[X] My Assistant

[jasedm]

I was hoping that perhaps a umsf member could shed some light on our knowledge regarding perceived risk to Cassini from material in the Saturn system, and whether this has changed since orbit insertion.

This pertains specifically to the 'protective attitude' that Cassini is commanded to adopt during ring-plane crossings (with the high-gain antenna pointing in the direction of travel to act as a shield to the rest of the spacecraft)

This orientation obviously has costs in terms of hydrazine, data loss (ring-plane crossings are often at or near periapse, when multiple targets are within useful range) and must therefore affect command sequence-planning quite heavily

I was surprised at the low-level flybys at Enceladus, with the spacecraft in effect flying through the south-polar plumes, and also Cassini being directed through the G-ring arc (surely a largely unknown environment in terms of particles at the time) for the Aegaeon encounter.

The cosmic dust analyzer on board is perhaps less glamorous than the remote-sensing instruments, but I wonder if its data continue to indicate danger in crossing the ring plane just outside of the F ring?

Any answers much appreciated...

Jase

[jasedm]

Thanks for the detailed response Todd - much appreciated.

No doubt the 'expected particle flux threshold' has increased significantly since orbit insertion with the discovery of the dusty rings and ring arcs outside of the F ring

I'd be cautious too with $3+ billion worth of hardware to look after.

[Frank Crary]

Thanks for the detailed response Todd - much appreciated.
No doubt the 'expected particle flux threshold' has increased significantly since orbit insertion with the discovery of the dusty rings and ring arcs outside of the F ring
I'd be cautious too with $3+ billion worth of hardware to look after.

I think that's what Mark Showalter said when they based the original hazard assessment on his Voyager-based E ring model...

Just for reference, there are only six more dust hazard periods which will require pointing the high gain antenna to ram. Those are all Janus-Epimetheus ring crossings in 2015-2017, and all about 10-15 minutes long, plus turn time. (This doesn't include the final orbits inside the D ring; analysis and plans for that are still pending.) All the other hazard periods just require closing the main engine cover. Also, although there was some early talk about it, Cassini has never turned to keep instrument optics out of the ram direction. There was lots of analysis and testing on mirror samples before they decided this would be ok. (Part of the reason for all the testing and analysis was to impact those turns would have had on science: If "turn optics out of the ram direction when the spacecraft is in the E ring" were a rule, imaging during the inbound leg of an Enceladus encounter would have been forbidden.)