I don't understand! Rotating frame? I see Orion pass by around 00:30 to 00:36, that's a clue.

Why the first two passes are on the same side (in this view) but the rest alternate? edit: This is because the first orbit has a very different period.

What kind of orbits are not considered "Gravity orbits"?

What is an MWR orbit?

What kind of orbits are in white (not labeled in the legend)?

It looks like the dark side of Jupiter is mostly facing us - the sunlit face is mostly facing away from us. You can see a crescent of light on the right side at the beginning, then on the left side later on. I thought Juno will never experience an eclipse during its time studying Jupiter.

I think I see an "Extra science orbit" in yellow at 00:55, but no De-orbit maneuver in red. I was looking forward to the Juno-shattering Kaboom! See question 1, and question2, and Marvin the Martian circa 1950 for background.


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Jupiter rotates quite rapidly -- it's rotational period is only ten hours. The camera on that animation is almost keeping up with Jupiter's rotation. The rotation of Jupiter beneath Juno's orbital track is where the apparent twist is coming from -- the path is being rendered Jupiter-surface relative. Note that the very eccentric orbit means that Juno's speed is changing dramatically over the course of each pass -- accelerating toward perijove (near the equator) and decelerating on the way out; it's close to the planet for only a few hours out of each two-week-long orbit.

MWR is Juno's Microwave Radiometer. I believe the "MWR orbit" versus "gravity orbit" distinction simply tells which instruments are going to be active on each pass -- the MWR versus the gravity experiment -- which has secondary impact on other aspects like the spacecraft's communication protocols. There's more information on those orbits near the end of this very informative page. Here's information from Wikipedia about the instruments.

  • $\begingroup$ I think there's some serious mis-matching of timescales here. According to the video caption on YouTube, it's 33 orbits over 15 months. Each orbit is a about 14 days (except the first) and the time Juno would take to move along one of those lines in the video is only 0.06 days or about 9 milliseconds in the video @ periapsis. The stars look to be moving fast enough to make about 1.3 complete revolution during the video, or about 1 rev per year, which matches the movement of the sunlit portion, So the view is orbiting around Jupiter with a period of one Earth year. Curiouser and curiouser! $\endgroup$ – uhoh Jul 7 '16 at 5:00
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    $\begingroup$ Ahh, good point. Jupiter would rotate ~33 times between passes. Assume the apparent rotational speed is due to aliasing: en.wikipedia.org/wiki/Aliasing $\endgroup$ – Russell Borogove Jul 7 '16 at 5:03
  • $\begingroup$ Ha!!! Excellent. So the light/dark side of jupiter doesn't match the position of the oribits, right? Shouldn't the entire 15 month trajectory remain sunlit? Also, oh rats, it's past five minutes, I can't edit my comment and change "periapsis" to "perijove" - I learned a new word today! (but the spell-checker didn't) $\endgroup$ – uhoh Jul 7 '16 at 5:07
  • $\begingroup$ By the way, those links are excellent - thank you for those! There is a lot there to take in and think about. $\endgroup$ – uhoh Jul 7 '16 at 5:33

How to understand this NASA animation of Juno's passes near Jupiter?

Like much of the stuff coming out of JPL and SWRI regarding Juno, this leaves me unimpressed. The animation has labels that are unexplained, a slowly rotating Jupiter that is unexplained, big jumps in time whose presence was not divulged, and an obviously nonsense star field that I suspect was added just for the "Wow!" effect.

I see Orion pass by around 00:30 to 00:36, that's a clue.

It is a clue that this is not a good video. It would have been better to have left the background black.

Here's my best guess with regard to how what you are seeing was created:

  1. Juno's 36 orbits about Jupiter were simulated and then expressed in terms of a Jupiter-fixed frame. Only the parts in the close vicinity of Jupiter are depicted.

  2. As a time-lapsed animation, almost all (97.6%) of this will be extremely boring because Juno is not in the video frame. The only interesting parts are the 8 hours of the 14 day orbit where Juno passes very close to Jupiter. These 8 hours are the scientifically interesting bits. The boring bits were skipped over.

