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To get more statistical significance for the suspected flyby-anomaly (or to refute it), it would be desirable to track as many hyperbolic earth flybys to within 1mm/s as we can get. Can we track natural objects approaching/leaving earth with this accuracy by long-term observations?

Laser tracking of manmade objects may be easier. Think of a swarm of passive reflectors, spring-emitted way before perigee of an earth gravity-assist, so they pass with different distance and leave in different directions. But I fear that we will never see such a maneuver with a significant plane change, because missions rarely ever leave the ecliptic. With the observations so far, in- and outbound declination seems significant, especially going from high declination back to low would possibly give insight. Will the effect be reversed?

I doubt we will ever see a mission dedicated to this effect, so studying it with natural objects would be useful.

user
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Andreas
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  • Natural objects = an occasional, uncharacterized, rotating (possibly tumbling), irregularly shaped object of unknown mass, poorly characterized radar reflectivity/directionality as well as optical reflectivity and emissivity? That kind of natural object? Sounds hard, and even if one thinks that one has an order mm/sec measurement, it would be hard to convince others that there are no systematic errors anywhere. Should wait until conditions can be impeccably well controlled and verified and then independently verified. – uhoh Nov 05 '16 at 14:47
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    @uhoh Yes, it sounds unreasonable if you remember that even tracking luna is done with a reflector. I was however not sure, what long-term integration of observations can do about this. – Andreas Nov 05 '16 at 14:52
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    One of OSIRIS-REx's major tasks is to carefully characterize the 3D mass distribution and to carefully map the reflectivity and emissivity of Bennu, to improve on the estimations of the non-gravitational effects that will affect it's orbit. For the experiment you are proposing, the natural bodies will be much low mass - because high mass NEOs are (luckily) infrequent! Low mass means the uncertainties in the non-gravitational effects will be magnified, and may overshadow any hope to extract meaningful data. So ambiguous reflector + uncertain force – uhoh Nov 05 '16 at 15:06
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    @uhoh Why wouldn't the anomaly be apparent for satellites in Earth's orbit? 1 mm/s is 31 km per year. – LocalFluff Nov 05 '16 at 15:20
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    @LocalFluff If we understood it's nature, we would know. As far as I know, it was never observed in elliptical orbits. All we know about it comes from a few observations, so we are basically guessing. We need more data. I am not biased and will not be disappointed if someone explains it with mainstream physics. – Andreas Nov 05 '16 at 15:31
  • @LocalFluff I didn't say anything about satellites in Earth's orbit one way or the other. The question asks about using NEOs, not satellites. In any event, I think you have to do a fly-by in order to test the "flyby-anomaly". The question does not explain much, so you've got to read about it in detail. – uhoh Nov 05 '16 at 15:31
  • @uhoh Hmm, I speak of hyperbolic flybys. For the core question of tracking accuracy, this detail will make no difference. – Andreas Nov 05 '16 at 15:34
  • @Andreas I think all flybys are by necessity hyperbolic, no? Parabolas are a mathematical abstraction with zero probability (as are circles), and ellipses are bound orbits. Of course there are all kinds of weird n-body orbits without names as well. The comment was about satellites in Earth's orbit, which to me means elliptical orbits, which means not flybys. I'm guessing that with all the satellite data and laser ranging à la LAGEOS, gravitationally bound orbits don't show the flyby anomaly. – uhoh Nov 05 '16 at 15:46
  • @uhoh I beg your pardon and agree, hyperbolic flyby is a pleonasm. I will leave it in the question though... – Andreas Nov 05 '16 at 16:00
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    For good accuracy, radar is useful. You can get a very accurate axial velocity measurement with Doppler radar (1 mm/s doesn't seem out of the question). Radial velocity depends on being able to correlate multiple measurements into a single track. – Hobbes Nov 05 '16 at 16:06
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    Here http://www.lpi.usra.edu/books/AsteroidsIII/pdf/3004.pdf are some results about 4179 Toutatis, a resolution as fine as 125 ns (19 m in range) and 8.3 mHz (0.15 mm/s in radial velocity) was achieved. – Uwe Nov 07 '16 at 15:47
  • @Uwe Thank you, I read through that publication and found that it answers my question in depth. It seems that it dates back to 2002, given the fact that delay resolution improved by factor 40 in roughly ten years, I would expect they can do even better today. – Andreas Nov 07 '16 at 22:10

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Arecibo can measure speeds with an accuracy on the order of 1% in scanning mode (i.e. just observing asteroids as they pass through the field of view). Distances can be measured to 10-8 (10 ppb), I suspect this is done in a different, more accurate mode.

Emily Lakdawalla discusses this in her blog, inlcuding this graph that shows the position accuracy of one asteroid using optical observations only, or using Goldstone radar observations, with radar being 50 times more accurate:

Radar is much more accurate than optical observations only

This article quotes position accuracy of 10 m, and axial speed accuracy of 1 mm/s.

Hobbes
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  • Note the ratio of quoted position accuracy in the Space.com article (10 m) to distance (324,600 km) is about $3\times 10^{-8}$, right in line with the NASA article. – Chris Nov 21 '16 at 15:23
  • Optical gives position accuracy perpendicular to the line of sight while radar (one dish, doppler) gives position accuracy along the line of sight. Of course with multiple dishes you can get more transverse position information. That plot is position prediction accuracy, not position measurement accuracy. They are related, but one is not the same as the other. The Emily Lakdawalla blog link is very helpful - as they all are! – uhoh Nov 22 '16 at 17:31