Saturn as I long to see it

[steuard]

LJ doesn't seem to want me to embed the video, so I'll just give a link to the original site; it's worth watching full screen.

The movie there was assembled from a huge number of still photos of Saturn taken by the Cassini probe, and it's absolutely fantastic. The best part is the full-color section, which starts a little before the one minute mark. I continue to find it amazing that we live in an era when we can actually see these sights "for real" like this... and I hope that one day, we human beings will be able to see it in person.

Comments

[springbok1.livejournal.com]

Thanks for posting the link; that was beautiful and breathtaking.

[kirin]

Glorious.

[akjdg.livejournal.com]

I assume Cassini was largely a ballistic object on this fly by, yet it approaches to inside Saturn's rings, but then stops, and pulls outside the rings before passing a moon. Is there an orbit I missed (didn't seem so from the sun angles)? This seems like a very high energy maneuver for such a probe to perform.

over-thinking the time-lapse aside, tres cool.

[steuard.livejournal.com]

Yeah, I wondered a bit about that, too, but I hadn't really stopped to think about it. I had assumed that there *was* an orbit that happened along the way that I just didn't notice because my attention was occupied by other things. But now that I look more carefully, I'm not quite sure what they've done here.

I don't trust "sun position" as a guide to what's going on, because probe motions could potentially take a substantial fraction of a Saturn year (not that I really expect that, but it's not impossible). But I'm still uncomfortable, because the camera's angular momentum about Saturn appears to reverse direction (relative to the plane of the rings) three times during the course of the movie. That would be an amazingly high energy maneuver. (I mean, I know they have some maneuvering budget, but a path like that would be tremendously wasteful.)

So I see two possibilities. It could be that the probe was doing some exciting gravitational slingshot tricks along the way, and the camera direction was chosen to focus on the motion around Saturn rather than showing the moons/whatever that provided the assist. (Maybe watching the moons' surface spinning by below made viewers motion sick?) But I didn't see any large looking moons hanging out in the right places in the wider shots. Or it could just be that Cassini has taken enough images with enough resolution from enough various positions in the Saturn system that the creators could piece together an entire video along a path of their choosing by combining images with appropriate crops and zooms. I'm leaning toward that explanation.

[akjdg.livejournal.com]

For whatever my druthers are worth, I would prefer to think this grand video was faithful to Cassini's trajectory, and not a freeform composition derived from Cassini imagery. Why not just resort to CGI?

That said, I think you're right, but am not really sure. The time scales seem off, but I'm not confident I know what they should be.

1. From an energy budgeting viewpoint, I would expect Cassini would be moving slow relative to the Saturn system upon arrival. Excessive velocity equals spending more energy than was needed to get Cassini into this solar orbit, and a harder time inserting it into Saturn orbit. If this is accurate (and they didn't give it a swifter kick for scheduling or targeting purposes), I would expect enough time to elapse during this scene to see some motion in the Saturnian bodies.

2. If an insertion burn was needed upon arrival at Saturn (reasonable enough), what we see here is about the last thing I'd expect to see- head straight for the planet, and then fire like mad to back off???

3. The craft's spin rate relative to its apparent speed through the near-Saturn environment is so slow as to be useless for stabilization of its earth-pointed antennae, which is presumably why it would have a spin (I suppose the image sampling rate could be aliasing the spin rate, or the spin is not intentional, and is a harmless artifact of maneuvering burns). The camera and antennae must be gimballed to keep everything pointed where it needs to be.

4. None of the moons (in particular Mimas) are perceptibly rotating while in view, but perhaps because they are tidally locked with Saturn?

5. Upon closer inspection, the sun angles may not be consistent. As Cassini moves inside the rings, the sun is behind the viewer to the upper left (abut 1:30 or so). As Cassini moves back beyond the rings, the sun is now behind and to the upper right. I can't say that this is wrong, but it seems odd. It's hard to keep my bearings straight.

Oh well. Fun to test my intuitive sense of... orbital physics? against a video. Can't say as I'm sure which to believe.

The musical composition is very nice.