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Juno perijove 4, February 2, 2017
mcaplinger
post Feb 19 2017, 11:41 PM
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QUOTE (Gerald @ Feb 19 2017, 02:05 PM) *
The later perijoves haven't yet been determined...

http://www.unmannedspaceflight.com/index.p...st&p=233216 shows a list (dates only) through PJ9. I have a later list, of course, but am not authorized to share it.


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Floyd
post Feb 20 2017, 01:53 AM
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Adding 53.5 days to last known perijove is difficult, but not beyond the math skills of some on this forum.

Edit: Sorry for the Snark--I thought the question was about the day not the second...


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mcaplinger
post Feb 20 2017, 03:35 AM
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QUOTE (Floyd @ Feb 19 2017, 05:53 PM) *
Adding 53.5 days to last known perijove is difficult, but not beyond the math skills of some on this forum.

The orbit period is not precisely a constant because there are trim maneuvers, especially later in the mission to avoid eclipses. If you only want to know it to a few hours' accuracy, adding a constant may be good enough.


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Gerald
post Feb 20 2017, 09:01 AM
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PJ03 Image #73 has been taken 6h42m before PJ04, if I calculated correctly. This may provide some idea about the effect of a few hours.
For predicting any potential Juno transits through a moon's shadow, much more accurate data are required, of course.
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Roman Tkachenko
post Feb 20 2017, 03:28 PM
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QUOTE (mcaplinger @ Feb 8 2017, 11:45 PM) *
Thanks, Roman. It's images like this one that keep me going in the face of all the negative clueless remarks on reddit about the supposed "mediocrity" of Junocam.

Thank you, Mike!
Btw I've made a new, not so overprocessed version of this image.
Here's a high-resolution version


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PhilipTerryGraha...
post Feb 21 2017, 04:31 PM
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Here's what Eyes on the Solar System has in its current simulation of the Juno mission, with all dates in UTC:

PJ5 - March 27, 2017
PJ6 - May 19, 2017
PJ7 - July 11, 2017
PJ8 - September 1, 2017
PJ9 - October 24, 2017
PJ10 - December 16, 2017
PJ11 - February 7, 2018
PJ12 - April 1, 2018
PJ13 - May 24, 2018
PJ14 - July 16, 2018
PJ15 - September 7, 2018
PJ16 - October 29, 2018
PJ17 - December 21, 2018
PJ18 - February 12, 2019
PJ19 - April 6, 2019
PJ20 - May 29, 2019
PJ21 - July 21, 2019
Deorbit - September 11, 2019


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Gerald
post Feb 21 2017, 06:05 PM
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The most accurate published times for perijoves 6 to 8 I'm aware of are
PJ06 2017 May 19, 17:44:04 UTC
PJ07 2017 July 11, 1:55:56 UTC
PJ08 2017 September 1, 21:50:01 UTC
But I think, that the times will be off by up to several minutes, since for PJ05, there is already a discrepancy of 66 seconds to the current prediction in SPICE.
The data are of 2016 December 28 from the latest update of the professional Earth based observation plan.
(This site is easier to read, at least in my browser, but might become obsolete with the next update.)
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mcaplinger
post Feb 21 2017, 06:43 PM
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The most accurate source of PJ times I know of are in the .orb files on the NAIF website. The most recent one is https://naif.jpl.nasa.gov/pub/naif/JUNO/ker...0912_161027.orb but only goes through orbit 22.


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PhilipTerryGraha...
post Feb 21 2017, 07:21 PM
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QUOTE (mcaplinger @ Feb 22 2017, 05:43 AM) *
The most accurate source of PJ times I know of are in the .orb files on the NAIF website. The most recent one is https://naif.jpl.nasa.gov/pub/naif/JUNO/ker...0912_161027.orb but only goes through orbit 22.


I'm thinking that this is the one that Eyes is using. Exact dates and times as to what's simulated.


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Gerald
post Feb 21 2017, 09:45 PM
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For the simulation you require more than just the apo- and perijoves. The same NAIF/SPICE directory contains also the file spk_ref_160829_190912_161027.bsp with more detailed information. Together with other kernel files you can simulate most of Juno's behaviour. I'm using the trajectories to create reprojected JunoCam products like these intermediate images (portions mirrored).
That said, the perijove dates and times should be sufficiently accurate to compare them with predicted shadows of the moons.
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mcaplinger
post Feb 21 2017, 10:04 PM
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QUOTE (Gerald @ Feb 21 2017, 01:45 PM) *
For the simulation you require more than just the apo- and perijoves.

Well, there are two steps: the first is to figure out if there are any eclipses near a perijove pass, and the second is to determine if the shadow would be visible from Juno. For step 1 you don't need to know where Juno is exactly.

Keep in mind that later in the mission Jupiter isn't even in the Junocam FOV for a lot of the time as the orbit plane migrates away from the terminator, so that's another constraint.


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JRehling
post Feb 22 2017, 08:58 PM
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QUOTE (mcaplinger @ Feb 14 2017, 02:53 PM) *
It's not inferior, it's just different. The driving requirement was to be able to image the full disc of Jupiter from above the pole, which led to a very wide field of view, utterly unlike the instruments that it's being compared to.


This is closely related to the phenomenon in amateur astronomy wherein vendors of (often, cheap) telescopes advertise the magnification as the most telling statistic about a telescope. Whereas, one realizes that for many objects, one actually wishes to decrease magnification, and a very smart purchase is a focal reducer which gives you a wider field of view and more light per pixel, to reduce exposure times in photography and brighter-seeming objects for direct viewing.

As a teenager, I used a short focal length eyepiece with a large telescope to get an 800x magnification on Saturn. It was terrible, dim and shimmering and muddy, like looking at an amorphous shape on the bottom of a poorly-lit swimming pool.

When you take a picture of your friends and family, you don't usually zoom in on their noses close enough to show the pores in their skin. More-zoomed-in is not always better. Somehow, in astronomy, people forget that.
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PhilipTerryGraha...
post Today, 05:11 PM
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Congrats to Roman for what is now his third image featured in the NASA Photojournal! biggrin.gif


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Roman Tkachenko
post Today, 11:26 PM
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QUOTE (PhilipTerryGraham @ Feb 24 2017, 09:11 PM) *
Congrats to Roman for what is now his third image featured in the NASA Photojournal! biggrin.gif


Thanks! smile.gif


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