no fuel.

    A constant but very gentle acceleration and you run the sails much like you would on an earthbound sailboat.

    Such a system would have a nearly unlimited lifespan, assuming you maintain the sails, which would inevitably get holes punched in them by meteors and such. They would be kilometers across and would be unwieldy devices at best but it would be free transportation once they are constructed in space. They would have to be made as strong as possible, as thin as possible, a lot thinner than saran wrap, for instance, and highly reflective and controlled by control cables a lot thinner than human hair and a lot stronger.

    Do all that and you have a space bus.