Juno Perijove 58, February 3, 2024 Options

[volcanopele]

for 17:49 this is what I get:



This does add coverage to the west of what 17:50 can get, particularly Masubi, and at decent resolution, 1.1 km/pixel at center of disk. 17:53 doesn't seem to add much and some of that can be recovered by starting the last set a minute earlier (17:55)

I will note that the leading hemisphere is the other big gap in our map of Io where the best resolution data from Galileo/Voyager/New Horizons was ~7–8 km/pixel and this would definitely help fill that gap.

[mcaplinger]

17:53 doesn't seem to add much and some of that can be recovered by starting the last set a minute earlier (17:55)

17:53 is a backup against timing errors or possible unrecoverable loss of 17:52.

There are constraints on how close the sets can be and I don't think the last set can be moved in.

But I hear you and I'll see what I can do.

[volcanopele]

I presumed that if the third block of four gets shifted forward a minute, so starting at 17:49 instead of 17:50, the fourth block could also be moved up a minute.




Here is a set of preview images starting with the 17:49 opportunity and including 17:53. The last image is the 17:56 opportunity. There is no meaning to the difference in brightness in the Jupiter-shine areas, just me being fast and quick in Photoshop and not paying attention to what exposure setting I used.

[mcaplinger]

for 17:49 this is what I get... This does add coverage to the west of what 17:50 can get, particularly Masubi, and at decent resolution, 1.1 km/pixel at center of disk.

Except Junocam isn't seeing the center of the disk at that point. IMHO 17:49 is too oblique.

I considered bumping everything back 30 seconds so starting at 17:49:30 but that's not a clear winner to me either, thoughts?

And you have to consider that due to spin phase uncertainty the position is uncertain by a spin period.

Whatever we do, I have a soft deadline of EOD today to decide.

[volcanopele]

17:49:30 still has Masubi in the FOV but it is much closer to the limb. Still a better view than 17:50:00. and it has the benefit of having a higher resolution view of East Kanehekili (second highest priority "new volcano" target IMHO at Io from JIRAM data after Tonatiuh) that at least with the current predicts we would miss at 17:49. We would lose the best full-color dayside opportunity.... but there would still be two opportunities. I still think that 17:50 is preferable to 17:49:30 as we get full-disk color at highest resolution (given current predicts of the rotation).

Looking at 17:48:30, so looking at the worst case scenario I am not actually suggesting starting that early, Io is still in the JunoCam FOV. We lose Masubi as it isn't quite in the FOV yet, but Shamshu and Janus would be there, Janus would be a bit more marginal there. My point is that even in the worst-case scenario for the rotation phase, 17:49 would still be useful for gap filling. For added context, during IVO planning we had an entire flyby just to get this coverage.

For context, Janus is a lava lake much like Pele. In the IR, Janus looks almost identical to Pele, but has fewer volatiles (IOW, there's no giant red ring around it)

[mcaplinger]

Have you compared the amount of Jupitershine in this encounter with the previous one? It looks similar, but I was surprised reviewing the PJ51 imaging that the nightside was much dimmer than it was in PJ57.

Probably this is just a Jupiter phase and Io orbit position thing, but the tools I have to look at this are clumsy.

[volcanopele]

comparing 55C00035 with 57C00030 and 57C00022, I get roughly similar pixel values for places like around Fjorgynn Fluctus. Color still looks better for the PJ57 images. No apparent signal in BLUE in the orbit 55 images, it looks to be almost entirely noise. for PJ57, the darkest features like Guawa Patera and Fjorgynn Fluctus and the brightest terrain shows up (bright material near Gauwa and Fjorgynn, and around Acala Fluctus). I presume that this is a factor of noise, reducing effective resolution. So PJ57 data, particularly 57C00022 looks great, but the effective resolution is still reduced by a factor of 2-3 compared to the dayside. but that drop of resolution still makes it better than Galileo/Voyager data.

