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New Horizons: Approach Phase, OpsNav - 25 January 15 to 28 June 15
lollipop
post May 13 2015, 05:19 PM
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Is the error build up due to the increasing apparent diameter of the system as NH gets closer between frames?
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Gerald
post May 13 2015, 06:12 PM
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The decreasing distance (radial velocity) seems to be considered.
My best guess is, that the shift is caused by the proper motion / transverse velocity (applying the astronomical notions for velocities of stars by replacing the solar system barycenter by New Horizons).
For a more accurate modelling the transverse velocity components of Pluto/Charon and New Horizons need to be considered.
Previously I've assumed the transverse velocity as zero/negligible.
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Habukaz
post May 13 2015, 09:21 PM
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NH raw images (binned) with timestamp today have been released, which is interesting considering the fact that images at these distances have a significant probability of containing hitherto undiscovered/unpublished moons.


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john_s
post May 13 2015, 10:33 PM
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All the obvious geometrical effects are included in the predictions of the positions of the objects in the images- this is all done with SPICE which knows how to make those calculations. The offsets are mostly because the spacecraft orientation is only determined to within a certain precision, that is bigger than the resolution of the camera, so you can't predict the exact pixel objects will land on from the spacecraft pointing data alone. In fact the first thing we do when analyzing the images is to determine accurate pointing by comparing the star positions to a catalog. I'm not sure why the error would show systematic drifts with time, but it might be just coincidence.

John
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Gerald
post May 13 2015, 11:33 PM
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It seemed to me to be a drift of the Pluto/Charon barycenter relative to the star background, somewhere near 3e-3 degrees over more than three weeks.
I could imagine a slightly curved trajectory of New Horizons due to the Sun's field of gravity, or an effect of Pluto's orbital motion, or just some glitch in my processing or perception.
But that's just preliminary ideas; I haven't done a fully accurate analysis (yet), and may post a revision later.
(I'm intending to take a look at the hazmat images, first.)

For an accurate analysis of the orbits of the moons, however, it will likely be necessary to determine or rule out the presumed drift.
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tanjent
post May 14 2015, 12:42 PM
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To a first approximation, the spacecraft and the Pluto-Charon system are approaching each other along the unequal legs of a right triangle, so why shouldn't the barycenter move with respect to the background star field? The barycenter is not the bulls-eye of a stationary target.
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lollipop
post May 14 2015, 04:12 PM
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I've been straining my brain over tanjent's idea. In rough numbers, Pluto is moving at about 5km/s towards the point where closest approach will occur. NH is moving towards the same point at about 14km/s. Imagining the third side of the triangle as the line joining NH to Pluto, the three sides will shrink in proportion to each other so that the direction of the line joining NH to Pluto stays approximately constant. I say approximately because the paths are curved, they aren't really aiming at exactly the same point etc. Imagining myself riding along with NH, I'm not surprised that Gerald finds a very small drift for the barycentre - the apparent motion of Pluto relative to the background stars as seen from NH would be much less than that seen from the Sun.
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chemman
post May 14 2015, 05:13 PM
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When I first looked at the new processed images from the NH spacecraft showing the motion of all four of the small moons, I couldn't help but notice that there was a diffuse blob that starts out beside Hydra and is apparent in the last 3 of the frames. Let me just say I understand this is probably just an artifact. But I haven't quite been able to convince myself of this so I started wondering what if it was real. So in the interest of mostly just pure speculation, what if it is an ejecta plume from an impact event on Hydra (I know what are the odds that we would just happen to observe this). I'm not familiar enough with the orbital mechanics of this system to try and say if the apparent motion of the object would even fit such a scenario. Thoughts?

http://www.nasa.gov/image-feature/nasa-s-n...est-known-moons


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scalbers
post May 14 2015, 05:22 PM
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QUOTE (lollipop @ May 14 2015, 04:12 PM) *
Imagining myself riding along with NH, I'm not surprised that Gerald finds a very small drift for the barycentre - the apparent motion of Pluto relative to the background stars as seen from NH would be much less than that seen from the Sun.

