Ah, the flyby anomaly. I had a lot of fun with that back in 2008 and maybe the game is not yet finished. Spacecraft Earth flybys are used by NASA to save on fuel. If they want to get a probe to Jupiter for example, but don't want to launch the heavy fuel needed, then what they do is launch the probe slow, loop it round another planet and bring it in behind Earth in its orbit, and the Earth then pulls the spacecraft forward and transfers some kinetic energy to it. An analogous method was used by Marty McFly in Back to the Future: he hitched a skateboard ride by holding onto a car. These flyby spacecraft are monitored as they zoom past the Earth and in 1990 the Galileo probe gained 4 mm/s of speed more than it should have. This was not a lot given the actually heliocentric (relative to the Sun) speed of 31 km/s, but well outside the uncertainty. This also happened for a few other flybys as well, the largest anomaly being for the NEAR (Near Earth Asteroid Rendezvous) probe which gained 14 mm/s speed from apparently nowhere. Anderson et al. (2008) collected all the data together and showed something that got me very excited at the time: there was a pattern. Spacecraft that came in at the equator, and left nearer the spin axis (the pole), sped up more!
After a lot of thinking and calculation I managed to show that MiHsC predicts something like this. When a spaceship comes in at the equator the mutual accelerations between it and typical masses inside the spinning Earth are big because the acceleration vectors are often along the same line (the Earth mass accelerates towards the spin axis, the craft also towards that axis). So MiHsC predicts the Unruh radiation seen has a short wavelength and fewer waves are disallowed by the Hubble-scale Casimir effect, so the inertial mass is close to the normal mass. Conversely, when the craft exits at the pole, the mutual acceleration between it and the masses in the Earth is smaller since the acceleration vectors are now perpendicular, so MiHsC predicts longer Unruh waves, more of which are disallowed by the Hubble edge, and the craft loses inertia slightly. To conserve momentum it has to speed up. Calculations show that this does a pretty good, but not perfect, job of predicting the flybys without any adjustable parameters (see my paper below). The way I derived this result is not perfect though, since I have not yet calculated the 'total' mutual acceleration including the spacecraft's own acceleration, and this I need to do. For this I could use the brilliant NASA Horizons web-interface, that I've used before, and where spacecraft trajectories are available for free. http://ssd.jpl.nasa.gov/horizons.cgi
What reminded me of the flybys was a recent article, in the Spanish SINC website (see SINC reference below) which piqued my interest by saying that "One of the last [flybys] was that of the spacecraft Juno in October 2013, from Earth en route to Jupiter. NASA has not yet published data on this journey, but everything indicates that its speed as it flew over our planet was once again different to estimates". This was news to me because I pestered ESA and NASA last year and they told me there was no Juno anomaly. It's probable that the comment in the recent article was based more on expectation than evidence, but ESA/NASA have not yet published anything formally on the Juno flyby. MiHsC predicts a small positive anomaly (but as I said before I don't yet consider the motion of the spacecraft itself, which needs trajectory modelling). Time to do some fortran programming..
References
Antreasian P.G. and J.R. Guinn, 1998. Paper no 98-4287 presented at the AIAA/AAAS Astrodynamics specialist conference and exhibition, Boston.
Anderson J.D., J.K. Campbell, J.E. Ekelund, J. Ellis, J. Jordan, 2008. Phys. Rev. Letts., 100, 091102.
McCulloch, M.E., 2008. Modelling the flyby anomalies using a modification of inertia. Mon. Not. Royal. Astro. Soc., Letters, 389 (1), L57-60. Link to pdf
SINC: http://www.agenciasinc.es/en/News/An-anomaly-in-satellites-flybys-confounds-scientists
2 comments:
Somewhat late here but you set me wondering. You also mentioned in an earlier post about the falling gyroscope anomaly and it occurred to me that the spacecraft would all have gyroscopes for stabilization.
So perhaps a missing ingredient could be the relative orientation and direction of rotation of the on-board gyroscopes?
The onboard gyros are something I had not considered. I'll look into it, thanks.
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