posted 02-24-2005 01:44 PM            

quote:

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Originally posted by Blackarrow:
Does anyone know if Cassini has enough fuel left to reduce speed while passing Titan and go into orbit around Titan?

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At launch Cassini had 6,905 lbs propellants (nitrogen tetroxide and monomethylhydrazine) - just love that latter chemical word!

It used just under half that amount of propellant during the 96 minute SOI burn last year. During its orbits of Saturn until 2008 it has 157 trajectory maneouvres to accomplish under the current flight program - some of which include adding the energy derived from the flyby's of Titan.

Because of the difference in orbital inclations it would require a plane change burn - where some considerable amount of propellant would be required. Additional flight plan software would need be developed and uploaded and several TCM's achieved to put Cassini in the right position for a TOI burn.

Would it have such a propellant quantity available left in 2008?

If it did achieve orbit of Titan what additional information could it gather beyond that already being gleaned between now and and its last flyby of Titan in May 2008?

It's a good question though and I'll root a bit deeper for more info.

posted 02-24-2005 03:41 PM            

Reading through the material though did highlight some information that is relevant.

Each Titan flyby is primarily aimed at producing the desired spacecraft orbit for other moon flybys rather than optimised for Titan flyby science.

Secondly, low flybys of Titan tend to favour radar imaging and atmospheric science whereas other science experiments favour higher flybys. It mentions, in particular, that the remote sensing packages hich rely on the raection wheels to maintain spacecraft stabilisation. At a low flyby orbit (and by inference an orbit about Titan) would have problems since at low altitudes the the motion of Titan beneath is too fast for the reaction wheels to keep up.

Therefore, any orbital mission about Titan using Cassini, would obviously be comprimised in the results it might achieve.

The main "attractor" on Cassini is, of course, Saturn and any residual propellant would have to be sufficient to overcome that planet's gravitational pull.

Several large burns have already taken place including the Earth, Venus flyby's and the SOI insertion burn and therefore propellant margins must be at about the 2/3rd's used mark - at a guess? Around 2,000 lbs, maybe less, probably left?

posted 02-26-2005 06:09 AM            

The problem is that detailed engineering data of measurements (propellant, attitude etc) made onboard Cassini are not - as you would expect - in the public domain! If they are - haven't found them!

The closest detail is in press kits, some PI preflight papers and the major burn press releases.

It might be able be 'modelled' (if sufficient accurate data was available) using the "Satellite Toolkit" software?

Toward the end of prime Mission in June 2008 they are going to do a "Titan 180 degree transfer" maneouvre. Not yet been able find out what this is about.

If you look at today's orbit on the "Where Is Cassini Now", it is in a long elongated elliptal orbit almost 90 degrees to Titan orbit looking down onto orbit plots.

I think the largest problem of trying insert into a Titan orbit will be the need for sufficient propellant quantities to undertake the required maneouvres.

A simple Hohmann transfer might be able achieve it by doing a burn to leave the Saturnian orbit,then coast toward Titan and then a burn - with plane change - to enter into a orbit about Titan? But these burns would need considerable propellant quantities which it will not have at end mission?

There may be some other more esoteric trajectory types but don't have enough info to determine that.

posted 02-26-2005 01:34 PM            

The total thrust available to Cassini during its many tours of Saturn is only 500 meters per second.

The reason it undertakes the close Titan flybys is that it can change the spacecraft Saturn-relative velocity by many hundreds of meters per second enabling it to do the flybys of several other Saturnian moons.

On average this imparts about 770 meters/second per flyby of Titan.

The small amount of remaining propellant is used to provide for very small trajectory change manoeuvres or to turn it for science experiment pointing requirements and for re-alignment of the antennas with Earth for good communication paths.

There are 45 targeted encounters that will need 135 manoeuvres during the 'prime mission'.

Cassini needs to make a sequence of three small manouvres after each Titan flyby to set its self up again for the next Titan flyby trajectory. These account for about 8 to 11 meters/second for the full sequence.

posted 03-04-2005 06:06 AM            

These were the images that are displayed as 'raw' images on the UniAZ site.

Because of the orientation of the craft on surface, the camera was pointing in one direction only and several images of the "same scene" therefore appear.

What we may see in the future are cleanedup images but doubt if they will show any further detail beyond what we have already seen.

posted 03-04-2005 09:50 AM               

Yeah, I would love to see a return to Titan. Fascinating place.

posted 03-05-2005 08:19 AM            

quote:

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Originally posted by Blackarrow:
Does anyone know if Cassini has enough fuel left to reduce speed while passing Titan and go into orbit around Titan?

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Not even at this stage in its mission - even if we wanted to.

I still have not yet had time to workout the kinda burn times that would be needed to accomplish this type of Titan orbit scenario.

Just for the fun of it and get a feel for what values of propellants would be needed.

Need to work out how long the burn time would be to accomplish thrusting out of an orbit about Saturn and into an orbit about Titan. Probably need a Hohmann transfer burn out its orbit of Saturn with a plane change burn and orbit insertion burn at Titan.

posted 06-08-2005 03:46 PM            

They have also released an image showing part of Titan with a volcano in the upper right part and what appears to be like a lava flow from it. Further down in the image (lower left) on wider part of this flow this 'lava flow' is where Huygens landed.

posted 03-09-2006 12:15 PM               

NASA's Cassini spacecraft may have found evidence of liquid water reservoirs that erupt in Yellowstone-like geysers on Saturn's moon Enceladus. The rare occurrence of liquid water so near the surface raises many new questions about the mysterious moon.

"We realize that this is a radical conclusion - that we may have evidence for liquid water within a body so small and so cold," said Carolyn Porco, Cassini imaging team leader at the Space Science Institute, Boulder, Colo. "However, if we are right, we have significantly broadened the diversity of solar system environments where we might possibly have conditions suitable for living organisms."