[X] My Assistant

[djellison]

Cool eh?

I'm afraid my IcySats knowledge is terrible - and I just go from what the raw images website tells me..and it says Tethys....if anyone can fill me in on the 'other' one

Hands up if you thought the darker moon was going to go infront of the brighter moon !

Doug

[SigurRosFan]

What's next?

[jmknapp]

Is the upcoming flyby of Tethys quite a bit closer than originally planned? According to the countdown applet on the Cassini website http://saturn.jpl.nasa.gov/home/index.cfm in 4 days or so there will be a Tethys flyby at 1,500 km. However, the itinerary at http://saturn.jpl.nasa.gov/operations/satu...ur-dates-05.cfm has the flyby distance at 29,773 km. What happened? Or am I reading it wrong?

[Bjorn Jonsson]

Is the upcoming flyby of Tethys quite a bit closer than originally planned? According to the countdown applet on the Cassini website http://saturn.jpl.nasa.gov/home/index.cfm in 4 days or so there will be a Tethys flyby at 1,500 km. However, the itinerary at http://saturn.jpl.nasa.gov/operations/satu...ur-dates-05.cfm has the flyby distance at 29,773 km. What happened? Or am I reading it wrong?

Cassini's trajectory was tweaked a bit to achieve a 1500 km flyby of Tethys. This also lowered the Hyperion flyby distance from 1000 km to 500 km.

I will probably be posting an animation of the Tethys flyby tomorrow.

So was its 60,000 km flyby of Iapetus last New Year's.

Actually that flyby later was raised to 120,000 km.

[elakdawalla]

The original JPL commentary on the "Tethys Tweak" can be found in a couple Significant Event reports:
http://saturn.jpl.nasa.gov/news/sig-event-....cfm?newsID=556
http://saturn.jpl.nasa.gov/news/sig-event-....cfm?newsID=558

And some comments from planner Amanda Hendrix in a story I posted on April 15:
http://www.planetary.org/news/2005/cassini..._plan_0415.html

Cassini mission planner Amanda Hendrix explained that there was a Tethys flyby already planned for Cassini on September 24 that would take the spacecraft within 32,000 kilometers of the moon. "But then one of the navigators found that there was an opportunity to get much closer and it wouldn’t require that much delta V." In other words, getting closer to Tethys wouldn't cost much of Cassini's fuel, which is a precious resource that has to be conserved for the benefit of the rest of the four-year primary mission and any extended mission.

"There were a couple of trade-offs, though," Hendrix continued. "The existing timeline had some significant RADAR observations of Saturn, absolutely unique science doing radiometry observations of Saturn that they didn’t have planned out anywhere else in the tour. So one of the requirements [of changing the orbit] was that we not mess up any of that. We managed to make a plan where we could get close to Tethys and preserve the radiometry observations. But the question was, do we want to use up some of the fuel to do this?"

In the end, navigators managed to produce a close Tethys flyby at a cost of only 8 meters per second (18 miles per hour) of change to Cassini's velocity. For the entire primary mission, Cassini has a total of 400 meters per second (900 miles per hour) available for setting up interesting observing opportunities.

The new orbital path has Cassini passing within 1,000 kilometers (600 miles) of Tethys, and "it’s going to be a really cool Tethys encounter because we’ll be right over Ithaca Chasma," Hendrix says. Furthermore, the tweak will also bring Cassini within 500 kilometers (300 miles) of lumpy Hyperion two days later.

--Emily