Cassini, The 24 images from Cassini's Venus Flyby Options

[tedstryk]

I looked through the image sets from Cassini's Venus flyby. They all seem to not show the planet or be blank flat fields against the cloud tops, except for one. This one seems to show the terminator. Am I imagining this?

[deglr6328]

??? I didn't think they took iss data because of budget constraints.

[tedstryk]

As Cassini approached Venus for the second time, it was determined that during the flyby, Venus would serendipitously pass through the ISS field of view. This was used to take flatfields for the CCDs, as the cloudtops are some of the most blank things out there at a lot of wavelengths. But this one seems to show some detail.

[Decepticon]

So no real image science was taken!? What a waste.

[Bjorn Jonsson]

So no real image science was taken!? What a waste.

This would have been difficult to do since Cassini doesn't have a steerable platform for the remote sensing instrument so the entire spacecraft has to be rotated to point the instruments at specific targets. How the spacecraft could be pointed at Venus was highly constrained by the fact that the high gain antenna had to act as a sunshade by pointing at the sun.

[tedstryk]

This would have been difficult to do since Cassini doesn't have a steerable platform for the remote sensing instrument so the entire spacecraft has to be rotated to point the instruments at specific targets. How the spacecraft could be pointed at Venus was highly constrained by the fact that the high gain antenna had to act as a sunshade by pointing at the sun.

Basically, it could have been done if money had been allocated and software had been written before the mission. But to save costs, much of Cassini's flight software was written after launch, and it was using pretty early versions at the time. Had elaborate planning to be done to make sure that nothing was pointed at the sun that shouldn't be and or for too long, which would be a very complex task at Venus for a spacecraft designed to operate at Saturn, some observations could have been made. But this would have taken a lot of planning money, and with the software not being fully tested yet, too much of a risk. Better to miss out on some Venus data than blind the spacecraft years before SOI!

[Bjorn Jonsson]

I looked through the image sets from Cassini's Venus flyby.  They all seem to not show the planet or be blank flat fields against the cloud tops, except for one.  This one seems to show the terminator.  Am I imagining this?[/img]

No, I think you are correct - I tried reprojecting the image to simple cylindrical projection using the viewing geometry information in the index.tab file (although the north azimuth is frustratringly often corrupt in the index.tab files). According to this longitude 297.25 should be near the center of the image. The subsolar point is at lat=-0.02456, lon=27.86458. This is roughly consistent with the terminator being visible in this particular image.

[tedstryk]

Thanks. I have done some toying with the other 23 images, and the others seem to show nothing of interest (either blank or truely flat fields) or are incomprehensible (seems as if Venus is overexposed just out of field). Am I correct in this (sorry to keep asking questions - I am paranoid after my Miranda mess-up).

[Phil Stooke]

Hey, don't worry about messing up, Ted! We've all done that... me included. Did you see my Home Plate debacle? But this is a very forgiving place.

Phil

[djellison]

But this is a very forgiving place.

I Fed-Ex'd you a horses head re: Homeplate, did you not get it



Doug

[tedstryk]

Thanks...It was quite an awful moment. I was looking back at the Miranda image, and I was sure the features beyond the limb were too well connected to the features on the day side to be artifacts. Then as I looked through the layers one by one, I made the discovery that the reason the terrain on the "night side" looked so much like the terrain on the day side is that it was the same terrain in the out-of-alignment image.

[Phil Stooke]

The horse's head looks really nice next to my teddies.

Phil