Juno to test unexplained slingshot maneuver accelerations

[GeneCash]

So folks have noticed that when a spacecraft does a flyby of Earth to pick up speed in a slingshot maneuver, it gets slightly more speed than it "should" - they don't know if it's tracking errors or what, but they're giving Juno the hairy eyeball to see if it does the same thing. It's on the order of mm/sec, but it's a pretty big discrepancy with the accuracy they work at.

Great writeup by the BBC at http://www.bbc.com/future/story/20131009-spacecraft-tests-sling-theory/all

[K^2]

Relativistic fly-by could be measurably different from a classical one. If there is a real discrepancy, and it's not due to tracking error or ablation/leak-related acceleration, I'd check what GR has to say about it.

[Ralathon]

Relativistic fly-by could be measurably different from a classical one. If there is a real discrepancy, and it's not due to tracking error or ablation/leak-related acceleration, I'd check what GR has to say about it.

I'm fairly sure they already did that. Quoting from the wiki:

"The impact of General Relativity, in its weak-field and linearized form yielding gravitoelectric and gravitomagnetic phenomena like frame-dragging, has been investigated as well:[9] it turns out to be unable to account for the flyby anomaly;"

[rkman]

Relativistic fly-by could be measurably different from a classical one.

Why would you think NASA doesn't know that? Nowadays GR is used in all mission planning.

http://en.wikipedia.org/wiki/Flyby_anomaly

Possible explanations of the flyby anomaly include

- Unaccounted Transverse Doppler effectâ€â€i.e. the redshift of light source with zero radial and non-zero tangential velocity.[6] However, this cannot explain the similar anomaly in the ranging data;

- A dark matter halo around the Earth;[7]

- A Modification of Inertia resulting from a Hubble-scale Casimir effect (MIHsC);[8]

- The anomaly may be due to the rotation of the Earth. This rotation induces an azimuthally symmetric gravitational field.[10]

Edited October 10, 2013 by rkman

[K^2]

Nowadays GR is used in all mission planning.

They absolutely do not, because solving for metric with such precision is not possible. Linearized GR is sometimes accounted for, but it does not cover everything.

"The impact of General Relativity, in its weak-field and linearized form yielding gravitoelectric and gravitomagnetic phenomena like frame-dragging, has been investigated as well:[9] it turns out to be unable to account for the flyby anomaly;"

Right, linearized GR. If the effect is non-linear, you are not going to see it without doing a proper solution.

[Deadpangod3]

... Is the earth positioned so that Everest or a large mountain is on the horizons when this happens?

With a mountain range sticking up ahead it could pull it more and make it speed up slightly more.

[DisarmingBaton5]

Has it been hit by a Hanland missile from behind? Damn Hanland, now they're after NASA!

[grawl]

Why would you think NASA doesn't know that? Nowadays GR is used in all mission planning.

http://en.wikipedia.org/wiki/Flyby_anomaly

Possible explanations of the flyby anomaly include

- Unaccounted Transverse Doppler effectâ€â€i.e. the redshift of light source with zero radial and non-zero tangential velocity.[6] However, this cannot explain the similar anomaly in the ranging data;

- A dark matter halo around the Earth;[7]

- A Modification of Inertia resulting from a Hubble-scale Casimir effect (MIHsC);[8]

- The anomaly may be due to the rotation of the Earth. This rotation induces an azimuthally symmetric gravitational field.[10]

I'd go for the 4th solution

[Technical Ben]

Hmmm. If it is a significant anomaly, requiring an additional consideration for calculations, would it change redshift conclusions?

[Payload]

I'm going with electromagnetic anomaly as well. Seems like it makes the most sense. I know satellites sometimes use the planets magnetic field for reaction control.

That is a much stronger force than that of gravity or ablation/gas ejection.

Though because you said they are gaining instead of losing it makes the electromagnetic theory pretty shaky. It would be a much more believable theory if it slowed the object.

[John FX]

Either it`s waves of magnetism from earths rotating megnetic field causing it to `surf` a little or spacetime is twisted in the region around earth from the mass rotating and it `surfs` again due to a lack of symmetry would be my guesses off the top of my head. That or it`s the sun again like voyager.

I`ll be interested to see what they find out.

[rkman]

That or it`s the sun again like voyager.

Are you sure you don't mean the Pioneer anomaly, which was not due to the sun?

http://en.wikipedia.org/wiki/Pioneer_anomaly

[K^2]

Either it`s waves of magnetism from earths rotating megnetic field causing it to `surf` a little or spacetime is twisted in the region around earth from the mass rotating and it `surfs` again due to a lack of symmetry would be my guesses off the top of my head.

Magnetic fields do no work. And even if it's due to gradients, there has to be a net charge for it to matter. I highly doubt that it's an electromagnetic effect.

Space-time around Earth is twisted due to frame dragging, and that does not require any asymmetry. I don't know if that can actually effect the net velocity change without such, however.

[John FX]

Are you sure you don't mean the Pioneer anomaly, which was not due to the sun?

http://en.wikipedia.org/wiki/Pioneer_anomaly

Nope, I meant what I said. I know about the pioneer anomaly which was incorrectly attributed to thermal radiation from the power generator and is still unknown. I mentioned voyager to reduce confusion about the RTG etc. My opinion is that the sun interacts with cosmic space in a way that a small metallic craft placed inbetween would cause sunward accelleration. It depends whether the slingshots are all in the shadow of the earth to decide if it is the same force for me but sunward accelleration in the shadow of the earth during a slingshot would provide extra speed during a slingshot in the manner described.

to be precise, I meant the suns counteracting of an external effect itself being cancelled by being in the shadow of the earth/within the magnetic field/close to a large mass, so not the sun per se.

As I say, this is all off the top of my head so is likely to be wrong. It will be interesting to see what they come up with.

Edited October 11, 2013 by John FX

[rkman]

Nope, I meant what I said.

Source on there being any such thing as a 'Voyager anomaly'? (instead of being spin stabilized it used attitude control thrusters, causing to much noise in its acceleration profile to detect an anomaly)

I know about the pioneer anomaly which was incorrectly attributed to thermal radiation from the power generator and is still unknown.

How do you "know" that - what is the evidence?