[X] My Assistant

[Rakhir]

Death of a Spacecraft: The Unknown Fate of Cassini
http://space.com/businesstechnology/061108_cassini_fate.html

I like the Cassini Mercury crash option, even if unlikely.

Rakhir

[stellarlight]

Some questions:

Although it seems fascinating to send Cassini to Jupiter or Mercury, I have some doubts...

1.- How long will last the Cassini RTGs? If they are going to last 10 years more, I can not understand why NASA is planning to end this mission if they can stay at Saturn some years... Moreover, id the energy from the RTGs will be very low after 2010, is it really useful to send the spacecraft to Jupiter or another place? There´s a lot of things more to do at Saturn...

2.- Could NASA use Cassini as a Titan or Enceladus orbiter?

Thanks.

[JRehling]

Some questions:

Although it seems fascinating to send Cassini to Jupiter or Mercury, I have some doubts...

1.- How long will last the Cassini RTGs? If they are going to last 10 years more, I can not understand why NASA is planning to end this mission if they can stay at Saturn some years... Moreover, id the energy from the RTGs will be very low after 2010, is it really useful to send the spacecraft to Jupiter or another place? There´s a lot of things more to do at Saturn...

2.- Could NASA use Cassini as a Titan or Enceladus orbiter?

Thanks.

In every machine that will eventually fail, there is going to be one critical part that fails first. With Cassini, it will be when it runs out of attitude-stabilizing fuel. Of course, the team can indefinitely extend that lifespan by limiting manuevers, but a spacecraft that is "alive" but cannot be manuevered isn't worth much. Theoretically, Cassini could be left in place for a very long time without making ANY manuevers and then finish its mission in the far future by making its final manuevers then. But there isn't any apparent great reason to do that... at Saturn, anyway.

The RTGs will not be an issue for Cassini. In just about any conceivable future, it will run out of attitude control before the RTGs grow weak.

Given that they want to control the final fate of the craft, they will have some sort of endgame. That will have to begin before the reserve of attitude control fuel is quite zero. Some of these elaborate endgames involve using the small margin that may be left over for one last set of observations.

I think the problem with the Saturn-ejection scenarios is that they would take so many manuevers to MAKE them happen that the fuel budget would be blown. Jason relays that they are effectively impossible, so I'll accept that... with chagrin (goodbye, Uranus encounter).

Titan/Enceladus orbit would also require way more fuel than Cassini has left. The use of the radio dish to aerobrake Cassini through Titan's upper atmosphere has been discussed and dismissed: it's just not engineered for that.

I think what we're looking at is an extended mission equal to about 50-75% the duration of the primary mission with lots of focus on Titan and some on Enceladus, some fortuitous flybys of the other icy moons, but none of Iapetus. A nice endgame might be to have the craft crash into Saturn with the HGA pointed at Earth the whole time, so that some close-up science at the rings and Saturn can be broadcast in real time as the final minutes tick off.

[TritonAntares]

...
I think what we're looking at is an extended mission equal to about 50-75% the duration of the primary mission
with lots of focus on Titan and some on Enceladus,
some fortuitous flybys of the other icy moons, but none of Iapetus.
A nice endgame might be to have the craft crash into Saturn with the HGA pointed at Earth the whole time,
so that some close-up science at the rings and Saturn can be broadcast in real time as the final minutes tick off.

Sad to read that Iapetus will obviously not be observed closely during the extended mission
as the orbit of CASSINI will not go much farther out than Titan's.

I don't know exactly which regions of Iapetus will be imaged in next year's close encounter,
the following image shows some frames - but they're probably not up to date...


I guess there are regions that won't be observed at all then, whether they're in shadow,
not in the right position for 1000 km passing CASSINI or not visible at all.

Wouldn't it be senseful to put CASSINI - after the extended mission - on a longer elongated orbit passing Iapetus outbound
over its anti-saturn hemisphere showing Roncevaux Terra between the 'Snowman' and the 'White Mountains' a few times?
I don't know how manageable this scenario concerning CASSINI's fuel resources is,
but it sounds far not so weird like some ideas discussed here - like going to Chiron, a KBO, Uranus, Jupiter or even Mercury (!).

Bye.