10kBq Jaro wrote:

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Amazing.... that no-one seems interested in putting Cassini in polar orbit around Titan, to completely map it's surface with radar....
http://aviationnow.com/avnow/news/channel_aerospacedaily_story.jsp?id=news/CASS12275.xml
Aerospace Daily & Defense Report
NASA Considering Extending Cassini Mission Through 2010

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Weren't spacecraft very arthritic in those days? Cassini is in Saturn orbit; Titan is in Saturn orbit; Cassini couldn't come within its radar's range of Titan without picking up a km/s or two, which sounds trivial, but it may well absolutely not have that much delta 'V' on board. Not enough for a Titanian orbital insertion.

--- Graham Cowan, former hydrogen fan
boron as energy carrier: real-car range, nuclear cachet

There is an excellent Cassini trajectory animation on ESA's web site, "Where is Cassini now?" at http://www.esa.int/SPECIALS/Cassini-Huygens/SEMD6E2VQUD_0.html

....click on the middle arrow above the picture, to play the animation.

It shows that around February 2007, Cassini comes close to matching Titan's orbit around Saturn -- from which it shouldn't be too difficult to slip into polar orbit around the moon (i.e. very small delta-v required).

GoogleNaut wrote:

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I did send ESA an email requesting details on such an encounter--hopefully they will give it some attention.

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Great ! ....I also sent a request, to JPL's Cassini web site.

I suspect though, that the answer may be unrelated to this discussion -- unlike the Huygens lander, Cassini hasn't been sterilised, and there may be concerns about contaminating Titan.

I should add that, of course, were Cassini to be put into orbit around Titan, that orbit would eventually decay and Cassini would crash into Titan.....

-- Edited by 10kBq Jaro at 19:48, 2005-12-28

Not necessarily. If Earthly bacteria were trapped within graphite composite sandwhich structural panels, then reentry heat may not reach too far within the structure before the craft comes apart--small pieces will decelerate at hundreds of g's, and within a relatively short time thousands of pieces would flutter gently down through Titans dense atmosphere...

Unlike Galileo, which slammed into Jupiter's atmosphere at well over 100,000 miles per hour causing almost instant vaporization of the probe, Cassini, if it were in orbit about Titan, would enter at an almost liesure 10,000 to 12,000 miles per hour--much less even than a satellite reentering Earth's atmosphere. Also Titan has a very dense and tall atmosphere (better than 1000 km deep,) so a craft has plenty of time to disassemble and decelerate.

Now whether microbes could survive or thrive: the answer to the first is probably yes, microbes could 'survive' but they would be freeze dried and immobile in my opinion, as Titan is much too cold to sustain any Earthly forms as we know them. Can they Thrive?: Not likely. If a piece containing Earthly bacteria were to somehow land in a Titanian version of a hot spring--then contamination could become a real possibility. However, I'd have to say that the probability of this happening is pretty low. That's not to say zero probability--only vanishingly small...

I haven't gotten so much as a peep....I guess we'll just have to see what turns up for you, Jaro!

Ty

http://space.com/businesstechnology/061108_cassini_fate.html

Death of a Spacecraft: The Unknown Fate of Cassini

By David Powell

Special to SPACE.com

posted: 08 November 2006

The Cassini spacecraft is roughly halfway through its looping voyage of the Saturn system and is continuing to return a bounty of data on the ringed planet and its moons. Yet all journeys must have an end and Cassini's eventual fate is now being discussed.

"Current planning is for a two year mission extension that ends on July 1, 2010," said Robert Mitchell, NASA's Cassini mission program manager. "However, presuming that the spacecraft continues to function well, it's reasonable to expect that one or more further extensions will be supported."

Sometime around 2012, Cassini, like the ocean-going ships of old, will need to be decommissioned. However, the spacecraft cannot be towed to some nearby shore to be dismantled; she must either drop anchor, be scuttled, or cast off her gravitational moorings altogether.

"Perhaps the most likely option is to leave Cassini in a long-lived orbit that would have little to no risk of ever hitting anything," Mitchell said. "Another is to impact Saturn like Galileo did at Jupiter, although there are some complications with this one."

The complications arise from the beautiful wafer-thin rings that girdle the planet and the fact that in order to dive into Saturn, Cassini would have to pass through them-a risky maneuver that could render the spacecraft uncontrollable.

Crash landing?

"Another option is to identify one of Saturn's icy moons as an acceptable candidate and impact the spacecraft onto it," Mitchell said.

Yet this option also holds an inherent risk arising from the three plutonium bearing Radioisotope Thermoelectric Generators (RTGs) Cassini uses as a power source.

"The issue is the heat that would be generated by the RTGs and the environment that would be created (melted ice) that could be conducive to the viability of any Earth organisms that might have survived on the spacecraft to that point," says Mitchell.

Mission planners make great effort not to contaminate alien worlds with terrestrial life.

The third option: raise anchor and escape the Saturn system altogether. Such a maneuver would require numerous flybys of Saturn's largest moon Titan to sling the spacecraft free of the ringed planet's environs.

If Cassini were to be cut adrift in this manner, her controllers have two further choices: either bring her sunward or let her escape deeper into the outer solar system.

Many options

Should Cassini be directed back toward the inner solar system it is likely her final port of call would be Jupiter, Mitchell explained, "One possibility is to escape Saturn and then most likely put the spacecraft on an impacting trajectory with Jupiter. This appears to be feasible, but the flight times get to be rather long."

Cassini's leisurely final journey need not end at Jupiter; rather the giant planet's gravity could fling Cassini into position for an impact on Mercury. Such an impact would provide valuable data on the composition of Mercury's surface and could feasibly occur around 2021 to be observed by the BepiColombo spacecraft.

Alternatively, if Cassini were cast into the solar system's outer depths there is a small chance she may provide further scientific reward in the form of a flyby of an outer planet or Kuiper Belt object.

"Some very preliminary analysis indicates that this might be possible. However, the flight times involved and the status of spacecraft consumables at that time make anything like this quite an unlikely option," says Mitchell.

NASA is to make the final decision on Cassini's eventual fate later in the mission.