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Posted by: Gustavo B C May 14 2018, 02:34 AM

Cassini took a few pictures of the Huygens lander two days after (Dec. 27) it was released from the main probe on Dec. 25, 2004 to check on its trajectory, which was found to be correct within the expected error range. This is one of them, more exposed on the left and less exposed on the right (click for full res):

https://flic.kr/p/HtE6wn

It's not too impressive, but I found it neat

LMK if this isn't the right place to post this or if it should be posted in an existing thread - sorry if that's the case!

Posted by: Explorer1 May 14 2018, 03:20 AM

Almost looks like a disc, not a point! How far away were the two spacecraft at the time?

Posted by: tasp May 14 2018, 04:43 AM

IIRC, the excellent Haynes manual book noted 50 kilometers more or less.

The book also fleshed out the release details. The rails holding Huygens imparted a spin to it, and a slower rotation to Cassini (due it's greater mass) that gave confidence the probe was spinning at the
correct rate.

Cassini had it's thrusters switched off till Huygens was far enough away plume impingement would not be an issue. Also, the magnetometer instrument noted the combined rotation rates of both and
that was in spec too..

I can't recommend the Haynes book enough, it is excellent and a wonderful resource !! [ADMIN NOTE: And was written by UMSF member Ralph Lorenz! ]

Happy to have learned of it here.

Posted by: Gustavo B C May 14 2018, 06:19 AM

Going by the NASA's Eyes app, they were just under 81.2 km apart. Going off a measurement I found of 2.7 meters for Huygens' size, that makes it just under 0.002 degrees in angular size. Considering the NAC had an FOV of 0.35°, that is ~0.5% of the 1024 pixel side of the sensor - just over 5 pixels, which is approximately what you can see in the darker photo, so yes, it is a disc rather than a point! Unless I'm doing everything wrong...

Posted by: rlorenz May 15 2018, 06:51 PM

If memory serves, there were two imaging sessions. First was a WAC (9x9 ?) mosaic to find the probe, and this was used to cue a NAC image (which is the one that exhibits a disc, with a bit of shadowing, that I show in the Haynes book)