Enceladus and Image Resolution
A few weeks ago, in response to a post I made regarding raw images from this month's Enceladus flyby, whether we'll be seeing better than 25m/px resolution later in the mission"? Good question, I had no idea at the time. Anyways, a few days, at a colloquium given by Zibi Turtle here at the University of Arizona mentioned that we will probably not get better images than 25 m/pixel, despite coming within 100 km of Enceladus in March 2008 (which would yield sub-meter resolution images if ISS took images at C/A). Range-to-target smear (smear caused by the spacecraft motion to and from a target during the exposure) not withstand, there is another problem which I hadn't considered. The E-ring. Enceladus' orbit is smack dab in the middle of the densest part of the E-ring, and just as before and after the SOI burn, Cassini needs to turn close to C/A so that the high-gain antenna protects the spacecraft from E-ring particles. Since Cassini doesn't have a scan-platform and the camera and antenna boresights are perpendicular to each other, the camera can't point at Enceladus and protect itself from E-ring particles at the same time.
posted by Jason Perry at 6:58 PM
3 Comments:
Jason - thanks for following up on that. Gotta say I'm quite bummed. I was really hoping for some MOC-resolution images. I can be so greedy that way. (And I would have thought Enceladus would be the easiest moon to get low-smear images of, since it's so bright the exposure times would presumably be quite short.) (And don't get me started on the lack of a scan platform... grrrr.)
Maybe, if we're really lucky, they might try some wacky stuff on the extended mission that would be too risky to try now.
Thinking about the closest approach geometry suggests this to me: at CA, by definition, the trajectory is parallel to the surface. Any line passing close to a sphere is perpendicular to the extended radius and parallel to the surface at the closest point. So the antenna facing forward and the camera facing the satellite is not a problem if they are mounted perpendicular to each other. That's not true during the approach but it always is at CA. However, if smear is an issue you are still out of luck!
I figured smear was the big problem, and that possibly the mission controllers don't want to try to slew the spacecraft to correct for smear in order to keep the antenna pointed as favorably as possible into the e-ring. Still, I gotta say it's frustrating, since I figured exposure times for the most reflective body in the solar system would be short enough to help cut down a lot on smear even before introducing fancy stuff like slewing the spacecraft.
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