What Causes The Unexplained Additional Velocity Gained During Flyby Accelerations?

[th.w.heller]

I came across a very interesting article in the September 20, 2008 New Scientist about flybys around the earth used to slingshot spacecraft giving them sufficient velocity to reach the outer planets. Oddly, however, often the speed imparted to the craft appears to be slightly but significantly greater than expected. For example, during the Galileo's 1990 flyby of the earth the probe gained an unexpected 3.9 mm/sec en route to Jupiter. A variety of potential causes for this have been eliminated (atmospheric drag, interactions with the magnetic field, tidal effects, the effect of the earth's equatorial bulge). One empirically determined factor has, however, been implicated - the greater the trajectory's angle with the earth's equator the greater the extra speed gained. The article gives Stephen Adler's explanation using dark matter in and around the earth but "admittedly, Adler's model appears contrived." Is there a reasonable explanation for this?

[kaneda]

An idea: Earth like other planets is not a solid ball but actually semi-liquid inside. It stands to reason that like a centrifuge, a denser (spinning) mass inside would go towards the equatorial area spinning at 1,000 mph than an area far away from the equator which is spinning at maybe 100 mph. On the planet this would balance out between a faster spin and a greater attraction. It cannot be assumed that the "bulge" is just more of the same. In space, there is only the greater mass at the equator pulling something in space, so effectively slowing it down.

[James R]

Without knowing the details of the anomaly, it is very difficult to know where to start to speculate about possible solutions.

[Trippy]

It has (also) been suggested that teh Flyby Anomalies (including the most famous one - the PIoneer anomaly) may in fact simply be the result of the Transverse doppler effect - a factor which is typically ignored in the calculations.

I'll have a dig around and see if I can find a link to the article when I get home from work.

[D H]

A intro on the flyby anomaly, from the Planetary Society: http://www.planetary.org/news/2008/0228_Researchers_Investigate_New_Cosmic.html28 February, 2008. A new study by researchers from the Jet Propulsion Laboratory shows that spacecrafts that swing by the Earth are subject to a small but unexplained increase in their velocity. Is an unknown physical force at work, or something far more mundane?

Some exotic explanations were proposed, including the Unruh effect (McCulloch, M.E., "Can the flyby anomalies be explained by a modification of inertia? (http://arxiv.org/abs/0712.3022)", submitted 18 Dec 2007 to arxiv.org) and dark matter (Adler, S.L., "Can the flyby anomaly be attributed to earth-bound dark matter? (http://arxiv.org/abs/0805.2895)", submitted 19 May 2008 to arxiv.org).

The answer is probably a lot more mundane: It is probably just sloppy math (Mbelek, J.P., "Special relativity may account for the spacecraft flyby anomalies (http://arxiv.org/abs/0809.1888)", submitted 11 Sep 2008 to arxiv.org).In the following, we show that SR transverse Doppler shift together with the addition of velocities are sufficient to explain the
flyby anomalies. Thus, GR does not need to be questioned and the flyby anomaly is merely due to an incomplete analysis using conventional physics.

[Trippy]

A intro on the flyby anomaly, from the Planetary Society: http://www.planetary.org/news/2008/0228_Researchers_Investigate_New_Cosmic.html28 February, 2008. A new study by researchers from the Jet Propulsion Laboratory shows that spacecrafts that swing by the Earth are subject to a small but unexplained increase in their velocity. Is an unknown physical force at work, or something far more mundane?

Some exotic explanations were proposed, including the Unruh effect (McCulloch, M.E., "Can the flyby anomalies be explained by a modification of inertia? (http://arxiv.org/abs/0712.3022)", submitted 18 Dec 2007 to arxiv.org) and dark matter (Adler, S.L., "Can the flyby anomaly be attributed to earth-bound dark matter? (http://arxiv.org/abs/0805.2895)", submitted 19 May 2008 to arxiv.org).

The answer is probably a lot more mundane: It is probably just sloppy math (Mbelek, J.P., "Special relativity may account for the spacecraft flyby anomalies (http://arxiv.org/abs/0809.1888)", submitted 11 Sep 2008 to arxiv.org).In the following, we show that SR transverse Doppler shift together with the addition of velocities are sufficient to explain the
flyby anomalies. Thus, GR does not need to be questioned and the flyby anomaly is merely due to an incomplete analysis using conventional physics.

Thanks - I didn't have my Pioneer Anomaly links on me, and the last arxiv paper you linked to (Sept 11 2008) was precisely the one I was thinking of.

[th.w.heller]

Thanks DH for the links. The simpler explanation as you suggest is almost always the best (if less exciting). Much appreciated, TWH.