[mcaplinger]

Have you compared the amount of Jupitershine in this encounter with the previous one? It looks similar, but I was surprised reviewing the PJ51 imaging that the nightside was much dimmer than it was in PJ57.

I think the difference (wait for it) is that Jupiter doesn't shine on the part of Io away from Jupiter, only on the part facing Jupiter. Duh.

So one shouldn't expect Jupitershine on inbound-to-Io images, only on outbound-from-Io images.

[kymani76]

I'm not totally sure, but I believe it is possible to present above discussion in a map form.

The view above shows Io as seen from Jupiter at the time of the flyby. In other words, the center of map projection is at Io's sub-Jupiter point.
This means we are looking at the hemisphere illuminated by Jupiter-shine.

I've used this article to estimate how much of Io's disk Juno can see at selected times.
(17:49 in red, 17:49:30 in green; 17:50 in blue). I used values of 0.25, 0,265 and 0.28 respectively for f to account for the rising altitude, giving me range circles for parts of Io visible to Juno at these times.
You can really see how much the coverage changes in very short time.

I still have to account for Junocam FOV as I suspect not the whole visible disk fits into the camera view, but I haven't figured out how to account for that yet.

And yes, there is no Jupiter-shine on the inbound track.

[mcaplinger]

I still have to account for Junocam FOV as I suspect not the whole visible disk fits into the camera view, but I haven't figured out how to account for that yet.

It's not easy. To do it completely correctly, you need to know the pointing of the spacecraft as a function of time. For many of these flybys, including this one, the spacecraft spin axis (Z) is pointed at Earth, which makes it a little easier. So the Junocam FOV is a locus roughly +/- 30 degrees from the XY plane and spun about the Z axis. If a point on Io is in that locus we can see it, if it's not then we can't. I could imagine sampling a full range of lat/lon, checking to see if that point was in the locus, and drawing a little X there if it was, or something similar.

BTW, after much analysis I decided I couldn't take an image at 17:49, but one did fit at 17:48:30 so I took one there with TDI 12, then three images at 17:50 (TDI 12), 17:51 (TDI 2), and 17:52 (TDI 2). All RGB.

2024-034T17:32:00 RGB 6, 2
2024-034T17:39:00 RGB 2, 12
2024-034T17:48:30 RGB 12
2024-034T17:50:00 RGB 12, 2, 2
2024-034T17:53:30 RGB 12, 6

You have until Monday to change my mind

[volcanopele]

Even for my simulations, I account for the JunoCam FOV by looking at the predicts in Cosmographia and trimming off the excess in Photoshop from the maps I reproject in ISIS.

as far as the timings go, 17:48:30 is even more marginal than 17:50. It does do some gap fill east of Shamshu Patera but it misses Masubi and barely gets Janus. If that's just how the timings work, I mean, that's still really nice resolution at Shamshu and points east. 17:53:30 looks pretty good though maybe reverse the TDIs? 17:53:30 is good for a nice full global shot in sunlight.

Regardless, I'm sure these will be amazing. I'm so thrilled that we are getting such great sub-Jovian/leading-hemisphere coverage!

[mcaplinger]

For posterity, Jason's last message arrived too late to affect command generation, so what I said on 1/12 reflects what we commanded.

I'm never sure how timestamps work on this forum, I'm sending this at 12:46 PST or 20:46 UTC on 1/16.

Now, we wait.

[kymani76]

I made some progress querying SPICE. Here is what I think might be a plot of Junocam's boresight projected on Io's surface for the period from 17:32 to 17:56.
The plot looks a little confusing and I'm still studying how this information might convert to image footprints for specific times.

[volcanopele]

With the timings and TDI settings Mike provided above, here are preview images (combining USGS basemap with PJ57 data, greyscale is USGS basemap and a simulation of Jupiter-shine):

[john_s]

Thanks! How will the resolution on Loki compare to PJ57?

John