Yes it makes sense to have a small drift from the curvature for NH's and Pluto's paths. This seems consistent with being a few percent of the drift of Pluto in the sky as seen from the sun, given NH's speed relative to Pluto. Unless Gerald is referring to an error in the drift vs the drift itself. If Celestia or similar software has NH added to it, then this drift can be independently evaluated?


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john_s
post May 14 2015, 05:42 PM
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QUOTE (chemman @ May 14 2015, 10:13 AM) *
When I first looked at the new processed images from the NH spacecraft showing the motion of all four of the small moons, I couldn't help but notice that there was a diffuse blob that starts out beside Hydra and is apparent in the last 3 of the frames.


When you push the image processing as hard as we had to do to see Styx in this sequence, all kinds of artifacts start to emerge- that fuzzy blob is probably some sort of internal reflection. We could have manually cleaned up the release image to remove everything we weren't sure was real, but we decided a "warts and all" release would give a better idea of what the data are really like, and the challenges of working with the images (plus, we don't have that kind of time smile.gif ). We'll have much better images soon, of course.

John
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alk3997
post May 14 2015, 05:46 PM
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QUOTE (chemman @ May 14 2015, 11:13 AM) *
When I first looked at the new processed images from the NH spacecraft showing the motion of all four of the small moons, I couldn't help but notice that there was a diffuse blob that starts out beside Hydra and is apparent in the last 3 of the frames. ... Thoughts?


I believe each of the four smaller moons is now 1 pixel wide and was teased out of background noise. The blob you see is much less than the original 1 pixel, so it's just an imaging artifact.

Also don't forget that the spacecraft had a different attitude relative to the Plutonian system during some of these images so the direction of the artifacts may change with each image.

Andy

P.S. Sorry John for the duplicate. I started typing just as you hit send.
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Gerald
post May 15 2015, 12:03 AM
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Here a stitch of seven 2015-05-11 "Search for sources of hazmat" 6-image stacks:
Attached Image


It has been rather easy to identify Nix and Hydra. But I wasn't able to find Styx and Kerberos. Here a crop of a heavily processed version, obtained by subtracting an appropriately brightness-stretched version of the OpNav Campaign 3 stitch, and in parallel subtracting a processed Google Sky image roughly simulating the LORRI images, then combining the two differences to filter out stars as far as possible:
Attached Image

I've tried several processing techniques, but none was successful in revealing the two smallest known moons of the Pluto/Charon system.
I guess, that the data loss due to jpeg compression and reduced bit depth has swallowed the tiny signal of the two moons.
Some discrepancies (pointed out in some preceeding post) to Google Sky have been reproducible.

Some images of OpNav Campaign 3 aren't yet included in my processing. Might be, that adding the latest images of the sequence, and considering the potential transverse velocity component will add up to a perceivable signal.
I hope, I'll be able to investigate this over the week-end.
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Gerald
post May 17 2015, 02:05 PM
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"Search for soures of hazmat", stitching by median-filtering, blink gif

and differencing of cleaned and summed images:
Attached Image
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Gerald
post May 25 2015, 12:40 PM
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Some more elaboration of the presumed parallax:
A two-image blink gif consisting of two cleaned, stacked, registered and cropped OpNav Campaign 3, LORRI 4X4, images, taken with an interval of about 32 days:
Attached Image

I'd say, it shows the parallax of the Pluto/Charon system evidently with respect to the background stars.
The increasing apparent angle between Pluto and Charon is evident, too.
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Gerald
post May 25 2015, 03:52 PM
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21 sets of OpNav Campaign 3, LORRI 4x4 images, source images and stacked version, synopsis:


Edit: Album of registered versions of the stacked images.
Reference point and rotation angle for respective applied (north-south aligned) registration: Attached File  metadata_OpNav3_reg_trunc.txt ( 2.06K ) Number of downloads: 290
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