  3. A frozen 3D image of Jupiter was added to the animation. Having a frozen image is not quite correct as different parts of Jupiter rotate at slightly different rates. Over Juno's 36 orbits, the equatorial regions will have rotated eleven times more than will have the polar regions. This is not shown in the video.

  4. The entire simulation was set into a slow animated rotation to show that these 36 science passes do a nice job of evenly covering Jupiter.

  5. A star field was added for "Wow!" effect. If done correctly, the star field would move quickly (the 8 hour long science pass is more than 80% of Jupiter's rotation period) and then jump to reflect the 13 days and 16 hour time jump, move quickly and then jump, doing that 36 times. This star field is purely synthetic (i.e., it's bogus).

What kind of orbits are not considered "Gravity orbits"?
What is an MWR orbit?
What kind of orbits are in white (not labeled in the legend)?

Regarding the coloring and labels on the orbits, Two of the nine experiments being conducted by Juno are mutually incompatible with one another. These two experiments turn out to be two of Juno's primary reasons for being, which are peering into Jupiter's atmosphere and assessing its gravitational field.

Juno doesn't have any sensors to measure gravity (sensing gravity is very, very hard). Instead, variations in Doppler shift in the science data return from Juno as received on Earth give clues to Jupiter's gravity field. This means using the high gain antenna, which in turn means that Juno needs to orient itself so the high gain antenna points at Earth. (The high gain antenna is not pointable except by pointing Juno as a whole.)

The microwave radiometer (MWR), which is used to peer into Jupiter's atmosphere, has conflicting requirements on Juno's pointing. The radiometer needs to be pointed toward Jupiter and the spacecraft needs to be oriented so as to minimize multipath interference. (If you have a smartphone with a GPS receiver, you may have noticed that it doesn't work so well in downtown areas with tall skyscrapers. That's because of extreme multipath interference.) Pointing the HGA toward Earth is a non-option when the MWR is is use.

The two orbits in white represent the very first orbits about Jupiter, where the MWR is not yet active and high precision orbit monitoring via X-band and Ka-band Doppler shift is not yet being performed. The "gravity orbits" are where that Doppler monitoring is being performed, and the "MWR orbits" are where the microwave radiometer is active.

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    $\begingroup$ I understood Juno has a magnetometer to measure the magnetic field. the MWR is to measure water. missionjuno.swri.edu/spacecraft/juno-spacecraft $\endgroup$ – kim holder Jul 7 '16 at 14:15
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    $\begingroup$ Thanks, @kimholder. I'll fix that. It's not just water, it's lots of other stuff as well, but all in Jupiter's atmosphere. It was a very easy fix. $\endgroup$ – David Hammen Jul 7 '16 at 14:22
  • $\begingroup$ OK, well I really appreciate your answer. People do animations for all sorts of reasons other than official public outreach, and then add them to YouTube because, really, that's what people do these days. It's usually thought to be better than the alternative of keeping it hidden on one's own hard drive. It certainly has sparked some good discussion and thought here, which I think is great! But ya, it maybe should carry a bit of a disclaimer in this case, because of the mixed and discontinuous time scales. The photorealisms (stars, sunlight, rotation) and streak-motion are quite misleading. $\endgroup$ – uhoh Jul 7 '16 at 14:27
  • $\begingroup$ The spacecraft is always sunlight - correct? (See the link I've included in the question). So seeing a trace/streak appear on the dark side of Jupiter is just plain wrong - isn't it? On another note: this other NASAJuno video has more explanation and disclaimer. $\endgroup$ – uhoh Jul 7 '16 at 14:31
  • $\begingroup$ @uhoh -- The vehicle does have two hefty batteries, and the periods of eclipse, if any, will be short in duration. But are there any? That's one of millions of technical details that are hidden from the public. (Almost every single technical detail on this mission is hidden from the public. I am not thrilled as a taxpayer.) $\endgroup$ – David Hammen Jul 7 '16 at 14:35

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